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color index

(Encyclopedia)color index, in astronomy, difference in an object's brightness as recorded between any two well-defined bands of the electromagnetic spectrum by using optical filters of different colors. If blue and...

krypton

(Encyclopedia)krypton krĭpˈtŏn [key] [Gr.,=hidden], gaseous chemical element; symbol Kr; at. no. 36; at. wt. 83.798; m.p. −156.6℃; b.p. −152.3℃; density 3.73 grams per liter at STP; valence usually 0. Kr...

X ray

(Encyclopedia)CE5 Typical X-ray composite spectrum (intensity as a function of frequency) X ray, invisible, highly penetrating electromagnetic radiation of much shorter wavelength (higher frequency) than visibl...

Middleton, Conyers

(Encyclopedia)Middleton, Conyers, 1683–1750, English clergyman, one of the earliest English rationalistic theologians. A fellow of Trinity College, Cambridge, he became known through his disputes with Richard Ben...

airglow

(Encyclopedia)airglow, faint diffuse illumination of the sky originating in the upper atmosphere. Although it occurs at all times of day throughout the upper atmosphere, it is most typically visible to an observer ...

radiation

(Encyclopedia)radiation rāˌdēāˈshən [key], term applied to the emission and transmission of energy through space or through a material medium and also to the radiated energy itself. In its widest sense the te...

Hubble's law

(Encyclopedia)Hubble's law, in astronomy, statement that the distances between galaxies (see galaxy) or clusters of galaxies are continuously increasing and that therefore the universe is expanding. Hubble's law ...

observatory

(Encyclopedia)observatory, scientific facility especially equipped to detect and record naturally occurring scientific phenomena. Although geological and meteorological observatories exist, the term is generally ap...

Andromeda Galaxy

(Encyclopedia)Andromeda Galaxy, cataloged as M31 and NGC 224, the closest large galaxy to the Milky Way and the only one visible to the naked eye in the Northern Hemisphere. It is also known as the Great Nebula in ...

Millerand, Alexandre

(Encyclopedia)Millerand, Alexandre älĕksäNˈdrə mēlräNˈ [key], 1859–1943, French politician, president of France (1920–24). A Socialist member of the chamber of deputies, he was the first Socialist to se...