<P> The opposite phenomenon, polar night, occurs in winter, when the sun stays below the horizon throughout the day . </P> <P> Since the axial tilt of the Earth is considerable (approximately 23 degrees 27 minutes), the sun does not set at high latitudes in local summer . The sun remains continuously visible for one day during the summer solstice at the polar circle, for several weeks only 100 km closer to the pole, and for six months at the pole . At extreme latitudes, the midnight sun is usually referred to as polar day . </P> <P> At the poles themselves, the sun rises and sets only once each year on the equinox . During the six months that the sun is above the horizon, it spends the days continuously moving in circles around the observer, gradually spiralling higher and reaching its highest circuit of the sky at the summer solstice . </P> <P> Because of atmospheric refraction, and also because the sun is a disc rather than a point, the midnight sun may be experienced at latitudes slightly below the polar circle, though not exceeding one degree (depending on local conditions). For example, Iceland is known for its midnight sun, even though most of it (Grímsey is the exception) is slightly south of the Arctic Circle . For the same reasons, the period of sunlight at the poles is slightly longer than six months . Even the northern extremities of Scotland (and places at similar latitudes, such as St. Petersburg) experience twilight throughout the night in the northern sky at around the summer solstice . </P>

Greenland is often known as the land of midnight sun