For thousands of years mankind has sought to understand the phenomena observed in the sky and on the Earth. Why does the Sun rise and set? Which courses do the Moon and stars follow? Why does the Sun rise in the morning? These and many other questions have moved mankind since the beginning of time.
One of the most prominent ancient thinkers was Plato (428-347 BC). Even then he described the movements of the planets along circular paths, although he still saw the Earth as the center of the universe. Around 370 BC, Eudoxus of Cnidus put forward the theory that the stars revolve on individual strings inside a star sphere once per day.
Aristotle (384-322 BC), a student of Plato, believed that the Earth was stationary in a round universe and that the planets were moved through the combined action of 55 circles. This concept remained prevalent as the geocentric worldview until the end of the middle ages. It was developed upon by Aristarchus of Samos (310-230 BC) and culminated in a book by Ptolemy.
It was Nicolaus Copernicus (1473-1543) who radically changed our view of the world. With his heliocentric cosmology he placed the Sun at the center of the universe. He revealed his thoughts only to friends at first, as he already anticipated conflict with the church, state and other members of the scientific community. However, it was the scholar Johannes Kepler (1571-1639) who came under such attack when he brought forward exact calculations to support this theory. He suffered a similar fate as others who adhered to the theories of Copernicus, who were banned from teaching and sentenced to harsh prison sentences.
Galileo Galilei was one of those responsible for the Copernican system becoming established. Although he was forced to retract his convictions before the Inquisition, he secretly upheld them. Additionally he used a telescope of his own construction to make such discoveries as four of the moons of Jupiter, the rings of Saturn, irregularities on the surface of the Moon and sunspots.
Kepler's and Galileo's studies were the foundation of the work of Isaac Newton (1642-1727). Among other things, he pursued the question of how the planets remain on their courses. He found that the answer was the balance between the centrifugal_force of their rotation around the Sun and the force of gravity acting on them. In addition Newton worked on constructing a particularly powerful reflecting telescope and also studied the properties of light.
As a consequence of the fast development in optical astronomy, measurements concerning the dimensions of the solar system were made possible. Frederick William Herschel (1738-1822) began to systematically count the stars. In 1781, he discovered the planet Uranus. When he became royal court astronomer in the following year he could finally devote himself entirely to astronomy. Using a huge reflecting_telescope (1.20 meters in diameter, 12.2 meters focal length), Herschel discovered two of Uranus' moons and the sixth and seventh moon of Saturn. He discovered and catalogued over 800 binary_stars and described their movements. Herschel was the first to suggest that stars were formed from nebulae.
The introduction of photographic methods heralded the advent of astrophysics, which is concerned with the origin and development of astronomical objects. Henry A. Rowland (1848-1901) found 20,000 lines in the Sun's spectrum, George Hale (1868-1938) proved the presence of strong magnetic_fields around sunspots and Henrietta S. Leavitt (1868-1921) found a connection between the brightness of the Cepheid_variables and their periodic appearance.
Edwin P. Hubble (1889-1953) made a significant contribution to astronomy when he succeeded in determining the distance to the Andromeda nebula. This was the first proof of a star system outside of our own Milky_Way. Hubble also classified the different types of galaxies.
Important developments in radio astronomy were made by Karl Guthe Jansky (1905-1950). During his studies he discovered that some radio frequencies do not originate from the Earth but from the Milky_Way. The first radio_telescope was constructed in 1944 by Grote Reber. This later led to the discovery of pulsars and quasars.
Space probes, manned and unmanned spacecraft and satellites have been sent out for further exploration of the solar system.
