# Calculating the range of visible Right Ascension and Declination from specific location + time

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: ?

• astroplan's Observer class 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 May 22 '19 at 4:47
• 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. May 22 '19 at 13:59
• @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? May 22 '19 at 20:19
• @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. May 22 '19 at 20:25
• @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 May 22 '19 at 22:33