Motions of the sun, moon, and planets on the celestial sphere

Let's adopt the convention of imagining the sky once each sidereal day, when the same star is overhead.

We thus think of the celestial sphere with the stars fixed on it.

We can draw pictures of the positions of the sun, moon, and planets on the celestial sphere as viewed from the inside, as we see it.

• The plane of the earth's orbit projected onto the celestial sphere is called the ecliptic.
• The sun moves along the ecliptic. In which direction?
• The points where the equator intersects the ecliptic are called the equinoxes. (The times when the sun is there are also called the equinoxes.)
• The constellations of the zodiac (Aries, Taurus, ...) lie along the ecliptic.