The Earth in the Solar System

The Ecliptic

Imagine, for a moment that the Sun is actually in orbit around the Earth. This is after all what people believed for a long long time. The Sun takes about 365 days to go round the Earth. As the Earth spins around daily the Sun rises in the east and sets in the west.

Imagine also for a moment that the Earth's axis isn't tilted. The Sun appears to go round the Earth from our point of view. Its path in the sky is called the ecliptic. Notice that on this diagram the equator is on the ecliptic plane. The Sun, on this diagram, takes a year to orbit the Earth.

1. Imagine that the Sun moved round the Earth as shown on the diagram above.
If you lived in a country on the equator describe the apparent motion of the Sun every day.

Because the Earth's axis of rotation is tilted we must use a different diagram.

2. How would the apparent motion of the Sun change because the Earth is tilted?

This is a star chart (without any stars). The celestial equator is the straight blue line. The ecliptic, the path of the Sun, is the red line. It takes a year for the Sun to travel this path from right to left on this chart.

All the planets, except Pluto, and just about everything else that orbits the Sun lies on the ecliptic plane. This suggests that the solar system formed from a disc of material that was in orbit around the Sun.

3. The summer solstice is the day when the Sun is at its highest in the sky at midday. Where would that be on each of the diagrams above?