Astronomy and related astronomical terms

(the science of the celestial bodies: the sun, the moon, and the planets; the stars and galaxies; and all of the other objects in the universe)

The astronomer said,
As he raised his cup,
"Thank heavens my business
Is looking up."
—Ennis Rees, Pun Fun;
Scholastic Book Services; New York; 1965; page 13.
1. An atomic particle given off during nuclear fusion and which apparently has little or no mass and moves at the speed of light.
2. An elementary particle with no charge and a very small, perhaps zero, mass.

Produced in nuclear reactions in stars, the particle has a very weak interaction with matter.

An atomic particle having high mass but no electrical charge.

Neutrons are present in the nuclei of all atoms except hydrogen.

neutron star
1. The result of the collapse of the remnant from a supernova explosion if its mass exceeds the chandrasekhar limit, but is less than that required for gravity to continue the collapse down to a black hole.

The chandrasekhar limit is the upper limit for the mass of a white dwarf star beyond which the star collapses to a neutron star or a black hole. A star having a mass above this limit will continue to collapse to form a neutron star.

Its name derives from the fact that the object is so condensed that most of its material is in the form of neutrons.

Named after Subrahmanyan Chandrasekhar (1910-1995), a U.S. astrophysicist.

2. A very small core of a super-dense star composed mostly of neutrons (electrically neutral subatomic particles in the baryon family).

Neutron stars are estimated to be so condensed that a fragment the size of a sugar cube would weigh as much as all the people on the earth put together.

—As seen in the Scientific American Science Desk Reference;
John Wiley & Sons, Inc.; New York; 1999; page 169.
Nicolaus Copernicus (1473-1543)

A Latin version of the name Mikolaj Kopernik, the Polish astronomer who established the heliocentric model of the solar system; that is, the principle that the sun (not the earth) is the central point to which the motions of the planets are to be referred.

He was the first person in history to create a complete general system of the solar system (the Copernican system), combining mathematics, physics, and cosmology.

nova (s), novae (pl)
1. A faint star that suddenly increases in brightness by a factor of 10,000 or more, remains bright for a few days, and then fades away and is not seen again for very many years, if at all.

Novae (plural of nova) are believed to occur in close binary star systems, where gas from one star flows to a companion white dwarf. Such stars which are similar to those appearing in our galaxy have also been observed in other galaxies.

2. The sudden increase in brightness of a star, probably as a result of its interaction with another, very close, star forming a binary system.

The brightness increase is due to the blowing off of a large amount of hot hydrogen gas from the star's surface, the star probably being a white dwarf.

Stars are generally regarded as being unchanging on a human time scale, so the appearance of a newly visible star, or nova, is unusual.

Generally novae brighten suddenly within weeks or days, fade drastically during the following few weeks, then continue to fade more gradually for several years.

nuclear fusion
1. A process by which matter changes to energy.

The nuclei of lighter atoms fuse, or join, to form heavier nuclei, releasing energy.

2. The process which keeps stars, like the sun, luminous for billions of years.

In general, nuclear fusion involves the "fusing" together of atomic nuclei of low mass to form heavier nuclei. A vast amount of energy is released in the process.

The generation of chemical elements by the big bang, and by supernova explosions.
nucleus (s), nuclei (pl)
1. The central portion of an atom which has a positive charge and contains most of the atom's mass.
2. A comet which has a chunk of solid matter at the center of a comet's head.
3. The central part of a spiral galaxy that is very dense with stars.
A slight "nodding" of the earth in space, caused by the varying gravitational pulls of the sun and moon.

Nutation changes the angle of the earth's axial tilt (average of about 23.5°) by about nine seconds of arc to either side of its mean position, a complete cycle taking just over 18.5 years.

A measure of the amount by which a celestial object; such as, a planet, that differs in shape from a perfect sphere.

It is usually calculated from dividing the difference between the equatorial and polar diameters (or radii) by the equatorial diameter (or radius).

A site or facility for observing astronomical or meteorological phenomena.

The earliest recorded observatory was in Alexandria, north Africa, built by Ptolemy Soter in about 300 B.C.

The modern observatory dates from the invention of the telescope. Observatories may by ground based, carried on aircraft, or sent into orbit as satellites, in space stations, and on the space shuttle.

1. The hiding of one celestial body by another one.
2. The total or partial obscuring of a star or other celestial object by the moon or a planet.
Oort cloud
A cloud of comets lying about 50,000 to 100,000 astronomical units from the sun.

The Oort cloud is postulated as the source of comets entering the solar system and is named after the Dutch astronomer Jan Oort, who theorized its existence in 1950.

The Oort Cloud is a spherical region extending for trillions of miles or kilometers that contains debris flung outward by the giant planets after they formed.

It is believed that comets that orbit the sun in periods of thousands or millions of years usually come from the Oort Cloud.

—Compiled from information presented in
Astronomy, The World Book Encyclopedia of Science;
World Book, Inc.; 2000; page 93.
A measure of the absorption of incident radiation by a body, being the ratio of the total radiant energy incident upon a body to the amount that passes through it.
open cluster
A loose cluster of young stars of high luminosity found in or near the plane of the galaxy.

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