Celestial Sphere Basics

Question 1

What is the celestial sphere?

Answer 1

An imaginary sphere surrounding Earth onto which stars and celestial objects are projected.

Question 2

What is the celestial equator?

Answer 2

Projection of Earth’s equator onto the celestial sphere.

Question 3

What are right ascension (RA) and declination (Dec)?

Answer 3

RA = celestial longitude (measured in hours, minutes, seconds).
Dec = celestial latitude (measured in degrees north/south of celestial equator).

Question 4

What is the zenith?

Answer 4

The point directly overhead an observer.

Question 5

What is the horizon in celestial terms?

Answer 5

The apparent line dividing Earth and sky.

Question 6

What is spherical trigonometry used for in astronomy?

Answer 6

Calculating angular distances, positions, and transformations between coordinate systems.