# 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,
Is looking up."
â€”Ennis Rees, Pun Fun;
Scholastic Book Services; New York; 1965; page 13.
celestial latitude
The angular distance between a celestial body and the ecliptic, measured along a line at right angles to the ecliptic, which passes through both celestial poles. Its symbol is the Greek letter β or beta.
celestial longitude
1. Longitude measured (in degrees) along the ecliptic to the east from the vernal equinox.
2. The angular distance between a celestial body and the first point of Aries, measured along the ecliptic.

The Symbol for this term is the Greek letter λ or lambda.

celestial mechanics
1. The study of the motion of celestial bodies under the influence of gravitation from one or more other bodies.
2. The branch of astronomy that deals with the calculation of the orbits of celestial bodies, their gravitational attractions; such as, those that produce the earth's tides.

It also refers to the orbits of artificial satellites and space probes and is based on the laws of motion and gravity laid down by Isaac Newton (English mathematician, 1642-1727, and physicist; remembered for developing the calculus and for his law of gravitation and his three laws of motion).

celestial poles
1. The points in the sky where the earth's axis, extended into space, intersects with the celestial sphere.
2. The points at which the earth's rotation axis pierces the celestial sphere.

All of the stars appear to orbit around this point, whose approximate position in the north is marked by Polaris, the "polestar".

There are three main types of celestial radio emissions:
1. Thermal emissions which occur as a result of the acceleration of electrically-charged particles in a hot gas.
2. Synchrotron or non-thermal, emissions are produced by the acceleration of charged particles, but the acceleration is caused by a magnetic field.
3. Radio spectral-line emissions are concentrated in a narrow band around one specific frequency; just as an optical spectral line corresponds to a single frequency in the visible electromagnetic spectrum.
4. Radio line emissions usually originate in clouds of hydrogen gas, a relatively common constituent of the universe, which is found in our galaxy's spiral arms, among other places.

celestial sphere
1. The imaginary sphere surrounding the earth, with the stars and other astronomical objects attached to it.
2. An imaginary sphere on the inside of which the celestial bodies seem to lie.

The positions of bodies; such as, stars, planets, and galaxies are specified by their coordinates on the celestial sphere.

Cepheid variable
1. One of a group of highly luminous yellow or orange super giant stars, whose brightness varies in a regular manner as the result of stellar pulsations.
2. A yellow super giant star that varies regularly in brightness every few days or weeks as a result of pulsations.

The time that a Cepheid variable takes to pulsate is directly related to its average brightness; the longer the period, the brighter the star.

Cepheus is a constellation of the northern hemisphere near Cassiopeia (a W-shaped constellation in the northern hemisphere near Polaris) and Draco (a large faint constellation of the northern hemisphere).

Chandrasekhar limit
A limiting mass, below which a star can become a white dwarf and above which gravity is capable of continuing the collapse to; such as, a neutron star.
charge-coupled device, CCD
1. A means of converting the electromagnetic energy of photons of a particular wavelength into a digital video signal which can be displayed on a television screen.
2. A device for forming images electronically, using a layer of silicon that releases electrons when struck by incoming light.

The electrons are stored in pixels and read off into a computer at the end of the exposure. CCD's have now almost entirely replaced photographic film for applications: such as, astrophotography where extreme sensitivity to light is so important.

charge-coupled device, charge-coupled devices, CCD
Since the mid-1970's, a new type of detector called the charge-coupled device has gained popularity in astronomy.

The CCD is an electronic detector that replaces photographic plates or film.

It converts light into a electric charge, which is used to form images on a computer screen.

The charge-coupled device was developed as a replacement for television camera tubes and is commonly used in today's camcorders.

Modern astronomical CCD's are much larger, with as many as 16 million separate detectors, or pixels.

Because they are far more sensitive to light, charge-coupled devices produce better pictures than traditional photographic methods and astronomers can see extremely faint galaxies in almost any part of the sky.

chromosphere
1. The layer in the sun's atmosphere between the photosphere and the corona.
2. A layer of mostly hydrogen gas about 10,000 kilometers or 6,000 miles in depth above the visible surface of the sun and many other stars just above the photosphere.

During eclipses, the solar chromosphere glows pinkish red from the hydrogen emissions.

circumpolar star
A reference to a star, asterism, or constellation that is close enough to the celestial pole that, depending on the latitude at which a person is observing, it never appears to set.
circumpolar stars
Those stars that are of such a declination which in a particular latitude they never set.
civil day
There are two 12-hour periods, A.M. an P.M., but these are never used astronomically so the 24-hour clock is used.
comet
1. A small body made of ice, dust, and rocks which orbits the sun.
2. A collection of gas, dust, and volatile ice that travel around the sun, generally in very eccentric orbits.

The source of such bodies may be the oort cloud (cloud of comets).

3. A body, probably resembling a "dirty snowball", between 0.1 and 100 kilometers across, which travels through the solar system in an ecliptical orbit of random inclination to the ecliptic.

A comet grows a tail if it goes close enough to the sun.

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