Given a specific coordinate and a specific object, calculate times of conjunction for a given time span

[cnighswonger]

What I want to do is to specify an object, a coordinate, and a time span and be given back a list of conjunctions within some margin of error of the specified coordinate.

Is there any such high level functionality in Skyfield? Or will I need to dig in?

TIA

[brandon-rhodes]

That's a great question — the almanac module already has a search routine for conjunctions of planets with the Sun:

https://rhodesmill.org/skyfield/almanac.html#opposition-and-conjunction

It might be a simple adjustment to have a routine that does conjunctions between objects. Then you could give it a planet and, say, a Star object whose RA and Dec were at your coordinate of interest. My guess is that you'll want to dig in and try adapting the Sun-planet routine to look for conjunctions instead with a body the user passes in. Here's the code of the current routine:

python-skyfield/skyfield/almanac.py

Lines 168 to 189 in 2b3e23d

	def oppositions_conjunctions(ephemeris, target):
	"""Build a function to find oppositions and conjunctions with the Sun.
	See :ref:`oppositions-conjunctions` for how to call this routine and
	interpret the results.
	"""
	earth_at = ephemeris['earth'].at
	sun = ephemeris['sun']
	def leading_or_trailing(t):
	"""Return whether the target is east or west of the Sun."""
	e = earth_at(t)
	_, slon, _ = e.observe(sun).apparent().ecliptic_latlon()
	_, tlon, _ = e.observe(target).apparent().ecliptic_latlon()
	return ((slon.radians - tlon.radians) / pi % 2.0).astype('int8')
	if target.target == 301:
	leading_or_trailing.step_days = 14 # Moon
	else:
	leading_or_trailing.step_days = 40 # Mercury (the fastest planet)
	return leading_or_trailing

See if you can get it working for something besides the Sun, I'll be interested to hear your results!

What kinds of conjunction are you searching for? Knowing a bit more about the problem would help us advise you on the approach.