This is a photograph taken by the Hubble telescope which is in a spacecraft 600 kilometers above the Earth. Its mirror is 240 centimeters in diameter, and because it is far above the dusty, cloudy atmosphere of the Earth, it can see much more clearly into outer space. Distances in space are so huge that we cannot measure them in kilometers and astronomers use ‘light years’_that is, the distance light would travel in a year. Light travels at 299,792,458 meters per second, that is well over one billion kilometers an hour which means nearly 9.5 trillion kilometers (9,500,000,000,000) in a year. The Hubble telescope has photographed stars as distant a 12,000,000,000 light years away. We just cannot understand such distances.
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We read stories and see films of space travel to distant stars but, of course, this is quite impossible. Apollo 11, which took the US astronauts to the Moon in 1969, was launched on 16 July and the moon landing was on 20 July four days later. Today rockets can travel at a speed of 40,000 kph. The nearest star is 32,000,000,000 km from the earth and to reach it will take 91.3 years. Most of the billions of star in the universe are in huge clusters called galaxies. Our solar system is in the galaxy known as the milky way. As you can see from the photograph, galaxies are in gigantic spirals; the milky way is 100,000 light years across_about 9,500,000,000,000,000,000 kilometers! Nebulae ( sin gular; Nebula ) are clouds of dust, hydrogen, helium and other gases, found between the stars