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