I have time in J2000 format, ie. seconds after noon on 1-1-2000, which I want to convert to UTC time in an array with the format [year-month-day hour:min:sec.millisec]. Is there some function in AstroPy or something similar to do the conversion?
Input: Time in J2000: 559889620.293 seconds
Desired Output: Time in UTC: 2017-09-28 16:53:40.293
If you want to use astropy you could use Time and TimeDelta from astropy.time:
>>> from astropy.time import TimeDelta, Time
>>> from astropy import units as u
>>> (Time(2000, format='jyear') + TimeDelta(559889620.293*u.s)).iso
'2017-09-28 16:53:35.293'
The Time(2000, format='jyear') is a good alternative if you don't want to remember what the baseline for julian dates (noon on 1.1.2000) is.
The offset is constant, so you can just add it:
>>> OFFSET = datetime(2000,1,1,12) - datetime(1970,1,1)
>>> datetime.utcfromtimestamp(559889620.293) + OFFSET
datetime.datetime(2017, 9, 28, 16, 53, 40, 293000)
You can simply add a timedelta to a base datetime.
import datetime
datetime.datetime(2000, 1, 1, 12, 0) + datetime.timedelta(seconds=559889620.293)
returns:
datetime.datetime(2017, 9, 28, 16, 53, 40, 293000)