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In Pyephem is there a way to list Greenwich Siderial Time GST so that I can convert Right Ascension RA to Greenwich Hour Angle GHA?

>>>import ephem                                       
>>>j=ephem.Sun()                               
>>>j.compute('2018/11/10 23:00:00.0')                 
>>>print('%s %s' %  (j.ra, j.dec))                          
15:04:08.77  -17:19:41.4

I am using idle-python2.7, I am not familiar enough with Pyephem to determine where/when the first point of Aries is. With this I can convert ra-->gha. The above gives the ra/dec for the Sun for date/time shown

stovfl
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J.Clark
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  • Could you show some example code? That would make it easier to see what exactly you need. – mkrieger1 Nov 10 '18 at 17:16
  • >>>import ephem >>>j=ephem.Sun() >>>j.compute('2018/11/10 23:00:00.0') >>>print('%s %s' % (j.ra, j.dec)) 15:04:08.77 -17:19:41.4 I am using idle-python2.7, I am not familiar enough with Pyephem to determine where/when the first point of Aries is. With this I can convert ra-->gha. The above gives the ra/dec for the Sun for date/time shown. Thanks! – J.Clark Nov 10 '18 at 23:56
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    I found a post with a solution dec1st_2012_user 1867570, He created an object with RA=0deg and worked out the Greenwich Siderial Time GST from there. BR/JC – J.Clark Nov 12 '18 at 20:24
  • Thanks so much for finding that existing answer! I've edited its title to make it clearer, and used the "duplicate" button to create a link here. – Brandon Rhodes Nov 17 '18 at 09:12
  • I learned so much researching this! My basic motivation was to have an alternate source for getting GHA/RA other than the Nautical Almanac. I first tried using the JPL Horizons web interface, but I found a huge difference in Sun DEC over the NA by about 29min. Then I used PyEphem and found the answer to my question on stack! I also found an earlier answer to why the DEC is different due to the nature of the "epoch" (Skyfield & Nautical Almanac 2016/7/23). I wonder if you can adjust JPL web to set this? Anyways thanks for the valuable info. BR/JC – J.Clark Nov 18 '18 at 15:37

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