How to compute rising / setting times for stars and deep sky objects with Skyfield?

Question

I'm trying to compute rising and settings times for various objects with the Skyfield library. While the task is quite easy and well documented for planets (using the almanac.rising_and_setting function), it is not too clear to me how to do this with Stars and Deep Sky Objects.

Btw, how do I load NGC catalogues?

Answer 1

If you have the RA and declination coordinates for any object, whether for a star or anything else, you can create a Skyfield Star that represents its position in the heavens:

https://rhodesmill.org/skyfield/stars.html#building-a-single-star-from-its-coordinates

You can then pass that object — barnard in the example code at the above link — to almanac.rising_and_setting() exactly as you would pass a planet. The code would look like the example here:

https://rhodesmill.org/skyfield/almanac.html#risings-and-settings

— except that your call would look like:

f = almanac.risings_and_settings(eph, barnard, bluffton)

There is not currently a way to load the NGC catalogs — I’ve never actually taken a look at how they are formatted online, nor have I seen a Skyfield contributor offer anything yet. If you have a link to your favorite online source for the NGC catalog, though, we could take a look? Open an issue if you find an online NGC catalog and think that Skyfield should learn to read it.