Why couldn't bastards inherit titles?

Question: Why were bastards historically not able to inherit nobility or monarchy from  their parents? What about being a bastard made one unfit to rule? For example William IV of the UK was succeeded by his niece Queen Victoria instead of any of his children because all 10 of them were bastards.
Comment: Seems to be a Catholic religious decree in the mid-8th century - illegitimate children were (are) considered sinful, and ended up with many legal disabilities, such as property and title inheritance, right up until the late 20th and early 21st centuries across Europe and the Americas. Apparently, there was a papal decree made to Offa of Mercia that bastard children could not inherit the throne.
Comment: In many cases, only the firstborn, or a selected 'heir' actually inherited title, so it wasn't just singling out bastards. Not enough titles to go around.
Comment: @jamesqf If someone is born in a marriage, the father is automatically assumed to be the husband, unless guilt is proven. That is a rather common legal practice in most civilizations. If a servant's 20 years old son says his father is the king who died 10 years ago (and have 5 other siblings from 5 other father) generally the burden of proof is on him. When we play this game back to a couple of generations (e.g. in case a hereditary line dies out)...
Comment: 1) There are cases when bastards raised a claim to titles (even crown), supported by their father. 2) Bastards, by definition, have only shaky proofs about the real fatherhood. 3) Bastards are often born to less prestigious families, even common people. 4) Since marriage between nobles was generally part of a political pact, a bastard inheriting anything is potentially canceling such contracts. 5) Inheritance is never clean cut: if there is no firstborn legitimate male heir, there are always a problem. Why would anyone let illegitimate children into these pillow fights?
Comment: The bastard cannot inherit from both parents, and often both parents had lands under their control. Is not about being fit or not, is about the right to inherit from as many sources as possible to increase the power. Nobility after all is the control over land.
Comment: I think it would benefit everyone here if you could provide the instance in which you are talking about since it seems you have a specific one in mind. Or if not maybe research one that is close to what you are talking about to give us some context to go off of.
Comment: @Greg: Re your #2, bastards have neither more nor less proof of actual fatherhood than anyone else.  See e.g. Homer "It's a wise child that knows its own father."
Comment: @Greg: But the born in a marriage assumption is simply a handy myth, a bit of cultural self-delusion.  It's like the way women always say that a young baby looks just like it's father, even though to an unbiased observer, babies only look like other babies.  The idea is to persuade the possibly jealous putative father that he really is the biological parent.
Comment: But in a case where the persons only child was a bastard they still would not inherit
Comment: It was simply a cultural prejudice, in the same way that women didn't inherit the crown unless there were absolutely no male alternatives.  Or that people were allowed only one spouse, who had to be of the opposite sex, &c.
Comment: edited to give an example
Comment: Related: https://history.stackexchange.com/questions/12521/which-bastards-became-kings
Comment: @HorusKol very good.   That should be posted as an answer
Answer: Because for society as a whole, a peaceful transition of power is infinitely more important than honoring whatever rights a bastard might claim.
The most dangerous time for any kingdom (or nation, really) is the interregnum between the passing of the old leader and the assumption of power by the next.  Kingdoms which had a well-ordered process surely tended to survive better than those that didn't.  And the most important aspect of that process was that the successor be recognized as being legitimate by the broadest population and that legitimacy was as unimpeachable as possible.  The competence of the new king is secondary to his legitimacy.  It usually takes years for the costs of incompetence to become apparent and good advisors can mitigate the damage, but the price of civil war is immediate and extreme.
Most kings understood the importance of a successful transition - not just for their heirs but for their subjects.  Therefore they subscribed to the process of making their heir - not just fathering children, but reinforcing the legitimacy of the their heir by every means possible.  The relationship with the mother would be sanctified by marriage.  The mother must be of as high a station as possible.  The heir would would be granted as many titles as possible.  In most societies, and particularly in Europe, the clergy would further reinforce the inheritance in every way possible, including general condemnations of bastardy.
There were other proscriptions besides the one against bastardy.  In Europe in general, monks and priests were barred from the throne, so one way to eliminate a rival was to force them into the priesthood.  (Or, if you were a Merovingian, just kidnap him long enough to give him a tonsure.  That seemed to be enough.)  From a modern perspective, it might seem silly to prevent a member of the best educated segment of society from reaching the throne.  But this was a useful tool for ensuring the main goal: a peaceful transfer of power.
Comment: +1, Hence, the "the King is dead, long live the King!" thing.
Comment: A large part of it was also the importance placed on *monogamous* marriage, particularly as an instrument of politics and diplomacy. Other societies that allowed multiple wives don't seem to have the same degree of hangups about bastards.
Comment: My grandfather died, and there is a legal process about property and inheritance. It is just 2 sons, 3 small houses. After the justice had all the documents, all taxes paid, we thought it would be quick. Then the clerk said "everything is ok, but it can not go forward now, we must wait some months". WTF? Why should we sit and wait if all is fine? "Because some other son may appear to claim his due" Recognizing bastardy has always a large cost in confusion, uncertainty (and legal fees) even today. 200 years ago bastards had no rights at all - inheritance was easier, and lawyers were less fat
Answer: Most "bastards" were sired by their fathers with women of a lower rank than the fathers. Kings and princes would seldom have access to "princesses" (who were protected and treated like vestal virgins until they married) outside of wedlock, but they would have numerous relations with other women, ranging from servants to lesser nobility, who were "too low" to marry. Because of the "ineligibility" of the mothers, the children were not eligible to receive the full inheritance of their fathers. (Bastard children were sometimes allowed a "truncated" inheritance.) James Stewart, Earl of Moray (a truncated inheritance), was the older brother of Mary, Queen of Scots from such a situation.
There was even an institution called morganatic marriage, under which a king would "marry" a non-noble woman, but their children would not inherit his title because the mother was not an "eligible" woman. When Archduke Francis Ferdinand of Austria Hungary married a Bohemian Countess, the marriage itself was (barely) recognized, but their children were barred from ascending to the throne; he was supposed to marry someone "higher." So the countess received the title of "princess," which was lower than "archduchess" in Imperial Austria-Hungary.
What I wrote started with kings and princes, but of course, the principle applied to the rest of society.
Comment: Why the down vote? Good answer.
Comment: @TheHonRose: I've had a number of answers downvoted for alluding to "the facts of life," even when relevant to the question.But the upvotes more than cancel out the one downvote.
Comment: +1 for pointing out a huge part of it was to do with the European conception of marriage. The other answer is good too for explaining why the system was sustained, but this is more persuasive as the root cause.
Comment: Minor quibble: Archduke/Archduchess outranks Prince/Princess - as note that Countess Sophie was ***only*** granted the title of Princess (German: *Fürstin*) after marrying Franz Ferdinand. *Prince* and *Princess* are *royal* titles, while *Archduke* and *Archduchess* are *imperial* titles.
Comment: @PieterGeerkens: Done. Thanks for your help.
Comment: @PieterGeerkens: Added a new line to make your point.
Comment: But you haven't corrected the error just above it incorrectly equating *Prince* and *Archduke*.
Answer: Different societies around the world had different succession practices, customs, rules, or laws.
Ancient Roman laws restricted inheritance to the legitimate sons and daughters of a man.  Since the marriage of Gaius Julius Caesar with Queen Cleopatra VII Philopater of Egypt was with a foreigner and not recognized by Roman law, their son  Ptolemy XV Caesarion was illegitimate by Roman law and not eligible as Caesar's heir.
The tens, hundreds, or thousands of pagan societies in Europe each had their own rules of succession to property and thus to any hereditary lordships and kingdoms they may have had.  Thus there was much variation in whether illegitimate children could succeed.
As Christianity spread across Europe and became the majority religion in country after country, the Christian clergy defined marriage as a Christian religious sacrament, though secular non Christian marriages continued to valid for centuries in many parts of Europe - so long as there was no paganism involved.
The Christian clergy also gradually succeeded in limiting inheritance to legitimately born children.
Examples of European rulers of illegitimate birth, and/or problems caused by accusations of illegitimacy include:

[Added 07 May 2017] King Pepin of Italy/Lombardy (773-810), second son of Charelmagne, died in 810 and his illegitimate son Bernard (797-818) was appointed King of Itlay or Lombardy despite his illegitimate birth.  Bernard's descendants the Counts of Vermandois were the last branch of the Carolingian Dynasty.

[added 05-18-2017] But here it is pointed out that only one source claimed that King Bernard was
illegitimate.http://fmg.ac/Projects/MedLands/ITALY,%20Kings%20to%20962.htm#PepinIItalyB1

[added 05-18-2017] Emperor Charles III (839-888) tried to make  his illegitiamte son Bernard (c. 870-891/92) his heir in 885 and 886.

https://en.wikipedia.org/wiki/Bernard_(son_of_Charles_the_Fat)[2]

German King and future Emperor Arnulf (c. 850-899) - who may himself have been illegitimate - made his illegitimate son Zwentibold (c. 870-900) King of Lotharingia in 893.

