posidonius was the individual who is credited with establishing the size of earth using the star canopus.
who was the individual who is credited with establishing the size of earth using the star canopus?
posidonius
a parallel later ancient measurement of the size of the earth was made by another greek scholar, posidonius. he noted that the star canopus was hidden from view in most parts of greece but that it just grazed the horizon at rhodes. posidonius is supposed to have measured the angular elevation of canopus at alexandria and determined that the angle was 1/48 of circle. he used a distance from alexandria to rhodes, 5000 stadia, and so he computed the earth's circumference in stadia as 48 times 5000 = 240,000. some scholars see these results as luckily semi-accurate due to cancellation of errors. but since the canopus observations are both mistaken by over a degree, the "experiment" may be not much more than a recycling of eratosthenes's numbers, while altering 1/50 to the correct 1/48 of a circle. later, either he or a follower appears to have altered the base distance to agree with eratosthenes's alexandria-to-rhodes figure of 3750 stadia since posidonius's final circumference was 180,000 stadia, which equals 48×3750 stadia. the 180,000 stadia circumference of posidonius is suspiciously close to that which results from another method of measuring the earth, by timing ocean sunsets from different heights, a method which is inaccurate due to horizontal atmospheric refraction.
history of geodesy
the "star canopus" diving accident was an incident in scotland in november 1978 that claimed the lives of two british commercial divers. during a routine dive beside the beryl alpha platform in the north sea, the diving bell of the diving support vessel ms "star canopus" was lost when its main lift wire, life support umbilical, and guide wires were severed by an anchor chain of the semi-submersible "haakon magnus". the bell dropped to the seabed at a depth of over 100 metres (330 ft). its two occupants, 25-year-old lothar michael ward and 28-year-old gerard anthony "tony" prangley, were unable to release the bell's drop weight in order to return to the surface because it was secured to the bell frame with secondary locking pins. since there was not a bell stage to keep the bottom door of the bell off the seabed, the divers could not exit the bell to release the pins. despite the efforts of three rescue vessels – "intersub 4", "tender carrier", and "uncle john" – the bell was not recovered for over thirteen hours, by which time ward and prangley had died of hypothermia and drowning.
star canopus diving accident