50 Facts About the Solar System

The sky has always fascinated humans who frequently associated it with their particular mythology. Astronomers have looked at our Solar System with a more scientific eye and have discovered that it is full of surprises.

The Sun

1. Sunspots are cool areas on the visible surface of the Sun


They have a temperature of about 3000oC compared to the normal temperature of 6000oC

2. The spectrum of the Sun is crossed by fine dark lines


They are called Fraunhofer lines and are named after the German physycist who first studied them in detail.

3. The Sun’s fuel is hydrogen


It is changed into helium by nuclear fusion reactions which is the source of the heat and light of our star.

4. The Sun is about half way through its life


It is 4.5 billion years old and has enough hydrogen to continue for about another 5 billion years.

5. The Sun has a strong magnetic field which sometimes releases large quantities of charged particles into space as a solar flare


Solar flares can damage satellites orbiting the Earh and interfere with communications on the surface of our planet.

6. The Sun is a yellow dwarf star with a spectral class of G2V


When it’s hydrogen supply is used up, it will become a red giant star, engulfing Mercury, Venus and the Earth.

7. The Sun is just one of at least 100 billion stars in our Galaxy (the Milky Way)


It orbits at a distance of about 30,000 light-years from the centre of the Galaxy and takes about 250 million years to complete one orbit.

8. The visible surface of the Sun is called the photosphere and its ‘atmosphere’ is called the corona


The corona can be seen at the time of a total solar eclipse.

9. Ancient civilisations believed that the Sun orbited the Earth


It wasn’t until the 17th centuy that it became widely accepted that the Sun was effectively at the centre of the Solar System.

10. The Sun is rotating

rotating Sun animated gif.

  Its equator rotates about once every 26 days but the poles rotate more slowly, taking 30 days.


The Moon and the Earth

11. The Moon is getting further away


Each year, the moon is about 4cm further away from the Earth.

12. The Moon is only the 5th largest natural satellite in the Solar System


Ganymede, Titan, Callisto and Io are larger, but the Moon is the largest when compared to the planets they orbit.

13. The Moon’s rotation is synchronised


That means that it rotates in the same number of days that it takes it to complete one orbit. That is the reason we always see the same side of the Moon. The picture above shows the far side of the Moon.

14. The footprints and Lunar Rover tyre tracks will remain as clear as the day they were made for millions of years


There is no atmosphere on the moon and therefore no weathering. Given time, they may be covered by particles of dust landing on the moon from space.

15. The Moon is one quarter the diameter of the Earth


It is believed that the Moon was formed when a huge asteroid hit the Earth in its very earliest days of formation. Because of its small size, on the Moon you would weigh only one sixth of what you weigh on Earth.

 16. The Earth is the only planet with liquid water on its surface


Without liquid water, life as we know it could not exist. The first life may have begun around hydrothermal vents like the one shown above.

17. The Earth is about 93 million miles (150 million kilometres) from the Sun


That is 8 light minutes away. To drive to the sun at motorway speed would take you over 150 years!

18. The Earth is the only planet in our Solar System not to be named after a Greek or Roman god


19. The rotational speed of the Earth is slowing down

Tidal friction.

The effect is very small and is caused by tidal friction. The rotational momentum of the Earth is gradually being transferred to the Moon, which is therefore increasing in speed. This will stop when the length of the day is the same as the length of the month.

20. The magnetic field of the Earth protects us from the harmful effects of the Solar Wind


The magnetic field creates the Van Allen belts, regions or space near the Earth that trap the particles of the Solar wind.

The Inner Planets

21. Mercury is the most cratered planet of the Solar System


It has no significant atmosphere and so the craters are not weathered.

22. Mercury has a magnetic field

Cross section of the planet Mercury.

Planets with magnetic fields usually spin quickly and have a molten core. Mercury spins only once every 59 days and was thought to be completely solid until this discovery by the spacecraft Mariner 10.

23. Mercury is the fastest moving planet in the Solar System

Mercury orbits quickly.

It has an average orbital speed of 112,000mph (180,000kph) taking it round its highly elliptical orbit in just 88 days.

24. The planet Venus has a retrograde rotation


It rotates anti-clockwise which is unusual and may be the result of a large collision in its early history.

25. A day on Venus is longer than its year

Orbit of Venus.

Venus takes 243 Earth days to spin once on its axis but it orbits the Sun in only 225 days.

26. It has the highest average surface temperature (about 470oC) of all the planets


It is subject to a ‘runaway greenhouse effect’ because of the thick atmoshpere of mainly carbon dioxide. The image above was taken by the Russian spacecraft Venera 9 and was the first image to be taken on the surface of another planet.

27. The surface of Venus was mapped using radar

Radar map of the surface of Venus.

During 1990 and 1991, the Magellan spacecraft used radar to ‘see’ through the dense atmosphere. There are two highland areas, but 80% of the surface consists of volcanic plains.

28. In 1877 Giovanni Schiaparelli, an Italian astronomer, produced the first detailed map of Mars

Mars map.

The map showed what he called ‘canali’ which has been mis-translated as ‘canals’, suggesting that Mars supported an advanced civilisation. ‘Canali’ translates as channels and they were an optical illusion.