[Added 07 May 2017] Edgar the Peaceful (c. 943-975,) King of the English, had two young sons by two different women.  Edward (c. 962-978) was possibly the illegitimate son of Edgar and a woman possibly named Aethelflaed, and Aethelred (c. 966-1016) was his legitimate son with Queen Aelfthryth who he married in 964.

When Edgar died one party wanted to make Edward king because he was years older and possibly for all we know legitimately born, while another party wanted to make the certainly legitimate Aethelred king despite being less ready than Edward.
Edward was chosen king, and on March 18, 978, was murdered while visiting Aelfthryth and Aethelred, thus becoming Saint Edward the Martyr while Aethelred became the next king, ready or not.

Duke Oldrich of Bohemia (c.975-1034) was Duke from from 1012 to 1032 and again in 1034. Bretislaus I (1002/05-1055), his illegitimate son with a peasant woman named Bozena, daughter of Kresina, became Duke of Bohemia in 1034 and is the ancestor of all later Dukes and kings of Bohemia.

Though Denmark became Christian in the 10th century, King Sweyn II Estridsson (died 1076) had no surviving legitimate children.  The next five kings until 1134 were his illegitimate sons, and the last illegitimate king was Sweyn III (ruled 1145-1157).

Norway became Christain over decades around the year 1000. The 18 kings and rival kings of Norway from 1093 to 1269 included only three of legitimate birth, and 15 of illegitimate birth, including 3 who showed up and claimed to be foreign born illegitimate sons of former kings.

[Added 07 May 2017]  When King William II of Sicily died in 1189, the rightful heirs were his aunt Constance and her husband Emperor Henry VI.  But William's illegitimately born cousin Tancred, Count of Lecce, became king but died in 1194 and Sicily was conquered by the Emperor.

In Ireland and Wales any son recognized by his father was considered a potential successor, legitimate or not.  Thus there were many illegitimate born kings and nobles in Ireland and Wales. It was highly unusual and considered rather unjust, for example, for Prince Llywelyn the Great ap Iorwerth (c.1172-1240) to try to make his only legitimate son Dafydd (1212-1246) his sole heir and exclude his several illegitimate sons from succession.

[added 4-22-2017] In 1238, Emperor Frederick II married his illegitimate son Enzo (c. 1218-1272) to the heiress of Torres and Galluria in Sardinia and appointed Enzo King of Sardinia.

[added 04-22-2017]  Manfred (1232-1266), Prince of Taranto, illegitimate son of Emperor Frederick II and Bianca Lancia, who was possibly legitimated by his parent's alleged later marriage, became regent of the Kingdom of Sicily 1254-1258 and made himself King of Sicily in 1258.

Margaret the Maid of Norway (1283-1290) became the rightful heir of Scotland when her grandfather Alexander III died in 1286.  When Margaret died there was no obvious heir and over 13 competitors sought the crown of Scotland in "the Great Cause".

Seven of the competitors were descended from illegitimate children of members of the Scottish royal family.
https://en.wikipedia.org/wiki/Competitors_for_the_Crown_of_Scotland#:~:text=When%20the%20crown%20of%20Scotland,Floris%20V%2C%20Count%20of%20Holland.

Robert Stewart (1316-1390) High Steward of Scotland 1326-1371, became King Robert II of Scotland in 1371.  He had several illegitimate children with his mistress Elizabeth Mure.  He married her in 1336 but some considered the marriage uncanonical, so he got a papal dispensation and married her again in 1349, thus legitimating their children including John Stewart, born in 1337 to 1340.

Elizabeth Mure died and Robert Stewart married again in 1355 to Euphemia de Ross and had several children. Robert also needed a papal dispensation for the second marriage.  Apparently both wives may have been too closely related to Robert Stewart.  The children of each marriage considered their claim to the throne better than that of their half siblings.
Robert II's son John (1336/40-1406) was selected as heir in 1371 despite any doubts about his legitimacy, and reigned as King Robert III 1390-1406.  Robert III's son and heir King James I (born 1394) was murdered on 21 February 1437 by conspirators including Robert Stewart, Master of Atholl, grandson of Walter Stewart (c. 1360-1437), Earl of Atholl, Caithness, and Strathearn, son of Robert II and Euphemia de Ross.  Perhaps the Atholl branch hoped to gain the throne from the descendants of Elizabeth Mure.

King Alfonso XI of Castile & Leon had an illegitimate son Henry II (1334-1379) who revolted against his legitimate half brother King Pedro I the cruel and finally killed him in 1369, founding the House of Trastamara.

When King Ferdinand I of Portugal died in 1383, his daughter and heiress Beatrice was married to King John I of Castile (son of Henry II), but Ferdinand's illegitimate half brother John I was selected King in 1385 and defeated the Castilians, founding the House of Aviz.

John of Gaunt (1340-1399) Duke of Lancaster, while married to his second wife Constance of Castile (daughter of Pedro the Cruel), had four children by his mistress Catharine Swynford.  Constance died in 1394 and John married Catharine in 1396.  Their children, the Beauforts, were legitimated by the church and by King Richard II.  Later John's oldest son, King Henry IV decreed that the Beauforts were not legitimate enough to inherit the throne.

In the War of the Roses, King Henry IV's Lancastrian heirs claimed that only legitimate and male lineage descendants were eligible for the English crown, while the Yorkists claimed that they had the senior right through female line descent.
In 1471 the last legitimate descendants of King Henry IV were killed and most Lancastrians decided to accept the Yorkist claim.  Those die hard Lancastrians who demanded a claimant of totally legitimate birth would have to take King Alfonso V of Portugal (1432-1481), grandson of John of Gaunt's oldest child Philippa, wife of king John I of Portugal (see number 15 above), or if the claimant also had to be English, Henry Holland (1430-1475), 3rd duke of Exeter, grandson of John of Gaunt's next oldest daughter Elizabeth.
But they were junior in female lineage descent from the Yorkist claimants.  So other Lancastrians might have supported the legitimated line of the Beauforts.  But the last legitimate male Beauforts were also killed in 1471.
There were plenty of female line descendants of the Beauforts, but of course the Lancastrian claim to the throne denied inheritance through females. Lady Margaret Beaufort (1441/43-1509) was the female with senior Beaufort lineage, and the mother of the eventual usurper King Henry VII (1457-1509), who was thus the great grandson of the illegitimate but legitimated John Beaufort, first Earl of Somerset.
But Margaret Beaufort's first cousin Henry Beaufort (1436-1464), 3rd duke of Somerset, had an illegitimate son Charles Somerset (c. 1460-1526), made first Earl of Worcester in 1514. It is said that he was legitimated, but I don't know at what date.  Thus the Dukes of Beaufort descended from him might be considered the rightful heirs of the Lancastrian kings.

King Alfonso the Magnanimous (1396-1358) of Aragon, Valencia, Majorca, Sardinia, Corsica, Sicily, etc., and King of Naples, had no legitimate children.  His brother John II inherited most of his lands, but his illegitimate son Ferdinand I (1423-1494) inherited the Kingdom of Naples.

King Edward IV of England (1442-1483) married Elizabeth Woodville on an unknown date, possibly in 1464, and had her crowned queen on 26 May 1465.  She was the acknowledged queen of England, and their son Edward (born 2 November 1470) was made Prince of Wales in 1371.

Edward IV died on 9 April 1483.  Edward Prince of Wales was proclaimed king Edward V.
Ralph Shaa preached a sermon on 22 June declaring that Edward IV had made a marriage contract with another woman, making his marriage with Elizabeth Woodville invalid and their children illegitimate.  It was a big deal to challenge a long standing public marriage, and the church would try marriage cases carefully.   But, perhaps due to the soldiers of Richard Duke of Gloucester who controlled London, an assembly of lords and commons decreed that Edward V and his siblings were illegitimate and proclaimed Richard king. Edward V and his brother Richard disappeared in the Tower of London.
Richard III's first parliament in 1484 passed the act Titulus Regius claiming that Edward IV's children were illegitimate.  Already in 1483 Henry Tudor had promised to marry Edward IV's oldest daughter Elizabeth, her brothers seemingly believed dead already.  Henry invaded, usurped the throne from the usurper Richard III, married Elizabeth, and repealed the Titulus Regius.

[added 04-22-2017] King Matthias I Corvinus (1443-1490) of Hungary, Croatia, and Bohemia declared his illegitimate son by Barbara Edelpok, John Corvinus (1473-1504) to be his successor.  But the diets of Hungary and Bohemia elected Vladislaus Jagiellon King when Matthias died.

[added 05-18-2017] In 1533 Henry VIII (1491-1547) married Anne Boleyn (c. 1501-1536) and decreed his marriage with Catherine of Aragon (1491-1536) void, and their daughter Mary (1516-1558) was declared illegitimate by the First Succession Act.  In 1536 Anne Boleyn was beheaded and her daughter Elizabeth (1533-1603) was declared illegitimate by the Second Succession Act.  The Third Succession Act of 1543 returned Mary and Elizabeth to the line of succession while they were still considered illegitimate.

Mary became Queen Mary I in 1553.

[added 05-18-2017] Elizabeth became Queen Elizabeth I in 1553 despite still being illegitimate by English law.

