What is Angular Size?

Angular size is method of measuring how big something in the sky appears.

If you think of the sky as a big ball surrounding the Earth then you can imagine a grid system laid out on the ball. Since the ball is round and we don’t the know the size of it the easiest grid pattern would be degrees (or radians).

There are 360 degrees in a circle. That means that any one time you can see 180 degrees of the sky (the rest is below the horizon).

With 180 degrees from horizon to horizon then over head is 90 degrees up.

Even though you might think of the Sun and Moon as large objects in the sky they are really only about 1/2 of a degree in angular size. (That means you could fit 180 moons from the horizon to the zenith overhead.)

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