<p>I want to write a program which, when given a date, a time, latitude and longitude, returns a list of the planets, Messier objects and NCC catalogue objects what are visible in the sky at that time and place?</p>

<p>Are there any APIs which can do this or would I have to calculate the positions?</p>

<p>Preferably, this should be accessible using JavaScript</p>

CC BY-SA 3.0
2018-01-14T18:15:04.157Z
You want to find the sky position (alt and az) from the equatorial coordinates, time and observer position. (ra dec, time, long and lat) This has been asked before. I will try to find the duplicate.
James K
CC BY-SA 3.0
2018-01-14T18:23:53.527Z
@JamesK I think I know what you're referring to, but the answer suggests the now discontinued Google Earth Sky Map API
Beta Decay
CC BY-SA 3.0
2018-01-14T19:00:00.347Z
I think it is this answer https://astronomy.stackexchange.com/questions/8390/cancelling-out-earth-rotation-speed-altazimuth-mount/8415#8415 There is another question that I can't find now. It asks why someone's algorithm isn't working quite correctly, and the reason is no accounting for precession.
James K
CC BY-SA 3.0
2018-01-14T20:09:46.957Z
Logically of a catalog of several thousand visible objects, from any location on Earth and ignoring weather conditions, about half of them will be theoretically visible.  It may be more efficient (computationally) to just use automatic graphics clipping to  not display the non-visible objects than to actually try and work out which ones are visible.  This will depend on the specifics of your application and hardware, but worth considering.
StephenG - Help Ukraine
<observational-astronomy><astrometry><javascript>
How do you find the positions of celestial objects in the sky?
Beta Decay
# How do you find the positions of celestial objects in the sky?

(Asked by: username_0 on 2018-01-14)

I want to write a program which, when given a date, a time, latitude and longitude, returns a list of the planets, Messier objects and NCC catalogue objects what are visible in the sky at that time and place?

Are there any APIs which can do this or would I have to calculate the positions?

Preferably, this should be accessible using JavaScript

**Tags:** observational-astronomy, astrometry, javascript
> **Comments:**
> **username_1**: You want to find the sky position (alt and az) from the equatorial coordinates, time and observer position. (ra dec, time, long and lat) This has been asked before. I will try to find the duplicate.  
> **username_0**: @JamesK I think I know what you're referring to, but the answer suggests the now discontinued Google Earth Sky Map API  
> **username_1**: I think it is this answer https://astronomy.stackexchange.com/questions/8390/cancelling-out-earth-rotation-speed-altazimuth-mount/8415#8415 There is another question that I can't find now. It asks why someone's algorithm isn't working quite correctly, and the reason is no accounting for precession.  
> **username_2**: Logically of a catalog of several thousand visible objects, from any location on Earth and ignoring weather conditions, about half of them will be theoretically visible.  It may be more efficient (computationally) to just use automatic graphics clipping to  not display the non-visible objects than to actually try and work out which ones are visible.  This will depend on the specifics of your application and hardware, but worth considering.  

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