Astronomy and related astronomical terms

A measure of the year based on twelve lunar months: The lunar calendar is formed by employing the time it takes the Moon to revolve around the Earth), which lasts about 354.37 days.

The passage of the Moon into the Earth's shadow: A lunar eclipse is a phenomenon in which the Earth covers up the full Moon, either partially or completely.

1. The volume of space, surrounding a planet, controlled by the planet's magnetic field, and acting as a magnetic "shell": The Earth's magnetosphere extends 64,000 kilometers or 40,000 miles toward the Sun, but many times this distance on the side away from the Sun.

2. The magnetic field of a planet in space: A planet's magnetosphere is molded by the solar wind into a teardrop shape, its point directed away from the Sun.

A measure of the brightness or luminosity of a star or other celestial object: The larger the number referring to the magnitude, the fainter the object.

Zero, or first magnitude, indicates some of the brightest stars.

Still brighter are those of negative magnitude, such as Sirius, whose magnitude is -1.46.

The diagonal belt of stars on the Hertzsprung-Russell diagram stretching from the high temperature and luminosity region of the diagram down to the low temperature end: A star's position in the belt depends on its mass, and once on the Main Sequence, a star remains there for most of its existence.

The layer of rock between the core of a moon or terrestrial planet and its surface crust: Jill read that the mantle of the Earth existed under the top covering of the Earth, or crust, and above its central core.

A regions on the Moon with a higher than normal gravitational field: Mascoms are probably a result of abnormally dense material just beneath the lunar surface.

The amount of matter contained in a body: A mass is measured in grams, kilograms (kg), or tons.

An empirical relation between the mass and luminosity, both usually expressed in solar units, for main sequence stars: The mass-luminosity relation was predicted by Eddington in 1924.

For sunlike stars, the luminosity varies as the 3.5 power of the mass.

The power is smaller for lower mass stars.

1. A physical substance that occupies space, possesses mass, and is ultimately convertible to energy: Matter can be a gas, liquid, or solid.
2. The substance of the universe; made up of atomic particles, atoms, and molecules.

Matter exists in four familiar states: solid, liquid, gas, and plasma (gas consisting of electrons and ions).

Our universe gives measurements of length, weight, and area in metric units: Scientists use the metric system when measuring the unverse in their work.

Temperatures are measured in degrees Celsius (°C), also called centigrade, and in kelvins (sometimes abbreviated K).

Kelvins are used by astronomers to describe very high temperatures; such as, those in the sun and other stars.

The circle that passes through both poles on a sphere, cutting the equator at right angles: The meridian is located on maps in order to help people to describe the position of a certain point.

The streak of light caused by a meteoroid that passes through Earth's atmosphere and the burning meteoroid, which is also called a "shooting star": A meteor is the band or line of illumination seen in the night sky signifying the burning up of interplanetary material.in the Earth's atmosphere

1. An interplanetary material or a meteoroid that survives passage through the earth's atmosphere and arrives on earth's surface without completely burning up.
2. A piece of rock or metal from space that reaches the surface of the earth, moon, or other celestial body.

Most meteorites are thought to be fragments from asteroids, although some may be pieces from the heads of comets. Most are stony, although some are made of iron and a few have a mixed rock-iron composition.

1. A solid body smaller than an asteroid that orbits the sun.

Both meteors and meteorites were meteoroids.

2. The general terms for meteors and micrometeroids, the latter usually having masses of less than a microgram.