<P> Observers at heights appreciably above sea level can experience extended periods of midnight sun as a result of the "dip" of the horizon viewed from altitude . </P> <P> The term "midnight sun" refers to the consecutive 24 - hour periods of sunlight experienced north of the Arctic Circle and south of the Antarctic Circle . Other phenomena are sometimes referred to as "midnight sun", but they are caused by time zones and the observance of daylight saving time . For instance, in Fairbanks, Alaska, which is south of the Arctic Circle, the sun sets at 12: 47 am at the summer solstice . This is because Fairbanks is 51 minutes ahead of its idealized time zone (as most of the state is in one time zone) and Alaska observes daylight saving time . (Fairbanks is at about 147.72 degrees west, corresponding to UTC − 9 hours 51 minutes, and is on UTC − 9 in winter .) This means that solar culmination occurs at about 12: 51 pm instead of at 12 noon . </P> <P> If a precise moment for the genuine "midnight sun" is required, the observer's longitude, the local civil time and the equation of time must be taken into account . The moment of the sun's closest approach to the horizon coincides with its passing due north at the observer's position, which occurs only approximately at midnight in general . Each degree of longitude east of the Greenwich meridian makes the vital moment exactly 4 minutes earlier than midnight as shown on the clock, while each hour that the local civil time is ahead of coordinated universal time (UTC, also known as GMT) makes the moment an hour later . These two effects must be added . Furthermore, the equation of time (which depends on the date) must be added: a positive value on a given date means that the sun is running slightly ahead of its average position, so the value must be subtracted . </P> <P> As an example, at the North Cape of Norway at midnight on June 21 / 22, the longitude of 25.9 degrees east makes the moment 103.2 minutes earlier by clock time; but the local time, 2 hours ahead of GMT in the summer, makes it 120 minutes later by clock time . The equation of time at that date is - 2.0 minutes . Therefore, the sun's lowest elevation occurs 120 - 103.2 + 2.0 minutes after midnight: at 00.19 Central European Summer time . On other nearby dates the only thing different is the equation of time, so this remains a reasonable estimate for a considerable period . The sun's altitude remains within half a degree of the minimum of about 5 degrees for about 45 minutes either side of this time . </P>

When does the arctic circle experience 24 hours of darkness