Front

Traditionally, groups of stars forming imaginary patterns; in modern astronomy, defined regions of the sky containing recognized star patterns, as identified by the IAU.

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Constellations

Front

The organization responsible for identifying and defining the 88 constellations in the sky.

Back

International Astronomical Union (IAU)

Front

An imaginary sphere surrounding Earth on which stars and constellations appear to be located.

Back

Celestial Sphere

Front

An imaginary line on the celestial sphere that divides it horizontally into the Northern and Southern hemispheres.

Back

Celestial Equator

Front

The points on the celestial sphere where the projection of Earth's rotation axis intersects.

Back

Celestial Poles

Front

The imaginary horizontal plane at the eye level of the observer.

Back

Astronomical Horizon

Front

The line that visually divides the Earth and the sky.

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True Horizon

Front

The point in the sky directly overhead the observer.

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Zenith

Front

The point directly opposite the zenith, pointing towards the gravitational pull.

Back

Nadir

Front

A smaller, recognizable pattern of stars within a larger constellation.

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Asterism