Could some explain what I need to do to see a star that, from my point of view, is behind a mountain:

enter image description here

Obviously, if it's one mountain, and not a very high one, I can just climb it to see what's behind. But what if it's a mountain range or a very high mountain?

enter image description here

Intuitively, I know I can move away from it to change the angle, and see the star. But what's the math behind it? And how does going up (or down, maybe?) help?

  • 3
    $\begingroup$ I'm stuggling to see the problem. It's no different from being unable to see an object because something opaque that's in the line of sight between you and whatever you want to see. $\endgroup$
    – Dr Chuck
    Dec 24, 2020 at 10:48
  • 9
    $\begingroup$ If the mountain is to your east, wait 2 hours. If it's to your west, wait 22 hours. $\endgroup$
    – Mike G
    Dec 24, 2020 at 14:01
  • 1
    $\begingroup$ @MikeG the last sentence of the question already acknowledges this to some extent, and asks for the math behind it. You've arrived at two actual numbers, if you can demonstrate the mathematics you've used to get them, then that's the answer. $\endgroup$
    – uhoh
    Dec 26, 2020 at 23:02

1 Answer 1


Moving away will help. If the mountain is very steep, and you are standing right next to it, you can only see objects that are directly above or behind you. Example: if the mountain is 100 ft tall, and you move 100 ft away, then you can see objects in the sky that make a 45 degree angle off the horizon. Angle = inverse tangent (mountain height / distance from mountain)


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