Angular Diameter Calculator

d = 2 arctan(size / 2D)

Physical Diameter

Size Unit

Distance

Distance Unit

Formula

angular diameter = 2 arctan(physical size / (2 x distance))

What is angular diameter?

Angular diameter is the apparent size of an object measured as an angle. The Moon is about 0.5 degrees.

Why do objects appear smaller farther away?

Angular diameter decreases with distance. Twice the distance means half the angular size.

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