Artificial satellites sent from the Earth orbit around the earth. The ones near the Earth orbit faster than the ones far away. A satellite 35,900 Km above the Earth's surface, takes 24 hours to orbit once. The satellite is always above the same point on the Earth's surface as the planet rotates. Geostationary orbit is also called as geosynchronous ' orbit. Such satellites are used to receive telephone and television signals and retransmit them over long distances.
The distance around the Earth, that is, it's circumference around the equator is 40,091 kilometres. The diameter (the distance across the centre of the Earth ) at the equator is 12,756 kilometres. The Earth is slightly smaller when measured between the poles (12,713 kilometres), so it is not an exact sphere. If the Earth is weighted on a weighing machine, it would be nearly 6x10 tonnes.
T he largest land mammal of all time was the giant hornless rhinoceros Indricotherium , which lived in the Oligocene epoch. It stood 5.5 metres high at the shoulder and its head would bypass a modern giraffe. Brontotheres stood at 2.5 metres at the shoulder. The horse like animal Moropus was a little smaller. All these animals browsed in the open plains.
Radar was invented during 1930s. Many countries worked on radar at this time, but the first successful radar was built by Britain in 1935. Radar works by sending out radio signals that bounce off distant objects. The radar set detects the signals that return and produces a picture indicating the position of the objects . British and American scientists worked together to invent methods of using short waves called microwaves.
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