Terminator (solar)
From Wikipedia, the free encyclopedia
The terminator is the line between the illuminated, day side and dark, night side of a planetary body (also known as the "grey line" or the "twilight zone"). It is defined as the locus of points on a moon or planet where the line through the sun is tangent. The line separates the portions of the earth experiencing daylight from the portion of the planet experiencing darkness. While one half of the earth is illuminated at any point in time, the location of the terminator line varies by time of day due to the rotation of the earth on its axis as well as the revolution of the earth around the sun. The seasons impact the location of the terminator line most dramatically.
In the frame of reference of a rotating planet, the terminator sweeps across the surface of the planet bringing sunrise on one side of the planet and sunset on the opposite side.
Examination of the terminator can yield information about the surface of the body; for example, a fuzzy terminator indicates the presence of an atmosphere.
On the spring and fall equinoxes (around March and September 21), there is no tilt of the earth with respect to the sun so the terminator line is parallel with the axis of the earth and with the lines of longitude.
The terminator line is at its greatest angle with respect to the axis on the winter and summer solstices (around December and June 21), when it is approximately 23.5 degrees off the axis.
Excluding travel near the poles, Concorde was the only passenger airliner able to overtake the terminator. On certain early evening transatlantic flights departing from Heathrow or Paris, it was possible to take off at night and catch up with the sun — from the cockpit you could see the sun rise in the west.
[edit] External links
- Current terminator
- aa.usno.navy.mil - Website calculating synthetic images (B&W or color) representing the terminator for a given time (date & hour)
