When travelling northward, astronomers should check the sunset-sunrise schedule for their destination before packing. As summer fades away, the twilights shorten and deepen, and true nights begin to set in. At Anchorage (around 61 degrees N) there can never be a midnight Sun, but one would instead experience a bright twilight at the deepest part of night at 1 A.M. There would be no true night until at least 54 degrees N and it would be quite short. With this in mind, one would find a bright civil twilight at midnight as far south as 60 degrees N on June 20. Most people agree that night has begun when the Sun is twelve degrees below the horizon and the sky appears dark from horizon to horizon. This is the twilight that people still find bright enough for outdoor activities (except astronomy). The period known as civil twilight lasts from sunset to the point when the Sun is six degrees below the horizon. The farther south from the circle one travels, the shorter and darker the twilight will be. Areas immediately south of the Arctic Circle have a bright twilight at midnight. On June 20, all areas from the North Pole to latitude 66 degrees N experience a midnight Sun. The period of the midnight Sun lasts only a few days near the Arctic Circle but increases to a full six months of sunshine at the North Pole. To keep it simple, we will consider only the Northern Hemisphere where we live. Therefore, a midnight Sun can be seen further south at 66-degrees north latitude. The atmosphere acts as a lens and actually lifts the Sun’s image about one-half degree higher when, in reality, it may be just below the horizon. These circles lie at 66.5 degrees north and south latitude. Only areas within the Arctic and Antarctic Circles experience periods when the Sun remains either above or below the horizon twenty-four hours a day. The atmosphere always provides a twilight that separates day from night. Nowhere on Earth do we suddenly go from bright sunlight to complete darkness. We failed to take one major factor into account. This clearly illustrated day and night, and if the globe was tilted, the effect of the midnight Sun, or no Sun at all, could be noted at the poles. The big mistake began in science class when a globe of the Earth was held up to a light in a darkened room.
Slowly you notice the sky begins to brighten as dawn approaches! The Sun rises by 3:30 A.M., ending a very strange night. the twilight is deep, but only the brightest stars are visible. A stubborn twilight lingers, and lingers.
You look forward to some great astrophotos in the dark Alaskan skies. It is a beautiful late June day and you have flown out of Syracuse on an early flight landing in Anchorage, Alaska, late in the afternoon.
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