我发现当我将（Alt，Az）转换为（Ra，Dec）然后回到PyEphem时，我得不到我的开头。下面是一个简单的例子。
import ephem
print ephem.__version__
# '3.7.3.4'
gbt = ephem.Observer()
gbt.long = '-79:50:23.4'
gbt.lat = '38:25:59.23'
gbt.pressure = 0 # no refraction correction.
gbt.epoch = ephem.J2000
# Set the date to the epoch so there is nothing changing.
gbt.date = '2000/01/01 12:00:00'
# Should get the north pole right?
ra, dec = gbt.radec_of(0, '38:25:59.23')
# Not the north pole... error might be abberation.
print dec
# 89:59:30.5
# Now check internal consistancy by reversing the calculation.
pole = ephem.FixedBody()
pole._ra = ra
pole._dec = dec
pole._epoch = ephem.J2000
pole.compute(gbt)
# Should get what I started with right?
alt = pole.alt
# Not what I started with... error unknown.
print alt
# 38:26:26.7
正如评论中指出的那样，尽管30英寸比维基百科规定的最大效果为20英寸，但并不完全是北极可能只是恒星畸变。
当我进行反向计算时，我没有得到同样的事实，这让我很困惑。有什么建议吗？