The angular diameter of an object as seen from a given position is the diameter measured as an angle. It satisfies the formula δ = arctan(diameter / distance).

In astronomy the size of objects in the sky are often measured in terms of their angular diameter as seen from Earth, rather than their actual size.

The angular diameter of Earth's orbit around the Sun, from a distance of one parsec, is two arcseconds.

This table shows the angular sizes of the most important Solar System bodies.

Sun	30'
Moon	29' - 33'
Venus	10" - 58"
Jupiter	32" - 49"
Saturn	16" - 20"
Mars	4" - 16"
Uranus	3" - 4"
Neptune	2"

Alpha Centauri A: ca. 0.01"