Descriptionary

blue moon the rare occurrence of a full moon appearing twice in one month.

Clavius a large, walled plain 145 miles across in the Moon's southeast quadrant; from its depressed inte­rior, walls rise 17,000 feet.

Copernicus one of the most famous of the Moon's craters, 56 miles in diameter.

crater an impact hole or depression caused by a meteor.

craterlet a small crater.

cusp a horn of the crescent moon.

domes mound structures resembling pingoes on Earth.

gibbous of a Moon phase, between half and full.

harvest moon the full moon that rises early in the evening nearest the time of the autumnal equinox, September 23, providing illumination for the fall harvest.

hunter's moon the first full moon following the harvest moon, providing illumination for hunters.

Luna in Roman mythology, the goddess of the Moon.

lunacy a form of insanity once thought to be caused or influenced by the Moon.

lunar eclipse darkening of the Moon caused by the Earth coming between it and the Sun.

lunar month the period between successive new moons: 29 days, 12 hours, 44 minutes.

mare a large dark plain on the Moon, in ancient times thought to be a sea. Its plural form is "maria."

Mare Imbrium the "sea of showers"; a circular plain, or mare, 700 miles in diameter in the northeast quadrant of the Moon.

Mare Tranquillitatis the "sea of tranquillity"; the sight of Moon landings, in the northwest quadrant.

new moon in a position between the Sun and Earth, the first phase of the Moon, with its unlit side fac­ing Earth; at sunset, it may appear as a very narrow crescent.

nimbus moon the Moon with an apparent halo or nimbus, caused by the refraction of light by ice crys­tals in high, thin cirrus or cirrostratus clouds of Earth.

occultation the passing of the Moon in front of another celestial body, thus obscuring it.

Oceanus Procellarum the "ocean of storms," larg­est of all lunar marias, with an area of 2 million square miles.

perigee the point of the Moon's orbit nearest to Earth.

phases the dark side of the Moon facing Earth is called the new moon (more accurately defined as a "black" moon because it is invisible from Earth). The first sliver of moon is called the crescent. The thick­ened crescent is the first quarter. Between the half and full moon is the gibbous, followed by full and a reversal of phases.

ray an impact line or crack radiating out from some craters.

rille a narrow trench.

selenian pertaining to the Moon.

selenography the study of the Moon's surface.

selenology the study of the Moon.

terminator the line separating the daylight side from the night side.

Tycho the famous rayed crater, 54 miles in diameter in the southeast quadrant.

wane shrinking phase of the Moon.

wax growing phase of the Moon.

particles and particle physics

accelerator a machine that uses electric or magnetic fields to accelerate a beam of charged particles to a very high level of speed and energy.

alpha particle a positively charged particle made up of two protons and two neutrons.

amu atomic mass unit.

annihilation the collision and disappearance of a particle and an antiparticle, and the subsequent for­mation or appearance of a different particle and antiparticle.

antiparticle see antimatter.

antimatter antiparticles (antifermions) with the opposite properties of particles. If a particle has a positive charge, the antiparticle will have a nega­tive charge. The reverse is also true. The muon, for example, has a negative charge and the antimuon has a positive one.

antiquark the antiparticle of a quark.

atom the smallest particle of any element or matter. It consists of a nucleus containing protons and neu­trons, and electrons that move around the nucleus.

atomic mass the weight or mass of an atom as expressed in unified atomic mass units, with one unit equal to У12 of the mass of a carbon-12 atom.

atomic mass unit unit of atomic weight, with one unit equal to У12 of the mass of a carbon-12 atom.

atomic number the number of protons in a nucleus. Atoms of the same element have the same atomic number.

atomic theory the theory that everything is made up of atoms and subatomic particles and that physical phenomenon can be explained by their interactions.

atomic weight the weight of one atom of a given element, expressed in atomic mass units.

atom smasher an accelerator.

baryon a hadron composed of three quarks and subject to strong interactions.

beta particle a high-energy electron or positron ejected by a radioactive nucleus.

B-meson an extremely short-lived meson.