Is this how to compute Greenwich Hour Angle with P

问题:

I have been using python3 and pyephem to study celestial navigation mostly working through some calculations that would have to be done by hand in any case.
For the sight reduction part I am trying to have pyephem output data comparable to the nautical almanac, mostly greenwich hour angle and declination. To get the hour angle of the first point of aries, I tried adding a body using ephem.readdb at 0.0 RA and 0.0 dec. But after reading the doc further I think this is working.

#!/bin/python3

import math , ephem
#  zero longitude
gmt_long = '0:0:0'          #  deg, min, sec
myloc_date = ( '2012/12/02 22:00:00' )
# observer for greenwich  gst
utcz = ephem.Observer()
utcz.date = myloc_date
utcz.long = gmt_long
print ( utcz.date )
print (" gst hours", utcz.sidereal_time() )
print (" gst   deg", ephem.degrees( utcz.sidereal_time() ) )

Compare the last line of output with the aries column in the nautical almanac for the date

online version of nautical almanac www.tecepe.com.br

回答1:

Yes, this does look to be the correct approach; each of your steps makes sense, and so the agreement between your result and the Almanac is meaningful. Here, for anyone else who wants to make the comparison, is the particular page from the Almanac that you reference:

http://www.tecepe.com.br/scripts/AlmanacPagesISAPI.dll/pages?date=12%2F02%2F2012