Civil Twilight

Morning civil twilight begins when the geometric center of the sun is 6º below the horizon (-6º), civil dawn, and ends at sunrise. Evening civil twilight begins at sunset and ends when the geometric center of the sun reaches 6° below the horizon (-6º), civil dusk. Learn more on Wikipedia.

Celestial Equator

The projection of the Earth's equator out into space. At the Celestial equator, stars seem to travel in a straight line. Learn more on Wikipedia.

Circumpolar Star

A star that, as viewed from a given latitude on Earth, never sets (that is, never disappears below the horizon), due to its proximity to one of the celestial poles. Learn more on Wikipedia.

Celestial Pole

The north and south celestial poles are the two imaginary points in the sky where the Earth's axis of rotation, indefinitely extended, intersects the imaginary rotating sphere of stars called the celestial sphere. Learn more on Wikipedia.


Instrument for determining directions (azimuth), as by means of a freely rotating magnetized needle that indicates magnetic north. Learn more on Wikipedia.

Crop Factor

The ratio of the sensor format relative to a 35 mm frame. Learn more on Wikipedia.

Circle of Confusion (CoC)

It is the largest on-film/sensor circle that you can see as a well defined point on an 8''×10'' print when viewed at from a "normal" viewing distance of 2 to 3 feet. Anything larger is seen as a small circle, not a point and is therefore perceived as out of focus. Learn more on Wikipedia.

Clip Length (Time lapse)

The desired length of the video clip that portrays the event.