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Questions About Uranus
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- Uranus cannot be seen from the Earth without a telescope.
- The seventh planet from the Sun, it was not known in ancient times, unlike the planets from Mercury to Saturn.
- Uranus was first seen by William Herschel in 1781 during a survey of the sky using a telescope. In 1782 George III appointed Herschel as Astronomer Royal.
- William Herschel was born in Hanover, Germany. He moved to England in 1757 in order to follow a career as a musician but after buying a book on astronomy he became interested only in watching the sky.
- Herschel also discovered 2 of Uranus’ moons with a larger telescope.
Uranus has a total of 27 moons, most of whom are named after characters in Shakespeare’s Midsummer Night’s Dream. The five major moons are called Titania, Oberon, Miranda, Ariel and Umbriel. Umbriel is not from Shakespeare but is the “melancholy sprite” in a poem by Alexander Pope.
Figure 1: Uranus and its moon Ariel, the white dot, and Ariel’s shadow.
- Uranus is one of the “gas giants”, the four outer planets which are entirely composed of gas, Jupiter, Saturn, Uranus and Neptune.
- Most of the centre of Uranus is a frozen mass of ammonia and methane, which gives it the blue-green colour. The atmosphere also contains hydrogen and helium.
- Uranus orbits the Sun lying on its side and takes 84 years to complete one orbit. The Earth goes round the Sun in 365 days, one year.
- Because Uranus is lying on its side as it orbits the sun, for nearly a quarter of its orbit one pole of the planet is in complete darkness.
- Uranus takes 17.9 hours to turn once on its own axis, faster than the Earth, which takes 24 hours and gives us the change from day to night.
- Uranus was the ancient Greek God of the heavens whose sons were the Giants and Titans.
- Uranus is the smallest of the four “giants”, but is still several times larger than the Earth. It has a diameter of 29297 miles, or 47, 150 kilometres, compared to the Earth’s diameter of just under 8000 miles, or 12,760 kilometres.
- Uranus is 1782 million miles, or 2869 million kilometres from the Sun. Figure 1 does not show the distances from the Sun to scale, but Figure 2 lets you have an idea of how much further Uranus is from the Sun than the Earth.
- Distances in the Solar system are measured in Astronomical Units (AU), with the Earth’s distance from the Sun being 1 AU. Uranus is 19.2 AU from the Sun. Figure 2 shows the distances of the first seven planets from the Sun, measured in AU.
- In 1977 Uranus passed in front of a star and astronomers observing the planet through giant telescopes saw nine rings around the planet. These are very faint and not easily seen, unlike the rings around Saturn.
- Photographs sent back by the Voyager spacecraft in the 1980s showed a further two rings round the planet.
- The Hubble Space telescope found two more very faint rings, very distant from the planet, between 2003 and 2005, so we now know of a total of 13 rings.
- Scientists do not yet understand exactly what causes these rings or exactly what they consist of.
- From the time when Uranus was first observed scientists noticed that at certain points in Uranus’ orbit the planet was being pulled further out into space.
- In the 19th century certain astronomers worked out that this must be because of the pull of gravity from another planet beyond Uranus.
- By making mathematical calculations based on the observations of Uranus, two astronomers, Adams and Le Verrier, identified where this other planet must be.
- The planet which was exerting a gravitational pull on Uranus was Neptune, 10.9 AU further out into space.
Nineplanets, by Bill Arnett
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