[added 05-18-2017] King Henry VIII might have even considered making his illegitimate son Henry FitzRoy, Duke of Richmond and Somerset (1519-1536), his heir if need be.  The Second Succession Act of 1536 had a clause granting Henry the right to chose his successor, legitimate or not.

In 1714 the absolutist King Louis XIV of France and Navarre forced the Parliament of Paris to recognize his illegitimate but legitimated sons Louis Auguste (1670-1736), Duke of Maine, and Louis Alexandre (1678-1737), Count of Toulouse and Duke of Penthievre as Princes of the (royal) Blood and in line to the succession after the legitimate heirs.  When Louis XIV died in 1715, the Duke of Orleans, regent for young Louis XV, immediately had the Parliament of Paris reverse that action.

Albert I (1848-1922) Prince of Monaco, had a problem in the 1910s, since his only child the future Prince Louis II (1870-1949) had no legitimate children and the next heir was the German Duke of Urach, unpopular with the French government.  So Louis's illegitimate daughter Charlotte (1898-1977) was legitimated in 1911 and adopted in 1918 and declared the heir to the throne.

In 1944 Charlotte renounced her rights to the throne in favor of her son, Prince Rainier II (1923-2005).
As these examples show, it was very rare for an illegitimate child to succeed to the throne during the High Middle Ages (c. 1001-1300) or the Late Middle Ages (c. 1301-1500) and later eras.  It was also increasingly rare and uncommon as time went on for illegitimate sons to inherit noble titles and fiefdoms.
But haven't I forgotten Duke William the Bastard of Normandy who became King of England in 1066?  No.  It doesn't matter if William the Bastard was of legitimate or illegitimate birth, because he had exactly zero hereditary (or any other type) claim to the throne of England, except right of conquest.  Might makes right and all that.
William the Bastard was not only not first in line for the throne, but he wasn't second, or third, or fourth, or fifth, or 100th or 1,000th, or anything. We can't even say he was last in line for the throne, because he would have to be in line for that to be true.  William had no known descent from any king of England or from any member of the house of Wessex  or from any Anglo-Saxon king of any kingdom, or even from any Anglo-Saxon serf or slave.
As a foreign invader and usurper William the Bastard doesn't count as someone who inherited a throne despite illegitimate descent from previous monarchs.
But of course, as andejons pointed out, he did inherit the Duchy of Normandy despite being a bastard.  William's mother Herleva was the daughter of Fulbert of Falaise whose occupation is uncertain.
And also see the answers to this question:
https://history.stackexchange.com/questions/12521/which-bastards-became-kings?noredirect=1&lq=1[4]
Comment: William started out as duke of Normandy, a title he gained through inheritance. The question was about noble and royal titles. Otherwise this is a very thorough answer.
Answer: They could!
In certain countries, at least. Norway and Denmark's early medieval rulers were bastards more often than not; Denmark had six bastard sons becoming kings in a row, and Norway possibly eight. One of the more well-known English kings, William the Conqueror, is also known as William the Bastard, and started out from his inherited Normandy.
Whether being born in wedlock gave you right to inherit or not is a matter of custom, and not something that is inherently better: you can certainly find bitter feuds between siblings all born in wedlock. This custom is something that ties in strongly to Christian ideology surrounding marriage, and the producing of children as the only legitimate reason to have sex. Since Christianity was the dominant ideology in Europe in roughly the same era monarchs and nobles  held most power, it was mostly in areas that were not yet or recently converted and where Christian ideas had not fully taken root that bastards could become kings.
Comment: Henry VIII bequeathed the throne by Will to 1) Edward VI, his (legitimate) son by Jane Seymour, then to 2) Mary I and 3) Elizabeth I. Both his daughters had been declared illegitimate and, although restored to the succession, were never, IIRC, legitimised.
Comment: @TheHonRose: Most likely because neither Mary nor Elizabeth *recognized* their illegitimacy - so simply presumed it *null and void*.
Comment: @PieterGeerkens - but surely the point is not whether the putative heir *recognised* his/her illegitimacy but whether the ruling elite accepted their claim to the throne - legitimate or not. Edward VI tried to change the succession in favour of the legitimate and Protestant Jane Grey, but the ruling class supported Catholic and "illegitimate" Mary.

Why couldn't bastards inherit titles?


How is it ensured that a parabolic shape forms while polishing a telescope mirror?

Question: I understand polishing the mirror with a successively finer abrasive can create a curvature, but how is it possible to obtain a uniform curve that forms a parabola while polishing by hand?
Comment: @CarlWitthoft No jig will ever be precise enough to polish a parabola into a telescope mirror. The acceptable error is less than 0.1 microns. The process is all about special polishing techniques that adjust an initial high precision surface, pushing it towards the desired shape.
Comment: These are two useful links : [Joy of Mirror Making](http://www.bbastrodesigns.com/JoyOfMirrorMaking/RoughGrinding.html) and [Parabolizing a Telescope Mirror](http://www.bbastrodesigns.com/JoyOfMirrorMaking/Parabolizing.html) both from the same very useful web site.
Comment: Also, in grinding the precision is far too low to even matter whether you're aiming for a sphere or a parabola. It doesn't matter at all. Don't waste your time making jigs. The emphasis in this stage is not on precision, but on removing glass (rough grinding) and smoothing out the surface (fine grinding). It's only later in polishing and figuring that the distinction is meaningful. I'm talking here exclusively about optics for the IR / visible / UV range. All this would be much clearer if you actually go through the process of making optics at least once.
Comment: @StephenG nice pages there -- but sadly no discussion of a parabolic grinder, just how to test curve while in process.  I seem to recall some articulated jigs based on the pencil-and-string geometry approach, http://www.gizmology.net/parabola.htm , that allow you to lap the surface parabolically, but can't find a design online.
Comment: @FlorinAndrei  I've seen machines with precision better than that, albeit expensive.  However, what I was suggesting was a jig which cuts a parabolic shape to begin with, rather than starting with a sphere and 'morphing' to a parabola via radius-dependent grind time.
Comment: @CarlWitthoft If you're talking about lens and mirror making machines, I've built one myself. But the precision of the generated surface doesn't come from the machine in the way most people think - i.e. you can't say the machine has a precision of 0.1 microns or less. The process has that precision, and that's different.
Answer:
How is it ensured that a parabolic shape forms while polishing a telescope mirror?

While a spherical shape is fairly easy to abtain, a parabolic shape definitely isn't!
It's a combination of special polishing strokes, and feedback via control and testing.
https://stellafane.org/tm/atm/mirror-refs/strokes.html
Normal polishing strokes (center over center, 1/3 diameter amplitude) tend to make a sphere. When all goes well, the surface of the mirror tends to become spherical, or very close to it. This is not different from grinding, only more precise. When two surfaces are rubbing against each other in a ball-and-socket type of joint, any irregularities will be removed and both surfaces will "want" to become spherical, or close to it.
When making telescope mirrors, the so-called "normal stroke" is what accomplishes that in the best way.

Now here's the essential detail: no matter what other curve you're trying to obtain (parabola, hyperbola, ellipse), for the purpose of making telescope mirrors all these curves are very close to a circle, within a fraction of a micron.
So a typical process has an initial goal of making a sphere (cross-section is a circle). This is not mandatory, but it's easier to first make a sphere, and then apply "corrections" to it. You can definitely make a parabola directly, but the process is more complex.
For telescope mirrors, the parabola that's needed is basically a circle that's deeper in the center, and more shallow towards the edge. So, if you start with a spherical mirror (circular section) and use polishing strokes that tend to deepen the center in a gradual way, you can get pretty close to a parabola. This is known as a "parabolizing stroke".

Keep in mind that as you apply that stroke, the center keeps deepening. At some point the correction will become deeper than a parabola and the mirror will become hyperbolic. That's sometimes what you actually need (if you make a hyperbolic mirror for a Ritchey-Chretien telescope). Or if you stop too early, the mirror is elliptic, which is used in other designs. The parabola is the thin edge between the elliptic and hyperbolic domains.
You start with a mirror where the cross-section is a circle (spherical mirror). You begin to apply the W stroke. The circle immediately becomes a very shallow ellipse, which keeps deepening. At some point, for a very short time, that ellipse becomes a parabola. As you keep doing the W stroke, the parabola then changes quickly and now you have a hyperbola which just becomes more and more deep.
The key here is testing. You apply the parabolizing stroke for a short while, then stop and test the mirror. There are many testing techniques; the Couder mask is simple enough and very popular; or you could use an interferometer if you have (or can build) one. Is it still elliptic? Keep parabolizing. Has it become hyperbolic? Reset to a sphere and try again. Or adjust the stroke if either the edge or the center are being corrected too fast.
Apply parabolizing strokes. Test. Modify technique if necessary. Repeat. That's all there is to it.

