<p>Galactic coordinates are sun centred with a zero longitude chosen to align with the centre of the galaxy when the measurements were made in 1958.</p>
<p>As defined, the galactic coordinates don't rotate, and so the position of Sag A* is very slowly drifting. Currently Sag A* is about 4 arc-minutes from the defined zero longitude, but decreasing by 5.7 milli-arcseconds per year (a tiny amount)</p>
<p>The task is ill defined, You can convert between different coordinate systems of the sky, but they all must be centred on the solar system.</p>

CC BY-SA 4.0
2020-02-14T22:57:46.090Z
Okay, just to clarify, the galactic coordinate system is moving with the same velocity as the sun, right? Or can it be taken as stationary relative to the galactic center?
Alec Hewitt
CC BY-SA 4.0
2020-02-14T23:26:39.037Z
It is centred on the sun, so moving with the sun,
James K
CC BY-SA 4.0
2023-11-14T08:34:02.370Z
If it's moving with the sun, what do you mean when you say the galactic coordinates don't rotate?
Jon
CC BY-SA 4.0
2023-11-14T21:17:08.450Z
They don't rotate.  The 0 longitude points to a location that is fixed relative to very distant sources (like quasars)  And since the sun is orbiting the galaxy, the position of Sag A* will very slowly move relative to these coordinates.  In 100 million years, the 0 longitude will no longer point anywhere close to the centre of the galaxy (but there will be no humans around to worry about this)
James K
CC BY-SA 4.0
2020-02-14T20:47:29.750Z
2023-11-14T22:49:00.317Z
2023-11-14T22:49:00.317Z
James K
<p>I am given equatorial coordinates and I need to transform them into a coordinate system that is at rest relative to the center of the galaxy. The closest thing I could find is galactic coordinates which seems like they are fixed with the sun at the center. Wouldn't this meant that they are moving with the same velocity as the sun and they are rotating?</p>

CC BY-SA 4.0
2020-02-15T02:07:43.777Z
These are related and you may find them helpful as well: [Where is the center of the Milky Way located?](https://astronomy.stackexchange.com/q/27964/7982) and also [can you translate a GPS coordinate to a Galactic coordinate?](https://astronomy.stackexchange.com/q/23917/7982) and also [How was the galactic plane established?](https://astronomy.stackexchange.com/q/23927/7982)
uhoh
<coordinate><galaxy-center><galactic-center>
What coordinate system is at rest relative to the center of the galaxy?
Alec Hewitt
# What coordinate system is at rest relative to the center of the galaxy?

(Asked by: username_0 on 2020-02-14)

I am given equatorial coordinates and I need to transform them into a coordinate system that is at rest relative to the center of the galaxy. The closest thing I could find is galactic coordinates which seems like they are fixed with the sun at the center. Wouldn't this meant that they are moving with the same velocity as the sun and they are rotating?

**Tags:** coordinate, galaxy-center, galactic-center
> **Comments:**
> **username_1**: These are related and you may find them helpful as well: [Where is the center of the Milky Way located?](https://astronomy.stackexchange.com/q/27964/7982) and also [can you translate a GPS coordinate to a Galactic coordinate?](https://astronomy.stackexchange.com/q/23917/7982) and also [How was the galactic plane established?](https://astronomy.stackexchange.com/q/23927/7982)  

---

## 1 answers

### Answer by username_2 on 2020-02-14. Score: 3 | Accepted answer

Galactic coordinates are sun centred with a zero longitude chosen to align with the centre of the galaxy when the measurements were made in 1958.

As defined, the galactic coordinates don't rotate, and so the position of Sag A\* is very slowly drifting. Currently Sag A\* is about 4 arc-minutes from the defined zero longitude, but decreasing by 5.7 milli-arcseconds per year (a tiny amount)

The task is ill defined, You can convert between different coordinate systems of the sky, but they all must be centred on the solar system.

> **Comments:**
> **username_0**: Okay, just to clarify, the galactic coordinate system is moving with the same velocity as the sun, right? Or can it be taken as stationary relative to the galactic center?  
> **username_2**: It is centred on the sun, so moving with the sun,  
> **username_3**: If it's moving with the sun, what do you mean when you say the galactic coordinates don't rotate?  
> **username_2**: They don't rotate.  The 0 longitude points to a location that is fixed relative to very distant sources (like quasars)  And since the sun is orbiting the galaxy, the position of Sag A* will very slowly move relative to these coordinates.  In 100 million years, the 0 longitude will no longer point anywhere close to the centre of the galaxy (but there will be no humans around to worry about this)  

---

