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. The crossing of a small celestial body in front of a larger one.

Venus and Mercury are in transit across the disk of the sun when seen from the earth.

2. The passage across the observer's meridian of a celestial body, or the crossing of the face of one body; for example, the sun, by the path of another; for example, Mercury or Venus, from the observer's viewpoint.
Trojan group
A group of minor planets that are clustered around two of the Lagrangian positions of the Jupiter-sun system; that is, a point in space at which a small body, under the gravitational influence of two large ones, will remain approximately at rest relative to them.

The first Trojan was Achilles, discovered in 1906.

These minor planets revolve around the sun in the Lagrangian points of Jupiter’s orbit and they are positions where a small body can be held, by gravitational forces, at one point of an equilateral triangle whose other points are occupied by Jupiter and the sun.

About forty Trojan planets are known; Achilles, the first, was discovered by Max Wolf in 1906. Of the named Trojans, Achilles, Hector, Nestor, Agamemnon, Odysseus, Ajax, Antilochus, Diomedes, and Menelaus are near the Lagrangian point 60° ahead of Jupiter. Patroclus, Priamus, Aeneas, Anchises, and Troilus are about 60° behind Jupiter.

—Compiled from information located at
"Trojan planets" in Encyclopædia Britannica Online.
twenty-one centimeter radiation
The common name given to radio waves emitted at 1,420 megahertz as the result of the "flipping over" of the electron in a hydrogen atom in order to oppose the spin direction of the central proton.

The radiation is an example of line emission.

UFO, unidentified flying object
Any light or object seen in the sky whose immediate identity is not apparent.

Despite unsubstantiated claims, there is no evidence that UFO's are alien spacecraft. When investigated, the vast majority of sightings turn out to have been of natural or identifiable objects, notably bright stars and planets, meteors, aircraft, and satellites, or to have been perpetrated by pranksters.

1. A region of complete shadow resulting from the total obstruction or blocking of light.
2. The darkest portion of the shadow cast by an astronomical object during an eclipse, especially that which is cast on earth during a solar eclipse.
3. Te main dark inner cone of shadow cast by one body onto another body during an eclipse.

Any point lying within the umbra will observe a total eclipse of the object. The umbra is also the name given to the darkest part of a sunspot.

1. The totality of space, matter, and radiation that is potentially comprehensible.
2. The whole cosmic system of matter and energy of which earth, and therefore the human race, is a part.

Humanity has traveled a long road since societies imagined earth, the sun, and the moon as the main objects of creation, with the rest of the universe being formed almost as an afterthought.

Today it is known that the earth is only a small ball of rock in a space of unimaginable vastness and that the birth of the solar system was probably only one event among many that occurred against the backdrop of an already mature universe.

3. All of the space and its contents, the study of which is called cosmology.

The universe has been determined to be mostly empty space, dotted with stars collected into vast aggregations called galaxies for as far as telescopes can see.

The most distant detected galaxies and quasars (quasi-stellar objects) lie ten billion light-years or more from the earth, and are moving farther apart as the universe expands.

Ursa Major, Great Bear
The third largest constellation in the sky, in the north polar region.

Its seven brightest stars make up the familiar shape, or asterism, of the Big Dipper. The second star of the handle of the dipper, called Mizar, has a companion star, Alcor.

Two stars forming the far side of the bowl act as pointers to the north star, Polaris. Dubhe, one of them, is the constellation's brightest star.

Ursa Minor, Little Bear
The "Little Dipper" or small constellation of the northern hemisphere. It is shaped like a dipper, with the bright north pole star Polaris at the end of the handle.
In theory, space that contains no matter.
Van Allen radiation belts
1. Two zones of charged particles around the earth's magnetosphere, discovered in 1958 by U.S. physicist Jame Van Allen.

The atomic particles came from the earth's upper atmosphere and the solar wind, and are trapped by the earth's magnetic field.

The inner belt lies above the equator, and contains protons and electrons from the solar wind.

2. One of two regions, lying at about 1,900 miles, 3,000 kilometers, and 12,500 miles, 20,000 kilometers, above the equator, in which charged particles, trapped in the earth's magnetosphere, oscillate between the magnetic poles.

The particles are caught from the solar wind or produced by collisions between air molecules and cosmic rays.

variable star
1. A star whose brightness changes over time.
2. A star whose luminous output varies significantly with time.

Such variation may be regular; that is, eclipsing variable stars, or irregular, as with flare stars.

In addition, the variation can be intrinsic, because of changes within the star itself, or extrinsic, as the result of the interaction of one star with another.

Veil Nebula
A supernova remnant formed as a result of a supernova explosion about 30,000 years ago.

Still expanding, the nebula will eventually become indistinguishable from interstellar gas.

vernal equinox
The equinox, or celestial equator, which occurs about March 21.
Very Long Baseline Interferometry, VLBI
The technique of linking together several radio telescopes spaced by hundreds and even thousands of miles to achieve very high resolution observations of distant objects; such as, quasars.
A zodiacal constellation of the northern hemisphere, the second largest in the sky.

It is represented as a maiden holding an ear of wheat, marked by the first-magnitude Spica, Virgo's brightest star.

The sun passes through Virgo from late September to the end of October.

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