Astronomy Terms

So much about galaxies remains a mystery. We know what they're made of and that we live in one (the Milky Way), but how many galaxies are in the universe?

By Craig Freudenrich, Ph.D.

Space collisions are the universe's car wrecks. Only in outer space, it's stars, asteroids and even galaxies doing the smashing.

By John Fuller

Some scientists believe that space is infinite. But is it? If it isn't, what form does space take? Is it a dodecahedron or a triple torus?

By Jonathan Strickland

When a star dies, it becomes a black hole. Once something passes through the it's gone for good, never to be seen or heard from again. If we lived next to a black hole, would it suck us in too?

By Marshall Brain

You've heard of the big bang, of course, but do you have any idea as to what was happening during that massive flurry of activity billions of years ago?

By Robert Lamb

So much of our cosmological history starts with the much-discussed Big Bang, but what led up to that cataclysmic moment? And did time even exist back then?

By Robert Lamb & Patrick J. Kiger

While routinely scanning the stars, NASA scientists came across something they didn't expect to see: a vast area of space empty of stars, planets and matter.

By Jacob Silverman

We take much for granted about our universe, like it's getting bigger. What if the universe stopped expanding and started collapsing inward with a giant crunch?

By William Harris

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.

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.

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.

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.

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

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.

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.

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

The nebular theory, also known as nebular hypothesis, presents one explanation of how the solar system was formed, proposed by Pierre Simon de Laplace in 1796.

By Yara Simón

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

Perihelion and Aphelion, The perihelion is the point on the orbit of a planet or comet that is closest to the sun.

Perturbation, in astronomy, is a disturbance in the orbit or motion of a heavenly body.

Planetarium, is an educational device for showing the locations and movements of the planets and other objects in the universe.