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Small-angle Formula




The small-angle formula is a Mathematical approximation, used in Astronomy . It relates the linear size (''D'') of an object to its Angular size (α) and its distance from the observer (''d'') and is a valid approximation if α is small.

The approximate formula is:

D


Here, α has to be measured in Arcsecond s.

The number 206,265 is approximately equal to the number of Arcsecond s in a Circle (1,296,000), divided by .

The exact formula is
D

and the above approximation follows from this because tan(''x'') is approximately equal to ''x'' if ''x'' is small.