General astronomy

General astronomy

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General astronomy

alpha-particle

Astronomy; General astronomy

1) Nucleus formed by the α-process (q.v.) (see even-even nuclei.) 2) Particle first discovered in radioactive α decay, and later identified as helium nuclei (two protons and two neutrons bound ...

actinium

Astronomy; General astronomy

soft, silvery-white, radioactive metal which glows in the dark

active galaxy

Astronomy; General astronomy

1) Active galactic nuclei are very luminous. Their energy output is in two forms: nonthermal continuum and thermal emission line. 2) Any galaxy which is emitting large quantities of non-thermal ...

active optics

Astronomy; General astronomy

Controlling the shape of a telescope mirror at a relatively slow rate.

aeon (eon)

Astronomy; General astronomy

In astronomical terms, a unit of time equivalent to 1 billion years.

aether

Astronomy; General astronomy

1) In Aristotelian physics, the fifth element, of which the stars and planets are made. 2) In Classical physics, an invisible medium that was thought to suffuse all space.

airglow (nightglow)

Astronomy; General astronomy

Light in the nighttime sky caused by the collision of atoms and molecules (primarily oxygen, OH, and Ne) in Earth's geocorona with charged particles and X-rays from the Sun or outer space. The ...