<p>Given a specific date and time, and coordination of a location on earth, how can I calculate (myself, or using a python package) range of visible RA and Dec? </p>

<p>For example (but I'm looking for a general solution and formula):</p>

<p><strong>input:</strong> </p>

<ol>
<li><p>date and time: 2019-05-01 23:00:00</p></li>
<li><p>earth coordinates: 32.0853° N, 34.7818° E</p></li>
</ol>

<p><strong>output:</strong> </p>

<ol>
<li><p>RA min: ?</p></li>
<li><p>RA max: ?</p></li>
<li><p>Dec min: ?</p></li>
<li><p>Dec max: ?</p></li>
</ol>

CC BY-SA 4.0
2019-05-22T04:47:31.070Z
[astroplan's Observer class](https://astroplan.readthedocs.io/en/latest/api/astroplan.Observer.html#astroplan.Observer) contains a lot of methods which could be helpful for getting started as it can give you the local sidereal time at twilight of your choosing. What RA this corresponds to will depend on how much Hour Angle range you want to allow
astrosnapper
CC BY-SA 4.0
2019-05-22T13:59:26.827Z
There may be some detail missing from your question, but as asked, these are the answers:
 1. RA min: 0h.
 2. RA max: 24h. All hours of Right Ascension are visible within 32 degrees of the celestial pole. :-)
 3. Dec min = latitude - 90 = 32.0853 - 90 = -57.9147 degrees (ignoring refraction and atmospheric extinction.)
 4. Dec max = 90 degrees. The celestial pole is visible.
JohnHoltz
CC BY-SA 4.0
2019-05-22T20:19:44.223Z
@JohnHoltz - thanks! I was indeed asking without fully understanding the domain.. So still didn't get it - in the general case (earth coordinates = x N, y E), what would be the formula for the RA?
KeshetE
CC BY-SA 4.0
2019-05-22T20:25:25.710Z
@astrosnapper - thanks! I will take s look at that! What do you mean by the Hour Angle I wish to allow? I want to assume the terrain is completely flat, and describe (using RA and Dec) the visible sky area at a given location and a given time.
KeshetE
CC BY-SA 4.0
2019-05-22T22:33:18.717Z
@KeshetE If you were doing this for a telescope on a equatorial mount for instance, you may be mechanically limited by how many hours of Right Ascension you can observe either side of the meridian. If your telescope can do +/-5 hours Hour Angle either side before hitting a stop and the Local Sidereal Time was say 12h, then you can observe from 7h to 19h in RA. If you considering down to the horizon then this doesn't apply and you can consider +/-12 hours of Hour Angle
astrosnapper
<coordinate><star-maps>
Calculating the range of visible Right Ascension and Declination from specific location + time
KeshetE
# Calculating the range of visible Right Ascension and Declination from specific location + time

(Asked by: username_0 on 2019-05-21)

Given a specific date and time, and coordination of a location on earth, how can I calculate (myself, or using a python package) range of visible RA and Dec?

For example (but I'm looking for a general solution and formula):

**input:**

1. date and time: 2019-05-01 23:00:00
2. earth coordinates: 32.0853° N, 34.7818° E

**output:**

1. RA min: ?
2. RA max: ?
3. Dec min: ?
4. Dec max: ?

**Tags:** coordinate, star-maps
> **Comments:**
> **username_1**: [astroplan's Observer class](https://astroplan.readthedocs.io/en/latest/api/astroplan.Observer.html#astroplan.Observer) contains a lot of methods which could be helpful for getting started as it can give you the local sidereal time at twilight of your choosing. What RA this corresponds to will depend on how much Hour Angle range you want to allow  
> **username_2**: There may be some detail missing from your question, but as asked, these are the answers:  1. RA min: 0h.  2. RA max: 24h. All hours of Right Ascension are visible within 32 degrees of the celestial pole. :-)  3. Dec min = latitude - 90 = 32.0853 - 90 = -57.9147 degrees (ignoring refraction and atmospheric extinction.)  4. Dec max = 90 degrees. The celestial pole is visible.  
> **username_0**: @JohnHoltz - thanks! I was indeed asking without fully understanding the domain.. So still didn't get it - in the general case (earth coordinates = x N, y E), what would be the formula for the RA?  
> **username_0**: @astrosnapper - thanks! I will take s look at that! What do you mean by the Hour Angle I wish to allow? I want to assume the terrain is completely flat, and describe (using RA and Dec) the visible sky area at a given location and a given time.  
> **username_1**: @KeshetE If you were doing this for a telescope on a equatorial mount for instance, you may be mechanically limited by how many hours of Right Ascension you can observe either side of the meridian. If your telescope can do +/-5 hours Hour Angle either side before hitting a stop and the Local Sidereal Time was say 12h, then you can observe from 7h to 19h in RA. If you considering down to the horizon then this doesn't apply and you can consider +/-12 hours of Hour Angle  

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## 0 answers

