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?
6
-
$\begingroup$ The position of the vernal equinox varies depending on where you are and what time it is. $\endgroup$– user21Sep 10, 2017 at 17:12
-
$\begingroup$ I realize that and was hoping if there is any formula determining its distance depending on latitude and longitude. $\endgroup$– Sardor GulyamovSep 11, 2017 at 13:08
-
$\begingroup$ Are you looking for the elevation and azimuth of the vernal equinox at a given time and place? astronomy.stackexchange.com/a/14508/21 has equations for that $\endgroup$– user21Sep 11, 2017 at 13:31
-
$\begingroup$ Do you mean the vernal equinox or the First Point of Aries - ie the point at which the celestial equator and the ecliptic meet? $\endgroup$– adrianmcmenaminSep 12, 2017 at 11:35
-
$\begingroup$ 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 $\endgroup$– Sardor GulyamovSep 12, 2017 at 17:29
|
Show 1 more comment
2 Answers
$\begingroup$
$\endgroup$
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.
$\begingroup$
$\endgroup$
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.
