Saha, Meghnad (1894-1956) - astrophysicist from India who studied the compositions of stars. He worked out an equation (named after him) that relates how the temperature of a star is proportional to the ionization of its elements.
Schiaparelli, Giovanni Virginio (1865-1910) - Italian astronomer who in the 1880's created maps of Mars. On these maps he began the currently accepted naming practice of the planets features, he also reported seeing channels, which other astronomers mistranslated as canals, and which led to the belief that intelligent life on Mars had created them.
Schlesinger, Frank (1871-1943) - American astronomer who created the standards when using photography to measure stellar parallax. In 1924 he published the General Catalogue of Stellar Parallax which listed the measurements of parallax for 1,870 stars.
Schwarzchild, Karl (1873-1916) - the first scientist to calculate the gravitational affects that take place near a black hole. He is credited with the term "Schwarzchild Radius" which is the boundary for any black hole.
Secchi, Pietro Angelo (1818-1878) - Italian astronomer and Jesuit priest who was one of the first scientists to use spectroscopy in astronomy. Between 1864 and 1868 he studied the spectra of over 4,000 stars. He was also one of the first to use photography in astronomy.
Shapley, Harlow (1885-1972) - American astronomer who spent much of his career studying globular clusters. Based on their positions he theorized that the Sun and the Earth are near the edge of the Milky Way and not near its center which had previously been accepted.
Shu-ging (1231-1316) - astronomer and mathematician who improved the tables of the Sun and Moon. He made new measurements of the Sun and the solstices, and added new instruments to observing.
Sina, Abu-Ali Al-Husain ibn Abdullah ibn (980-1037) - also known as Avicenna, a physician and philosopher. He made stellar observations and wrote on astronomy and Ptolemy.
Sosigenes (c. 50 BC) - Greek astronomer whose is most known for convincing Julius Caeser to abandon the lunar calendar in use for the solar calendar. A modified version of this calendar is still in use today.
Ssu-ma Chi'en [Sima Qian] (145-90 B.C.) - historian and astronomer who completed tables of the position of the Moon.
Struve, Otto (1897-1963) - great-grandson of Wilhelm Struve, his astronomical studies included the discovery of interstellar matter and the processes by which stars evolve.
Struve, Wilhelm (1793-1894) - German astronomer who while the director of the observatory in Pulkovo, Russia observed and cataloged 3112 double stars. He also was the first astronomer to determine the parallax of the star Vega.
Thales (624-547 BC) - Greek merchant who was the originator of the geocentric theory. He proposed that the Earth was a disk-shaped object which floated in a cosmic ocean.
Titius, Johann Daniel (1729-1796) - established an empirical rule relating the mean distances of the Sun and the planets that would later be published by Johann Ehlert Bode. It has since been called Bode's Law or the Titius-Bode Rule.
Tombaugh, Clyde (1906-1997) - American astronomer who in 1930 discovered the dwarf planet Pluto using the telescope at the Lowell Observatory.
Tsu Ch'ung Chi (430-501) - astronomer and mathematician. He calculated pi and devised a new calendar which never was used. He also determined the precise times of the solstices.
Ulugh Beg - grandson of the Mongol conqueror Tamerlane independently determined the positions of stars between 1420-1437 and was one of the few Middle Eastern astronomers who did not use the positions plotted by Ptolemy.
Van De Kamp, Peter (1901) - Dutch-American astronomer who in 1943 made the first possible discovery of a planet outside our solar system, around the star 61 Cygni. Later two other possble planets were detected orbiting Lalande 21185 and Barnard's Star.
Vogel, Hermann Carl (1841-1907) - German astronomer who was the first to identify spectroscopic binary stars. Through ordinary telescopes these stars are only seen as one, only using a spectroscope can they be split into two.