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.
heliocentric theory
A theory for the motion of the planets that has the sun at its correct place in the center of the solar system.
Hertzsprung-Russell diagram
A plot of stellar temperatures (or, equivalently, spectral types or colors) and absolute magnitudes (or, equivalently, luminosities).

Most stars are within a diagonal belt, the main sequence, with white dwarfs and giants on either side.

Hubble's law
The relation between the red shift of a a distant galaxy and its distance from us, the constant of proportionality being Hubble's constant.

The reciprocal of Hubble's constant can give an estimate of the age of the universe in the big bang theory.

A conic section.

Some comets enter the solar system on hyperbolic paths, which indicates that they swing around the sun and leave the solar system, never to return.

image photon counting system, IPCS
An electronic detector system that has contributed to the knowledge of astronomy.

This detector is a four-stage, magnetically-focused image intensifier, coupled via a lens to a plumbicon television camera tube.

A plumbicon is the development of the vidicon television camera tube in which the photosensitive material is lead oxide.

A plumbicon is a registered trademark of Philips for its Lead Oxide (PbO) target vidicons or camera tubes in which a charge-density patterns are formed by photoconduction and stored on photoconductor surfaces that are scanned by electron beams; usually, of low-velocity electrons; used chiefly in industrial television cameras.

image tubes
An image intensifier which is a form of electron tube in which an image is focused onto an input photocathode.

The resulting emitted electrons are accelerated within the evacuated tube by a very high voltage.

Image intensifiers are used in many instruments; such as, cameras, spectrographs, and acquisition and guidance systems.

inclination, dip
1. For planets, the angle between the plane of the ecliptic and the plane of the planet's orbit or the angle between a line perpendicular to the plane of the ecliptic and the planet's axis of rotation.

For satellites, orbital inclination is expressed relative to the parent planet's orbital plane.

2. In terrestrial magnetism, the angle through which a freely suspended magnet would dip below the horizon in the magnetic north–south meridional plane; one of the magnetic elements.

At the aclinic line (dip equator) the inclination is zero; at either magnetic pole (dip pole) the inclination is 90°.

3. The angle between the plane of the satellite orbit and the earth's equatorial plane.

An inclination angle of less than 90° is referred to as a prograde orbit, while an inclination angle greater than 90° is called a retrograde orbit.

inferior planet
Any planet whose orbit is smaller than that of Earth.

The result is that Venus and Mercury are the two inferior planets of the solar system.

inferior planet conjunction
When a planet passes between the earth and the sun.
The combination of two waves, for example electromagnetic waves, producing regions of high intensity (where the waves combine) and low intensity (where they tend to cancel each other).
A technique in which two waves, usually of electromagnetic radiation; such as, light or radio waves, are combined to produce an interference pattern.

Radiation from a distant source can be analyzed by this method, and very small angles can be accurately determined.

interstellar dust
Small, solid grains of matter, thinly distributed between the stars; sometimes concentrated in nebulae (glowing or dark patches in the sky).
interstellar gas
Matter in a gaseous state thinly distributed between the stars; mostly hydrogen with some helium and other elements which are sometimes concentrated in nebulae (patches in the sky).
invisible radiation
On either side of the band of visible radiation are electromagnetic radiations which are invisible, but which can nevertheless be perceived.

People know about the stars because they can be seen and because of this, optical telescopes are the traditional instruments of astronomy; however, it must not be forgotten that light is only one form of electromagnetic radiation, and that it forms only a narrow band in the electromagnetic spectrum.

An electrically charged atom, or group of atoms, that has lost or gained electrons.

A loss makes the resulting particle positively charged; a gain makes the particle negatively charged.

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