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The Sun is a star.

It is the largest object in the solar system and was the first to form.

The Sun’s huge gravitational pull keeps many other objects - planets, dwarf planets, asteroids and comets - in orbit around it.

The Sun alone contains 99.8% of the total mass in the solar system.

Planets

The Earth is one of eight planets in the solar system.

The planets orbit the Sun at different distances.

The following sentence may help with remembering the order of the names of the planets from the Sun outwards:

My Very Easy Method Just Speeds Up Naming

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune

The different planets have different properties and conditions.

In general, as the distance from the Sun increases:

• the temperature decreases, for example, Mercury is 430 °C whereas Neptune is -200 °C;
• the time taken to orbit the Sun increases, for example, Mercury orbits the Sun once every 88 Earth days, but Neptune orbits the Sun once every 165 Earth years.

Astronomers have divided the planets into two groups of four:

• The four inner planets (Mercury, Venus, Earth and Mars), which:
  • are small, solid, rocky, dense planets;
  • are close to the Sun, and so are warmer than the outer planets;
  • have craters, mountains, volcanoes, valleys.
• The four outer planets (Jupiter, Saturn, Uranus and Neptune), which:
  • are large balls of gas - you couldn't stand on the surface of the planet because it's not solid;
  • have a small, solid core;
  • are much further from the Sun, and so are cooler than the outer planets;
  • are much bigger than the rocky planets;
  • are called gas giants.

When the solar system formed, rocks (and other dense, heavy materials in the dust cloud such as iron and uranium) tended to gather closer to the Sun, and these materials combined together to form the inner planets.

Lighter gaseous substances were pushed further away from the Sun and formed the outer gas giants.