This photometer is used to measure the brightnes of objects in space with great accuracy. The Hubble Space Telescope (HST) was designed to see seven times further into space than had been posible before, without the distortion caused by the Earth's atmosphere. It is a reflecting telescope and its main mirror has a diameter of 2.5 metres. Work began in 1977 and the HST was finally launched by the Space Shuttle Discovery on 24th April 1990. Problems with its giant mirror meant that it did not initially work as well as expected. Corrective optics were installed in 1993, greatly improving the telescope's performance, enabling it to produce images showing the Universe in unprecedented detail, including objects up to 13 billion light years away.
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