Parsec

The distance at which the angle (annual parallax) subtended by the average radius of the Earth's orbit is 1". Equivalently, the distance at which one astronomical unit subtends ...

parsec

Astronomy; General astronomy

(pc): distance at which an object would have a parallax of one arc second. Equals approximately 3.26 light years or about 206,265 astronomical units.

gyroscope

Astronomy; Astrometry

An instrument that is made of a disk or wheel that spins about an axis like a top. Gyroscopes are used to keep spacecraft in the right position.

stars

Astronomy; Astrometry

Stars are a luminous conjunction of plasma held together by gravity. The light that comes from the stars is produced by thermonuclear fusions of hydrogen in its core. During the ...

Absolute Zero

Astronomy; Astrometry

The temperature at which the motion of all atoms and molecules stops and no heat is given off. Absolute zero is reached at 0 degrees Kelvin or -273.16 degrees Celsius.

Atmosphere

Astronomy; Astrometry

A layer of gases surrounding a planet, moon, or star. The Earth's atmosphere is 120 miles thick and is composed mainly of nitrogen, oxygen, carbon dioxide, and a few other trace ...

aurora

Astronomy; Astrometry

A glow in a planet's ionosphere caused by the interaction between the planet's magnetic field and charged particles from the Sun. This phenomenon is known as the Aurora Borealis ...

Black Hole

Astronomy; Astrometry

The collapsed core of a massive star. Stars that are very massive will collapse under their own gravity when their fuel is exhausted. The collapse continues until all matter is ...