<p>I think you mean to ask, "What is the local sidereal time of Greenwhich?". </p>

<p>To calculate the GMST (Greenwich Mean Sidereal Time): </p>

<blockquote>
  <p>To an accuracy within 0.1 second per century, Greenwich (Mean) Sidereal Time (in hours and decimal parts of an hour) can be calculated as GMST = 18.697 374 558 + 24.065 709 824 419 08 * D , where D is the interval, in UT1 days including any fraction of a day, since 2000 January 1, at 12h UT (interval counted positive if forwards to a later time than the 2000 reference instant), and the result is freed from any integer multiples of 24 hours to reduce it to a value in the range 0–24.</p>
</blockquote>

<p>[<a href="http://en.wikipedia.org/wiki/Sidereal_time" rel="nofollow">source</a>]</p>

CC BY-SA 3.0
2014-05-18T10:02:57.097Z
2014-05-18T10:02:57.097Z
astromax
<p><a href="http://en.wikipedia.org/wiki/Right_ascension" rel="nofollow">Right Ascension</a> is a celestial coordinate, not a terrestrial one.</p>

<p>RA is used to locate a star on sky, and is measured between a fixed point in the sky (the crossing of the Ecliptic and the Celestial Equator) and the star's meridian.</p>

<p>It corresponds to terrestrial coordinate Latitude.</p>

<p>Thus, Greenwich has no Right Ascension.</p>

CC BY-SA 3.0
2014-05-19T07:28:24.357Z
2014-05-19T07:28:24.357Z
Envite
<p>If I know specific time, t0, how can I calculate RA of Greenwich?</p>

<earth>
How to calculate right ascension of Greenwich?
user1686
# How to calculate right ascension of Greenwich?

(Asked by: username_0 on 2014-05-18)

If I know specific time, t0, how can I calculate RA of Greenwich?

**Tags:** earth


---

## 2 answers

### Answer by username_1 on 2014-05-18. Score: 2

I think you mean to ask, "What is the local sidereal time of Greenwhich?".

To calculate the GMST (Greenwich Mean Sidereal Time):

> To an accuracy within 0.1 second per century, Greenwich (Mean) Sidereal Time (in hours and decimal parts of an hour) can be calculated as GMST = 18.697 374 558 + 24.065 709 824 419 08 \* D , where D is the interval, in UT1 days including any fraction of a day, since 2000 January 1, at 12h UT (interval counted positive if forwards to a later time than the 2000 reference instant), and the result is freed from any integer multiples of 24 hours to reduce it to a value in the range 0–24.

[[source](http://en.wikipedia.org/wiki/Sidereal_time)]


---

### Answer by username_2 on 2014-05-19. Score: 1

[Right Ascension](http://en.wikipedia.org/wiki/Right_ascension) is a celestial coordinate, not a terrestrial one.

RA is used to locate a star on sky, and is measured between a fixed point in the sky (the crossing of the Ecliptic and the Celestial Equator) and the star's meridian.

It corresponds to terrestrial coordinate Latitude.

Thus, Greenwich has no Right Ascension.


---

