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ezscienceindex

Absolute zero: The coldest possible temperature, at which a substance has no heat energy.

Acceleration: The rate at which the velocity of an object changes. Gravity on Earth, for example, causes all objects (if you ignore friction) to fall with an acceleration of 32 feet per second.

Acid rain: Cloud or rain droplets containing pollutants, such as oxides of sulfur and nitrogen.

Ampere: Unit that measures an electric current's rate.

Amplitude: The height of a wave crest (or depth of a trough) measured from a point of equilibrium. More.

Aftershocks: Small temblors, caused when rocks continue shifting after an earthquake, that may last for two years after an earthquake. They usually decrease over time.

Air mass: A large body of air having similar horizontal temperature and moisture characteristics.

Alpha Centauri: The closest bright star, but not the closest star; that's Proxima Centauri, at 4.2 light years away.

Anticyclone: A large area of high pressure around which the winds blow clockwise in the Northern Hemisphere.

Antimatter: Matter made of antiparticles (antiprotons, antielectrons, and antineutrons).

Aphelion: A planet's farthest point from the sun during orbit (applies to comets, too).

Asteroids **includes animations

Asthenosphere

Astrobiology

Astronomical Unit (AU): Average distance from Earth to the Sun, or about 93 million miles.

Atmosphere of the Earth *includes images

Atmospheric pressure high and low **includes animations

Atom: inside an atom **includes animations

Aurora borealis: Sheets of vibrant light visible at northern latitudes, caused by charged solar particles igniting gases in Earth's atmosphere.

snapshots
09/09: Northern lights corona