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Our Solar System


Our Solar System

  • A planet is a large heavenly body which orbits our sun, and is held in orbit by the force of gravity.
  • Planets do not make their own light. They shine by reflected light from the sun.
  • The name 'planet' comes from the Latin word meaning 'wanderer', which refers to the fact that the planets that we see do not follow the same path as the stars across the night sky.
  • The planets are named after Roman gods, such as Mars, the Roman god of war.
  • The Time of Revolution is the time it takes for a planet to orbit once around the sun. For example, Earth takes one year to revolve around the sun.
  • The Time of Rotation is the time it takes for a planet to rotate or spin once on its own axis. For example, Earth takes one day or 24 hours to rotate once on its axis. All planets except Venus and Uranus rotate anticlockwise. The side of the planet which is lit by the sun can be much hotter than the side which is dark.
  • Some planets have their own moons or satellites. For example, Earth has one moon.
  • All nine planets have an atmosphere composed of gases.
  • The nine planets in order from the sun are:
  • Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

  • A mnemonic to remember the order is: My very easy memory jingle seems useful naming planets.
  • Distances in our solar system can be measured in kilometres or astronomical units. An astronomical unit is the distance between the sun and Earth (150 million kilometres).

MERCURY

  • Closest planet to the sun.
  • Much smaller than Earth.
  • Force of gravity is only one-third of Earth's.
  • Very thin atmosphere containing hydrogen, helium, oxygen and sodium.
  • Temperature varies from +430oC on the lit side to -180oC on the dark side.
  • No moons.
  • Revolution time is 88 days.
  • Rotation time is 59 days.

VENUS

  • 2nd planet from the sun.
  • Incorrectly called the 'morning star' or 'evening star' because it is very bright in the sky at sunrise and sunset.
  • Slightly smaller than Earth.
  • Thick atmosphere of mostly carbon dioxide with clouds of sulphuric acid.
  • Winds up to 360 km/h.
  • Temperature ranges from +40oC to -170oC.
  • No moons.
  • Its Revolution time is 226 days, which is shorter than its Rotation time of 243 days.

EARTH

  • 3rd planet from the sun.
  • Fifth largest planet.
  • Blue colour because of the oceans that cover most of the surface.
  • Only planet known to support life.
  • Thick atmosphere of nitrogen, oxygen and carbon dioxide.
  • Temperatures range from +60oC to -90oC.
  • Revolution time is 365 days.
  • Rotation time is 1 day.

MARS

  • 4th planet from the sun.
  • Reddish colour because of its rusted surface.
  • Polar ice caps.
  • Appears quite bright in the night sky.
  • Atmosphere of mostly carbon dioxide, with some nitrogen, oxygen and water vapour.
  • Temperatures range from +17oC to -87oC.
  • Two moons.
  • Revolution time is 1 year 321 days.
  • Rotation time is 25 hours.

JUPITER

  • 5th planet from the sun.
  • Largest of the planets, and is over 1000 times larger than Earth.
  • Clouds give it a banded appearance because it spins so fast.
  • Great red spot.
  • Atmosphere is mostly hydrogen and helium, with some methane and ammonia.
  • Temperatures range from +17oC to -125oC.
  • 16 known moons.
  • Revolution time is 11 years 9 months.
  • Rotation time is 10 hours.

SATURN

  • 6th planet from the sun.
  • Yellow appearance, with a ring system made of rock, frozen gases including some water.
  • At least 20 moons.
  • Atmosphere is mostly hydrogen and helium, with some methane and ammonia.
  • Winds up to 1700 km/h.
  • Temperatures range from +27oC to -176oC.
  • Revolution time is 29 years 6 months.
  • Rotation time is 10 hours.

URANUS

  • 7th planet from the sun.
  • Blue colour.
  • Atmosphere of hydrogen, helium and methane.
  • Temperature is about -216oC.
  • 15 known moons.
  • Revolution time is 84 years.
  • Rotation time is 17 hours.

NEPTUNE

  • Blue colour, with five thin rings.
  • Atmosphere of hydrogen, helium and methane.
  • Temperature about -218oC.
  • 8 known moons.
  • Revolution time is 248 years.
  • Rotation time is 6 days.

PLUTO

  • Usually Pluto is the outermost planet from the sun, but during the next few years, Pluto is the 8th planet and Neptune is the 9th one.
  • Atmosphere is mostly methane.
  • Temperature is about -223oC.
  • Revolution time is 248 years.
  • Rotation time is 6 days.