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.
synodic period
1. The length of time during which a body in the solar system makes one orbit of the sun relative to the earth; that is, returns to the same elongation.

Because the earth moves in its own orbit, the synodic period differs from the sidereal period, which is measured relative to the stars.

The synodic period of the moon, which is called the lunar month, or lunation, is 29 1/2 days long which is longer than the sidereal month.

2. The time required for a body in the solar system to return to the same or about the same position relative to the sun as seen from the earth.

The moon's synodic period is the time between successive recurrences of the same phase; that is, the period between one full moon and the next full moon.

T Tauri star
1. One of a group of stars that have irregular light curves, and which are believed to represent the stage in a star's evolution shortly before it appears on the main sequence.

The stars characteristically have rapid rotation and throw off much material in stellar winds.

2. Any of a class of very young stars having a mass of the same order as that of the sun.

So called after a prototype identified in a bright region of gas and dust known as the Hind’s variable nebula, the T Tauri stars are characterized by erratic changes in brightness.

They represent an early stage in stellar evolution, having only recently been formed by the rapid gravitational condensation of interstellar gas and dust.

These young stars are relatively unstable, though contracting more slowly than before, and will remain in that condition until their interior temperatures become high enough to support thermonuclear reactions for energy generation.

More than 500 T Tauri stars have so far been observed. The sun is thought to have gone through the T Tauri stage in its beginning.

A zodiacal constellation in the northern hemisphere near Orion, represented as a bull. The sun passes through Taurus from mid-May to late June.
The movement of plates that make up the lithosphere of a planet.

Such movements produce fold mountains and other surface features.

A small, rounded glassy stone, found in certain regions of the earth; such as, Australasia.

Tektites are probably the scattered drops of molten rock thrown out by the impact of a large meteorite.

terestrial planets
Mercury, Venus, Earth, and Mars.
The shadow-line boundary between night and day on a planet or moon.
thermal emission
The type of electromagnetic radiation emitted when electrons and atoms forming part of a hot gas interact by collisions; the resulting radiation is continuous, as opposed to discrete, line emission.
thermonuclear reaction
Nuclear fusion that occurs at extremely high temperatures.
tidal force
1. The minimum distance to which a large satellite can approach its primary body without being torn apart by tidal forces.

If the satellite and primary body are of similar composition, the theoretical limit is about two and a half times the radius of the larger body.

The rings of Saturn lie inside Saturn's Roche limit and may be the debris of a demolished moon.

The limit was first calculated by the French astronomer Édouard Roche (1820–83). Artificial satellites are too small to develop substantial tidal stresses.

2. The force arising from differences in the strength of gravity experienced over different parts of an object.

Such a force is responsible for the tides, and for the breakup of a body straying within the Roche limit of a planet.

When comets pass close to a massive body like the sun or Jupiter, they may break up due, at least in part, to the tidal forces encountered.

tide, tides
1. The effect arising from the differential gravitational effect of one body on another.

This usually manifests itself in the distortion of the shape of the body; especially, the surface layers.

2. Periodic changes in the shape of a planet, moon, or star caused by the gravitational attraction of a body near it.

The moon tugs on earth's oceans, causing high and low tides; while Jupiter's gravitational attraction on its moon Io causes ground tides; and when two stars are very close together, they pull each other's atmospheres into distorted shapes.

The largest moon of the planet Saturn.

It was discovered in 1655 by the Dutch mathematician and astronomer Christian Huygens, and is the second largest moon in the solar system. Ganymede, of Jupiter, is larger.

Titius-Bode law, Bode's law
1. An empirical rule giving the approximate distances of planets from the sun.

It was first announced in 1766 by the German astronomer Johann Daniel Titius but was popularized only from 1772 by his countryman Johann Elert Bode.

Once thought to have some significance regarding the formation of the solar system, Bode’s law is now generally regarded as a numerological curiosity with no known justification.

2. An empirical law that generates the distances of planets and the position of the minor planet belt from the sun in astronomical units.
An object formed by joining the two ends of a cylinder producing a doughnut shape with a circular cross-section.

A magnetic field inside the orbit is always twice as strong as the magnetic field on the orbit, the radius of the orbit remains constant, so that the acceleration chamber can be made in the shape of a torus, or doughnut.

The poles of the magnet are tapered to cause the field near the orbit to weaken with increasing radius.

The moment during a total solar eclipse during which the sun completely disappears from view.

The light of totality is much brighter than that of the full moon but is quite different in color. The duration of totality is brief, typically lasting two to five minutes.

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