| Term: | Arctic circle |
| Definition: | The line of latitude 66 deg 34 min N (often taken as 66N). Along this line the sun does not set on the day of the summer solstice, about June 21, and does not rise on the day of the winter solstice, about December 22. From this line the number of twenty- four-hour periods of continuous day or of continuous night increases northward to about six months each at the North Pole. |
| Term: | Arctic circle |
| Definition: | Latitude of 66.5 North. The southern limit of the area of the Earth that experiences 24 hours of darkness or 24 hours of day at least one day during the year. |