See also: Sun path and Solar azimuth angle Timelapse video of twilight and sunrise in Gjøvik, Norway in February 2021 The sunrise equation, however, which is used to derive the time of sunrise and sunset, uses the Sun's physical center for calculation, neglecting atmospheric refraction and the non-zero angle subtended by the solar disc. Īccounting for atmospheric refraction and measuring from the leading edge slightly increases the average duration of day relative to night. Near the poles, the time-of-day variation is exaggerated, since the Sun crosses the horizon at a very shallow angle and thus rises more slowly. Variations in atmospheric refraction can alter the time of sunrise by changing its apparent position. The offset between the dates of the solstice and the earliest or latest sunrise time is caused by the eccentricity of Earth's orbit and the tilt of its axis, and is described by the analemma, which can be used to predict the dates. After this point, the time of sunrise gets later each day, reaching its latest sometime around the winter solstice. In late winter and spring, sunrise as seen from temperate latitudes occurs earlier each day, reaching its earliest time near the summer solstice although the exact date varies by latitude. The analemma can be used to make approximate predictions of the time of sunrise. These changes are driven by the axial tilt of Earth, daily rotation of the Earth, the planet's movement in its annual elliptical orbit around the Sun, and the Earth and Moon's paired revolutions around each other. The timing of sunrise varies throughout the year and is also affected by the viewer's latitude and longitude, altitude, and time zone. See here for the sunrise chart of a different location Near the equator, the variation of the time of sunrise is mainly governed by the variation of the equation of time. See also: Daytime length variations with latitude and seasons Time of sunrise in 2008 for Libreville, Gabon. These two angles combine to define sunrise to occur when the Sun's center is 50 arcminutes below the horizon, or 90.83° from the zenith. The apparent radius of the Sun at the horizon is 16 arcminutes. Īlso, unlike most other solar measurements, sunrise occurs when the Sun's upper limb, rather than its center, appears to cross the horizon. At the horizon, the average amount of refraction is 34 arcminutes, though this amount varies based on atmospheric conditions. The stage of sunrise known as false sunrise actually occurs before the Sun truly reaches the horizon because Earth's atmosphere refracts the Sun's image. Measurement Angle with respect to horizon This diagram of the Sun at sunrise (or sunset) shows the effects of atmospheric refraction Civil twilight being the brightest, while Astrominical twilight being the darkest. The period after the Sun rises during which striking colors and atmospheric effects are still seen.The beginning of morning twilight is called astronomical dawn. Twilight, the period in the morning during which the sky is brightening, but the Sun is not yet visible.However, the term sunrise commonly refers to periods of time both before and after this point: Īstronomically, sunrise occurs for only an instant: the moment at which the upper limb of the Sun appears tangent to the horizon. Īrchitect Buckminster Fuller proposed the terms "sunsight" and "sunclipse" to better represent the heliocentric model, though the terms have not entered into common language. The illusion of a moving Sun results from Earth observers being in a rotating reference frame this apparent motion caused many cultures to have mythologies and religions built around the geocentric model, which prevailed until astronomer Nicolaus Copernicus formulated his heliocentric model in the 16th century. The term can also refer to the entire process of the solar disk crossing the horizon.Īlthough the Sun appears to "rise" from the horizon, it is actually the Earth's motion that causes the Sun to appear. Sunrise (or sunup) is the moment when the upper rim of the Sun appears on the horizon in the morning. Sunrise on the Jersey Shore at Spring Lake, New Jersey, U.S.
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