B - C.

Baade, Walter (1893-1960) - while studying the Andromeda Galaxy in 1942 he discovered that it was composed of two types of stars which he called Population I and II. I are younger stars and II are older. By adjusting the period-luminosity for the different stars he increased the distance to the Andromeda Galaxy.

Barnard, Edward Emerson (1857-1923) - American astronomer who in 1892 discovered the fifth satellite of Jupiter, Amalthea. He also first observed the star with the fastest known proper motion, known as Barnard's Star. It is one of the closest stars to our solar system.

Bayer, Johann (1572-1625) - created a list of 788 stars based upon the positions found by Tycho Brahe. The stars are listed in each constellation starting with the brightest to the faintest using a Greek letter and the possessive form of the Latin name of each constellation.

Bell Burnell, Susan Jocelyn (b. 1943) - American astronomer, using a radio telescope that she helped to build, she discovered the pulsar. Later she was able to detect three more of these peculiar stars.

Bessel, Friedrich Wilhelm (1784-1846) - German astronomer who in 1838 became the first person to determine the parallax of a star outside our solar system. He measured the parallax of the star 61 Cygni, and was able to then determine the distance to the star from this measurement.

Bode, Johann Ehlert (1747-1826) - published an empirical rule relating the mean distances of the Sun and the planets that had earlier been created by Johann D. Titius. It has since been called Bode's Law or the Titius-Bode Rule.

Bok, Bart Jan (1906-1983) - astronomer whose main contribution was the study of interstellar dust and gas clouds that lead to star formation. He theorized that small, dark nebulae (now known as Bok Globules) are the sources of new star formation.

Bradley, James (1693-1762) - the third Astronomer Royal of England, he discovered the phenomena known as aberration in which the atmosphere and motion of the Earth bend incoming starlight. He also published some of the most detailed and precise catalogs of star positions available at the time.

Brahe, Tycho (1546-1601) - Danish astronomer who was the first European scientist since ancient times to systematically catalog the positions and magnitudes of the stars. This was done in order to correct for changes in the positions of stars as reported by Ptolemy, over a thousand years earlier. He accomplished this from an observatory called Uraniborg on the island of Hven.

Callippus (370-310 BC) - Greek astronomer and student of Eudoxus who improved upon his theory by adding 8 more spheres to the universe, leading to a total of 34. He also took accurate measurements of the seasons to obtain a closer to true measurement of the length of the year.

Cannon, Annie Jump (1863-1941) - American astronomer who with colleagues at Harvard Observatory created the classification system used to identify the spectral types of stars.

Cassini, Giovanni Domenico (1625-1712) - Italian astronomer who became the director of the Royal Observatory in Paris. He is credited with the discovery of 4 smaller moons of Saturn, and in 1672 calculating a parallax of Mars that resulted in an Earth/Sun distance that was accepted into the eighteenth century.

Chandrasekhar, Subrahmanyan (1910-1975) - Indian-American astronomer who primarily studied white dwarf stars. He established a limit to the amount of mass such a star is capable of having: 1.4 times the mass of the sun. This figure is known as the "Chandrasekhar Limit".

Christy, James - American astronomer who in 1978 from the U.S. Naval Observatory in Flagstaff, Arizona discovered the moon of Pluto, named Charon.

Clark, Alvan Graham (1832-1897) - American optician who designed high quality telescopes and in 1862 first observed the white dwarf companion star of the star Sirius.

Cleomedes - Roman astronomer, wrote a manual on astronomy titled Circle Theory of the Celestial Phenomena, and correctly described the refraction of sunlight above the horizon as a cause of certain astronomical events.

Copernicus, Nicholaus (1473-1543) - Polish astronomer who disputed the accepted Ptolemaic view of the universe (the Sun, Moon, and planets revolve around the Earth). He wrote a lengthy book, De Revolutionibus, in which he debates the accuracies of Ptolemy's ideas, and introduces the heliocentric theory, the Earth and planets revolve around the Sun.