Note: I am using jargon in the text above. "Deeper" really means "more strongly curved". "Shallower" really means "less strongly curved". The difference between circle and parabola is that the parabola is more strongly curved in the center, while the curvature at the edge is less strong. The circle has constant curvature everywhere, by definition.
This doesn't necessarily mean the center of the mirror is physically more depressed; while doing any strokes, the whole surface keeps being polished down all the time. But the relative curvatures of center vs. edge may change.
Deeper vs shallower are terms that reflect the physical process, whether the tool applies more or less pressure on a certain area of the mirror (so polishing goes faster or slower there). But the geometric attribute that the process actually changes, that we are interested in, is the radius of curvature. Where the tool applies more pressure, the radius of the curvature decreases rapidly (the surface becomes more strongly curved).
Deeper and shallower are practical terms related to process. More or less strongly curved are theoretical terms related to geometry. When you make mirrors, after a while these terms become linked in your mind.

It helps if you're familiar with the conic sections:
https://en.wikipedia.org/wiki/Conic_section

red = circle
orange = ellipse
green = parabola
blue = hyperbola
Comment: `+1` I hope you don't mind the small edit to this excellent answer! fyi I've just asked the following mirror-making-relaged question: [Why is this telescope so short? How hard is it to make such a fast primary?](https://astronomy.stackexchange.com/q/33337/7982)


Wizard - Enterprise Application - Number of Steps

Question: We are Redesigning an Enterprise Application (Desktop Web App) where the User needs to Create Configuration (for Video Streams (Live), Storage, On-Demand Streams, etc.,). These configurations require the User to provide various inputs like Ingest Server details, Type of Encoding, Security settings of Streams and more. So, this is demanding a wizard with around 7-8 Steps. Is it fine to have more than 5 steps in a Wizard? I am having a strong opposition from the product team here saying that having more than 5 steps would be difficult to the User. Could you please lead me to any studies on this? IMO, it should be fine for a Enterprise App to have 7-8 Steps Wizard, because Users of these Apps would usually be power Users. And they understand that they are Creating complex Configurations.
Comment: One quibble: the point of a "wizard" (typically) is to walk naive users through a complex task. A "power user" is exactly the type of person who doesn't need a wizard, preferring something that prioritizes efficiency over learnability.
Answer: I have to say, I agree with your product team. Although there is no rule that states that you must not exceed the number of steps required for a wizard. Ideally you should strive to keep the number of steps to its minimum (short and concise). This is to prevent user from dropping off half way when they are going through your wizard. Or worst going back and forth to verify their settings. Having that many steps also mean that you have to include a "Save" button in each page to save their configuration.
Have a chat with your product team on your IA again. Since wizard are usually meant for "one" time setup, you could perhaps push some of these configuration settings to the on boarding process (when they first access the app).
Power users or not, good usability should be universal and should accommodate a diversity of user, theirs needs and under any circumstances.
Answer: I would disagree with your product team. Wizards are created just for that to give orientation to the users where they are in the process (especially if its a long task). However, having more steps in a process doesn't gives you necessarily worse performance than having just one or 3 steps, it depends on a lot of variables. You should strive to divide the steps based on type of information, like security questions, server access information, etc.
Of course your best guess is to make one version with 7-8 steps, and one with 4-5 steps and make 5 user test on each version. This way you will learn the advantages and disadvantages of each variant, and will best decide how to design it.
Here we can give you just recommendations, but they may not be true for your case. The best thing you can do is user test because every interface is different with different users using it and so on.


Trademarked name in domain name

Question: Lets says someone purchases a domain name such as www.Google.photography. This is not a generic top-level domain (.photography). If say I intend to use this site non-commercially to allow users to share photography and specify that this site is not affiliated in any way with Google Inc, is this legal practice? Could Google demand I remove this and if so would they win this? What if I am not a US citizen? What if after I bought it I offered to sell the domain to Google in case they wanted it before I started any development? Of course, I do not hold anyone accountable for any answers, this is just a hypothetical question.
Answer: I will respond to your general hypothetical.  You ask numerous questions and variations which I will not address.
In practice, Google would send you a demand letter, and then you would look into the cost of defending a lawsuit and would shut down the domain.  Whether their letter explicitly threatens a lawsuit depends on the particular philosophy of their trademark attorney--sometimes Trademark demand letters do not mention litigation because they prefer to be the ones filing the lawsuit, rather than having you file one preemptively.
The vast majority of cases are resolved by the demand letter.  Occasionally someone has to file a lawsuit.
Note that this is under Trademark law.  There is also an anti-cybersquatting law (ACPA) that can form the basis for a lawsuit, or you may find yourself in an ICANN dispute resolution proceeding.  https://en.wikipedia.org/wiki/Anticybersquatting_Consumer_Protection_Act

Trademarked name in domain name


Can I install 12.10 on an external HD that will become an internal drive in another system without changing my Windows 7 system?

Question: How can I install 12.10 on an external hard drive that I plan to put into another computer that will only run Ubuntu?  I have this drive connected to my Windows 7 and the reason I'm asking is because I have tried to install from the DVD directly into this other computer without luck as the install errors out halfway through the install.  The details on the error messages are all very cryptic so I won't bother to include them - I just need to know how to install on this now external drive that will soon be the primary drive for this other computer without hosing up my Win 7 box as I don't want that machine to become a dual booter.  Please help!  Also I almost forgot - the HD I'm installing on (that I removed from the other computer is IDE - could this be the problem?  Thanks.
Answer: I do not know if IDE could be a problem but try to install from boot menu using advanced tools and create the boot partition in the external hard drive. This might solve the problem.


Is there a way to make the background of an image transparent?

Question: Like explained here:
Making the background of an image transparent in Gimp
But via CLI!
I'm using Gimp on Ubuntu, and I would like to do this on a bunch of images..
Even if it doesn't do a perfect work obviously..
Comment: There are thousands of tutorials on youtube for GIMP
Answer: Gimp is likely overkill (and is a pain to work with for batch...). Although ImageMagick has no color-to-alpha operation, someone came up with a "formula" that works very well:
convert in.png \( -clone 0 -fill "#55f883" -colorize 100 \) \( -clone 0,1 -compose difference -composite -separate +channel -evaluate-sequence max -auto-level \) -delete 1 -alpha off -compose over -compose copy_opacity -composite out.png

Where #55f883 is your background color. Replace convert with magick convert in recent versions.
ImageMagick is the imagemagick package in your distro.
Answer: The problem of removing the backgrounds and leaving the essential objects intact automatically or with a couple of clicks is still unsolved. Surely there are propellerheads who have done serious math and programming efforts to find something useful to help the background removal, but the best semiautomatic tools still are  the selection tools, which select uniformly enough colored areas or follow an edge which is pointed coarsely with the mouse cursor.
So, if these tools + fully manual erasing and clipping path drawing are not enough, you are out of luck. The REAL magic wand still waits its inventor.
ADD due the comment:
If one knows before taking the photos that the backgrounds must be removed, he takes the photos in front of uniform backgrounds - your green screen behind the target is a common solution. If the target gets all light from white lamps, nothing from the single color background and the background color is nonexistent in the target, then the background removal can be automated. That's done in movie editing software which must process hundreds of images in seconds. Surely it's also programmed as scripts for photo editing software, but I have not such script.
In GIMP there's a tool which changes a selected color to transparency. It's Colour to alpha. For good result the selected color must be fully saturated.
I have taken hundreds of photos and removed their backgrounds in the following way for printed catalogs:
Take 2 photos keeping all absolutely in the same place (=a sturdy camera stand, timed shooting). The first photo has all lights on, the second photo has only uniformly lighted bright background, but the target is in the dark.
The black silhouette and white background have high contrast. One click with the magic wand selects the background easily. The selection is used to delete the background in the full light image, which is placed into another layer.
The 2 photo method does not work for alive targets, but it is not dependent on target colors and can be easily done with modern large led panels which are the background; one is needed also under the target.
The black silhouette needs often some minor tweaks, so this method isn't easily automatized.
Comment: What if I shot all images in the same place with the same green background? Can this help?
Comment: @Cirelli94 there's more data.


Markdown editor for OSX (ssh connection) navigate through ftp folder to load and upload modified .md

Question: I'm looking for a OSX desktop application in which I can edit plain markdown documents. I found many but none with ssh connection to navigate and choose which .md have to edit. I try ulysse app but only connect to google drive, icloud etc. Stackedit great but no navigation throught server. So if anyone have tips.
Answer: TextWrangler and BBEdit are great syntax hightlighting editors that support remotely editing documents via sftp. See this question and answer on Syntax Hightlighting Editors for more info.


