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I am pretty new to astronomy and the project I am currently working on requires some knowledge of equatorial coordinate system. As long as I have been researching this question, I understood that vernal equinox is the origin of this system. At this moment I am stuck with task of finding distance on celestial sphere between west(on horizon) and vernal equinox. So, how do you count this distance?

Sardor Gulyamov
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  • The position of the vernal equinox varies depending on where you are and what time it is. –  Sep 10 '17 at 17:12
  • I realize that and was hoping if there is any formula determining its distance depending on latitude and longitude. – Sardor Gulyamov Sep 11 '17 at 13:08
  • Are you looking for the elevation and azimuth of the vernal equinox at a given time and place? https://astronomy.stackexchange.com/a/14508/21 has equations for that –  Sep 11 '17 at 13:31
  • Do you mean the vernal equinox or the First Point of Aries - ie the point at which the celestial equator and the ecliptic meet? – adrianmcmenamin Sep 12 '17 at 11:35
  • Oh, actually I am looking for a way of finding star's position(with given right ascension and declination) on sky for given latitude and longitude at a given time – Sardor Gulyamov Sep 12 '17 at 17:29
  • I do actually mean this point. – Sardor Gulyamov Sep 12 '17 at 17:30

2 Answers2

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The right ascension of the point on the horizon and due west is LST - 6 hours, where LST is the Local Sidereal Time. The LST can be calculated from knowing the date, time, and longitude. The declination of the west point is 0 degrees. So the angle between that right ascension and 0 hours right ascension (the vernal equinox) is just the difference between the two.

JohnHoltz
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Unless you want to develop the answer from first principles, then I suggest you use formulas already published. One source is "Astronomical Algorithms", by Jean Meeus. http://www.willbell.com/math/mc1.htm

I don't have a copy of this boo, so I can't guarantee that it contains what you want.

I have no connection with the author or the publisher.

Dr Chuck
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