17
Angular
sizes
•Quite often we will need to find linear size of some object, given its distance and its angular size
Note – the book leaves out the units of
“arcsec”. Do not make that mistake yourself.
An example different than the one in the book: How large is the sun?
The angular diameter of the sun is about 0.50. To
convert that to arcseconds use:
0.5 deg ´ 60 arcmin/deg ´ 60 arcsec/arcmin =
1800 arcsec
The sun is 1.5 ´ 108 km
away (= 1 astronomical unit). So
From our text:
Horizons, by Seeds
I can derive this
formula in class if there is sufficient interest – ask me!