Native xterm mouse scrolling in tmux

Question: I have decided to try tmux as GNU screen replacement and wonder if there is a way to scroll with mouse as in xterm?
It is possible to enable native xterm scrolling with Shift + PageUp in tmux by
set -g terminal-overrides 'xterm*:smcup@:rmcup@'

But this does not work for mouse. I have option
setw -g mouse-mode on

in my tmux.conf, but this leads to tmux copy mode. With
setw -g mouse-mode off

mouse scroll doesn't work at all.
Is it possible to enable native xterm mouse scrolling while in tmux?
Answer: setw -g mode-mouse copy-mode

You still have to enter copy-mode with Shift + PageUp

Native xterm mouse scrolling in tmux


What are planks and box jumping

Question: I've seen these terms a couple times here already.  Also, is there a good place to ask these questions?  I feel "what are some good exercise terms and their meanings" would get closed.
Comment: Flagged for move to meta as I think we should have this discussion on meta before we answer the question here.
Comment: I am not sure that this question belongs on meta.  Asking what terms mean (the first part of the question) is not a question about the site.  The second part of this question could just be answered by reading the [faq](http://fitness.stackexchange.com/faq) (:
Answer: Box Jumping is one type of Plyometrics exercise that is based off high impact jumping routines.  Plank is a type of AB workout that focus on holding a position with your back skyward, elbows on the floor supporting the body while keeping your back straight maintaining a straight line from your shoulders, to the hips, to the knee while tip toeing.  While you are at the Plank make sure to keep breathing.  In fact, keep a consistant breathing pattern while doing any exercise.  Keep your stomach, butt, and leg muscles tight during the exercise.
Answer: Planks are an excellent way to build up your "six-pack", as well as numerous other muscle groups. Follow the link to see an image of what it looks like. It's ridiculously easy to do, and can be done anywhere, at any time. I do it both as part of my workout routine and as a short pick-me-up while in the office.
Two points to remember about the plank:

Keep your back and legs straight. Continually check yourself to make sure you haven't sagged.
Keep breathing normally. Don't hold your breath.

Once you have it down, try holding the position for longer and longer. There are also many variants that you can find by searching online; ways to make it easier (rest on knees), ways to make it harder (put toes on a balance ball or against the wall), and other stuff as well.

What are planks and box jumping


Cooking time and temperature for one oven and two different dishes

Question: I want to warm a 9.6lb spiral ham (275- 15 minutes per lb) and cook a macaroni and cheese casserole (375 for about 30-45 min) in the same oven and have them ready at the same time.  How do I do this?
Comment: Possible duplicate of [Cooking ham and scalloped potatoes](https://cooking.stackexchange.com/questions/80910/cooking-ham-and-scalloped-potatoes)
Comment: It's true that we'd probably benefit from a canonical question about this sort of thing, and at that point would be able to close many things as duplicates. But since it's not a one-size-fits-all thing (larger vs smaller temperature gaps, things that benefit from being served soon after baking, etc), individual specific questions like that proposed one tend not to make good duplicates.
Answer:
Heat ham at 275.
Remove ham and hold. Covered with foil and maybe towels to hold heat.
Raise oven temp, bake mac & cheese.
Ham should still be warm when mac and cheese done.

If it were me, I'd return the ham to the oven for the last fifteen minutes or so to crisp the skin a bit with the higher temperature.
Answer: The ham (not a spiral) I did yesterday said 350 for 10-15 minutes per lb.
My Mac & cheese recipe (BH&G) bakes at 350 for 35-40 minutes.
I would cover the ham with foil, bake it at 350, and put the mac & cheese in the oven for the last 35 minutes.
I didn't do them both yesterday, but if I did, that's probably how I'd do it.


How can you tell if you can reuse an arrow?

Question: Title says it all really, if I were out practice shooting on a boss, or if I were hunting, how could I tell if I can reuse the arrows I've just shot?
Answer: While there are a variety of different arrows, there are some common signs you can look out for.
First of all are the fletchings. If they are supposed to be straight, check if they still are. Others have a bend or curve in them, if this is the case check if the curve is still correct. Also check to make sure they are fully attached to the arrow.
Second most common problem is the nock. Make sure it hasn't weakened and become loose.
Next is the shaft. Make sure it is still straight. You can either look down its length from the head (away from your eye) or spin it on your palm. The latter takes quite a bit of practice. For wooden arrows make sure there are no chips, scrapes or gouges out of the shaft. If there are it will have to be replaced.
Head / points. This is more of a concern on arrows where these can be changed. If you have such an arrow make sure they are well tightened, threaded correctly, and sit straight to the arrow. For anything with barbs make sure they are not bent.
Most commonly the only issue you will face shooting a boss is loss or damage of fletchings, and these can easily be replaced. Arrows are commonly made of aluminum, carbon fiber, or a mix of the two. Simple target shooting is unlikely to bend them. The only commonly used bow that uses wooden arrows is a longbow.
Hunting is different. If the animal moves, or you hit a bone, it can damage your arrows quite easily. I will add hunting with a bow is not a suggested idea unless you really know what you are doing. There are a lot more variables to take into account than hunting with a gun.
For a full day of shooting using twelve arrows, you might damage one, and only minor damage that you could repair yourself. They are made to withstand a lot of use. As an example mine cost £29 each. If I had to keep replacing them I would have no money left.
Comment: I have very little experience, but most of the damage I have seen is from arrows hitting each other. As such, maybe someone wishing to reduce damage should shoot at longer range (looser groups) with a larger target (to avoid missing altogether)?
Comment: The aim in target shooting is it get as close a group as possible, even at a long range. Most arrows can withstand hitting one another unless one directly hits another, point to nock. Even so nocks and fletchings are cheap and can easily be replaced.
Comment: Multi spot (usually triple spot) faces are made for exactly the problem of grouping too tightly at close range. They work just the way it sounds, shoot each arrow at a different target face on the same butt. A robin hood (hitting an arrow exactly end on, so that it splits) is only cool the first time. After that, it's just expensive and annoying.


When higher grades are more common than lower grades

Question: The usual assumption in education is that grades follow some sort of normal curve.
My question is about situations where the grade distribution curve is a rising one. More A's than B's, and more B's than C's, etc. In educational setting: Is there a name for this situation? Are there studies or methodologies related to it? Any references are welcome. (My question is not about the mathematical detail of a probability distribution function, it is about the occurrence of such distributions of grades in education, or about teaching styles that are related to them etc.)
Comment: "The usual assumption in education is that grades follow some sort of normal curve." If so, this constitutes one of the more persistent myths among teachers. A lot of my classes have a bathtub-shaped distribution (exactly opposite from a normal curve). One of the ways that grading to a curve is pernicious is that it wipes out the true observation of skill levels.
Comment: These are results from Polish high school exit exam: https://i.imgur.com/ZR4jdWt.png (some discussion at https://www.reddit.com/r/dataisbeautiful/comments/1bqf9r/unusual_distributions_of_scores_on_final/; sample size is roughly 330 thousand students). Normality is a myth.
Comment: ... in other  words, I would like to be in the business of teaching things, not in the business of ranking students. At the time I was told "But the Med schools need those grade averages!" My thought was "Then let the Med schools do the testing." At any rate, short of the ideal, I think a percentile system would be preferable to letter grades.
Comment: You talk about a grade distribution curve in terms of letters, which to me implies a curve established by a teacher or institution, like announcing on the first day "In this class, unless outcomes are unusual, 60% of students will get A's, 30% will get B's, and 10% will get C's", or do you mean that scores are coming off of some evaluation, and the resulting scores have that distribution?  (And in that case, how are scores getting turned into letter grades---is there some pre-specified relation between numeric scores and letters?)
Comment: @HenryTowsner  The course starts with typical pre-set score levels. A's are above 90, B's above 80 etc. At the end of semester there are more students in the 90's bracket than in the 80's etc.  So we do not artificially set quotas for each type grade as in top 40% get A's, the next 30% B's, the next 20% C's and the last 10% D's.
Comment: 30 years ago I taught computer science at Boston College. Even then, grade inflation was a problem, and it has only gotten worse. It is due to external factors such as cultural expectations. Ideally? Grades are a variable result in a fixed time. I would prefer a fixed result in variable time. My favorite example is flight training. You can take as long as you want to pay for, and take the test as many times as you want to pay for. If you pass, you pass. If you don't, you can either keep trying or you can quit, with the only penalty being loss of time/money. ...
Answer: The student grades could be following an exponential distribution or a Poisson distribution.  Both of these distributions have been extensively analyzed statistically.
It is also possible that the distribution is one tail of a normal distribution, where the mean is greater than 100%.
Here are three scenarios that can result in such a grade distribution.  The three scenarios can be combined:

a. The algorithm for solving problems is fault-tolerant.  There are implicit or explicit checks built into each problem.  If a student makes a small number of mistake(s), they will catch them in time, and not lose any points.
b. Multiple independent mistakes are required to mess up problem(s) badly enough that points are taken off.
The student population has been pre-filtered, so that only students in the bottom half of a bell curve are in the class.
The grading standards emphasize "allowing students to succeed" or "minimizing an achievement gap".  In other words, the "bar is set low".

