E018 The Zodiac and 27 Nakshatras: An Astronomical Perspective – Part 2

Length of Rashis

Important Note: This article has been updated with better data on 29-Jun-2020. References to celestial grid coordinates have been replaced with Ecliptic grid coordinates and interpretations have been updated as well.


In the first part of this essay, we briefly touched upon the universe and 12 zodiac constellations on Sun’s ecliptic path. Furthermore, we have seen imaginary asterisms of constellations as seen in different parts of the world. If you haven’t happened to read first part of this article, you may be better-off starting from there. In this second part, we will look at length of zodiac constellation and compare it with data from astronomy. This characteristic of Rashis can be verified astronomically. Rashi lengths serve as basis for several astrological assumptions and calculations. The Kalapurusha concept heavily relies on the length of different rashis. Hence, a scientific validation could offer more insights to this astrological construct.

The layout of constellations look slightly different when we look at them from a geocentric (Equatorial Grid) vs sun-centric view (Celestial Grid and Ecliptic Grid). From the perspective of an observer on Earth, the Sun’s movement around the celestial sphere over the course of a year traces out a path along the ecliptic against the background of stars. Imaginary grid can be imposed on this ecliptic path keeping 0 degree latitude as ecliptic path. Since Earth is inclined in its axis by 23.5 degrees, the equatorial grid and ecliptic grids will look slightly tilted to each other. At the point of vernal equinox and autumnal equinox these two grids will intersect each other. Beyond these different grids, Galactic Grids can also be used to identify location of celestial objects. Any celestial object’s location can be identified as an intersection point of two axes on any of these grids.

Imagine you looking at 12 constellations covering around the Earth like a blanket. It would look something like the picture shown below. In this picture, the precession circle is also shown for reference. The current pole star Polaris has been identified.

Equatorial grid
Zodiac on Ecliptic Grid

The image above is based on equatorial grid based on latitude and longitude positions for a specific point in time. Due to the 23.5° tilt of earth on its axis, ecliptic path of the Sun would appear like a vertical ‘S’ shaped line with constellations lying on both sides of earth’s equator region, as you can see from picture above.

As defined by Wikipedia – The ecliptic is the plane of Earth’s orbit around the Sun. Keeping this path as 0° ecliptic latitude, imaginary lines called Ecliptic Grid can be super-imposed on solar system. We all know that different planets orbit around sun in their own elliptical paths. If we look all those paths far away from keeping Sun in center, their orbiting path would lie close to each other with as estimated distribution of ±7 ° on both sides of 0° ecliptic latitude.  The 12 Constellations that are placed on this 14° belt is considered in astrology. The picture below can provide you such a view of Rashis and ecliptic path of different planets on the ecliptic grid.

Ecliptic grid
Zodiac on Celestial / Ecliptic Grid

If these two grids viz Equatorial and ecliptic grids are overlaid on each other, it would provide a view like the one shown below. This view is primarily based on ecliptic grid with equatorial grid over imposed on it. A section of the picture with equinox points are highlighted to show the cross-over of these two grids. Since the ecliptic path also keeps changing over time, the ecliptic grid based on this path also changes over time.

Equatorial and Ecliptic Grids overlaid
Equatorial and Ecliptic Grids overlaid

Next, let us look at the ecliptic path without ecliptic grid.

Rashis and Ecliptic Paths
Rashis and Ecliptic Paths
  • In this picture above, you can see that the 12 zodiac constellations are in fact placed along the ecliptic path. At the same time, they assume different length and width.
  • As it turns out, some of the 27 stars we consider in Indian astrology (for example: Hasta, Purva Bhadrapada, Uttara Bhadrapada etc.) are placed far away from the ecliptic path.
  • You can also see that some of the 27 stars lie beyond the 12 constellations referred in astrology.
  • You can see that some star names constitute a star cluster rather than a single star (example: Hasta and Kritika).

Measuring distance between the zodiac constellations:

Before proceeding further, please note that zodiac asterisms and other data used in this article are primarily sourced through Stellarium software and Wikipedia resources. Significant effort has gone behind collecting, collating, validating, and analyzing data. However, it’s possible that few errors might have crept in, inadvertently. If you find any discrepancy in data, feel welcome to point out the inconsistencies and help improve this content.

Since all celestial objects are constantly moving, their specific position in a particular year are used as reference point to track their movement. I have used J2000 as my basis, which refer to the astronomical positions of the stars in the year 2000 AD.

Indian asterisms considered in this analysis are given below for your reference.

