What is the Solar System?
The Solar System is made up of the Sun at its centre and all the objects that move around it. These objects are held in their paths by the Sun's strong gravity. They include eight planets, their moons, and smaller bodies such as asteroids and comets.
Key idea
The Sun is the only star in the Solar System. Its gravity keeps the planets moving in almost circular paths called orbits.
The eight planets
In order from the Sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The four inner planets (Mercury, Venus, Earth, Mars) are small and rocky. The four outer planets (Jupiter, Saturn, Uranus, Neptune) are much larger and made mostly of gas.
| Inner planets | Mercury, Venus, Earth, Mars — small, rocky |
| Outer planets | Jupiter, Saturn, Uranus, Neptune — large, gas |
A planet does not make its own light. We see planets because they reflect sunlight. A moon is a natural body that orbits a planet; Earth has one Moon, while Jupiter and Saturn have many.
Example
Mercury is closest to the Sun and completes one orbit in only 88 Earth days. Neptune is farthest and takes about 165 Earth years for one orbit.
Why we have day, night and years
The Earth spins on its axis once a day, giving us day and night. It also travels once around the Sun in about 365 days, which we call one year.
Remember
- The Sun is at the centre; planets orbit it.
- Order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
- Planets reflect sunlight; they do not make their own light.