Calculate the next day when the star rises, whilst it's dark

[marcmayo]

Let's say we want to observe a star or a constellation (constellation would have min and max RA/DEC from the IAU constellation boundaries )
Can we somehow iterate through the next 365 days and tell at which day the star finally rises above the horizon, whilst it's dark (sun below -6degrees) ?

[cosinekitty]

Hi @marcmayo and welcome to the project! I can help you with this.

My approach for this would be to use the DefineStar function to define the star you are interested in as a custom body. Then you can pass this body to SearchRiseSet to find the next time it rises. When you find the rise time, use that same time to find the Sun's altitude angle via the Horizon function, as demonstrated at this line of the positions.js demo. If the Sun's altitude is still above −6°, you can use the AddDays function to add, say, 0.1 days to the rise time, and call SearchRiseSet again in a loop. Keep looping until you find the dark enough time.

I don't know which of the programming languages you are interested in, so I gave JavaScript links, but a similar approach will work for the C, C#, Python, or Kotlin versions.

I hope this helps, and let us know if you run into problems, or that it works fine as is.