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skyfielders / python-skyfield

Elegant astronomy for Python
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RA and Dec overhead #310

Closed skynoob-new closed 4 years ago

skynoob-new commented 4 years ago

Hello, For a given RA(Right Ascension) and Declination, how can i find where that is located on the earth as a subpoint. Pls give me an example for the same.

skynoob-new commented 4 years ago

Any help on this would be helpful. Thanks

skynoob-new commented 4 years ago

is my question correct or is it tough to achieve this?

skynoob-new commented 4 years ago

@brandon-rhodes can you pls help me on this

ghost commented 4 years ago

My thinking would be that the overhead right ascension would be the local sidereal time and the overhead declination would the latitude. I'll let Brandon confirm here. If what I'm saying is correct, we probably don't need a special new function to compute this.

brandon-rhodes commented 4 years ago

Your question raises a bigger question that I'm not sure how we'll address going forward: given a library with features that can be combined in many ways, does the documentation eventually need to expand to show all the ways they can be combined, or is there a way the documentation of the individual pieces can be so clearly explained that the parts can be put together independently by users?

I created the Examples page recently to absorb "how to put things together" questions. I'm not going to worry right now over whether, if only position_from_radec() and subpoint() had been better and more brilliantly documented, it would be clear that position_from_radec().subpoint() is the solution here. Instead, I've just added it as an example:

https://rhodesmill.org/skyfield/examples.html#what-latitude-and-longitude-is-beneath-this-right-ascension-and-declination

But, just in case: if anyone reading does see shortcomings in the documentation of position_from_radec() and subpoint() that could have led users to not imagine combining them, let me know and I'll try to get them fixed!