sunset
As sunset disappearance is the sun below the horizon called as well as the time of their loss in the daily course of the sun and the celestial phenomenon as such, with all its phenomena. The sunset is followed by the phases of dusk , which vary in length depending on the geographical latitude . The clear day ends with sunset . In some cultures - for example among the ancient Germans , in Judaism and in Islam - this marks the end of the day, after which the following day begins. In today's international calendar regulation, on the other hand, the beginning of a civil day falls at midnight (00:00).
Astronomical Phenomenology
The term sunset is a relic of the geocentric view of the world : Because it is not the sun that moves, but the viewer is moved across the day-night boundary on earth due to the natural rotation of the earth; the opposite is the sunrise .
With sunrise, meridian passage and culmination, setting is one of the most important aspects of astronomical phenomenology , which is why all astronomical calendars or yearbooks contain corresponding dates for the sun and moon. Due to the equation of time, the latest sunset does not coincide with the summer solstice , but only occurs around June 25th. Similarly, the earliest sunset in northern Germany occurs around December 14th, i.e. one week before the winter solstice, and in Switzerland around December 11th.
The apparent sun size varies between 31'28 "( angular minutes , arc seconds ) at the beginning of July and 32'32" at the beginning of January, resulting in a variance of approximately ± 1.7% over the course of the year. The mean apparent diameter of the sun is 31'59.3 ".
Due to the curvature of the rays of light (refraction and astronomical refraction ) in the earth's atmosphere , the sun's disk appears about 0.6 ° higher and slightly flattened at sunrise and sunset, but larger than at the zenith due to an optical illusion.
True and apparent sunset
The true sunset is the moment when the top of the sun's disk falls below the true horizon. The true horizon, also known as the geocentric horizontal plane, is the plane perpendicular to the observer's plumb line and passing through the center of the earth. At this moment there is a distance of about 2/3 of its diameter between the sun and the horizon.
The apparent or visible sunset occurs when the sun is already far below the horizon plane - it is the moment when the observed upper sun edge falls below the apparent horizon. The apparent horizon is the horizontal plane on the surface of the earth at the point of observation. In addition, there is an influence of the height of the observer or his eye above the earth's surface. The apparent sunset is therefore calculated for a geometric horizon height of −0.833 °.
General forecasts cannot take into account the real horizon courses of certain locations and calculate for an ideal mathematical horizon that is everywhere at the height of 0 °. To calculate such times see rise (astronomy) or visibility (astronomy) .
Outside the tropics, where the set point is on the horizon depends heavily on the season . At the equinox it is almost exactly in the west , in December / January, however, for Central Europe it is roughly in the south-west , and in June / July in the north-west . So the possible direction varies by almost 90 degrees:
- Astronomical views of sunsets
Sunset in Europe and Africa
(photomontage)
Sunset on Earth captured from space
(lower left corner of the image)
Sky coloring
Depending on the weather , the setting of the sun can be associated with an impressive play of colors, which sometimes not only shines in the sunset , but also has yellow, purple or even green tones. The color change is caused by Rayleigh scattering . The earth's atmosphere works with floating particles, the aerosols in the peplosphere as a diffusely scattering medium. The blue light component of the sinking solar disk is more strongly scattered, so that in relation a higher proportion of red light reaches the observer.
In extremely clear visibility conditions, a green glow or even a green flash can be observed, which is caused by a very slight prismatic effect of the atmosphere at certain temperature layers: the yellow-red solar disk disappears below the horizon, causing the (almost) disappeared sun to briefly appear at the top a green (blue) hem seems to flash.
Web links
- Calculate sunset for different locations in the German-speaking area (A, CH, D)
- Calculate sunset for different places in Germany
- Calculate sunset worldwide
- Table with sunrise and sunset times (worldwide twilight calculator)
- Calculation of day lengths depending on latitude and date (formulas) (English)
- graphical representation of worldwide sunrise, sunset and twilight times
- Current sun coordinates, hourly angles and sunrise / sunset for any location
Individual evidence
- ↑ Archived copy ( Memento of the original dated August 11, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ http://lexikon.astronomie.info/zeitgleichung/
