# Astronomy and related astronomical terms

#### (the science of the celestial bodies: the sun, the moon, and the planets; the stars and galaxies; and all of the other objects in the universe)

The astronomer said,
As he raised his cup,
"Thank heavens my business
Is looking up."
—Ennis Rees, Pun Fun;
Scholastic Book Services; New York; 1965; page 13.
Comet Hale-Bopp
Large and exceptionally active comet, which in March, 1997, made its closest approach to Earth since 2000 B.C., coming within 190 million kilometers or 118 million miles.

It has a diameter of approximately 40 kilometers or 25 miles and an extensive gas coma. Hale-Bopp has three tails: one consisting of dust particles, one of charged particles, and a third of sodium particles.

Comet Hale-Bopp was discovered in July, 1995, by two amateur U.S. astronomers, Alan Hale and Thomas Bopp.

communications satellite
Relay station in space for sending telephone, television, telex, and other messages around the world.

Messages are sent to and from the satellites via ground stations. Most communications satellites are in geostationary orbit, appearing to hang fixed over one point on the earth's surface.

compound
A substance formed by the chemical combination of two or more elements; for example, hydrogen and oxygen combine to form water.
conic sections
Mathematically, the geometric shapes obtained by slicing a cone at different angles relative to the base of the cone.

A circle is formed by slicing the cone parallel to its base, an ellipse by slicing at any angle less than that of the side of the cone relative to the base, and a parabola by slicing parallel to the side of the cone.

A hyperbola is formed by cutting the cone at an angle steeper than that of the side. To a good approximation, all celestial bodies within the solar system follow orbits which can be represented by conic sections.

conjunction
1. The alignment of two celestial bodies as seen from Earth.

A superior planet, or other object, is in conjunction when it lies behind the sun.

An inferior planet, or other object, comes to inferior conjunction when it passes between the earth and the sun.

It is at superior conjunction when it passes behind the sun.

Planetary conjunction takes place when a planet is closely aligned with another celestial object; such as, the moon, a star, or another planet.

2. The lining up of two celestial bodies so they lie in the same direction as seen from Earth.

Superior conjunction occurs when a planet lies on the other side of the sun from the earth.

Inferior conjunction occurs when a planet lies on the line joining the sun and the earth, and is closer to the earth.

constellation, constellations
1. One of the 88 areas into which the sky is divided for the purposes of identifying and naming celestial objects; such as, animals or mythical figures.

The first recorded constellation were arbitrary patterns of stars in which early civilizations visualized their gods, sacred creatures, and mythical heroes.

The constellations being presented now are derived from a list of 48 known to the ancient Greeks, who inherited some of them from the Babylonians.

The current list of 88 constellations was adopted in 1930 by the International Astronomical Union, astronomy's governing body.

2. A group of stars lying in a part of the celestial sphere.

The boundaries of the 88 accepted groups have been set by international convention; their positions are described in terms of right ascensions and declinations.

contact, contacts
The stage, or stages, of an eclipse, occutation, or transit when the edges of the apparent disks of astronomical bodies seem to touch.

At a solar eclipse, first contact is when the advancing edge of the sun first appears to touch the moon; the second contact is when the advancing edge of the sun seems to touch the other side of the moon, beginning totality; the third contact is when the trailing edge of the sun "touches" the trailing edge of the moon, ending totality; and the fourth contact marks the end of the eclipse.

convection
1. The vertical movement of energy or mass by circulating currents.
2. The transfer of heat through a fluid by the motion of the fluid itself.

Such motion is usually in the form of currents, in which the hotter, less dense material rises to be replaced below by cooler, denser material.

core
1. The innermost part of a moon, planet, or star.
2. The innermost, central region of a planet, often comprising metallic substances that, through the dynamo effect, produce a magnetic field.
corona
1. The outermost layer of the sun and many other stars; a faint halo of extremely hot (million-degree) gas.
2. A faint halo of hot (estimated to be approximately 2,000,000°C or 3,600,000°F) and tenuous gas around the sun, which boils from the surface.

It is visible at solar eclipses or through a coronagraph, an instrument that blocks light from the sun's brilliant disk.

Gas flows away from the corona to form the solar wind.

cosmic background radiation
Electromagnetic radiation left over from the original formation of the univiverse in the Big Bang.
cosmic radiation
Streams of high-energy particles from outer space, consisting of protons, alpha particles, and light nuclei, which collide with atomic nuclei in the earth's atmosphere, and produce secondary nuclear particles; primarily mesons (elementary particles responsible for the forces in the atomic nucleus); such as, pions and muons (types of subatomic particles), that shower the earth.
cosmic rays
1. Nuclear and subatomic particles moving through space at high speeds; radiated from the sun and other stars.
2. Streams of ionizing radiations from space, largely of protons, alpha particles, and other atomic nuclei.
3. Very high energy nuclei moving at velocities close to that of light which are probably produced by supernova explosions.

On striking the earth's atmosphere, they produce cascades of other particles (by collision with nuclei in the atmosphere) called air showers.

cosmic year
The time it takes the sun to travel around the center of the galaxy, roughly 22.5 million years.
cosmogony
1. The branch of astrophysics that studies the origin, evolution, and structure of the universe.
2. The study of the creation of the universe.

Also check out the Index of other Scientific and Technological Topics.