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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
G
Galactic Halo
The name given to the spherical region surrounding the centre, or
nucleus of a galaxy.
Galactic Nucleus
A tight concentration of stars and gas found at the innermost regions of
a galaxy. Astronomers now believe that massive black holes may exist in
the centre of many galaxies.
Galaxy
A large grouping of stars. Galaxies are found in a variety of sizes and
shapes. Our own Milky Way galaxy is spiral in shape and contains several
billion stars. Some galaxies are so distant the their light takes
millions of years to reach the Earth.
Galilean Moons
The name given to Jupiter's four largest moons, Io, Europa, Callisto &
Ganymede. They were discovered independently by Galileo Galilei and
Simon Marius.
Gamma-ray
The highest energy, shortest wavelength form of electromagnetic
radiation.
Geosynchronous Orbit
An orbit in which a satellite's orbital velocity is matched to the
rotational velocity of the planet. A spacecraft in geosynchronous orbit
appears to hang motionless above one position of a planet's surface.
Giant Molecular Cloud (GMC)
Massive clouds of gas in interstellar space composed primarily of
hydrogen molecules. These clouds have enough mass to produce thousands
of stars and are frequently the sites of new star formation.
Globular Cluster
A tight, spherical grouping of hundreds of thousands of stars. Globular
clusters are composed of older stars, and are usually found around the
central regions of a galaxy.
Granulation
A pattern of small cells that can be seen on the surface of the Sun.
They are caused by the convective motions of the hot gases inside the
Sun.
Gravitational Lens
A concentration of matter such as a galaxy or cluster of galaxies that
bends light rays from a background object. Gravitational lensing results
in duplicate images of distant objects.
Gravity
A mutual physical force of nature that causes two bodies to attract each
other.
Greenhouse Effect
An increase in temperature caused when incoming solar radiation is
passed but outgoing thermal radiation is blocked by the atmosphere.
Carbon dioxide and water vapour are two of the major gases responsible
for this effect.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z