<p>To locate an object you need a system of coordinates. </p>

<p>You need to define a plane (to define the latitude) and a direction (from which to measure longitude). On Earth, the obvious plane is the Equator. There is no obvious direction from which to measure longitude (which in the past led to different definition of longitude in France and Britain)</p>

<p>There is no single, natural plane in the sky. Several are possible: You can project the equator into the sky. You can use the plane of the Earth's orbit around the sun. You could use the plane of the galactic disc.</p>

<p>Using the Equator is simple, but rather Earth-centric. The Ecliptic system is more natural for solar system objects. The galactic system nice for deep space objects. The lack of a single natural plane in the sky means that several different coordinates systems can co-exist.</p>

<p>As an example Rigel, at RA 5h14'32'', Dec −08° 12′ 05''</p>

<p>Has a Lat-Long of:</p>

<ul>
<li>-31.11°  76.09°   Ecliptic</li>
<li>-4.40°    219.66°  Galactic</li>
</ul>

CC BY-SA 3.0
2017-06-16T08:12:35.963Z
Thank you! Could you recommend me a paper about the different definitions in the past which you mentioned? I am interested exactly in these developments of concepts: Where to measure something from? Is there another way to do it? etc. I am a historian and work with Akkadian texts. There (maybe you already know) there is a concept of Paths: Paths of Ea, Anu and Enlil (i.e. that we might call declination) and Path of the Moon (i.e. longitude)
Kiril Mladenov
CC BY-SA 3.0
2017-06-13T15:55:12.680Z
2017-06-13T15:55:12.680Z
James K
<p>Of course, I know what the ecliptic is and what equator is. The problem is I still can not understand why we need two systems for measuring the same thing - are each of them useful only in specific occasions? For example, which is preferred in marine navigation? I am interested in this practical side of the question</p>

<p>Can you give an example which positions a star, using both coordinate systems?</p>

CC BY-SA 3.0
2017-06-13T09:38:11.790Z
I'm voting to close this question as off-topic because it appears to be a homework question
adrianmcmenamin
CC BY-SA 3.0
2017-06-13T11:03:27.633Z
No, it is not a homework. I am just having difficulties with understanding the principle. Funny guess by the way : ))
Kiril Mladenov
CC BY-SA 3.0
2017-06-13T15:21:17.593Z
I did. Of course, I know what ecliptic is and what is equator. The problem is I still can not understand why we need two systems for measuring the same thing - are each of them useful only in specific occasions? For example,which is preferred in marine navigation? I am interested in this practical side of the question as I must admit (it should be obvious so far) that I do not have a degree in astronomy and in physics
Kiril Mladenov
CC BY-SA 3.0
2017-06-13T15:35:23.763Z
The answer is: certain things are easier to express/calculate in one coordinate system than the other. Anything involving the solar system and the motion of bodies in it, for example, is usually easier to express in ecliptic. Equatorial coordinates make stellar navigation easier, not to mention star tracking during prolonged exposures.
Sean Lake
<star><coordinate>
What is the difference between equatorial and ecliptical coordinate system?
Kiril Mladenov
# What is the difference between equatorial and ecliptical coordinate system?

(Asked by: username_0 on 2017-06-13)

Of course, I know what the ecliptic is and what equator is. The problem is I still can not understand why we need two systems for measuring the same thing - are each of them useful only in specific occasions? For example, which is preferred in marine navigation? I am interested in this practical side of the question

Can you give an example which positions a star, using both coordinate systems?

**Tags:** star, coordinate

> **Comments:**
> **username_1**: I'm voting to close this question as off-topic because it appears to be a homework question  
> **username_0**: No, it is not a homework. I am just having difficulties with understanding the principle. Funny guess by the way : ))  
> **username_0**: I did. Of course, I know what ecliptic is and what is equator. The problem is I still can not understand why we need two systems for measuring the same thing - are each of them useful only in specific occasions? For example,which is preferred in marine navigation? I am interested in this practical side of the question as I must admit (it should be obvious so far) that I do not have a degree in astronomy and in physics  
> **username_2**: The answer is: certain things are easier to express/calculate in one coordinate system than the other. Anything involving the solar system and the motion of bodies in it, for example, is usually easier to express in ecliptic. Equatorial coordinates make stellar navigation easier, not to mention star tracking during prolonged exposures.  

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## 1 answers

### Answer by username_3 on 2017-06-13. Score: 1

To locate an object you need a system of coordinates.

You need to define a plane (to define the latitude) and a direction (from which to measure longitude). On Earth, the obvious plane is the Equator. There is no obvious direction from which to measure longitude (which in the past led to different definition of longitude in France and Britain)

There is no single, natural plane in the sky. Several are possible: You can project the equator into the sky. You can use the plane of the Earth's orbit around the sun. You could use the plane of the galactic disc.

Using the Equator is simple, but rather Earth-centric. The Ecliptic system is more natural for solar system objects. The galactic system nice for deep space objects. The lack of a single natural plane in the sky means that several different coordinates systems can co-exist.

As an example Rigel, at RA 5h14'32'', Dec −08° 12′ 05''

Has a Lat-Long of:

* -31.11° 76.09° Ecliptic
* -4.40° 219.66° Galactic

> **Comments:**
> **username_0**: Thank you! Could you recommend me a paper about the different definitions in the past which you mentioned? I am interested exactly in these developments of concepts: Where to measure something from? Is there another way to do it? etc. I am a historian and work with Akkadian texts. There (maybe you already know) there is a concept of Paths: Paths of Ea, Anu and Enlil (i.e. that we might call declination) and Path of the Moon (i.e. longitude)  

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