In the 20th century increasingly powerful telescopes enabled astronomers to observe and calculate ever more distant events in space. Huge, distant galaxies and galaxy_clusters have been discovered.
After the discovery of the planet Neptune in the 1846, calculations indicated the existence of another even more distant planet. The astronomer Percival Lowell built an observatory at an altitude of 2200 meters to find this "Planet X". He died in 1916, without having fulfilled his ambition. Early astronomical observatories existed in Babylon and China around 2300 BC. These were special raised platforms on mountaintops, which provided a clear and unobstructed view.
In 1930 an astronomer at the Lowell Observatory finally discovered the object they had been looking for, which they then named Pluto. The question of a possible tenth planet as a cause for eccentricities in its course immediately arose. Improved observation instruments allowed for a more detailed examination of the planets. In addition to the planets, one Earth moon, two Mars moons, sixteen Jupiter moons, around twenty Saturn moons, fifteen Uranus moons, eight Neptune moons and one Pluto moon have already been discovered. Additionally, over 1600 asteroids and several hundred comets have been observed. In 1997, a new class of comet-like objects, which have been termed planetesimals, was discovered. They revolve around the Sun in the outer solar system beyond the orbit of Neptune.
Recent years have seen huge advances in the field of astronomical instruments. Instruments for recording radiation of various wavelengths, such as X-ray and infrared_radiation are examples of these. Numerous phenomena can be examined more closely. Photographic methods are also becoming more specialized. Cosmic matter, background_radiation that may have originated from the Big Bang and interstellar gases in which stars develop are the main objects of present and future studies. The Hubble_space_telescope, launched in 1990 by the space shuttle "Discovery", is of great significance for this endeavor. It is located in the Earth's orbit and allows for observations that would not be possible from the surface of the Earth.
