
Jacob W. answered 08/22/20
Chemistry, Astronomy Tutor for HS, College Chemistry, Astronomy
Angular width is measured using the following formula:
α=2arctan(D/2r)
where
α - Angular width
D- diameter or size of object, 3.9 inches
r - the distance to the object from the observer, 30.6 inches
If we plug everything in, we get:
α = 2 arctan (3.9 inches/(2*30.6 inches))
α = 2 arctan(0.06372549019 inches)
α = 7.2925 deg == 7.293 deg
For physical reference, your pinkie finger held at arms length is about half a degree, or the same size of the full moon.