<p>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.</p>

CC BY-SA 3.0
2017-09-13T02:18:06.557Z
2017-09-13T11:49:25.590Z
2017-09-13T11:49:25.590Z
JohnHoltz
<p>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.  <a href="http://www.willbell.com/math/mc1.htm" rel="nofollow noreferrer">http://www.willbell.com/math/mc1.htm</a></p>

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

<p>I have no connection with the author or the publisher.</p>

CC BY-SA 3.0
2017-09-13T07:10:46.167Z
2017-09-13T07:10:46.167Z
Dr Chuck
<p>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?</p>

CC BY-SA 3.0
2017-09-11T13:08:37.543Z
I realize that and was hoping if there is any formula determining its distance depending on latitude and longitude.
Sardor Gulyamov
CC BY-SA 3.0
2017-09-12T11:35:20.650Z
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
CC BY-SA 3.0
2017-09-12T17:29:40.090Z
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
CC BY-SA 3.0
2017-09-12T17:30:08.787Z
I do actually mean this point.
Sardor Gulyamov
<right-ascension>
Distance from W(West) to vernal equinox
Sardor Gulyamov
# Distance from W(West) to vernal equinox

(Asked by: username_0 on 2017-09-10)

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?

**Tags:** right-ascension

> **Comments:**
> **username_0**: I realize that and was hoping if there is any formula determining its distance depending on latitude and longitude.  
> **username_1**: Do you mean the vernal equinox or the First Point of Aries - ie the point at which the celestial equator and the ecliptic meet?  
> **username_0**: 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  
> **username_0**: I do actually mean this point.  

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## 2 answers

### Answer by username_2 on 2017-09-13. Score: 1

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.


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### Answer by username_3 on 2017-09-13. Score: 0

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.


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