BABYLONIAN ZODIAC ASTRONOMICAL COORDINATES

Abstract

Ecliptical coordinates of Babylonian zodiac signs are found. A simple and easy to use mapping manual is given.

1. Approach

Our goal here is to find the mapping between the contemporary astronomical coordinate systems and the coordinate system used in ancient Babylon which was the Babylonian zodiac. Having this mapping will make us able to project any celestial body on Babylonian zodiac using it’s contemporary astronomical coordinates. We are going to use following sources and tools:

• „The Babylonian Zodiac”, Robert Powell, Ph.D.
• Swiss Ephemeris – Sidereal Calculations
• Bright starts almanac fromhttp://www.alcyone.de/
• Astronomical calculator (12)

In order to find every zodiacal sign start coordinates we are using the ecliptical coordinates of Aldebaran. These coordinates are precession and nutation dependant and are calculated for given astronomical epoch. We will use the astronomical epoch J2000 here (01.01.2000).

2. Babylonian zodiac coordinates calculation

Here are various options about starting point of the fixed Babylonian zodiac as per different researches. The latest research works are using zodiac coordinates fixing using Aldebaran placed exactly at 15° 00′ 00“ Taurus. At the opposite side Antares is placed almost at the middle in the Scorpio. This option is given as “Äldebaran – Antares Ayanamsha” in Swiss Ephemeris project (2).
The equatorial astronomical coordinates for epoch J2000 as per bright stars almanac follows:

Star

RA, h

Decl, deg

Longitude, deg

Latitude,deg

Aldebaran (1)

04h35m55.2s

+16:30:33

69,78901345

-5.46743903

Antares (2)

16h29m24.4s

-26:25:55

249,76206354

-4.56992146

We convert equatorial coordinates to ecliptical ones using an astronomical calculator. Let us calculate the difference between the ecliptigal longitude of these two stars:

Long2 – Long1 = 249,76206354 – 69,78901345 = 179,97305009 deg = 179°58’23“

We notice that the difference is almost 180 degrees with only 2 angular minutes inaccuracy.

To find the coordinates of beginning of Aries sign L0 (0 Aries) over ecliptics we substract 45 degrees from the longitude of Aldebaran. This way we have:

L0 = 69,78901345 – 45 = 24,78901345

Having this we are able to calculate the ecliptical boundaries of each zodiacal sign for J2000 epoch in fraction of angular degrees.

Sign

Start

End

Aries

24,78901345

54,78901345

Taurus

54,78901345

84,78901345

Gemini

84,78901345

114,7890135

Cancer

114,7890135

144,7890135

Leo

144,7890135

174,7890135

Virgo

174,7890135

204,7890135

Libra

204,7890135

234,7890135

Scorpio

234,7890135

264,7890135

Saggitarius

264,7890135

294,7890135

Capricorn

294,7890135

324,7890135

Aquarius

324,7890135

354,7890135

Pisces

354,7890135

24,78901345

Having this we are able to project arbitrary celestial body over the fixed Babylonian zodiac, using the following algorithm:

• Finding the equatorial astronomical coordinates using almanac or astronomical software (RA и Decl) for epoch J2000 (01.01.2000).
• Calculating the ecliptical coordinates using free astronomical calculation tool (1, 2).
• Comparing the ecliptical longitude of the celestial body with the signs boundaries in the table. Finding the sign and the position within the sign using a simple substraction operation.

3. Example: finding the exact position of Regulus over the Babylonian fixed zodiac.

We open the almanac and found Regulus astronomical equatorial coordinates for epoch J2000:

RA:

DEC:

10h 8min 22,3sec

+11° 58′ 2“

We transform the coordinates in a suitable for the calculator format:

RA

DEC:

10h08m22.3s

+11:58:02

We put these data into the astronomical calculator and got following as a result:

Input: Equatorial J2000.0
RA or Longitude   DEC or Latitude   PA(East of North)
152.09291667      11.96722222       0.000000
10h08m22.30000s   +11d58m02.0000s
 Output: Ecliptic J2000.0
149.82908740      0.46483569        339.419054

Where 149.82908740 is the ecliptical longitude of Regulus in fragtion of angular degrees. We notice that Regulus lays between the sign Leo boundaries. But where in Leo exactly – is the next question we must answer. So we substract the Leo start ecliptical position from the ecliptical position of Regulus:

L_Regulus_Leo = 149,82908740 – 144,7890135 = 5,0400739.

We transform fraction angular degree to angular degrees, minutes and seconds using a calculator. Finally we got:

The exact position of Regulus over the fixed Babylonian zodiac is 5⁰02’24.27’’ Leo.

Vasil Vasilev, 12.09.2017

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