Celestial Sphere

An imaginary bowl an observer sees when he looks at the sky. The portion of the sphere an observer sees depends upon his position on earth, the time of the year, and the time of day.

Vernal Equinox

The first day of spring. An equinox is a day in which the length of the day equals the length of the night.

Autumnal Equinox

The first day of autumn. An equinox is a day in which the length of the day equals the length of the night.

summer Solstice

The first day of summer. The Summer Solstice is the longest day of the year.

Winter Solstice

The first day of winter. The Winter Solstice is the shortest day of the year.

Latitude

The angular distance North or South from the Earth's equator measured in degrees on the meridian of a point; Equator being 0° and the poles 90° N and 90° S.

Longitude

Distance east or west of the prime meridian, expressed in degrees or time.