Standardized tests are designed to have bell-curve grade distributions.  Some ways they do this are to:

Have lots of chances to score small amounts of points.
Have an average score that is in the middle of the possible range.
Create time pressure.  Slower students will score worse because they run out of time, or do not have time to check their work.
Have lots of trick questions (especially questions with double-negatives).  These questions tend to test "test-taking ability" or "general intelligence (IQ)" instead of the specific subject matter.
Have lots of questions with an "obviously correct" answer that is actually wrong.
Have a variety of difficulty levels of questions, so there are some questions that most students answer correctly, and some that most students answer incorrectly.
Comment: @Maesumi -- A normal distribution is built from lots of independent chances to get small differences in scores.  If your grading takes off points for small mistakes that the student could have caught later, you are more likely to have a normal distribution of grades.  If your grading allows students to catch some mistakes without penalty, you are more likely to have an exponential distribution of grades.  (You will tend to combine the students who rarely make mistakes with the students who catch mistakes in one bucket.)
Comment: Do you mean that the problem is broken into multiple stages, and student gets a red flag at each if it is incorrect?  Are there references or papers you can cite?
Answer: Although I have serious issues with "outcomes based" education, its philosophy does combat the pernicious notion that grades should have a normal distribution centered on "average."
It is not unreasonable to expect that most students will meet the learning objectives of a class. If most do not, then there might be something flawed with the preparation of the audience, or with the instructor, or with the purpose of the course. In this perspective, one might expect most grades to be A or B.
Comment: Specifically, if the class and the test aren't designed to distinguish between good students and excellent students, then the learning objective of the class might well be to get a score around 100%. This needn't necessarily be based on a big ol' educational philosophy, but you do have to resist the temptation to put "stretch goals" into the test. So for an obvious example, a one-day occupational training course should have a pass rate higher than the fail rate or else the time available is clearly inadequate for the material. So question then is, why grade at all rather than pass/fail?
Comment: @SteveJessop I used to have an issue with curving because it seemed eminently unfair that not all students could get an "A" just because of some arbitrary decision. Then I spent 6 years teaching. Now I have a problem with curving since I don't see why someone who knows nothing should get a "C".
Comment: @SteveJessop: I've been thinking about your comment for the past few days. With the amount of material over a semester (not a one-day workshop), it seems hard to expect 100% mastery of everything. So it seems like we should communicate to students a difference from "passing and allowed to take the next class, but will need to do extra work to succeed", vs. "passing with a few minor gaps to fill in", vs. "passing with total mastery to succeed at next course", etc., which winds up looking a lot like the standard A-B-C-D-F grades. For me this does argue to abandon +/- grades.
Comment: @DRF: That is such an insightful comment I may share it with others in future discussions, excelsior.


How to retain the ability to use SSH across different wireless networks

Question: I set up my Raspberry Pi to run on Linux, and I use it as a portable computer. I'm trying to find a way to maintain SSH across different networks while retaining the ability to manipulate it using SSH alone, from a phone. The SSH session does not have to be uninterrupted.
I thought perhaps I could find a way to know what the Raspberry Pi's IP address is so that the phone can connect to it with SSH, and so I ask:
Is something similar to nmap that I could use to find out all the occupied IP addresses on the network, using a phone, and find out or predict the Raspberry Pi's address?
If not, is there a way to use the same IP address on different wireless networks?
If not, how can I achieve this?
Answer: There are a number of automatic discovery systems that do this, bonjour/zeroconf/avahi being one of them. It's using multicast-dns (mDNS) to tell other devices on the same network what services it offers and under which names and connection parameters. On Linux this can be done using Avahi, which allows both automatic service broadcasting as well as manually defining what services it should show.
On the client systems you can use CLI and GUI utilities to list all mDNS devices and their services, but a common way is to just use it's default method: hostname.local
So if your pi is called "pi", using mDNS you can always reach it using "ssh pi.local" as long as you are on the same network and nobody else with the same name is online in that network at the same time.
Answer: You could use reverse ssh to an intermediate server, which would forward connections on port 22 to a specific port to your pi. On the pi you need to run something like this:
ssh -N -R 2243:localhost:22 server_username@server_ip_address

where 2243 is just an example for a port to use. Server_username username you would use to login into the server.
So once that's set up you would simply log in to to the server via ssh and from there ssh into your pi with something like:
ssh pi_username@localhost -p 2243

Answer: If your on Android there's an app in the Play store (I'm sure it's probably on the I store too) called Fing. It's a network scanner and reports the IP and hostname of all connected clients. Give you PI an easily identifiable hostname and use it to find the IP address.
It wouldn't be very easy to use the same IP on different networks. You'd need to reserve the address in advance to ensure it's not in the DHCP range or in use by another client already connected.
Answer: A solution that is not based on ssh directly, but based on a web service, remot3.it
You register you device RPI, you start a server (ssh ,vnc,) and you can connect from anywhere . You don't have to bother with wifi ip, as long you have an internet connection it is fine.
regards
CM
Comment: This may well work, but also opens a giant security hole that other network owners/admins may not appreciate or permit.


How can I share photos with friends of one certain friend?

Question: I want to share some photos with friends of one friend or just a few friends. One example why I'm asking this: there are some kind of party photos, I want to share them with certain friends and only their friends! I want them to appear for friends of friends in the pub I was last night, but I don't want them to appear for other people who maybe are my teachers, or people whose one friend is the boss of a the local business I'm working for because in this case, my teacher is a friend of my too and a friend of my friend is actually my boss in the "Facebook language".
Answer: Actually, you can. You need to tag that friend on every picture (just tag the lower left or right corner of the photos). Then, when sharing the album, share it only to friends and there is a check box to share to friends of friends who are tagged.
Answer: Facebook does not allow you to limit the visibility of a photo (or any other item) in the way that you are asking.
If a photo's privacy is not set to Public, Facebook allows you to prevent an explicit set of your friends from seeing it.  However, you cannot prevent specific people who are not your friends from seeing it.  Neither can you prevent friends who are not explicitly specified -- for example, "friends who are also friends of a specific person X" -- from seeing it.
And if the photo's privacy is set to Public, then you cannot prevent anyone from seeing it.


How to store a bicycle for an extended period of time?

Question: What's the best way to store a bicycle for an extended period of time, say 2 months?
Answer: Doesn't really matter.  Just try to avoid really wet places.  I have left bikes in the garage for years.  Or for months at a time between rides.  (Road bike during the winter, while I ride my MTB to work, and vica versa).
I have left them standing on the floor.  Hanging from both wheels in the ceiling.  I recall a thread on hanging from just the front wheel and consensus was it did not matter.
Comment: Also try to get the bike dry and then a quick wipe over with a oiled cloth can help prevent resting.
Comment: Same thing: storing my 2 bikes in the garage for almost whole winter. Before storing: just a regular check with tires pressure to normal. I store them under tentage to save at least from some dust.
Answer: Just make sure you give it a good once-over when you take it out to ride again. Make sure there's no rust and that everything that should be tight is tight and lubed is lubed.
Answer: Probably obvious, but don't leave it unattended outdoors, make sure it's properly locked and put somewhere where it's really hard to steal it.
Answer: Clean the bike, air the tires to a normal pressure, and make sure everything's lubricated that should be. Try to store it in an inside location that you are in every day. Nothing like deciding to get your bike out of storage, only to find that it's missing! If it's going to be sitting on the floor, then some type of cover may be appropriate to keep any dust or dirt away from the bike. If you can secure it with the normal bike lock, that would be an added prevention of theft. After a couple of months, all you should need to do is air up the tires and look forward to a ride.


Why different salaats have different number of rakaats?

Question: What is the motivation behind having different numbers for different prayers? Is there any significance attached to it, as in one prayer is different than others? Is this Allah's word (I doubt for I don't think its mentioned in Quran) or Sunnah? What are some credible/authoritative sources to know more about this?
Comment: See: http://islam.stackexchange.com/questions/7339/how-many-rakat-in-salat-fard-salat-only
Comment: Thanks for the link. Although it is detailed, it still didn't answer my question  - where the differences came from.
Answer: Prayer is the direct command of Allah conveyed to the Prophet (without intermediaries Jibril) at Isra 'Mi'raj. As for the number of rakaat in the sholah is delivered Prophet Muhammad and taught by the Prophet SAW
Rasulullah said:

"Pray ye as ye see me pray"

So we just have to listen and obey
Wallaahu a'lam
Answer: In coran there it is not precised the number of rakaaat but it's detailed in sunna and how profet Mohammed did every prayer .
the secret behind number of rak3at in every prayer only god know the reason behind it
Comment: **** Comments are not to be used for extended discussion or debate; they should be limited to only those which are directly relevant to the post itself. (courtesy ping @Dirt)


How to ask for a mail folder in applescript?

