<p>I remember answering a question on the origin of declination last year (<a href="https://astronomy.stackexchange.com/questions/14275/why-is-declination-positive-in-the-northern-hemisphere/14278#14278">Why is declination positive in the northern hemisphere?</a>) which led me to discover <a href="http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1942PASP...54...77W&amp;db_key=AST" rel="nofollow noreferrer">this paper</a> on the origin of celestial co-ordinate systems. In it they seem to indicate that the ancient Greeks were the first to use Right Ascension to describe locations in the sky around 300 B.C. 
Whereas Alt-Az co-ordinates (or variants of) have been around much longer because the horizon is an easy point of reference to start from. The first documented use comes from Babylonian times but the ancient Egyptians are also thought to have used a similar system as far back as 2000 B.C.</p>

<p>Reference paper: <a href="http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1942PASP...54...77W&amp;db_key=AST" rel="nofollow noreferrer">http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1942PASP...54...77W&amp;db_key=AST</a></p>

CC BY-SA 3.0
2017-06-12T11:25:19.190Z
2017-06-12T11:25:19.190Z
Dean
<p>Astrolabe, somehow can be taught as recent sky apps in which you can anticipate the exact position of stars, a very older version of course.But sextant is actually a tool for measuring angles (altitude of sun or any other star). </p>

<p>These definitions should not be considered so strict. Since ancient astronomers probably have used astrolabe as a tool for their research as well.</p>

CC BY-SA 3.0
2017-06-11T14:59:14.300Z
2017-06-11T14:59:14.300Z
arash
<p>When were the Alt-az system and the RA-dec system first used?</p>

<star><observational-astronomy><history><navigation>
When were the horizontal and equatorial celestial coordinate systems invented?
Kiril Mladenov
# When were the horizontal and equatorial celestial coordinate systems invented?

(Asked by: username_0 on 2017-06-11)

When were the Alt-az system and the RA-dec system first used?

**Tags:** star, observational-astronomy, history, navigation

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## 2 answers

### Answer by username_1 on 2017-06-12. Score: 1

I remember answering a question on the origin of declination last year ([Why is declination positive in the northern hemisphere?](https://astronomy.stackexchange.com/questions/14275/why-is-declination-positive-in-the-northern-hemisphere/14278#14278)) which led me to discover [this paper](http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1942PASP...54...77W&db_key=AST) on the origin of celestial co-ordinate systems. In it they seem to indicate that the ancient Greeks were the first to use Right Ascension to describe locations in the sky around 300 B.C.
Whereas Alt-Az co-ordinates (or variants of) have been around much longer because the horizon is an easy point of reference to start from. The first documented use comes from Babylonian times but the ancient Egyptians are also thought to have used a similar system as far back as 2000 B.C.

Reference paper: <http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1942PASP...54...77W&db_key=AST>


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### Answer by username_2 on 2017-06-11. Score: 0

Astrolabe, somehow can be taught as recent sky apps in which you can anticipate the exact position of stars, a very older version of course.But sextant is actually a tool for measuring angles (altitude of sun or any other star).

These definitions should not be considered so strict. Since ancient astronomers probably have used astrolabe as a tool for their research as well.


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