Astronomy and related astronomical terms

1. Two stars orbiting a common center of gravity.
2. A pair of stars revolving around a common center of gravity, held together by their mutual gravitational interaction.
3. A double star; a system containing two or more stars.

In an eclipsing binary, one star goes behind the other periodically, changing the total amount of light that we see.

A white dwarf which has stopped radiating energy.

1. A region of space in which mass is packed so densely that (according to Einstein's general theory of relativity) nothing, not even light, can escape.
2. An object whose matter has become so condensed that its gravitational field is striking enough to prevent light escaping from it.
3. In theory, a collapsed object (perhaps a massive star) whose gravitational field is so strong that under most circumstances no light or matter can escape.

The term was invented by the American physicist John Wheeler in 1968 (some sources say 1967). Within a few years, other usages had expanded the phrase for other applications; such as, to describe everything from large budget deficits to gaping legal loopholes.

The "black hole" is also used as a verb. In technological circles, to "black-hole" means to cut off data going to and coming from an address, particularly an address used by a spammer. This usage has been around since about 1997.

A manifestation of the Doppler effect in which an object appears bluer when it is moving towards the observer or the observer is moving towards it. Blue light has a higher frequency than other colors in the spectrum.

The blue shift is the opposite of the red shift.

A bright meteor or fireball.

1. A constellation of the northern hemisphere, dominated by the bright star Arcturus which is represented by a herdsman driving a bear (Ursa Major) around the pole.

Arcturus, or Alpha Boötes, is about 37 light-years from earth. The herdsman is assisted by the neighboring Canes Venatici, "the Hunting Dogs".

2. Etymology: from the Mid-16th century from Latin which came from Greek boōtēs, "plowman, Boötes"; from bous, "ox" + ōthein, "to push".

1. A gaseous body smaller in mass than a star, but larger than a planet.
2. An object less massive than a star, but heavier than a planet.

Brown dwarfs do not have enough mass to ignite nuclear reactions at their centers, but shine by heat released during their contraction from a gas cloud.

Some astronomers believe that vast numbers of brown dwarfs exist throughout the galaxy, but because of the difficulty in detecting them, none of them were detected until 1995, when U.S. astronomers discovered a brown dwarf, in the constellation Lepus (Hare).

The division of the year into months, weeks, and days and the method of ordering the years (past, present, and future).

From year one, an assumed date of the birth of Jesus, dates are calculated backwards (B.C., "before Christ" or B.C.E., "before common era") and forwards (A.D., Latin anno Domini, "in the year of the Lord", or C.E. "common era").

The faintest of the zodiacal constellations.

It lies in the northern hemisphere between Leo and Gemini, and is represented as a crab.

The sun passes through the constellation during late July and early August.

A promontory (a point of land that juts out into the sea) on the Atlantic coast of Florida, U.S.A., 367 kilometers or 228 miles north of Miami, that is used as a rocket launch site by NASA (National Aeronautics and Space Administration).

A zodiacal constellation in the southern hemisphere next to Sagittarius.

It is represented as a fish-tailed goat, and its brightest stars are third magnitude (measure of the brightness of a celestial object). The sun passes through it in late January to mid-February.

A reflecting telescope which has a mirror at its base with a central hole, allowing light reflected from this primary mirror to pass through it after being reflected by a convex secondary mirror.

1. The major division in Saturn's rings, which separates the A-ring from the B-ring.
2. A gap of about 1800 kilometers wide between the outermost rings of Saturn.

It was discovered by Cassini in 1675.

The period of a particle in Cassini's division is about two-thirds that of Janus, one-half that of Mimas, one-third that of Enceladus, and one-quarter that of Tethys.

1. A prominent constellation of the northern hemisphere, named for the mother of Andromeda.

It has a distinctive W-shape, and contains one of the most powerful radio sources in the sky, Cassiopeia A.

This is the remains of a supernova (star explosion) that occurred about A.D. 1702, too far away to be seen from earth.

2. Etymology: from Latin Cassiepa, Cassiopa, which came from Greek Kassiepeia, Cassiopeia, daughter of Cepheus and Andromeda, who was changed into a constellation of the northern hemisphere containing a spiral galaxy, Andromeda Galaxy, that can be seen with the naked eye.

The imaginary great circle that lies above the earth's equator and meets the celestial sphere.