## Angular Size

The angular size of an object is the angle subtended by the object at the position of our eyes. The angular size of an object increases with the size of the object and proximity to our eyes.

The diagram shows an ject of diameter
$D$
at a distance
$d$
. The angulae subtended is
$\alpha$
and the equation relating the three is
$\alpha = \frac{D}{d}$
.