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Questions About Neptune

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  • The discovery of the planet Neptune was one of the most exciting discoveries in astronomy.

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  • Neptune cannot be seen without a large telescope and was first seen in 1846 from the observatory in Berlin.

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  • BUT, the existence of Neptune had actually been “discovered” a year earlier, in 1845.

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  • Neptune is the 8th planet from the Sun.  Uranus, the 7th planet, was first discovered by means of a telescope in 1781.  Two astronomers (scientists who study the stars and planets), J.C.Adams in England and Urbain Le Verrier in France, had been puzzled by the shape of Uranus’ orbit.

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  • They worked out, using mathematics, that some large, more distant, body must be pulling Uranus towards it at certain points in the orbit.

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  • The Berlin observatory, following Le Verrier’s calculations giving the possible position of this object, searched for Neptune and found the planet.  They named it Neptune after the Roman God of the Sea.
    Neptune
    Figure 1: Photograph of Neptune taken from the Voyager spacecraft in 1989.
  • Neptune is the third largest planet in the Solar System, much smaller than the real giants, Jupiter and Saturn, and only a little bigger than Uranus.

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  • Neptune has a diameter of 29,297 miles, or 47,150 kilometres.  The Earth has a diameter of 7928 miles (12,760 kilometres).

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  • Neptune is one of the four “gas giants”.  Like Jupiter, Saturn and Uranus, it is composed only of gas.  Neptune is a great ball of hydrogen and helium.

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  • Like all the other planets in the Solar System, Neptune moves in an orbit round the Sun at the centre of the system.  It takes Neptune 165 of our Earth years to orbit the Sun.  The Earth orbits the Sun in 365 days, one year.

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  • In 2011 Neptune completed the first orbit of the Sun since its discovery 165 years before in 1846.

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  • Like all the other planets, Neptune turns on its own axis as it is orbiting the sun.  (Imagine walking round a large pond, but turning round and round as you go.)

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  • The Earth turns right round on its own axis in 24 hours, giving us the change from day, when we face the Sun, to night, when our part of the Earth turns away from the Sun.  Neptune spins slightly faster on its axis, taking just over 19 hours to turn right round.

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  • The Earth is 150 million kilometres from the Sun (93 million miles) and this measurement is taken as the standard for astronomical measurements of distance.  Astronomers say that the Earth is one Astronomical Unit (1 AU) from the Sun.  Neptune is unimaginably further.

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  • Neptune is 30.1 Astronomical Units from the Sun, a staggering 2793 million miles (4495 million kilometres) from the Sun, and 2700 million miles from the Earth.
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    Figure 2 : Distances of Planets from the Sun in Astronomical Units
  • Figure 1 does not show the distances between the planets to scale.  Figure 2 shows the true distances of the planets from the Sun.

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  • In the same year that Neptune was first seen, 1846, its first moon was also spotted and named Triton. Triton is a most unusual moon since it orbits Neptune in the opposite direction of Neptune’s own rotation on its axis.  All the other major satellites (moons) in the Solar System follow their planets round as they turn. Try orbiting the pond again, turning on your own axis, but this time take a friend to orbit round you.  If you are turning on your axis clockwise, have him go round you anticlockwise (be careful not to get so dizzy you fall in the pond!)

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  • Triton is about the same size as our own moon.  A smaller moon, Nereid, was discovered by telescope in 1949 and six further moons were discovered in the 1980s by the Voyager spacecraft.  All these moons are between Triton and Neptune.

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  • We now know that Neptune has 13 moons in total.  Since Neptune was the God of the Sea, all the moons are named after less important ancient Greek sea gods, like Triton, or sea nymphs, like Nereid.

Useful Websites

Neptune's Ring System

The seasons on Neptune

 

Alternate Images of Neptune



 
 
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