<p>The Galactic Coordinate system is a longitude-latitude coordinate system that is used to define the positions of objects in space, most commonly objects within our own galaxy. It uses the center of our galaxy as the focal point (i.e., where we consider $(0^{\circ},\:0^{\circ})$), much like we use the position just off Africa as the focal point of the Earth's lon-lat system. You can see a visual representation of this system below.</p>

<p><a href="https://i.sstatic.net/IG5EE.jpg" rel="noreferrer"><img src="https://i.sstatic.net/IG5EE.jpg" alt="enter image description here"></a></p>

<p>The reference point is of course from our solar system. Longitude is measured in the plane of the galaxy, going positive as you sweep to the left (thus following a right-hand rule). The symbol $\ell$ is generally used for galactic longitude. Latitude is measured above or below the plane, going positive "above" the plane and negative "below". We define above and below based on the right hand rule as applied to our galaxy's rotation. The symbol $b$ is generally used for galactic latitude.</p>

<p>If someone says an object is at galactic coordinate position $(\ell,b) = (180^{\circ},\:+45^{\circ})$, then the object will be located directly opposite the galactic center and above the plane of the galaxy.</p>

<p>Aside from being a lon-lat system, just as the Earth's is, it does not share any features with Earth's lon-lat system. That is, there's generally no relation between the two and the definition of one is not affected by the other.</p>

CC BY-SA 3.0
2016-06-23T15:45:25.220Z
Thank you for such an illustrative answer. **Concepts cleared**
Amogh Mishra
CC BY-SA 3.0
2018-03-12T20:07:42.273Z
Do I understand right, that one also need a third number (e.g. the distance from the galactic center) to uniquely identify the position of a star?
Paŭlo Ebermann
CC BY-SA 3.0
2018-03-14T17:19:46.533Z
@PaŭloEbermann Yes, the galactic coordinate system describes only the location of an object on the plane of the sky. To define its position in 3D space will require a third coordinate. A more sensible coordinate would be the distance from the Sun rather than the distance from the galactic core.
zephyr
CC BY-SA 3.0
2018-03-14T18:43:06.697Z
Ah, thank you ... I misread it that the galactic core is in the center, but actually the sun is.
Paŭlo Ebermann
CC BY-SA 4.0
2020-01-07T16:41:01.727Z
@zephyr The sun seems to be at the centre of your diagram, although the focus is at (0,0) on the right side of that circle looking figure. I don't understand the physical significance of a focus placed that way.
Karthik
CC BY-SA 4.0
2020-01-07T16:52:26.530Z
This coordinate system is purely an angular coordinate system. The angle (0, 0) tells which which way to face. It doesn't prescibe a physical location somewhere in the galaxy you can go do. However, when the user is "facing" (0, 0), they should be doing so from our solar system so that (0, 0) makes them face at the center of the galaxy. Is that more clear?
zephyr
CC BY-SA 4.0
2024-11-14T18:05:58.883Z
@zephyr That was clear, and an _excellent_ map. If you made it, thank you very much!
Miss Understands
CC BY-SA 4.0
2024-11-14T18:06:55.380Z
@zephyr ... But just to be clear, the sun is at both the north and South Poles, right?
Miss Understands
CC BY-SA 3.0
2016-06-23T14:18:46.240Z
2016-06-23T15:09:06.727Z
2016-06-23T15:09:06.727Z
zephyr
<p>It has to something with the positioning of sun and galactic center of the milky way but I wasn't able to understand how for a given star, its co-ordinates are calculated.</p>

<p>Some explanation would be appreciated.</p>

<milky-way><positional-astronomy>
What is the Galactic Latitude and Galactic Longitude? How is different from the latitude and longitude we use on Earth?
Amogh Mishra
# What is the Galactic Latitude and Galactic Longitude? How is different from the latitude and longitude we use on Earth?

(Asked by: username_0 on 2016-06-23)

It has to something with the positioning of sun and galactic center of the milky way but I wasn't able to understand how for a given star, its co-ordinates are calculated.

Some explanation would be appreciated.

**Tags:** milky-way, positional-astronomy


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## 1 answers

### Answer by username_1 on 2016-06-23. Score: 17 | Accepted answer

The Galactic Coordinate system is a longitude-latitude coordinate system that is used to define the positions of objects in space, most commonly objects within our own galaxy. It uses the center of our galaxy as the focal point (i.e., where we consider $(0^{\circ},\:0^{\circ})$), much like we use the position just off Africa as the focal point of the Earth's lon-lat system. You can see a visual representation of this system below.

[![enter image description here](https://i.sstatic.net/IG5EE.jpg)](https://i.sstatic.net/IG5EE.jpg)

The reference point is of course from our solar system. Longitude is measured in the plane of the galaxy, going positive as you sweep to the left (thus following a right-hand rule). The symbol $\ell$ is generally used for galactic longitude. Latitude is measured above or below the plane, going positive "above" the plane and negative "below". We define above and below based on the right hand rule as applied to our galaxy's rotation. The symbol $b$ is generally used for galactic latitude.

If someone says an object is at galactic coordinate position $(\ell,b) = (180^{\circ},\:+45^{\circ})$, then the object will be located directly opposite the galactic center and above the plane of the galaxy.

Aside from being a lon-lat system, just as the Earth's is, it does not share any features with Earth's lon-lat system. That is, there's generally no relation between the two and the definition of one is not affected by the other.

> **Comments:**
> **username_0**: Thank you for such an illustrative answer. **Concepts cleared**  
> **username_2**: Do I understand right, that one also need a third number (e.g. the distance from the galactic center) to uniquely identify the position of a star?  
> **username_1**: @username_2 Yes, the galactic coordinate system describes only the location of an object on the plane of the sky. To define its position in 3D space will require a third coordinate. A more sensible coordinate would be the distance from the Sun rather than the distance from the galactic core.  
> **username_2**: Ah, thank you ... I misread it that the galactic core is in the center, but actually the sun is.  
> **username_3**: @username_1 The sun seems to be at the centre of your diagram, although the focus is at (0,0) on the right side of that circle looking figure. I don't understand the physical significance of a focus placed that way.  
> **username_1**: This coordinate system is purely an angular coordinate system. The angle (0, 0) tells which which way to face. It doesn't prescibe a physical location somewhere in the galaxy you can go do. However, when the user is "facing" (0, 0), they should be doing so from our solar system so that (0, 0) makes them face at the center of the galaxy. Is that more clear?  
> **username_4**: @username_1 That was clear, and an _excellent_ map. If you made it, thank you very much!  
> **username_4**: @username_1 ... But just to be clear, the sun is at both the north and South Poles, right?  

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