## Ecliptic

- Recall that the ecliptic is the plane of the Earth's orbit around the Sun
- Recall that planets move in elliptical orbits, slightly inclined to the ecliptic
- Demonstrate an understanding that the planets appear to move within a band called the Zodiac

Planets follow orbits around the Sun. The path they follow is called the ecliptic. This is an imaginary line (or plane) between the Sun and the Earth. The Sun appears to follow this line in the sky throughout the year on a line that crosses 13 constellations. These constellations are known as the zodiac.

Not all planets follow this line exactly, they usually move a degree or two either side. This is called their inclination.

The ecliptic passes through 13 constellations which are known as the zodiac.

The Earth rotates, or spins, on an axis in the same way that a wheel spins on a bicycle. The axis runs from North to South Poles.

It orbits the Earth along a plane that most planets and objects follow around the Sun called the ecliptic. Over the course of a year the Sun 'appears' to move along this path. In fact it is the Earth moving around it.

Earth's axis is not in line with the ecliptic. It is titled at an angle of approximately 23.5°.

What this means is that the Earth's equator (an invisible band around the Earth at its widest horizontal, or longitudinal, diameter) is also titled.

Whether the Earth was formed with its axis titled or whether a large object knocked it at some point is open to question.

The titled axis of the Earth is responsible for giving us the seasons. It also makes doing astronomical calculations a lot harder!

The axis points to the Pole Star, or Polaris, in the Northern Hemisphere. If you stood at the North Pole, this star would appear directly above you. The axis of the Earth is not fixed. Earth actually wobbles slightly like a spinning top. This is called precession.

Some other planets also have titled axis to the plane of their orbit such as Mars and Uranus.

###### Questions
• Describe the ecliptic.
• Terms: Many people get confused between ecliptic and elliptic. What is the difference between them?
• What is the zodiac?