Venus phase #1059
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I wonder if there is a way to find out whether Venus is waxing or waning at a given instant of time without looking for minima and maxima first. But first there is the calculation fo the phase angle. Before I found out that there is a def venus_phase(t):
""" phase of venus at time t """
# position of Earth at time t
e0 = earth.at(t)
# time the light needs to get from venus to Earth
diff_t = e0.observe(venus).apparent().light_time
# timestamp when the light started at Venus to arrive at Earth at time t
try:
len(t)
tv = ts.tt_jd([x.tt for x in (t-diff_t)])
except TypeError:
tv = t - diff_t
# position of Venus at that time
v = venus.at(tv)
# direction of the Sun seen from Venus at that time
s = v.observe(sun).apparent()
# direction of the light starting at Venus to arrive at the position
# the Earth will be later on at time t
e = e0-v
# return the angle between the direction to the Sun and the direction
# to where the Earth will be
return s.separation_from(e)The results are very similar but not the same: Is that because of the comment in the source of Skyfield about light travel? Now I look how to get whether it's waxing or waning, but to no result so far. |
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I'm not sure, we would have to edit the
You could compute the phase angle one second in the future and see if it's more or less, which would tell you if it's waxing or waning. |
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Oh, yes, that is an idea. Thank you. |
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I'm not sure, we would have to edit the
phase_angle()method and see if the result matched your routine.You could compute the phase angle one second in the future and see if it's more or less, which would tell you if it's waxing or waning.