Our solar system

When you spot an especially bright point in the evening sky that doesn't twinkle, it's often not a star at all but a planet like Venus or Jupiter. They are our neighbours in the solar system: eight worlds circling the sun just like we do. Time for a little tour.

Eight planets in order

Seen from the sun, the order is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. A classic mnemonic helps: My Very Educated Mother Just Served Us Noodles. The first letters of the words are the first letters of the planets.

Rocky planets and gas giants

The four inner planets Mercury, Venus, Earth and Mars are small rocky planets with solid surfaces. The four outer ones, Jupiter, Saturn, Uranus and Neptune, are huge gas planets with no solid ground to land on. Jupiter is the largest: its diameter is about 11 times that of Earth. More than 1000 Earths would fit inside it. Uranus and Neptune, by the way, contain a lot of frozen water, ammonia and methane besides hydrogen and helium, which is why those two are also called ice giants.

Vast distances and the case of Pluto

For these vast distances, astronomers use the astronomical unit: 1 AU is the distance from Earth to the sun, about 150 million km. Mars orbits at roughly 1.5 AU, Neptune already at around 30 AU. And Pluto? It long counted as the ninth planet, but since 2006 it has been a dwarf planet: it is too small and too light to clear its orbit of other chunks of rock and ice. That is exactly what the official definition of a planet requires.