Ashwini mapping to Aries Zodiac constellation stars with mobile astrophotography
The process of measuring the apparent brightness of stars is called photometry (from the Greek photo meaning “light” and –metry meaning “to measure”). The stars fall into six brightness categories, each of which has a magnitude.
The brightest stars are catalogued as first-magnitudes stars, whereas those so faint and could barely be seen are sixth-magnitude stars. During the nineteenth century, astronomers attempted to make the scale more precise by establishing exactly how much the apparent brightness of a sixth-magnitude star differs from that of a first-magnitude star.
Measurements showed that we receive about 100 times more light from a first-magnitude star than from a sixth-magnitude star. Based on this measurement, astronomers then defined an accurate magnitude system in which a difference of five magnitudes corresponds exactly to a brightness ratio of 100:1.
In addition, the magnitudes of stars are decimalized; for example, a star isn’t just a “second-magnitude star,” it has a magnitude of 2.0 (or 2.1, 2.3, and so forth). So what number is it that, when multiplied together five times, gives you this factor of 100? The answer turns out to be about 2.5, which is the fifth root of 100. This means that a magnitude 1.0 star and a magnitude 2.0 star differ in brightness by a factor of about 2.5. Likewise, we receive about 2.5 times as much light from a magnitude 2.0 star as from a magnitude 3.0 star. What about the difference between a magnitude 1.0 star and a magnitude 3.0 star? Since the difference is 2.5 times for each “step” of magnitude, the total difference in brightness is 2.5 × 2.5 = 6.25 times.
The scale presently used to measure brightness of objects in sky is an inverse geometrical scale with brightness of sun at -26. With such a bright object, flooding atmosphere, other objects in sky are only visible to normal human eyes during night when sun is not visible. Full moon has a brightness of -12. Venus at its brightest has a brightness of -3. The brightest star is Sirius, which has a brightness of -1.5. On a clear dark night (without moon), the dullest object that can be seen by healthy human eye is considered to be +6.
The important fact to remember when using magnitude is that the system goes backward: the larger the magnitude, the fainter the object you are observing.
The following principles and assumptions can perhaps be used as the basis for establishing identity of Nakshatras :
*Nakshatra named by people at Vedic time, must have been visible to naked eye and hence must be brighter than +5, based on brightness definitions.
*Moon is said to visit the Nakshatra or star mansions. Moon traverse plane is inclined to sun motion plane and hence over a period of time, the moon trajectories form a band. Let us call it as the moon traverse band. It is typically 5 degrees around ecliptic. Hence for any star or group of stars to qualify as a Nakshatra, it must be within the moon traverse band or outside not exceeding a few moon diameters. One Moon diameter is about 0.6 degree as seen from earth.
* The Nakshatras should be about 13.33 degrees apart or to 1/27 of 360.
* It is also necessary that they belong to the Raashi’s or twelve Zodiacs.
Ashwini star:
Ashwini is the first of 27 nakshatras/Lunar mansions. If the moon was between 0:00–13:20 degrees Aries zodiac constellation, then it represents Ashwini nakshathra.
In astronomy, the twin signs that make up the nakshatra of Ashwini are called Alpha Arietis and Beta Arietis. Indeed, the ruling deities for Ashwini nakshatra are called the Ashwini Kumaras in Hindu Mythology.
Let us look at the three stars that map to the lunar mansion of Ashwini -
1. Alpha Arietis — Hamal = +2.01 brightness
2. Beta Arietis — Sheratan = +2.63 brightness
3. Gamma Arietis — Meesarthim = +3.9 brightness
Captured during May 2020, early morning 3:30 am east sky. You can identify the mapping of nakshatra with the three defined stars. (P.S to see the image properly, you might have to zoom near the Mesha mark)
Will meet you next with Bharani nakshatra captured. Until then have a great time. :-)
