- published: 05 Nov 2014
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Summer is the hottest of the four temperate seasons, falling between spring and autumn. At the summer solstice, the days are longest and the nights are shortest, with day-length decreasing as the season progresses after the solstice. The date of the beginning of summer varies according to climate, tradition and culture, but when it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, and vice versa.
From an astronomical view, the equinoxes and solstices would be the middle of the respective seasons, but sometimes astronomical summer is defined as starting at the solstice, the time of maximal insolation. A variable seasonal lag means that the meteorological center of the season, which is based on average temperature patterns, occurs several weeks after the time of maximal insolation. According to meteorologists, summer extends for the whole months of June, July, and August in the northern hemisphere and the whole months of December, January, and February in the southern hemisphere. Under meteorological definitions, all seasons are arbitrarily set to start at the beginning of a calendar month and end at the end of a month. This meteorological definition of summer also aligns with the commonly viewed notion of summer as the season with the longest (and warmest) days of the year, in which daylight predominates. The meteorological reckoning of seasons is used in Austria, Denmark, the former Soviet Union and Japan. It is also used by many in the United Kingdom. In Ireland, the summer months according to the national meteorological service, Met Éireann, are June, July and August. However, according to the Irish Calendar, summer begins on 1 May and ends on 1 August. School textbooks in Ireland follow the cultural norm of summer commencing on 1 May rather than the meteorological definition of 1 June.
Sunset or sundown, is the daily disappearance of the Sun below the western horizon as a result of Earth's rotation.
The time of sunset is defined in astronomy as the moment when the trailing edge of the Sun's disk disappears below the horizon. Near to the horizon, atmospheric refraction causes the ray path of light from the Sun to be distorted to such an extent that geometrically the Sun's disk is already about one diameter below the horizon when sunset is observed.
Sunset is distinct from dusk, which is the time when the sky becomes completely dark (apart from artificial light). This occurs when the Sun is about 18 degrees below the horizon. The period between sunset and dusk is called twilight.
Locations north of the Arctic Circle and south of the Antarctic Circle experience no sunset or sunrise on at least one day of the year, when the polar day or the polar night persists continuously for 24 hours.
Sunset creates unique atmospheric conditions such as the often intense orange and red colors of the Sun and the surrounding sky.
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