Summer solstice

The earth at midnight during the summer solstice in June 2017

The summer solstice (or estival solstice), also known as midsummer, occurs when a planet's rotational axis, or geographic pole on either its northern or its southern hemisphere, is most inclined toward the star that it orbits. On the summer solstice, Earth's maximum axial tilt toward the Sun is 23.44°. (Likewise, the Sun's declination from the celestial equator is +23.44° in the Northern Sky and −23.44° in the Southern Sky.) This happens twice each year (once in each hemisphere), when the Sun reaches its highest position in the sky as seen from the north or south pole.

The summer solstice occurs during the hemisphere's summer.^[2] This is the northern solstice in the Northern Hemisphere and the southern solstice in the Southern Hemisphere. Depending on the shift of the calendar, the summer solstice occurs some time between June 20 and June 22 in the Northern Hemisphere^[3][4] and between December 20 and December 23 each year in the Southern Hemisphere.^[5] The same dates in the opposite hemisphere are referred to as the winter solstice.

As seen from a geographic pole, the Sun reaches its highest altitude of the year on the summer solstice. It can be solar noon only along that longitude, which at that moment lies in the direction of the Sun from the pole. For other longitudes, it is not noon. Noon has either passed or has yet to come. Hence the notion of a solstice day is useful. The term is colloquially used like "midsummer" to refer to the day on which solstice occurs. The summer solstice day has the longest period of daylight, except in the polar regions, where daytime remains continuous for 24 hours every day during a period ranging from a few days to six months around the summer solstice.

Distinctions

Diagram of the Earth's seasons as seen from the north. Far left: summer solstice for the Northern Hemisphere. Front right: summer solstice for the Southern Hemisphere.

Although the summer solstice is the longest day of the year for that hemisphere, the dates of earliest sunrise and latest sunset vary by a few days.^[6] This is related to the fact that the earth orbits the sun in an ellipse and its orbital speed varies slightly during the year.^[7] Although the sun appears at its highest altitude from the viewpoint of an observer in outer space or a terrestrial observer outside tropical latitudes, the highest altitude occurs on a different day for locations in the tropics, specifically the sun is directly overhead (maximum 90 degrees elevation) at the subsolar point. This day occurs twice each year for all locations between the tropic of cancer and tropic of capricorn because the overhead sun appears to cross a given latitude once before the day of the solstice and once afterward. For example, Lahaina Noon occurs in May and July in Hawaii. See solstice article. For all observers, the apparent position of the noon sun is at its most northerly point on the June solstice and most southerly on the December solstice.

Full moon

2016 was the first time in nearly 70 years that a full moon and the Northern Hemisphere's summer solstice occurred on the same day.^[8] The 2016 summer solstice's full moon rose just as the Sun set.^[8]

Cultural aspects

Worldwide, interpretation of the event has varied among cultures, but most recognize the event in some way with holidays, festivals, and rituals around that time with themes of religion or fertility.^[9] In some regions, the summer solstice is seen as the beginning of summer and the end of spring. In other cultural conventions, the solstice is closer to the middle of summer.^[10]

Summer solstice sunset over the Mojave Desert 7:54 p.m. PDT (19:54) June 20, 2016

Solstice is derived from the Latin words sol (sun) and sistere (to stand still).

Date

Celebrations

• Day of Private Reflection (Northern Ireland)
• Fremont Solstice Parade (Fremont, Seattle, Washington, United States)
• Guru Purnima (India)
• Christmas typically marks the end of the summer solstice in the southern hemisphere.
• International Surfing Day
• International Yoga Day
• Juhannus (Finland)
• Jāņi (Latvia)
• Midsummer
• National Aboriginal Day (Canada)
• Tiregān (Iran)
• World Music Day

Winter solstice in the Southern Hemisphere

• Inti Raymi, Machu Picchu, Peru
• We Tripantu, (Mapuche, southern Chile)
• Willkakuti, an Andean-Amazonic New Year (Aymara)

Length of the day on the summer solstice of the north

The following tables contain information on the length of the day on the summer solstice of the northern hemisphere and winter solstice of the southern hemisphere (i.e. June solstice). The data was collected from the website of the Finnish Meteorological Institute on 20 June 2016^[11] as well as from certain other websites.^{[12][13][14][15][16][17][18][19]}

The data is arranged geographically and within the tables from the longest day to the shortest one.

See also

• Day length
• Equinox
• Midsummer's day
• Stonehenge
• Tekufah
• Winter solstice
• Xiazhi (Summer solstice in Chinese culture)

References

External links

• Table of dates/times from 1600–2400