<text><span class="style10">he Outer Planets (2 of 6)Saturn</span><span class="style7">The next planet out from the Sun is Saturn, with its magnificent system of rings. In 1610 Galileo became the first person to look at Saturn through a telescope. He saw the rings, but could not understand what they were, at first thinking that Saturn was a `triple planet'. It was not until 1659 that the Dutch physicist Christiaan Huygens (1629-95) realized Saturn's true nature. Most of our current information about Saturn has come from the three spacecraft that have flown by the planet: </span><span class="style26">Pioneer 11</span><span class="style7"> in 1979, </span><span class="style26">Voyager 1</span><span class="style7"> in 1980 and </span><span class="style26">Voyager 2</span><span class="style7"> in 1981.If we could cut a slice out of Saturn we would see a small rocky core at the center. Above this is a region of metallic hydrogen, followed by a deep ocean of liquid hydrogen. The outside layer of the planet is made of hydrogen gas, together with some helium. Tiny amounts of the gases methane, ammonia, ethane and phosphine have also been detected. Saturn has at least 18 satellites, including Titan, which has a dense nitrogen atmosphere.</span><span class="style10">Uranus</span><span class="style7">Uranus was discovered in March 1781 by Sir William Herschel (1738-1822), an amateur astronomer born in Germany but living in England. Herschel was making a routine survey of the sky when he came across an object that did not look like a star. At first he thought he had found a comet. The new object was watched care fully over the following months so that its orbit could be calculated. Once this was done, astronomers realized that Herschel had found a new planet.When the sky is very dark and very clear, Uranus can just be seen with the naked eye. However, the planet is always extremely faint and the observer has to know exactly where to look. A telescope will show Uranus as a small disc. Most of our information about Uranus was sent back by </span><span class="style26">Voyager 2</span><span class="style7">, which flew past the planet in January 1986.One of the strangest things about Uranus is that it orbits the Sun tipped on its side, which means that the calendar on the planet must be very odd indeed. At present the planet's north pole is pointing towards the Sun and anyone above the north pole of Uranus would have been in sunlight since 1966 and will not see the Sun set until 2007. This will be followed by 42 years of darkness while the south pole points towards the Sun. Although the south pole had been in darkness for 20 years, </span><span class="style26">Voyager 2</span><span class="style7"> found that it is slightly warmer than the north pole - which must give rise to some very peculiar weather.Uranus has an atmosphere of hydrogen and helium, which surrounds a layer of water, methane and ammonia ices. At the center of Uranus is a rocky core. Before </span><span class="style26">Voyager 2</span><span class="style7"> flew past the planet, Uranus was known to have 5 satellites. </span><span class="style26">Voyager</span><span class="style7"> found 10 more bringing the total to 15.Uranus also has a system of rings. These were discovered in 1977 when the planet passed between a star and the Earth. Astronomers saw the light from the star flash on and off as each of the rings passed in front of it. Nine rings were eventually detected from Earth, but </span><span class="style26">Voyager</span><span class="style7"> found two more.</span></text>
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<text><span class="style10">aturn and its rings</span><span class="style7">, photographed from a distance of 13.9 million km (8.6 million mi) as Voyager 2 was approaching the planet at a speed of about 42 000 km/h (26 000 mph). The shadow cast by the rings can clearly be seen in the planet's equatorial region.</span></text>
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<text>ΓÇó THE SUN AND THE SOLAR SYSTEMΓÇó THE INNER PLANETSΓÇó THE HISTORY OF ASTRONOMYΓÇó SPACE EXPLORATION</text>
