You can use the following equations to work out the (visual and actual) width [i]w[/i] of a distant object (whether it's flat or spherical), as long as you know its distance [i]d[/i] and angular width [i]θ[/i].

You can work out the (visual and actual) width of an object if you know its distance [i]d[/i] and angular width [i]θ[/i]. For a disc or something on a flat surface, you'll use the (arc)tangent, while for a spherical or cylindrical object, you'll use the (arc)sine.