Find entries starting with containing

accretion
Accumulation of dust and gas into larger bodies such as stars, planets and moons.

accretion disk
The whirling disk of gas that form around a compact object such as a white dwarf, neutron star or black hole as matter is drawn in.

aerosol
A sol (homogeneous suspension, more fluid than a gel) in which the dispersion medium is a gas (e.g. air) containing solid particles or liquid droplets.

agents of change
The constructive and destructive processes that reshape a planetary surface.

albedo
The ratio of the light reflected by a body to the light received by it. Albedo values range from 0 (pitch black) to 1 (perfect reflector). Our Moon has a very low albedo (0.07), while Venus has a high albedo (0.60).

albedo feature
A dark or light marking on the surface of an object that may not be a geological or topographical feature.

ammonia
A colorless gas made of nitrogen and hydrogen. It has a sharp smell. It can be mixed with water and used for household cleaning.

anti-Jovian
Refers to the side of a object facing away from Jupiter.

antipodal point
the point that is directly on the opposite side of a planet.

aphelion
(opposite of perihelion) the point in its orbit where a planet is farthest from the Sun; when refering to objects orbiting the Earth the term apogee is used; the term apoapsis is used for orbits around other bodies.

apoapsis
the point in the orbit farthest from the body being orbited. Used to describe orbits around bodies other than Earth. For Earth, the term apogee is used.

apogee
the point in the orbit of the moon or an artificial satellite when it is most distant from the center of the Earth. The term apoapsis is used for other bodies.

arcuate
formed like a bow; curved; arc-shaped.

asteroid
(also "planetoid") a medium-sized rocky object orbiting the Sun; smaller than a planet, larger than a meteoroid. Asteroids show no evidence of an atmosphere or other types of activity associated with comets. Asteroids can be lass that one-mile to almost 600 miles in diameter.
More on Asteroids >>

asteroid belt
A region of the solar system between the orbits of Mars and Jupiter (2.2 - 3.3 A.U.) in which most asteroids are located.

asteroid number
number assigned to an asteroid when it is discovered. It has no particular meaning except that asteroid N+1 was discovered after asteroid N.

astronomical unit (AU)
The average distance from the Earth to the Sun. One AU = 93 million miles or 149.6 million km. At 100 mph (160 kph) it would take more than 100 years to go 1 AU.

atmosphere
Gases surrounding any of the bodies in space; also known as air. Atmosphere = 1.013 bars = 1.03 kg/cm^2 = 14.7 pounds per square inch, standard atmospheric pressure at sea level on Earth.

aurora
(Latin for "dawn") a glow in a planet's ionosphere caused by the interaction between the planet's magnetic field and charged particles from the Sun. Seen on Earth as a green and red glow near the poles. (Photo credit: Jan Curtis)

aurora borealis
The "Northern Lights"; caused by the interaction between the solar wind, the Earth's magnetic field and the upper atmosphere. A similar effect happens in the southern hemisphere where it is known as the aurora australis.