Natural satellites are objects, such as moons that orbit planets and other bodies in space. Artificial satellites are devices that are launched to orbit around the Earth. The signals they transmit are picked up by radio telescopes and other equipment, providing us with useful information about the Earth and space, and enabling us to communicate over long distances.
Sputnik
Sputnik was the worlds first artificial satellite sent into orbit by the USSR on 4 October 1957. Sputnik, which means fellow-traveler in Russian, weighed 84 kg and was about the size of a basketball. It took about 98 minutes to orbit the Earth on its elliptical path, and transmitted a beep-beep signal for 23 days before the chemical (silver-zinc) batteries ran down. The launch of Sputnik marked the start of the space age and the battle for dominance fl space exploration between the United States and Russia, which was known as the space race.
Satellite speed
The lower a satellites orbit, the faster it must fly to avoid falling back to Earth. Most satellites fly in low orbits, 500 km above the Earth.
Amazing!
About 4000 satellites have been launched since Sputnik 1, by a total of nine countries Australia, China, France, India, Israel, Japan, Russia, UK, USA.
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