Sunrise

As sunrise is called both the passing ( emergence) of the horizon by the sun and the time of this event in the daily course of the sun and the sky appearance overall with all their ( and meteorological ) phenomena.

The sunrise follows the dawn, its opposite is the sunset. Cause of the phenomenon is the earth's rotation, moves the location of the viewer over the day - night boundary. He takes in Central Europe depending on the season 3 to 4 minutes in the tropics but only 2 minutes.

The word sunrise refers to the human observer, and thus to the earlier geocentric worldview. For the purposes of the Copernican heliocentric worldview that name is wrong: Not the sun rises, the location of the earthly observer rotates counter as a result of Earth's rotation of the sun. However, the term corresponds to appearances ( " Topozentrismus " ), is rooted in all languages ​​and would hardly be replaced by another short term.

From dawn until sunrise from the temporally staggered singing of songbirds an approximate determination of time is possible (see bird watch ).

Astronomical phenomena

The entrance is next to sunset, meridian passage and culmination of one of the most important aspects of the Astronomical phenomenology, which is why all astronomical calendars and yearbooks contain corresponding data for the Sun and Moon. The calculation of these time points is described in the article visibility ( astronomy). Sunrise and sunset times are generally related to the central place of Kassel in Germany, Austria on the 15th degree of longitude. The local times differ according to the true local time on it. In Cottbus, the sun rises about 35 minutes earlier than in Aachen.

Because of equation of time, the earliest sunrise does not coincide with the summer solstice, but already occurs around June 17. Analogously, the latest sunrise does not December 21, but for example in northern Germany until around December 29, one week after the winter solstice, in Switzerland only to 3 January. The difference with the emergence time on the day of the solstice is only about two minutes.

In fact, the moment of the east, the sun is defined as the moment at which the upper edge of the solar disk the geocentric (or true ) horizon exceeds. Falls below the upper edge of the solar disk that horizon is sunset.

From about ± 65 ° latitude polar proximity and because of the astronomical refraction caused by the curvature of the light rays in the Earth's atmosphere, only half the solar disk can exceed the true horizon. From about ± 67.41 °, the upper edge of the solar disk does not reach the true horizon (see also polar night ).

The apparent size of the sun varies between 31 ' ( minutes of arc ) and 28 "( seconds of arc ) to the beginning of July and 32'32 " at the beginning of January, so there is a variance of about ± 1.7 % for the year. The mean apparent diameter of the sun is 31'59, 3 ". Due to the curvature of the light rays in the Earth's atmosphere the solar disk appears lifted by about 0.6 ° and thus larger than it actually is in diameter.

General advance calculations can not account for real horizon curves of certain locations and expect for an ideal mathematical horizon, located anywhere in the amount of 0 °. For the calculation of such time points, see Sunrise ( astronomy).

Brightness characteristic

As the light intensity increases at dawn and runs during sunrise, can be well captured by measurements of the brightness. In addition to the purely phenomenological aspect of this is for aspects of biology or for the development of sunrise simulators (such as for use as a light alarm clock ) is important.

The brightness characteristics close to the time sunrise is heavily dependent on the season, the weather and the latitude. In a cloudless sky can be very well estimated by an exponential function of the brightness. The illumination intensity is doubled while every 5 minutes.

Is the light intensity and the time, the time of sunrise is. Accordingly, 10 lx ( lux), which is about the illumination of the street lights, already achieved about 15 minutes before sunrise, and brightness of an average office lighting (800 lx ) is exceeded about 16 minutes after sunrise. This formula is a half hour after sunrise (between -60 min and 30 min ) suitable for the latitude of Germany for a period of about one hour before until. In summer, the brightness decreases faster, slower than specified in the winter.

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