I'm developing a Planetarium software and I have no idea about how what stars and planets are visible today (mm/dd/yyyy hh:mm) given a latitude and longitude.
Reading this tutorial, I have found how to use latitude to determinate north celestial pole position.
But I don't know how can I know which stars are visible given longitude in a particular date.
I have searched a lot on Internet but I haven't found anything (maybe because I haven't searched with the right words).
How can I calculate which star is at Zenith given a longitude and a time (i.e. now)?
Best Answer
As you might know, we use RA (Right Ascension) and DEC(declination) to locate the stars in the sky. Now the RA and DEC co-rodinates of any star is fixed.
However, locally to locate a star we use ALT / AZ co-ordinate system. The ALT and AZ of a star depends upon the LAT/LONG of the place you are observing from and the time. There are many online converters which will help you convert from ALT/AZ to RA/DEC and vice verse.
The ALT of a star at the Zenith is 90 degrees. Therefore, look for stars ( trial and error or parse through a list) to find which stars for your present location and time has ALT = 90deg.
This might help you https://www.youtube.com/watch?v=ih7aGeFKBPE