Question: I apologise in advance since this will be a long question. I hope that somebody with applescript knowledge can help me. I am transferring whole of my Windows machines to Apple and I am stuck with one last little annoying thing. Within Outlook I had a macro running that asked me where to file a mail after sending it. I am used to file projects in separate folders and have the incoming and outgoing mail there together. Most of the items I send BTW go into the trash folder. In other words, my sent items folders is always empty.
For reference purposes I attach the original macro below.
I tried this through rules but now understand that Mail does not support rules on sent items. Then I ended up with the automator and applescript. I have found some examples on the internet that move selected mails to a specific (preset) folder. That is however not what I need, I need the script to ask me every time what folder to use.
The next thing I cannot found is some kind of automatic trigger when I send a mail. It would for instance be possible through an option "when a mail gets stored in sent mail". Or something similar. The next best thing is just a key board shortcut that starts the macro although this is pretty close to doing it manually by just moving sent mail to a specific folder.
Anyway, I hope my question is clear and some intelligent applescript guru amongst you has a way to deal with this.
Thanks in advance!
Arnoud

COPY OF MY ORIGINAL VBA CODE USED ON THE WINDOWS OUTLOOK SETUP
<code>Dim objFolder As MAPIFolder

 ' Variable declaration
 Dim objNS As NameSpace
 Dim colKeywords As New Collection
 Dim vntRecipients As Variant
 Dim bolExternalEmail As Boolean

 ' Set variables
 Set objNS = Application.GetNamespace("MAPI")

 ' Set up list of keywords that you use when attaching files
 colKeywords.Add "attachement"
 colKeywords.Add "Attachement"
 colKeywords.Add "attached"
 colKeywords.Add "Attached"

 ' Check for attechment keywords and check for number of attachments
 If checkForKeywords(colKeywords, Item.Body) And (Item.Attachments.Count = 0) Then

 ' If attachments should be in email ask for continue
 If MsgBox("Attachement missing. Send e-mail anyway?", vbYesNo) = vbNo Then
 Cancel = True
 Exit Sub
 End If

 End If

 ' Check for subject
 If Item.Subject = "" Then
 MsgBox "Please specify a subject"
 Cancel = True
 Exit Sub
 End If

 ' Only enable actions for emails
 If Item.Class = olMail Then

 ' Get folder to save email
 Set objFolder = objNS.PickFolder

 ' Check if folder has been specified
 If TypeName(objFolder) <> "Nothing" Then

 ' If folder has been specified move email
 Set Item.SaveSentMessageFolder = objFolder
 Else
 ' Otherwise do not send email and get back to email
 Cancel = True
 End If

 End If

send_message:
 ' Unset everything
 Set objFolder = Nothing
 Set objNS = Nothing

End Sub
</code>
Answer: While I don't know if AppleScript can do what you want, there is an Apple Mail plug-in called Mail Hub that will do what you want as well as add additional functionality. I'm a satisfied customer.


Transaction using too many pieces

Question: Transactions been formed with too many pieces of different ages, causing the transaction to have a huge size and therefore require very high fees.
Question
Is there a way to reduce the size of the transaction?
Story
I have a payment system that accepts bitcoins.
Therefore my client (the store owner) receives many transactions of relatively small amounts ($30 - $400 amounts).
And every now and then he tries to move what he has on his address to exchange that to dollars.
We use Blockcypher's API.
The problem is that when we construct the transaction, the script gets formed with all the sum of the different pieces, indicating which pieces will form the payment, as I see it, this is done using the age.
An example of how these pieces are in the input list is here:
<code>"inputs": [
  {
    "prev_hash": "094be5d93ec5a5299fc8f64501855010649e3bb15d56f41ac9b5291d0XXXXX",
    "output_index": 0,
    "script": "483045022100d73dd1a8499caac0d237f5f2df17786722b4e50120756bc63c4f5f513b4f4244022019d20416762f21870e63fe035e2a0599217bc62323430ca428c2d1c8930b67270121035a3ce00ccf0701a28f124e634f4243ef2b40650aad5b0433eba4feXXXXXXX",
    "output_value": 1883692,
    "sequence": 4294967295,
    "addresses": [
      "1Lpua75bYTfeVUaEYDEkzY1vxwaVFvUNNr"
    ],
    "script_type": "pay-to-pubkey-hash",
    "age": 498654
  },
  {
    "prev_hash": "1917bb8a51642541f9d4b20beeec02a57193d5ede91e7fc79a6b7aXXXXXXX",
    "output_index": 0,
    "script": "483045022100d5f54e8b89fe080b16236a742bce0d4512f83d382a683bee96a25d5c1ff41a0802206844d81b0c2d909e4d893733a7f317caaa49a408f69c0414cee0685ac96883850121035a3ce00ccf0701a28f124e634f4243ef2b40650aad5b0433ebaXXXXXXXX",
    "output_value": 2470000,
    "sequence": 4294967295,
    "addresses": [
      "1Lpua75bYTfeVUaEYDEkzY1vxwaVFvUNNr"
    ],
    "script_type": "pay-to-pubkey-hash",
    "age": 498665
  },
</code>
Is it really necessary to indicate the age of the pieces used?
Is there a way to reduce the size of the transaction script?
This is costing too much in fees to my client. We are talking transactions that costs hundreds or more dollars.
Thanks in advance.
Answer:
Is it really necessary to indicate the age of the pieces used?

The "age" is shown only in Blockcypher's API. Transaction itself does not have such field

Is there a way to reduce the size of the transaction script?

Yes. Use segwit
Comment: Is there a documentation on how to create SegWit transactions?

Transaction using too many pieces


Facebook SSO authorize in safari but not facebook app in my iphone

Question: I am following the guide exactly to integrate with Facebook. A weird issue that i run into is that, if I,

uninstall the facebook app in iphone
OR change the facebook.m implementaion to disable facebook app like
[self authorizeWithFBAppAuth:NO safariAuth:YES];

The authorize method works well in safari and get back the auth token in the url
However, if I am not doing the above 2, it will switch to facebook app, and after it says 'loading...' for a second, it gets back to me an url saying user denied. <code>(fbxxxxxxxxxxxxx://authorize#error_reason=user%5Fdenied&error=access%5Fdenied&error_description=The%2Buser%2Bdenied%2Byour%2Brequest%2E%3F%5F)</code>
Why it behaves so differently in the native app and browser? Is it a bug in FB iPhone app? I am using the same app and same user to test.
Answer: double check your iOS Bundle ID in facebook app setting, it has to be exact same as what you define in app.


Cut locus that is a geodesic

Question: Can we characterize surfaces $S$, for which cut locus $C_p(S)$ with respect to a point $p$ on $S$, is itself a geodesic between the points it passes through? This holds for example for a cylinder and therefore surfaces isometric to it which do have a cut locus. I am looking for more examples.
Comment: Do you assume that the cut locus is connected?
Comment: @wspin:  For closed (connected) manifolds, the cut locus will be connected automatically.  The idea is that for any $p\in M$, $M\setminus \{p\}$ deformation retracts onto the cut locus.  Since $M\setminus\{p\}$ is connected (unless $M = \mathbb{R}$), this implies the cut locus is as well.  When $M = \mathbb{R}$, every metric is isometric to the standard one, so there is no cut locus.  I don't know what happens for non-closed manifolds.
Answer: For the real projective plane with a round metric the cut locus of a point is a real projective line hence a geodesic.
Answer: If the manifold is compact a topological classification can be obtained as follows:
First observe that the cut locus of a closed connected manifold is connected, as noted in Jason De Vitos comment. In fact for $p \in S$ and $q \in S \setminus \{p\}$ consider a minimal geodesic $\gamma$ from $p$ to $q$. Mapping $q$ to $\gamma(t)$, where $t$ is the first time such that $\gamma$ can not be extended to a minimal geodesic from $p$ to $\gamma(t + \epsilon)$ for small $\epsilon > 0$ defines a map from $M \setminus \{p\}$ to $Cut(p)$. It is well known that this map is continous (but not trivial). Hence $Cut(p)$ is connected if $M$ is.
Let us assume that $S$ is compact and connected. Then $Cut(p)$ is compact as well. From your assumption and the above it follows that $Cut(p)$ is either homeomorphic to $\mathbb S^1$ or to a point. Via the map in the above argument one can moreover construct a homotopy equivalence $S\setminus\{p\} \cong Cut(p)$. Thus $S\setminus\{p\}$ is either homotopy equivalent to a point or a circle. In the first case it follows that $S$ is homeomorphic to $\mathbb S^2$. In the second case it follows that $S$ is homeomorphic to $\mathbb RP^2$, which is a bit harder to see, but follows from the calssification of surfaces.

Cut locus that is a geodesic


Do photographers avoid using zoom?

Question: Because most lenses do no have a fixed aperture, do most photographers avoid using zoom as to avoid messing up their settings and their established exposure?
Comment: Most of my zoom lenses do have constant maximum aperture.
Comment: It used to drive me mad...shooting in manual mode and then having underexposed shots because I zoomed in and it changed the maximum aperture. I changed my lens. On a side note, if you avoid using zoom or if you use a prime lens, it makes you think much more about composition, and that is usually an advantage
Comment: @laurencemadill Manual mode + Auto ISO works wonders for me.
Comment: @KamenMinkov I don't like automatic anything if I can help it :)
Comment: @laurencemadill Yeah, but there is use for everything - and manual mode with auto ISO can be regarded as a separate exposure mode (and AFAIK it exists as such on Pentax cameras).
Answer:
do most photographers avoid using zoom

No.
If "most photographers" avoided zoom lenses with variable aperture, there'd be fewer zoom lenses with variable aperture on the market. Furthermore, there are plenty of fixed aperture zoom lenses available at a range of focal lengths, so it's safe to say that photographers don't have to avoid zooms just to have fixed aperture in most zoom ranges.
I suspect that by photographers you might mean professional photographers, but even so, different photographers have different priorities. Are you talking about sports photography? Landscape? Portrait? Fashion? Photojournalism?

avoid messing up their settings and their established exposure?