Indian Zodiac
Indian Zodiac Asterisms

In the next image below, few stars in constellation of Mesha (Aries) and Rishaba (Taurus) have been identified with Hippacros names, which is commonly accepted. In this system, star names begin with name ‘HIP’.

Let us now look at the distance of the constellations based on these zodiac asterisms. These distance measurements are based on ecliptic grid, which consists of ecliptic longitudes and ecliptic latitudes. We can think of difference of ecliptic longitudes of two stars as horizontal distance between them, which we can refer as rashi length.

Method of measurement
Method of measurement

Accordingly, the beginning star of Mesha/Aries asterism is HIP 8832 A with Ecl. Long value of 33°11’05.30″. The final star of Mesha Rashi is HIP 14838 and its (Ecl. Long) 50°51’13.90″. To refer them in degree decimals, these would translate into 33.185 and 50.854, respectively. Hence, distance between these two points is 17.98 degree decimals. This formula can be extended to calculate distances between other Rashis as well.

In the first part, I had indicated that in Indian astrology, we do not have clearly defined boundary lines between Rashi / asterisms. Therefore, if we measure distance between beginning stars of two successive constellations, it can serve as length between those constellations. Accordingly, difference of ecliptic longitudes between HIP 8832A and HIP 15900 can be considered as length of Mesha (Aries).

The beginning and ending stars of each zodiac, as well as their ecliptic longitude data are given in the table below (marked with column ‘I’). The lengths of the zodiacs as per astrology text and my comparison based on astronomy data are also given in this table.

Before drawing any conclusions based on this table, please remember that this table is based on stars on the constellation asterisms and not based on the 27 stars we use in astrology. We will investigate the distance between these 27 stars in an upcoming article about stars.

Rashi Lengths
Rashi Lengths

To the best of my knowledge, I have not come across any degree level measurements for 12 constellations. The qualitative length described in some of tamil texts are subjective to different interpretations. I have given the approximate translation of them in column J (marked as J **). Through my analysis, I am providing more accurate measurements based on astronomy at degree-sec level precision (columns G, H and I). In addition, I have also made my grouping labels (Column K) based on their length. 

Key Observations:

  • Based on the length of rashi, zodiac constellations can be ordered in the descending order of Virgo, Pisces, Taurus, Leo, Sagittarius, Gemini, Scorpio, Cancer, Aries and Libra.
  • Since Capricorn and Aquarius are interspersed with each other and due to the method used in my calculation, Capricorn turns out to be of short length.
  • The constellation of Virgo is the longest of all.
  • Gemini has 30 degrees of length exactly.
  • Libra is the shortest zodiac.

Distance of zodiac asterisms

Let us look at visual representation of these distances in charts below. Distance between beginning and end stars of a constellation are given below (column marked as G in table above). Note that degrees and seconds have been converted to decimal degrees for ease of representation. In total, the 12 zodiac asterisms cover a distance of 315 degrees, which is 88% of the total distance (of 360 degrees).

Asterism distance
Asterism distance
  • Virgo asterism has the highest length, while cancer asterism has the lowest length.
  • The 5 constellations viz Virgo, Pisces, Taurus, Leo and Sagittarius respectively have more than 30 degrees of asterism length.

Next, let us look at gap between the constellation asterisms (Column H in Table).

Gaps between asterisms
Gaps between asterisms
  • There is some gap between 11 out of 12 asterisms. Some space sharing is observed between Aquarius and Capricorn.

The distance from first star of a zodiac to the first star of its successive zodiac (Column H of Table) are presented below.

There is some gap between 11 out of 12 asterisms. Some space sharing is observed between Aquarius and Capricorn.
The distance from first star of a zodiac to the first star of its successive zodiac (Column H of Table) are presented below.
Rashi Lengths

Please refer to what have already discussed as key findings right next the table above.

Synopsis

  • Based on the evidence from astronomy data, we can infer that lengths of 12 constellations slightly differ from astrology texts.  
  • If astronomy data from different asterisms hold good, then many of the interpretations of basic astrological constructs can be challenged, including lengths of different parts of Kalapurusha.
  • Moreover, if asterisms are more important, then it raises the question of why so many stars outside the zodiac and still referred as sub-divisions of 12 rashis.

Keep pondering on these, however, do not come to any decisive conclusions on rashi lengths just based on this analysis. You can reserve that decision making after my forthcoming essays on 27 Nakshatras.

The stars are calling me to share my analyses on them 😊. Stay patient for the next part of this essay where I will start delving into the star space. Astronomical data of our Nakshatras are interesting and can enlighten the astrologically inquisitive minds.

Feel welcome to share your comments below.

Thanks!

Courtesy:

Astronomy Software : Stellarium  

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