Aparant size of an object based on distance from it.

[Runaway]

Is there an equation I could use to determine how big something would appear to be at a certain distance from said object?

In particular I want to find how big the Earth would appear to be from half way from the Earth to the moon if a picture was taken of it with 1x zoom. in other words, how big would a sphere with a diameter of 12,756.1 km appear from 192,201.5 km away?

 

[chroot]

Hey Runaway,

It's actually pretty simple. Just draw a long skinny right triangle. The long side of the triangle is the distance between the observer and the object. The short side of the triangle is one-half the size of the object. If you put two of these skinny triangles side by side, you'd make a "cone." The angle at the tip of the cone is the apparent size of the object.

Are you comfortable with the trigonometry involved in solving for the angle?

- Warren