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.
aberration of starlight
1. The tiny apparent displacement of stars resulting from the motion of the earth through space.
2. Apparent displacement of a star from its true position, due to the combined effects of the speed of light and the speed of the earth in orbit around the sun (about 30 kilometers per second or 18.5 miles per second).
The burning away of the leading surface of an object; such as, a meteorite or an artificial satellite, by friction as it enters the earth''s atmosphere from space.

The ablation shielding on a re-entry vehicle; such as, the Space Shuttle, is designed to protect against or to minimize such action.

absolute magnitude, M
1. The magnitude a celestial object would appear to have if it were at a distance of ten parsecs (10 times 3.261633 light years or 32.62 parsecs).
2. A measure of the true or intrinsic brightness of a star as if all stars were the same distance (32.6 light-years) from the observer.
absolute visual magnitude, Mv
The absolute magnitude of an object measured through a special yellowish filter that approximates the visual range of the human eye.
absorption line
Dark narrow lines that represent absorption of energy at a particular wavelength of light.

Each element on the periodic chart absorbs energy at specific wavelengths of light which looks like a bar code.

absorption nebula
A nebula seen in silhouette as it absorbs light from behind; also, called a dark nebula.
absorption spectrum
The spectrum resulting when light from one source is passed through another material; for example, a tenuous gas.

The result is a series of dark bands crossing the spectrum, known as absorption lines.

1. An accumulation of dust and gas into larger bodies.
2. A process in which many smaller bodies congregate together under the action of forces to produce much larger bodies.

Such a force could be, for example, gravitation.

accretion ring
The ring of hot gas and dust that encircles a black hole, formed from material torn off the companion star to the black hole.

In losing its initial angular momentum, the hot material descends into the black hole, friction causing it to reach temperatures high enough to produce x-rays.

It is by the accretion ring emission that makes it possible for the presence of the black hole to be inferred.

active solar energy
As an energy source, such energy comes from the sun collected and stored using mechanical pumps or fans to circulate heat-laden fluids or air between solar collectors and a building.
aerolite, aerolites
The class of stony meteorite that includes the chondrite and achondrite types, both of which commonly consist of silicate material together with nickel and iron.

Chondrites are made up of small round granules of extraterrestrial origin found embedded in some meteorites while achondrites are lacking such small granules.

A faint glow in the atmosphere of a planet resulting from the recombination of the atmospheric atoms that have been broken up by the action of sunlight.
1. The fraction of incident light that is reflected in all directions from an uneven surface; especially, the surface of the earth.
2. The fraction of the solar radiation that is reflected back into space.
3. The ratio of the amount of light reflected from an object in all directions to the amount of incident light.

An albedo of 1.0 corresponds to a perfect reflector.

1. A reference to rocks whose primary constituents have not been formed in their natural or original places.
2. Material that is formed or introduced from somewhere other than the place it is presently found.
Almagest or Mathematike Syntaxis
An astronomical manual written about A.D. 150 by Ptolemy (Claudius Ptolemaeus of Alexandria).

It served as the basic guide for Islamic and European astronomers until about the beginning of the 17th century.

It came from a hybrid of Arabic and Greek ("the greatest"); however, Ptolemy's name for it was Mathematike Syntaxis, "The Mathematical Collection" because he believed that its subject, the motions of the heavenly bodies, could be explained in mathematical terms.

The opening chapters present empirical arguments for the basic cosmological framework within which Ptolemy worked. The earth, he argued, is a stationary sphere at the center of a vastly larger celestial sphere that revolves at a perfectly uniform rate around the earth, carrying with it the stars, planets, sun, and moon; thereby, causing their daily risings and settings.

Through the course of a year the sun slowly traces out a great circle, known as the ecliptic, against the rotation of the celestial sphere.

The moon and planets similarly travel backward; hence, the planets were also known as "wandering stars" against the "fixed stars" found in the ecliptic.

The fundamental assumption of the Almagest is that the apparently irregular movements of the heavenly bodies are in reality combinations of regular, uniform, and circular motions.

The Almagest arose as an Arabic corruption of the Greek word for greatest (megiste). It was translated into Arabic about 827 and then from Arabic to Latin in the last half of the 12th century.

Subsequently, the Greek text was circulated widely in Europe, although the Latin translations from Arabic continued to be more influential.

—The word entry was compiled from information located in "Almagest", Encyclopædia Britannica;
Retrieved, May 09, 2010, from Encyclopædia Britannica Online.

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