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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Schiaparelli, Giovanni Virginia (1835-1910), was an Italian astronomer. He is best known for his studies of Mars, begun in 1877, in which he described in detail the Martian canals.

Bradley, James (1693-1762), an English astronomer, discovered the aberration of starlight that provided the first direct proof that the earth revolves around the sun, and the nutation, or nodding motion, of the earth's axis.

Bell Burnell, Jocelyn (1943-), a Northern Irish astronomer, discovered the first four pulsars, neutron stars that emit pulses of radiation with a high degree of regularity.


Adams, John Couch (1819-1892), was a British astronomer and one of the discoverers of the planet Neptune.

Flamsteed, John (16461719), an English astronomer. Flamsteed was appointed the first astronomer royal, in 1675, and Greenwich Observatory was built for him in 1676.

Tsiolkovsky (or Ziolkovsky), Konstantin Eduardovich (1857-1935), a Russian rocket pioneer who is generally regarded as the father of space travel.

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.


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

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.

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.

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


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.

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.

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

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, 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.

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.


Astrophysics, the application of the theories and techniques of modern physics to astronomy.

Azimuth, the horizontal direction of an object, measured clockwise in degrees, minutes, and seconds of arc from true north or south along the theoretical horizon.

Bolometer, an instrument used to measure infrared, or heat, radiation. The bolometer is essentially a very sensitive thermometer.

Chronometer, a timepiece that is exceptionally accurate. Traditionally, the term refers to the marine chronometer, a rugged mechanical instrument used at sea to keep time for navigational purposes.


Cosmogony, the study of the origin and development of the universe as a whole and of the individual bodies that compose it.

Day, in astronomy, the average length of time between successive noons. Noon is defined as the instant when the sun is highest in the sky.