Unit 2: The Celestial Sphere

Front

Zenith

Back

Point on the celestial sphere that is directly over our heads - 90° above the horizon.

Front

Nadir

Back

A point directly opposite from zenith - 90° below the horizon.

Front

Celestial Sphere

Back

An imaginary sphere surrounding the Earth used by astronomers to describe the location and movement of celestial objects.

Front

Vernal Equinox

Back

March 21 (in the northern hemisphere). Day and night are both 12 hours long.

Front

North Celestial Pole

Back

An extension of the Earth's north pole projected upon the celestial sphere. All constellations appear to rotate around this point in the northern hemisphere.

Front

South Celestial Pole

Back

An extension of the Earth's south pole projected upon the celestial sphere. All constellations appear to rotate around this point in the southern hemisphere.

Front

Celestial Equator

Back

An extension of the Earth's equator projected upon the celestial sphere.

Front

The Ecliptic

Back

Plane in which the Earth moves around the Sun. Also the Sun's apparent annual path around the celestial sphere.

Front

Earth's tilt

Back

23 degrees, 27 minutes. Responsible for the seasons.

Front

Summer Solstice

Back

June 21, the longest day of the year (in the northern hemisphere).