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.

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

Brown Dwarf, a celestial object more massive than a planet but less massive than a star.

Chronology, the science of measuring time. Chronology divides time into regular divisions or periods, and assigns events their proper place and sequence by giving them dates.

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.

Cosmology, the study of the universe. It is both a scientific subject and a philosophical one.

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.

Double Star, a pair of closely-spaced stars that to the unaided eye usually appear as a single star.

Eclipse. An eclipse of the sun, or solar eclipse, occurs when the moon's shadow sweeps across the earth.

Ecliptic, the apparent annual path of the sun among the stars. The sun appears to follow a path through the stars because the earth revolves around the sun.

Epoch, in chronology (timekeeping), a point in time, such as 302 B.C. or October 30, 1936, or 7:34 A.M.

Equinox, During the course of a year, the sun appears to move northward for about six months and southward for about six months.

Evening Star, the name given to any of the five bright planets in the sky at sunset.

Hour, a unit for measuring time, defined as either 1/24 of a day or 3600 seconds (60 minutes).

Hourglass, a device for measuring time. In its usual form it consists of two cone-shaped or oval glass receptacles joined by a narrow neck.

Interferometer, an instrument that uses the interference patterns formed by waves (usually light, radio, or sound waves) to measure certain characteristics of the waves themselves or of materials that reflect, refract, or transmit the waves.

Magnitude, in astronomy, a unit of measurement of the brightness of stars. The scale of magnitude extends from negative numbers (for example, the minus first magnitude) for very bright stars to positive numbers (for example, the fourth magnitude) for dimmer ones.

Meteor. As the term is commonly used, a meteor is a small celestial body that enters the atmosphere of the earth.

Midnight Sun, a name given the sun when it can be seen at midnight during the Arctic or Antarctic summer.

Millennium, in a common Christian belief, the period of 1,000 years before the Last Judgment, during which time Christ and the saints will reign on earth.

Minute, a unit for measuring both time and space. As a unit of time, a minute is 60 seconds, or 1/60 of an hour.

Month, a unit of time. The calendar month is approximately 1/12 of the calendar year.

Nebular Hypothesis, an explanation of how the solar system was formed, proposed by Pierre Simon de Laplace in 1796.

Night, the period of darkness caused by the disappearance of the sun below the horizon.

Nova, (plural: Novae), a star that rapidly increases in brightness and then fades again.