I don't think this is a huge priority for "most photographers." When you zoom in or out, you're changing the shot significantly anyway; considering exposure again should be part of that process.
Answer: Most photographers will weight various factors to get a particular shot. If you can't get the framing you want while zoomed out, you'll zoom in. But if that changes the depth of field (because the aperture is now f/4.5 instead of f/2.8, or whatever), you need to weigh how important depth of field is to the shot. (Or don't weigh it, take the shot anyway, and see how it turned out.)
It's like any other parameter on a camera. You don't give up on a fast shutter speed just because there's less light. You compensate with a wider aperture or a higher ISO, or by adding your own light if the shutter speed is really important. Or, you try at a slower shutter speed and see if you can reasonably get the shot, or perhaps get a different shot that looks better at a lower shutter speed.
If you want to keep your aperture wide open and your lens doesn't allow it at closer zoom levels, you either move closer (zoom with your feet), zoom in anyway and deal with the larger depth of field, or compose the shot differently. It's all about choices. But I don't think most photographers are avoiding zooming very often.
Comment: To add to the answer of @user1118321, the maximum aperture is fix on most of the better zoom lenses, at least on the work horses such as 24-70/2.8, 24-105/4, 70-200/2.8 or 4 and many others. And some or even most of these lenses will not mess with focus while zooming.
Comment: Zooming in or out will change the depth of field anyway, even if you keep aperture the same.
Answer: I think zooms are even more popular than ever with photographers.  The optical quality of even a modern kit zoom is so good that it's often hard to justify using a prime, unless you specifically require a wider aperture.
The "fear of zooms" comes from the period long ago when most cheap zooms were considerable optical compromises for a serious photographer and when even the cheapest film SLR often had a 50mm f2 attached by default.
Those days are gone.
With the combination of really excellent high ISO performance on even the cheapest DSLR and good optics of a modern kit lens, it's often hard to justify using anything else.
Comment: Re "Those days are gone" when was this period?
Comment: Apparently either before your time or you're still suffering from the problem. :-)
Answer: I'd say the primary concern is composing the shot, and making the composition fill the frame. Exposure then follows on from that.
Composing the shot involves repositioning yourself and the camera, and filling the frame involves selecting the appropriate lens OR using the zoom.
If you don't have a zoom, then you're into switching between primes. Would all your prime lenses have the same maximum aperture? No, so if the choice of exposure settings is critical you'd need to reconsider/adjust them after you frame the shot.
Answer: Most people don't worry about it. We know this for sure because a) zoom lenses with variable max aperture are pretty much the only option on compact / point and shoot cameras without interchangeable lenses, and those are wildly popular, with ever-increasing zoom range as a selling point, and b) when you get to interchangeable-lens cameras, lower-cost zoom lenses are again the most popular by a wide margin.
And, again for most people, that's perfectly reasonable, because for most lenses the difference from the extremes is only a stop or so, and that means that if you're shooting in an automatic mode, changing ISO or shutter speed handles it just fine. It's a little annoying when in low-light situations where you're hitting the limits, but there it's mostly just annoying that the lens is slow, not that it's a little faster when zoomed out.
One might make the argument that these mass-market consumer picture-takers aren't Real Photographers, and therefore don't count. But that's not so. Because these basic zoom lenses are so low cost, and the quality of manufacturing relatively high even at that price, they are a very good value, and are popular among working professionals and serious enthusiast photographers as well.
Sure, there's a tradeoff, but it's a narrow one. Even if you are using manual exposure, it's only an issue when you're at the wide end of the aperture anyway. In many cases, you'll be at f/5.6 or beyond anyway.
But that said, many people do avoid zoom lenses with variable maximum aperture. See What are the advantages of a lens having a fixed maximum aperture? for a whole Q&A on the topic, but overall it's telling that almost all high-end zooms keep the maximum aperture constant throughout the range. (More discussion on this at How do constant aperture zoom lenses work?, too.)
And, to get very specific, all of this is certainly a factor in some people avoiding zoom lenses. It's not my only reason, but it definitely contributes to the fact that I don't own any zooms and haven't for the past almost decade. Those high-end constant-aperture zooms aren't just expensive — they're also big and heavy. For the price and weight, I can have a number of really nice, fast primes instead. I'm certainly not arguing that this should be the path of all photographers, or even what you do, but if you find that this does factor into your concerns and equipment preferences, don't be ashamed.
Comment: Good: But your primes don't all have the same max aperture, surely?
Answer: When time for taking photo is short, most photographers use AE (automatic exposure) - so changes in aperture are instantaneously compensated by shutter speed. Manual exposure is typically used in very controlled environment (eg studio) when there is plenty of time to re-adjust the aperture anyway.
So to answer your question: no, under typical conditions changes in aperture are not a noticeable issue. Unless you deliberately create a problem, eg by shooting manual in rapidly changing conditions.
Answer: There are a lot of feelings of inferiority amongst photographers, thus there is a lot of posturing amongst photographers.
There was a time (and it still occurs) where photographers would claim that "they don't use zoom lenses because primes are so much superior".  "I zoom with my feet" was a common phrase.  There was probably a time where this was true, but the sentiment has lasted long after the zoom hardware has improved.
You may also remember this sentiment regarding auto-focus and auto-exposure and well, just about every new development.
Humans are complex, so there are many other reasons why photographers avoid change.    I remember the rumblings of moving from view cameras to 4x5, and 4x5 to 35 mm.  I'm sure there were many heated exchanges between those that refused to switch from glass plates to film.
The best equipment is the stuff you have with you.  Go have fun and take pictures.  If you're happy with your pictures (or even if you're not) don't get sidetracked with other photographers telling you how you're supposed to be taking pictures.
Comment: Face detection is another one. I remember that getting so much mockery, and now it's good enough that it can provide continuous tracking of single eyes for portraits _well_ beyond what anyone can do manually, and I don't see nearly so much laughter.
Comment: @mattdm: I spend a huge amount of my time trying to keep the focus point on the eyes.  I'm gonna have to turn that on and try it out!  Thanks for the tip!
Answer: Its mostly about money.  Most of us use what we have.  You can buy very good constant aperture zoom lenses, but these tend to be much more expensive.For example the constant aperture 70-200mm f/2.8's from Canon or Nikon cost over $2,000.00 or the Sony over $3,000.
Since I have an old nikon DSLR, if money were no object, Id buy these two lenses:  the 24-70 (constant) f/2.8, and 70-200 (constant) f/2.8.  These are spectacular lenses, but the set would cost you about $4,000.00 for the set. And maybe I'd buy a Zeiss Otus 85mm f/1.4 for portraits (this one is $4,500.00).  For pro's, it might be no object, but for most of us shooting our kids soccer games and family get togethers, its out of our price range.
For most of us mere mortals we get a camera kit with a cheap kit lens like the 18-200mm f/3.5-5.6, and suffer with not enough light even in many daylight situations when zoomed at the tele end.  This lens is about 600.00 if you shop around.  And for portraits where you need more light, you could get a $220.00 50mm 1.8.  These are both cheap, plastic kit lenses, that are not nearly as sharp as the pro versions costing up to 10x more,  They will fall apart long before you're tired of them, and they don't render colors very well.   But most of us are not shooting cover photos for glamour magazines.
Back to your original question: if you're shooting a soccer game, and all you can afford (like me) is a cheap kit zoom, then that is what you use.   I have a cheap 50mm fixed lens, 220.00 but no way can I reach across the soccer field with that lens, although it does have a wide aperture of f/1.8.   The cheap zoom lens I have runs out of light in most situations, even in daylight, zoomed to the tele end, the best it provides is f/5.6, so I have to jack up the iso, and deal with the grain.  Around the house, or closer shots, I can use the 50mm but composition is a pain, and sometimes you just can't back up enough to get the shot, e.g. if you're inside the house.
Answer:
do most photographers avoid using zoom as to avoid messing up their
  settings and their established exposure?

No, because in certain contexts where versatility and speed of operation are needed, nothing can beat a zoom lens. But many professional photographers do use constant aperture zooms for the reason you mention and others (the fact that constant zooms are generally relatively fast, i.e. f/2.8 or f/4, is obviously also a big incentive).
Answer: No.
There is a sentiment that photographers use prime lenses. This is correct to a certain extent for portrait photographers and people doing studio work. Yes the best glasses are prime. So it is correct what you are alluding to.
However, there are many fields where zoom is very important. For example shooting wildlife. Though there are lot of photographers who use prime, still there are so many who vouch for zoom. For zoom helps to track the animal when they are moving towards are away from you.
So broadly speaking no they do not. Their choice is based on best glass available rather than the presence or absence of zoom.

Do photographers avoid using zoom?


How can I stop people from sending game requests?

Question: So how can I prevent them to send me game requests? I imagine there must be an arrangement in Facebook to let me stop sending me game requests.
Answer: You cannot block requests from all games in general. You can ignore requests from a partiicular app or a specific friend from your requests list.
Or, if you don't use any apps on Facebook (even those that are simply about allowing you to connect your FB account with another website), you can go to Applications tab in your privacy settings and disable Facebook Platform at all. After doing that you will not be able to use any of FB apps.
Answer: Or you can ask the annoying person to stop sending them. But sometimes they don't stop because FB is constantly nagging them to do so. Then your best bet is to block all app requests from that individual. Go to Privacy Settings -> App Settings -> Blocking, then add their name to the list under Block App Invites.