The celestial sphere

1. The Celestial Sphere By Alexander Knox

2. What is it? It’s a massive, imaginary sphere where all of the objects in the sky reside, with Earth located at its center. Why do we use it? When we peer into the night sky, the stars of constellations appear to be very close to one another. In reality, they may be very far apart from each other and at greatly varying distances from Earth. The stars are so far away, that as a result we lack depth perception when looking at them in the night sky. The ancient Greeks mistook this illusion of proximity to be reality. They conceived that the stars and constellations lied on a great celestial sphere that surrounds Earth. While only an illusion, this model is useful because it allows us to map the sky as we see it from Earth.

3. Points of reference North celestial pole - The point directly over Earth’s North Pole. South celestial pole – The point directly over Earth’s South Pole. Celestial equator – A projection of Earth’s equator into space, completing circling the celestial sphere. Ecliptic – The path the Sun follows as it appears to circle around the celestial sphere once each year. Ecliptic Celestial equator South celestial pole North celestial pole