Question

Approximately 9000 stars are visible to the naked eye in the whole sky (imagine that you could see around the entire globe and both the northern and southern hemispheres), and there are about 41,200 square degrees on the sky. How many stars are visible per square degree? Per square arcsecond?

Answer 1

`1.6 * 10^(-8)`

Step-by-step explanation:

The whole sky is considered as a sphere called as Celestial Sphere.

Total no. of stars visible to the naked eye in the whole sky = 9000

Area of the whole sky in degrees = 41200 square degrees

No. of stars in 1 square degree =
`(9000)/(41200)` = 0.218

Also 1 degree = 60 arcminutes

1 arcminute = 60 arcseconds

Thus, 1 degree = 3600 arcseconds

Thus, No. of stars visible in per square arcsecond =
`(0.218)/(3600* 3600) = 1.6 * 10^(-8)`