

There are two ways in which the term cusp is usually used in astrology:

· Sun sign notions of a loose ‘cusp’ area (cusp days) as seen in mass produced so-called horoscope columns based on day of the month — 19th-22nd — not on the precise timing and location of your birth.

· the actual line of distinction between signs as they change every 30-degrees in the tropical zodiac.

Sun sign cusps

You need to know more than just the day of the month you were born. You need your exact birth chart to know. Your birth chart can be obtained quickly and free of charge online.

I recommend two websites for getting your birth chart (using exact birth location and time):

Astrodienst http://www.astro.com/ offers the most in-depth array of free features for the serious student and professional astrologer, including a pdf document link right above your birth chart image that gives you a pdf document of the declinations.

The simpler option on the left lets you go straight to your chart image. The option on the right has the wide variety of options that might overwhelm beginners.

Astroseek https://horoscopes.astro-seek.com/birth-chart-horoscope-online which I will use here. This site does not require you to register for an account. It also gives the option for declinations, a necessary feature for full planet location and chart interpretation. I monochromed this example. Charts are normally in color.

Some definitions: how planet position is measured

Planet and luminary positions are measured at the center of their bodies. Therefore, the apparent diameter (angular diameter) of the luminary must be taken into account to know whether it has edged over a sign cusp. The forward portion of its body can be over the cusp into the next sign while the latter portion of it can still be in the previous sign.

SUN:

The central light giving body of our solar system has an angular (apparent) diameter of about half a degree. Its light reaches Earth in 8 minutes, 20 seconds. So there’s not much room for a lag factor in changing Solar energies.

Since the Sun moves 360° in a year of 365¼ days, it moves an average of just under 1° per day. So with the Sun’s angular diameter of just over half a degree, it will only spend about half a day each month in an actual cusp position.

So if the Sun position in your birth chart is not between 29°45′ of one sign and 0°15′ of the next, it is not on a cusp. It could be near the cusp, but that ‘cuspy’ nearness is another matter with a different significance. Same for the Moon.

Meaning of Sun on the cusp between signs

This is the one way where there is a mixture of energies of the two signs involved and when the interpretation of the Sun’s position must be a combination of the two signs involved. Generally, it will mean you alternate between active (+/fire/air) and passive (-/earth/water) modes of expression, depending on the signs involved.

MOON:

Earth satellite and light reflecting body has an angular diameter also about one half degree: 0°30′ at apogee (furthest from Earth) to 0°34′ during perigee (closest to Earth). Moon only spends around one hour 12-13 times a month actually on the cusp.

For certainty of any cusp position, the parallax effect of the Moon must be accounted for, which means using the topocentric calculation for the Moon’s position. That uses your actual birth location instead of Earth’s center for the line of sight into the Moon’s zodiac position. Most programs do not use this calculation, meaning if the Moon is near the horizon, meaning the position they indicate will be off by about 1°.

Other reasons you can feel like you are a combination of signs

The most common reasons are having Sun in one sign, Mercury and Venus in another, but with one or both still conjunct or parallel the Sun. Or you may have a cluster of other planets in a sign different from your Sun sign. Most us have birth charts with varying combinations like this. That is why we want to look at all of it in the birth horoscope, including the declinations where the parallel and contra-parallel aspects are.

Other planets near the cusps

Compared to the Sun and Moon, the other planets have nearly no angular diameter. They appear as dots of less than one minute arc (1/60th of a degree). Therefore, a true cusp position is rare. However, they may still be in that cuspy zone near the cusp.

Planets, especially luminaries in the cuspy zone (last couple degrees of each sign) create a condition in which a person feels consciously or subconsciously that a change of mode expression of that planet’s energy is in the works. That is in anticipation of the polarity/element/quality switch of signs, but cannot involve the energies of the next sign until it is passing over the actual cusp at least part way into it. It can create what Edgar Cayce referred to as a Uranus-like effect of unpredictability in how the person approaches decisions or patterns, or even indecision itself. This effect may be even more pronounced when a luminary is actually in a cusp condition part way into the first degree of a sign.

Ascendant Cusps

The Ascendant (Asc or AC) is the most specific personal point in the birth horoscope, the mundane definition of which is the meeting point of the ecliptic (Sun’s path) with the eastern horizon (place where Sun and other bodies ‘rise’ from geocentric perception in Earth rotation).

The Ascendant is a precise mathematical point that is rarely located exactly on a sign cusp. It is the 1st house cusp that forms the zero point starting place of your chart.

When the correct Ascendant figure is located in the last couple degrees of a sign there is a blended effect to the personality since the next sign often can cover the rest of the 1st house, as seen in the chart to the left with 29° Libra over the Asc and Scorpio over the rest of the 1st house. There are other ways a blended personality can occur, but I won’t cover that here.

So you can see astrology is the art of reading these various factors and their subtleties. That just can’t be done with mass produced sign-based descriptions and cusp dates that leave you with the impression you are part one Sun sign and part another. We need to look for the actual locations of the luminaries and planets, and be sure we are working with a exactly accurate chart for knowing the house cusp, which requires far greater precision.