A solstice is an event occurring when the
Sun appears to reach its
most northerly or southerly excursion relative to the celestial
equator on the celestial sphere. Two solstices occur annually, around
June 21 and December 21. The seasons of the year are directly
connected to both the solstices and the equinoxes.
The term solstice can also be used in a broader sense, as the day when
this occurs. The day of the solstice in either hemisphere has either
the most sunlight of the year (summer solstice) or the least sunlight
of the year (winter solstice) for any place other than the Equator.
Alternative terms, with no ambiguity as to which hemisphere is the
June solstice and December solstice, referring to the
months of year in which they take place. 
At latitudes outside the tropics, the summer solstice marks the day
Sun appears to reach its highest point in the sky. Within the
Sun appears directly overhead at solar noon days to 3
months before and after the summer solstice. This means the subsolar
point occurs twice each year at any tropical latitude.
The word solstice is derived from the
Latin sol ("sun") and sistere
("to stand still"), because at the solstices, the Sun's declination
"stands still"; that is, the seasonal movement of the Sun's daily path
(as seen from Earth) stops at a northern or southern limit before
1 Definitions and frames of reference
2 Relationship to seasons
3 Cultural aspects
3.1 Ancient Greek names and concepts
3.2 English names
Solstice terms in East Asia
4 In the constellations
5 Solstices on other planets
6 See also
8 External links
Definitions and frames of reference
For an observer on the North Pole, the
Sun reaches the highest
position in the sky once a year in June. The day this occurs is called
June solstice day. Similarly, for an observer on the South Pole,
Sun reaches the highest position on the
December solstice day.
When it is the summer solstice at one Pole, it is the winter solstice
on the other. The Sun's westerly motion never ceases as
continually in rotation. However, the Sun's motion in declination
comes to a stop at the moment of solstice. In that sense, solstice
This modern scientific word descends from a
Latin scientific word in
use in the late
Roman Republic of the 1st century BC: solstitium.
Pliny uses it a number of times in his Natural History with a similar
meaning that it has today. It contains two Latin-language morphemes,
sol, "sun", and -stitium, "stoppage". The Romans used "standing" to
refer to a component of the relative velocity of the
Sun as it is
observed in the sky.
Relative velocity is the motion of an object from
the point of view of an observer in a frame of reference. From a fixed
position on the ground, the
Sun appears to orbit around Earth.
To an observer in an inertial frame of reference, planet
Earth is seen
to rotate about an axis and revolve around the
Sun in an elliptical
path with the
Sun at one focus. Earth's axis is tilted with respect to
the plane of Earth's orbit and this axis maintains a position that
changes little with respect to the background of stars. An observer on
Earth therefore sees a solar path that is the result of both rotation
A solargraph taken from the
Atacama Pathfinder Experiment
Atacama Pathfinder Experiment at the Llano
de Chajnantor Observatory in the southern hemisphere. This is a
long-exposure photograph, with the image exposed for six months in a
direction facing east of north, from mid-December 2009 until the
southern winter solstice in June 2010. The sun's path each day can
be seen from right to left in this image across the sky; the path of
the following day runs slightly lower, until the day of the winter
solstice, whose path is the lowest one in the image.
The component of the Sun's motion seen by an earthbound observer
caused by the revolution of the tilted axis – which, keeping the
same angle in space, is oriented toward or away from the
Sun – is an
observed daily increment (and lateral offset) of the elevation of the
Sun at noon for approximately six months and observed daily decrement
for the remaining six months. At maximum or minimum elevation, the
relative yearly motion of the
Sun perpendicular to the horizon stops
and reverses direction.
Outside of the tropics, the maximum elevation occurs at the summer
solstice and the minimum at the winter solstice. The path of the Sun,
or ecliptic, sweeps north and south between the northern and southern
hemispheres. The days are longer around the summer solstice and
shorter around the winter solstice. When the Sun's path crosses the
equator, the length of the nights at latitudes +L° and -L° are of
equal length. This is known as an equinox. There are two solstices and
two equinoxes in a tropical year.
Relationship to seasons
Main article: Season
The seasons occur because the Earth's axis of rotation is not
perpendicular to its orbital plane (the “plane of the ecliptic”)
but currently makes an angle of about 23.44° (called the "obliquity
of the ecliptic"), and because the axis keeps its orientation with
respect to an inertial frame of reference. As a consequence, for half
the year the
Northern Hemisphere is inclined toward the
Sun while for
the other half year the
Southern Hemisphere has this distinction. The
two moments when the inclination of Earth's rotational axis has
maximum effect are the solstices.
June solstice the subsolar point is further north than any
other time: at latitude 23.44° north, known as the Tropic of Cancer.
Similarly at the
December solstice the subsolar point is further south
than any other time: at latitude 23.44° south, known as the Tropic of
Capricorn. The subsolar point will cross every latitude between these
two extremes exactly twice per year.
