Celestial sphere

Definition

The celestial sphere is an imaginary sphere that extends infinitely into space with Earth at its center, used to map the positions of stars and planets. Astronomers use it to simplify the complex motions of celestial bodies for observation and navigation.

5 Must Know Facts For Your Next Test

1. The celestial sphere is divided into two hemispheres by the celestial equator, which is an extension of Earth's equator.
2. The north and south celestial poles are extensions of Earth's poles onto the celestial sphere.
3. Right ascension and declination are coordinate systems used to pinpoint locations on the celestial sphere, analogous to longitude and latitude on Earth.
4. Stars appear to move across the sky along paths called diurnal circles due to Earth's rotation, making practical use of the celestial sphere important for tracking these movements.
5. The ecliptic is the apparent path that the Sun follows over a year on the celestial sphere, intersecting it at two points known as equinoxes.

Review Questions

• What coordinate system is used on the celestial sphere to locate stars?
• How does Earth's rotation affect our perception of star movement on the celestial sphere?
• What is the significance of the ecliptic on the celestial sphere?

Related terms

Right Ascension:

A coordinate in astronomy equivalent to longitude, used alongside declination to locate objects on the celestial sphere.

Declination:

A coordinate in astronomy equivalent to latitude, used alongside right ascension to specify locations on the celestial sphere.

Ecliptic:

The apparent annual path of the Sun across the sky, intersecting with Earth’s orbit plane at two points known as equinoxes.