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The Earth's orbit around the Sun

from 978-3-14-100790-9 from page 203 fig. 6
Diercke Karte The Earth's orbit around the Sun
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The Earth's orbit around the Sun
The rotation of our planet, which from Earth appears as the Sun moving across the sky, is the reason for the 24-hour cycle of night and day. The second movement of the Earth on an almost circular orbital path around the Sun - at an average distance of 149,6 million kilometres - is responsible for the cycle of a year; as seen from Earth this manifests itself as an apparent movement of the sun through a series of celestial constellations, for example from one vernal equinox to the next vernal equinox. This cycle has a length of 365.2422 days and is called a "tropical" or "solar" year. Because a calendar year cannot contain fractions of a day, the yearly deviation is accumulated and inserted on the 29th of February as a leap day approximately every four years. On its elliptical orbit the Earth is closest to the Sun in January (perihelion) and is farthest from the Sun in July (aphelion). Because the Earth moves more quickly when it is closer to the Sun, the northern winter is shorter than the summer.
The seasons of the year occur because the Earth's rotational axis is inclined at an angle of 23.5° to the perpendicular of the ecliptic plane - and, with the exception of long-term changes (axial precession), this axis will remain pointing to the north celestial pole close to the northern Pole Star. The northern hemisphere faces the Sun for the longest time on the 21st of June (summer solstice) – during this time the Sun does not sink below the horizon north of the polar circle. However, on December 21st (winter solstice) the Sun is invisible north of the polar circle all the time. At the time of equinox (20th of March, 23rd of September) the Sun is rising exactly in the east and setting exactly in the west, resulting in exactely 12 hours daylight and 12 hours night. In the summer, while the Sun in Europe rises in the northeast and sets in the northwest, there are much more than 12 hours daylight and much less than 12 hours night. In the winter, the opposite is true: the Sun rises in the southeast and sets in the southwest, resulting in much less than 12 hours daylight and much more than 12 hours night.
A. Schulz; Ü: J. Moar, M. Dahl

Keywords: astronomy Earth orbit outer space planet season Sun universe

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