- Gaia Hypothesis
- Named for the Greek Earth goddess Gaea, this hypothesis holds that the Earth
should be regarded as a living organism.
British biologist James Lovelock first advanced this idea in 1969.
Galilean moons
- Jupiter's four largest moons:
Io,
Europa,
Ganymede and
Callisto; discovered independently by Galileo and Marius.
Galle, Johann Gottfried 1812-1910
- German astronomer. Galle, along with Heinrich Louis d'Arrest, made
the first observation of Neptune based on calculations by Urbain Jean Joseph Le Verrier.
Although Galle was the first to observe Neptune, its discovery is usually credited to John Couch Adams (who made an earlier calculation) and Le Verrier.
Galileo Galilei 1564-1642
- Italian astronomer and physicist. The first to use a telescope to study the stars. Discoverer of the first moons of an extraterrestrial body (see Galilean Moons). Galileo was an outspoken supporter of Copernicus's
heliocentric theory. In reaction to Galileo, the Church declared it heresy to teach that the Earth moved and imprisoned him. The Church clung to this position for 350 years until Galileo was formally exonerated in 1992.
geosynchronous orbit
- A direct, circular, low-inclination orbit in which the satellite's
orbital velocity is matched to the rotational velocity of the planet;
a spacecraft appears to hang motionless above one position of the
planet's surface.
graben
- An elongated, relatively depressed crustal unit or block that is
bounded by faults on its sides.
granulation
- A pattern of small cells seen on the surface of
the Sun caused by the convective motions of the hot solar gas.
greenhouse effect
- An increase in temperature caused when the atmosphere absorbs incoming solar radiation but blocks outgoing thermal radiation; carbon dioxide is the major factor.
gravity
- A mutual physical force attracting two bodies.
