Astronomy and related astronomical terms

A prominent zodiacal constellation in the northern hemisphere represented as the twins Castor and Pollux.

Its brightest star is Pollux; Castor is a system of six stars.

The sun passes through Gemini from late June to late July. Each December, the Geminid meteors radiate from Gemini.

1. A reference to the solar system when it is regarded as having the earth as its center.
2. Measured from, or considered as if viewed from, the center of the earth.
3. Having the earth and its inhabitants as the center of a theory or belief.

Any theory of the solar system or the universe that places the earth at the center.

A description of the orbit of a satellite that circles the earth above the equator at a speed matching the earth's rotation; thus, appearing to remain stationary, or a satellite in such an orbit.

Most communications satellites are in geostationary orbit.

A large star that is highly luminous.

A spherical collection of star, the concentration of which increases greatly toward the center.

The stars are probably of the same age, and the clusters as a whole move in highly elliptical orbits that take them high above the galactic center.

1. Dense groups of thousands to millions of stars.
2. A spherically symmetric collection of stars which have shared a common origin.

A planet that can support life because it is neither too hot nor too cold, too big nor too small, too near its star nor too far; one whose size, temperature and composition are all just right for life.

1. The force by which two masses attract each other.
2. The mutual attraction existing between all objects with mass.

Newton's law of gravitation states that the force of attraction between two bodies varies as the product of the two masses and, inversely, as the square of the distance between them.

Einstein's theory of general relativity views the attraction as being a result of the curving of space and time by a massive object.

Quantum gravity considers the force to be the result of the exchange of particles known as gravitons.

1. Gravitational force at the surface of a planet or other body that pulls mass toward its center.
2. The pulling force (force of attraction) between any two masses in the universe.

On earth, gravity is experienced as a downward force that makes things fall toward the ground.

Common names and translations of Latin terms for the constellations Ursa Major and Ursa Minor in that order.

The trapping of infrared radiation from the surface of a planet by a dense atmosphere, opaque to heat radiation.

This effect occurs on Venus and on Earth.

The interface between the mantle of the earth and the outer core.

It lies about 1,800 miles (2,900 kilometers) beneath the earth's surface.

The comet that orbits the sun about every 76 years, named for Edmond Halley, who calculated its orbit.

It is the brightest and most conspicuous of the periodic comets and recorded sightings go back more than 2,000 years.

It travels around the sun in the opposite direction to that of the planets and its orbit is inclined at almost 20° to the main plane of the solar system and ranges between the orbits of Venus and Neptune.

Halley's comet is expected to reappear in 2061.

The emission of particles by a black hole, leading to the eventual explosion of the black hole in a burst of gamma radiation.