Astronomy and related astronomical terms

The angular distance measured along the earth's equator between the meridian passing through the point and the Greenwich Meridian or zero meridian.

1. A measurement of the total amount of energy given off from a star.
2. The total amount of energy radiated by a luminous object per unit time; for example, one second. Common units are watts.

A measure of the year based on twelve lunar months (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.

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.

Mascons (mass concentrations) are regions on the moon with a higher than normal gravitational field.

The amount of matter contained in a body; measured in grams, kilograms, or tons.

An empirical relation between the mass and luminosity, both usually expressed in solar units, for main sequence stars.

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 because scientists use the metric system 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.

1. 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".
2. The streak of light seen in the night sky signifying the burning up in the earth's atmosphere of interplanetary material.