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For other uses, see Sunrise (disambiguation).
The terminator in April. As the terminator moves westward across the globe, sunrise occurs north of east, and sunset north of west, except for a thin region near the poles that do not experience sunrise/sunset at all (midnight sun, polar night).
Sunrise is the time at which the first part of the Sun appears above the horizon in the east. Sunrise should not be confused with dawn, which is the (variously defined) point at which the sky begins to lighten, some time before the sun itself appears, ending twilight. Because atmospheric refraction causes the sun to be seen while it is still below the horizon, both sunrise and sunset are, from one point of view, optical illusions. The sun also appears larger on the horizon, but this is another optical illusion, similar to the moon illusion.
The apparent westward revolution of Sun around the earth after rising out of the horizon is due to the Earth\'s eastward rotation, a counter-clockwise revolution when viewed from above the North Pole. This illusion is so convincing that most cultures had mythologies and religions built around the geocentric model. This same effect can be seen with near-polar satellites as well.
As sunrise and sunset are calculated from the leading and trailing edges of the Sun, and not the center; this slightly increases the duration of "day" relative to "night." The sunrise equation, however, is based on the center of the sun.
The timing of sunrise varies with the time of year and the latitude of the location from which it is viewed. The precise time of day also varies in local time within a given time zone, determined by each location\'s precise longitude. Changes in timing of sunrise are driven by the axial tilt of Earth and the planet\'s movement in its annual orbit around the sun. Some apparent anomalies exist however. In the Northern Hemisphere, the latest sunrise does not occur on the winter solstice around December 21, but rather in early January. Likewise, the earliest sunrise does not fall on the summer solstice around June 21, but occurs earlier in June in the Northern Hemisphere. As one travels farther from the equator, the times of sunrise and sunset change throughout the year. Even on the equator, sunrise and sunset shift several minutes back and forth through the year, along with solar noon. These effects are plotted using an analemma.
Due to Earth\'s axial tilt, whenever and wherever sunrise occurs, it is always in the northeast quadrant from the March equinox to the September equinox and in the southeast quadrant from the September equinox to the March equinox. Sunrises occur precisely due east on the March and September equinoxes for all viewers on Earth, and the duration of day and night are precisely 12 hours on the Equinoxes.
The colors of the sky, throughout the day and at sunrise and sunset, are explained by the phenomena of both Rayleigh Scattering and Mie Scattering.
Rayleigh Scattering causes the hues of blue, violet, and green in the sky. Rayleigh Scattering is scattering of shorter wavelength light, (e.g. blue & violet), by air atoms and molecules, (not statistical variations in density of the Earth\'s atmosphere). The magnitude or strength of Rayleigh Scattering varies by the reciprocal of the wavelength raised to the fourth power, and hence, does not explain the beautiful variations of reds, purples, oranges, and peachy colors.
The latter colors are better described by Mie Scattering, low angle scattering of light off of dust, soot, smoke, and ash particles. Mie Scattering, (producing the colors of sunset and sunrise), is recognizable down-wind of and after dust storms, forest fires, and volcanic eruptions that inject large quantities of fine particulate matter into the atmosphere. A number of eruptions in recent times, such as those of Mount Pinatubo in 1991 and Krakatoa in 1883, have been sufficiently large to produce remarkable sunsets and sunrises all over the world.
Sometimes just before sunrise or after sunset the atmosphere refracts light, causing a blue or green flash.
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