29. There are permanent polar ‘ice’ caps on Mars

Mars polar ice cap.

These are in fact caps of frozen carbon dioxide at the north pole. The cap is around a metre thick, but the southern cap is thicker at about 8 metres.

30. The largest mountain in the Solar System is on Mars


Olympus Mons is a huge volcano that looms nearly 25km above the surface, that’s almost 3 times more than Mt. Everest.

The Outer Planets

 31. The Great Red Spot on Jupiter is a storm

Jupiter red spot.

The area of the storm is bigger than the Earth and it has been raging for hundreds of years.

32. Jupiter is two and a half times more massive than all of the other planets put together


The above image shows the size comparison between the Earth and Jupiter. Jupiter’s composition is more like that of a star but it is too small to have ignited. If it had, there would have been two ‘suns’ in our Solar System.

33. Europa, one of Jupiter’s moons, has the smoothest surface in the Solar system

Europa, moon of Jupiter.

This suggests that the surface is very young and that there could be an ocean of liquid water beneath the icy crust.

34. The clouds at the north pole of Saturn form a hexagonal shape

Hexagonal cloud formation on Saturn.

This was first seen during the Voyager mission and photographed more clearly by the spacecraft Cassini.

35. Water geysers have been seen on one of Saturn’s moons, Enceladus

Water geysers, Enceladus.

These were first observed in 2005 and are the source of material for one of Saturn’s rings.

36. Galileo Galilei was the first human to see the rings of Saturn through a telescope — he described them as looking like ears!

Voyager image of Saturn.

37. Uranus was discovered in 1781 by William Herschel


It is just about bright enough to be seen by the naked eye under clear, dark skies, but it moves very slowly and was not recognised as a planet until well into the age of astronomy with telescopes.

38. Uranus’s axis of rotation is tilted at 98 degrees to the orbit so it appears to rotate on its side

Uranus from the Hubble Space Telescope.

It is thought that a collision with a planet the size of Earth could have caused this to happen. The above photo was taken by the Hubble Space Telescope and is a false-colour infra-red image.

39. Neptune has some of the strongest winds of all the planets


Winds of almost supersonic speeds sweep through the atmosphere, which is coloured blue because the high methane content absorbs the red light.

40. Between 1846 and 1930, Neptune was regarded as the outermost planet

Le Verrier.

Pluto was discovered in 1930 and became the 9th and outermost planet. But in 2006, the International Astronomical Union (IAU) decided that it was to be called a dwarf planet and so Neptune once again became the outermost of the planets. The picture above shows Urbain Le Verrier, the French astronomer who used mathematics to predict where Neptune should be found.

Asteroids and Comets

41. The only asteroid that is normally visible to the naked eye is Vesta

Surface of Vesta.

This is the second most massive asteroid and was visited in 2011 by the spacecraft ‘Dawn’.

42. Trojan asteroids lie in the same orbit as a planet or moon

Trojan Asteroids and the asteroid belt.

They are found either 60o ahead or 60o behind the main orbiting body. Earth has only one known trojan.

43. An asteroid impact was responsible for the mass extinction of life at the end of the Cretaceous era

Chicxulub Crater, Yucatan peninsula.

An asteroid of about 10km diameter (6 miles) impacted the Earth at the tip of what is now the Yucatan peninsula.

44. The first asteroid to be discovered was Ceres in 1801

Structure of asteroid Ceres.

We now know Ceres to be a ‘differentiated’ asteroid — it has a crust, a water ice mantle and a rocky core.

45. Many of the meteorites that have landed on Earth have come from asteroids

Meteorite that has come from the asteroid Vesta.

These fragments of asteroids have been knocked out of the asteroid belt between Mars and Jupiter by collisions or by the gravitational forces of the Sun and Jupiter.

46. Halley’s Comet was the first comet to be visited by a spacecraft (Giotto)

1986 apparition of Hallet's comet.

It orbits the Sun every 75 – 76 years so for most people, it is a once in a lifetime event. It was named by French astronomer Nicolas de Lacaille in honour of the English Astronomer Royal, Edmund Halley, who correctly predicted its return.

47. In the past, comets were thought to signify that a ruler or other royalty was going to die

Halley's comet on the Bayeux tapestry.

In Shakespeare’s play Julius Caesar, his wife Calpurnia says “When beggars die there are no comets seen; The heavens themselves blaze forth the death of princes.”

48. The brightest comet of the 20th century was Comet Ikeya-Seki

Brightest comet of 20th century.

This was so bright that it could be seen easily in daylight. It is one of a group of comets known as the ‘Kreutz Sungrazers’.

49. The solid nucleus of a comet consists of ice and dust and is often coated with dark organic material

Comet nucleus 67P.

American astronomer Fred Whipple came up with the description of the ‘dirty snowball’ during the early part of the 1950s.

50. The tail of a comet always points away from the Sun.


The tail is created from dust and gases that are ejected from the comet as it is heated by the sun. The radiation and solar wind mean that the tail is always on the opposite side of the comet to the Sun.

Taught science for 16 years at a secondary school in the East Midlands.