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.
neutron star (s) (noun), neutron stars (pl)
1. The result of the collapse of the remnant from a supernova explosion: The mass of a neutron star 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.

The name of the neutron star is derived from the fact that the object is so condensed that most of its material is in the form of neutrons.

It was named after Subrahmanyan Chandrasekhar (1910-1995), a U.S. astrophysicist.

2. A very small core of a "super-dense" star: A neutron star is 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 (s) (proper noun) (no pl)

A Latin version of the biographical name Mikolaj Kopernik (1473-1543), 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.

Nicolaus Copernicus 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) (noun), novae; novas (pl)
The sudden increase in brightness of a star, probably as a result of its interaction with another, very close, star forming a binary system: A nova is a faint star that suddenly increases in brightness by a factor of 10,000 or moreand remains bright for a few days, and then fades away and is not seen again for very many years, if at all.

Novae 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.

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 (s) (noun), nuclear fusions (pl)
A process by which matter changes to energy: Nuclear fusion is the nuclei of lighter atoms that fuse, or join, to form heavier nuclei, releasing energy.

Nuclear fusion is the system 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.

nucleosynthesis (s) (noun), nucleosyntheses (pl)
The generation of chemical elements by the big bang, and by supernova explosions: Nucleosynthesis occurs when heavier chemical elements are formed from lighter atomic nuclei inside stars, for example, during a supernova explosion.
nucleus (s ) (noun), nuclei; nucleuses (pl)
1. The central positively charged portion of an atom: A nucleus contains most of the atom's mass.
2. A chunk of solid matter at the center of a comet's head: The nucleus of a comet is small and bright
3. The central part of a spiral galaxy that is very dense with stars: The nucleus of a galaxy is the small, substantial, and compressed part around which there is a multitude of stars.
nutation (s) (noun), nutations (pl)
A slight "nodding" of the Earth in space: A nutation is 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 takes just over 18.5 years.

oblateness (s) (noun), oblatenesses (pl)
A measure of the amount by which a celestial object, such as a planet, that differs in shape from a perfect sphere: The oblateness of a celestial body is usually calculated by dividing the difference between the equatorial and polar diameters (or radii) by the equatorial diameter (or radius).

observatory
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.

occultation
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.
opacity
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.
opposition
1. The moment at which a body in the solar system lies opposite the sun in the sky as seen from the earth and crosses the meridian at about midnight.
2. An object lying farther from the sun than the earth is at opposition when it lies on a line from the sun passing through the earth to the body in question.

The object is then directly behind the earth, and is fully illuminated as seen from the earth.

orbit
1. The path of one body in space around another body; such as, the orbit of the earth around the sun, or the moon around the earth.

When the two bodies are similar in mass, as in a binary star, both bodies move around their common center of mass.

The movement of objects in orbit follow Johann Kepler's laws, which apply to artificial satellites as well as to natural bodies.

2. The path followed by one object around another as a result of their mutual gravitational interaction.

As a result of the inverse square law of gravitation, planetary orbits are approximately conic sections.

Also check out the Index of other Scientific and Technological Topics.