Model of the Ecliptic Plane and the 13 Astrological Signs

The astrological symbols were chosen several thousand years ago. There were originally 13 symbols, but there was a later revolution in thought: God is perfect and mathematical formulas are perfect, therefor, god thinks in math. Astrology underwent a geometrical change, and each symbol was given an equal portion of the year. However, there was one problem: with 360 degrees in a circle, 360 divided by 13 symbols is a very messy number. To make the problem easier, they decided that the world really only needed just 12 symbols.

Also, the earth spins like a top, and as a top slows down, it wobbles. The wobble, for the earth's scale, takes roughly 26,000 years to complete one cycle. This causes the axes to point toward different points in the heavens and is responsible for making the dates of each astrological sign slowly change over large periods of time.

     The exact dates of the signs of the zodiac (circa 1977) are shown below. It appears that these dates are accurate for the year 2000 but I can't find any recent study on the position. The dates shift by one day every 78 years roughly, so one or two of the days may be off for the year 2000. However, if you *really* want to be accurate in finding your birth sign, they change yearly by minutes. You would need to get your birth to the second of GMT then figure out where noon lay at that time. Of course, there are some rather large gaps between the constellations that no one really bothers with. Those spaces aren't accurately depicted on this model.

    If you wanted to be picky, the ecliptic plane, the plane of the apparent path of the sun and planets, actually passes through 21 constellations, not 13, as noted by John Mosley of the Griffith Observatory and the Belgian astronomer Jean Meeus (1999). This does not include Pluto in the ecliptic plane or 4 more signs would need to be added (Bootes, Coma Berenices, Eridanus, and Leo Minor). The 21 signs are listed below.  

 The arrow points to the astrological sign of the month shown in the counter. The signs were originally based upon the constellations that the sun appears to pass through at absolute noon (the meridian). Since the sun is there in the sky at noon, on earth, it is impossible to see constellations when we're in that "astrological sign" except during a complete solar eclipse.

Astronomical Constellations of the Ecliptic

Constellation            Dates                 length of the period in days

Sagittarius          Dec 18     Jan 18     32

Capricornus       Jan 19      Feb 15     28

Aquarius             Feb 16     Mar 11     24

Pisces                Mar 12      Apr 18     38

Aries                  Apr 19       May 13    25

Taurus              May 14      Jun 19     37

Gemini              Jun 20       Jul 20       31

Cancer              Jul 21       Aug  9       20

Leo                   Aug 10       Sep 15     37

Virgo                Sep 16      Oct 30       45

Libra                Oct 31       Nov 22      23

Scorpius          Nov 23      Nov 29       7

Ophiuchus       Nov 30      Dec 17      18

Dates may fluctuate plus or minus a day from year to year.

From Dr. Lee T. Shapiro, 1977, Director of the Abrams Planetarium

at Michigan State University.  “The Real Constellations of the Zodiac”

Planetarian (magazine)

The below charts are reprinted from the Griffith Observatory Webpage

http://www.griffithobs.org/IPSRealConst.html

The 21 signs of the Zodiac:

Aquarius

Aries

Cancer

Capricornus

Cetus

Corvus

Crater

Gemini

Hydra

Leo

Libra

Ophiuchus

Orion

Pegasus

Pisces

Sagittarius

Scorpius

Scutum

Sextans

Taurus

Virgo