Hi All, I've been taking a bit of a crash course in astronomy for a raspberry pi project I'm toying with. I basically want to create a window to the night sky without the actual window but a screen to replace it. Barring the practicality (psh, who needs that) of doing this, it's been a lot of fun learning all this stuff. I've gotten to the point where given any lat/lng and time, I can calculate all the stars in the night sky from horizon to horizon. And I think given just a window with a squared up vertical/horizontal orientation, I can also calculate the stars in that range, even if the window moves up in elevation from the horizon. My math for this is something like: Assume the observer looking out is in the center of the window and estimate the distance to the window to get the angle of the observer's line of sight relative to the vertical window side. Doubling this (since your observer is centered) creates a range of azimuth angles. Do something similar but with the horizontal window sides to get your range of elevation angles. Any stars that are within these ranges are visible through the window. 1) Is my math correct for this? 2) Now let's say I were to give the window an arbitrary orientation so that my vertical sides and horizontal window sides are tilted by X degrees, what does my math become then? If an added visualization is needed, I think this problem is similar to how Star Walk is able to handle my tilting the phone one way or the other. How the heck is it able to calculate what stars are just ahead? Thanks for any help you can provide!