Science Dictionary

Do you know what a meteor is, or what scientists mean when they are talking about cryogenics? Our collection of science terms explains the meaning of some of the most common scientific ideas.

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Maarten Schmidt

Schmidt, Maarten (1929-) is a Dutch astronomer. He identified the starlike objects now known as quasars.

Mitchell, Maria

Mitchell, Maria (1818-1889), a United States astronomer. Her birthplace was Nantucket, Massachusetts.

Nasir al-Din Al-Tusi

Al-Tusi, Nasir al-Din (1201-1274) was one of the greatest scholars of his time and one of the most influential figures in Islamic intellectual history.

Copernicus, Nicolaus

Nicolaus Copernicus was a Polish astronomer who was the first to publish a book setting forth evidence that the earth and the other planets revolve around the sun.

Roemer, Olaus

Roemer, Olaus (1644-1710), a Danish astronomer. He was the first to measure the speed of light, using eclipses of Jupiter's moons.

Struve, Otto

Struve (STROO veh), Otto (1897 - 1963) was a Kussian-born American astronomer who belonged to a family of distinguished scientists that included six astronomers over four generations, he being the last.

Lowell, Percival

Lowell, Percival (1855-1916), a United States astronomer. In 1894 he established the Lowell Observatory at Flagstaff, Arizona.

Richard Woolley

Woolley, Richard (1906-1986) was the United Kingdom's astronomer royal from 1956 to 1971.

Burnham, Sherburne Wesley

Burnham, Sherburne Wesley (1838-1921), a United States astronomer. His General Catalogue of Double Stars (1906) contains data on 13,665 double stars, more than a thousand of which he discovered.

Langley, Samuel Pierpont

Langley, Samuel Pierpont (1834-1906), a United States astronomer, physicist, and aviation pioneer.

Newcomb, Simon

Newcomb, Simon (1835-1909), a United States astronomer. He calculated the movements of the moon, Mercury, Venus, Mars, Uranus, and Neptune more precisely than had been achieved previously.

Airy, Sir George Biddell

Airy, Sir George Biddell (1801-1892), a British astronomer. Airy was astronomer royal from 1835 to 1881.

Lockyer, Sir Joseph Norman

Lockyer, Sir Joseph Norman (1836-1920), an English astronomer. He was one of the first to study the sun and stars with a spectroscope.

Theodore Von Krmn

Von Kármán, Theodore (1881-1963) was a Hungarian-born American physicist and engineer who made great contributions to the field of aerodynamics and rocket technology.

Brahe, Tycho

Brahe, Tycho (15461601), a Danish astronomer. Tycho achieved fame by writing a book on the brilliant new star that appeared in 1572.

Leverrier, Urbain Jean Joseph

Leverrier, Urbain Jean Joseph (1811-1877), a French astronomer. Leverrier and John Couch Adams independently deduced the existence of the planet Neptune by mathematical calculations.

Slipher, Vesto Melvin

Slipher, Vesto Melvin (1875-1969), a United States astronomer. He made perhaps more basic contributions in various fields of astronomy than any of his contemporaries, Slipher is best known for his fundamental spectroscopic discoveries, especially of the rotations and atmospheres of planets.

Sitter, Willem de

Sitter, Willem de (18721934), a Dutch astronomer. He was a pioneer in applying Albert Einstein's theory of relativity to astronomy and developed a model of an expanding, curved universe.

William Wallace Campbell

Campbell, William Wallace (1862-1938), an American astronomer, made important measurements of the motion of stars.

Aberration of Light

Aberration of Light is a phenomenon in which a star or other celestial body, as viewed from the earth, appears to be slightly displaced from its true position.


Albedo, in astronomy, is the reflecting power of a celestial body that is not self-luminous.

Andromeda Galaxy

Andromeda Galaxy, a spiral galaxy that is larger than the Milky Way (the galaxy to which Earth belongs) but similar to it in structure, and the closest to ours.

Eros (asteroid)

Eros, a small asteroid (minor planet) discovered in 1898. It was the first asteroid known to come closer to the earth than the planet Mars.


Astrogeology is the science that applies the principles of geology to the study of solid bodies of the solar system other than the earth.


Transit, in astronomy, is the passage of one celestial body across the disc (face) of a larger, more distant body, or across the observer's meridian.