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Early astronomical measurements
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The first scientific measurement of a cosmic distance was accomplished, to the year 240 BC JC, by Eratosthenes of Cyrene - director of the Library of Alexandria, the then most advanced scientific institution in the world - who noticed that the June 21, when the Sun, at noon, was exactly at its peak in the city of Siena (Egypt), he was not also, at the same time, in Alexandria, some 750 km north of Siena. Eratosthenes concluded that the explanation must be that the Earth's surface, being round, was always furthest from the Sun at some points than others.
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How to measure distances?
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One of the greatest discoveries of the twentieth century in the field of physics was to the expansion of the universe. Cosmology and cosmogony were particularly benefited from the work of American astronomer Edwin Hubble (1889-1953).
While working at Mount Wilson Observatory, California, Hubble was able to discover a relationship between the rate at which galaxies move in radial direction and distance to meet.
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Radio Astronomy: space waves
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Radio astronomy, an important branch of astronomy, studying the heavenly bodies through their emissions in the domain of radio waves.
 In the late 1920s, a young American engineer. Karl Jansky was working in (New Jersey) in the investigation of the causes of radio interference from atmospheric sources involved with long distance transmissions. Jansky built an antenna structure formed by a cage-shaped Non metaLLic and suspended on the wheels of an old Ford, so a pudicra motor to rotate the antenna in different directions. Then began a long and patient work of data collection, which consisted in recording the different types of radio noise collected at different wavelengths, but particularly in the short waves from various directions in the sky.
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The Hubble Space Telescope
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The Hubble Space Telescope is located at the outer edges of the atmosphere, in a circular orbit around the Earth around at 593 kilometers above sea level it takes to travel between 96 and 97 minutes. It was launched into orbit on 24 April 1990 as a joint project of NASA and ESA. The telescope can obtain optical resolutions greater than 0, the second of arc. Weighs around 11,000 kilos, is cylindrical in shape and has a length of 13.2 m and a maximum diameter of 4.2 meters.
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In the period from the late nineteenth century to the Second World War, at least four pioneers of the missile and astronautics to remember: Konstantin E. Tsiolkovsky in Russia, Robert H. Goddard, U.S., Hermann Oberth in Germany, Robert Esnault-Pelterie, France.
Tsiolkovsky was born in September 1857. Mathematician and physicist, in 1898 first proposed the use of liquid fuels to replace the solid hata time employees, advancing the idea that the rockets could be powered by hydrogen and liquefied oxygen or liquid oxygen and fuel (just as in today).
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 The first astronomical observation instrument was the human eye, where opportunities are limited. The development of observational astronomy suffered these limitations until the early seventeenth century, when Galileo built the first astronomical telescope.
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 The Oort cloud is a large concentration of comets under the forces of sun and other stars. Article Oort Cloud, Paul R. Weissman, an expert on cometary dynamics, talks about these comets orbiting beyond Pluto. Here is reproduced a portion of this article that the author begins by posing the question of the number of comets that make up this huge cloud.
How many comets stay in the Oort cloud? The figure depends on the frequency with which the cloud of comets beyond the interplanetary space. According to the figure observed long-period comets, astronomers now estimate that contains six trillion comets, then, the bodies of any size more abundant in the solar system. Only one-sixth part of the external and dynamic cloud Oort described, the rest are in the nucleus, denser. Applying the best estimate so far of the average mass of a comet - 40.000 million metric tons - it appears that the total mass of comets in the Oort cloud is currently about 40 times that of Earth .
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