The Celestial Sphere

how to learn stargazing

What is the Celestial Sphere ?

By turning, our planet makes the stellar patterns disappear as the night progresses before making them reappear the next night. This imaginary sphere, which arouses the wonder of amateur and professional astronomers, is called the celestial sphere.

celestial sphere
Image courtesy of the Lunar and Planetary Institute

Important landmarks on the Celestial Sphere

Celestial Equator

This large circle on the celestial sphere belongs to the same plane as the terrestrial equator on Earth and is inclined at about 23 ° from the ecliptic.

North Celestial Pole

This is the northernmost point in the sky around which all the stars seem to turn, also called “Pole Star”, or Polaris.

Ecliptic

This is the trajectory drawn by the Sun on the celestial sphere.

Spring Equinox

When the Sun is at the point of intersection between the celestial equator and the ecliptic in the northern hemisphere, it is said to be at the vernal point. At this point occurs the March equinox, or vernal.

South Celestial Pole

Only visible from the southern hemisphere, the stars revolve around the faint South Pole Star, Sigma Octantis.

Right Ascension (RA)

It is the celestial equivalent of the terrestrial longitude projected on the celestial sphere. It is measured in hours (h), minutes (min) and seconds (s).

Fall Equinox

When the Sun is at the point of intersection between the celestial equator and the ecliptic in the Southern Hemisphere, it is said to be at the Fall equinox. The Fall equinox occurs at this point.

Declination (Dec)

Similar to the geographic latitude of the Earth projected on the celestial sphere. It is measured in degrees (°), minutes (‘) and seconds (“)