Glossary of Terms

Angular Momentum The result of the momentum of a rotating body and its distance from the axis of rotation.

Angular Velocity The rate of change of angle swept with respect to time.

Binary Star A star that is gravitationally bound to another and orbits the other star around a mutual center of mass. The majority of stars in the Milky Way Galaxy are in binary or other multi-star systems.

Black Hole A collapsed star whose mass is condensed into a single point is space. The gravitational force generated by a black hole is so strong, that not even light can escape.

Brown Dwarf A celestial body that resembles a star but does not emit light because it is too small to ignite internal nuclear fusion. Brown dwarfs are extremely difficult to detect and their existence was only recently confirmed.

Comet A celestial body, having a head consisting of a solid nucleus surrounded by a nebulous coma and an elongated curved vapor tail arising from the coma when it gets sufficiently close to the sun. Comets are thought to consist mostly of ammonia, methane, carbon dioxide, and water.

Kepler’s Laws Describe the revolution parameters of bodies in orbit.

Kuiper Belt An area of asteroids and debris just beyond the orbit of Pluto. Recent observations suggest the Kuiper Belt ends abruptly at approximately 50 AU.

Milankovitch Cycles The results of studying past global climate changes over millions of years. One of the causes of climate change is the precession of the equinoxes, which seems to have a period of 22,000 to 23,000 years, over millions of years.

Oort Cloud is Proposed as the source of comets, the area of debris spanning a distance of one to two light-years out from the Sun, and surrounding the solar system.

Precession This catch-all term is now used to describe both the phenomenon of the precessing equatorial point as well as the Earth movement itself.

Precession of the Equinox The age-old phenomenon whereby the equatorial point moves westward (precesses) through the twelve zodiacal signs.

Red Dwarf A small cool star. Approximately 100 times the mass of Jupiter. Can be difficult to detect against certain backgrounds such as galactic centers.

Sidereal Year The time required for one complete revolution of the earth around the sun, measured relative to the fixed stars, a time period equal to a mean of 365.2563 rotations of the earth.

Tropical Year The time required for one complete orbit of the earth, measured relative to the sun, a time period equal to 365.2422 rotations of the earth.

Tropica/Sidereal Delta The time difference between the two years above which is equal to the value of precession, approximately 20 minutes in time or 50 seconds of arc in a year.

Virtual Observatory A “virtual telescope” capable of processing many years of archived astronomical data for patterns or tracks of faint orbiting bodies.

Wobble The terminology used by Copernicus to describe the apparent movement of the Earth in the phenomenon known as the “Precession of the Equinox”. He said the precession of the equinox was caused by “wobble or libration”. He deemed this the “third motion” of the Earth.

Zodiac A band of the celestial sphere extending about 8° to either side of the ecliptic represents the path of the principal planets, the moon, and the sun. The 12 constellations within this band represent the constellations of the zodiac.