Also during the June solstice, places on the
Arctic Circle (latitude
66.56° north) will see the
Sun just on the horizon during midnight,
and all places north of it will see the
Sun above horizon for 24
hours. That is the midnight sun or midsummer-night sun or polar day.
On the other hand, places on the
Antarctic Circle (latitude 66.56°
south) will see the
Sun just on the horizon during midday, and all
places south of it will not see the
Sun above horizon at any time of
the day. That is the polar night. During the December Solstice, the
effects on both hemispheres are just the opposite. This also allows
the polar sea ice to increase its annual growth and temporary extent
at a greater level due to lack of direct sunlight.
Sun at the northern solstice.
Sun at the southern solstice.
Diagram of the Earth's seasons as seen from the north. Far right:
Diagram of the Earth's seasons as seen from the south. Far left:
Two images showing the amount of reflected sunlight at southern and
northern summer solstices, respectively (watts / m²).
Ancient Greek names and concepts
The concept of the solstices was embedded in ancient Greek celestial
navigation. As soon as they discovered that the
Earth is spherical
they devised the concept of the celestial sphere, an imaginary
spherical surface rotating with the heavenly bodies (ouranioi) fixed
in it (the modern one does not rotate, but the stars in it do). As
long as no assumptions are made concerning the distances of those
Earth or from each other, the sphere can be accepted as
real and is in fact still in use. The Ancient Greeks use the term
"ηλιοστάσιο" (heliostāsio), meaning stand of the Sun.
The stars move across the inner surface of the celestial sphere along
the circumferences of circles in parallel planes perpendicular to
the Earth's axis extended indefinitely into the heavens and
intersecting the celestial sphere in a celestial pole. The
the planets do not move in these parallel paths but along another
circle, the ecliptic, whose plane is at an angle, the obliquity of the
ecliptic, to the axis, bringing the
Sun and planets across the paths
of and in among the stars.*
The band of the
Zodiac (zōdiakos kuklos, "zodiacal circle") is at an
oblique angle (loksos) because it is positioned between the tropical
circles and equinoctial circle touching each of the tropical circles
at one point ... This
Zodiac has a determinable width (set at 8°
today) ... that is why it is described by three circles: the central
one is called "heliacal" (hēliakos, "of the sun").
The term heliacal circle is used for the ecliptic, which is in the
center of the zodiacal circle, conceived as a band including the noted
constellations named on mythical themes. Other authors use
mean ecliptic, which first appears in a gloss of unknown author in a
Cleomedes where he is explaining that the
Moon is in the
zodiacal circle as well and periodically crosses the path of the Sun.
As some of these crossings represent eclipses of the Moon, the path of
Sun is given a synonym, the ekleiptikos (kuklos) from ekleipsis,
The two solstices can be distinguished by different pairs of names,
depending on which feature one wants to stress.
Summer solstice and winter solstice are the most common names,
referring to the seasons they are associated with. However, these can
be ambiguous since the northern hemisphere's summer is the southern
hemisphere's winter, and vice versa. The Latinate names estival
solstice (summer) and hibernal solstice (winter) are sometimes used to
the same effect, as are midsummer and midwinter.
June solstice and
December solstice refer to the months of year in
which they take place, with no ambiguity as to which hemisphere is
the context. They are still not universal, however, as not all
cultures use a solar-based calendar where the solstices occur every
year in the same month (as they do not in the
Islamic calendar and
Hebrew calendar, for example).
Northern solstice and southern solstice indicate the hemisphere of the
Sun's location. The northern solstice is in June, when the
directly over the
Tropic of Cancer
Tropic of Cancer in the Northern Hemisphere, and the
southern solstice is in December, when the
Sun is directly over the
Tropic of Capricorn
Tropic of Capricorn in the Southern Hemisphere. These terms can be
used unambiguously for other planets.
First point of Cancer and first point of Capricorn refer to the
astrological signs that the sun is entering. Due to the precession
of the equinoxes, however, the constellations where the solstices are
currently located are Taurus and Sagittarius, respectively.
Solstice terms in East Asia
Xiazhi and Dongzhi (solar term)
The traditional East Asian calendars divide a year into 24 solar terms
(節氣). Xiàzhì (pīnyīn) or Geshi (rōmaji) (Chinese and
Japanese: 夏至; Korean: 하지(Haji); Vietnamese: Hạ chí;
"summer's extreme") is the 10th solar term, and marks the summer
solstice. It begins when the
Sun reaches the celestial longitude of
90° (around June 21) and ends when the
Sun reaches the longitude of
105° (around July 7). Xiàzhì more often refers in particular to the
day when the
Sun is exactly at the celestial longitude of 90°.
Dōngzhì (pīnyīn) or Tōji (rōmaji) (Chinese and Japanese: 冬至;
Korean: 동지(Dongji); Vietnamese: Đông chí; "winter's extreme")
is the 22nd solar term, and marks the winter solstice. It begins when
Sun reaches the celestial longitude of 270° (around December 22 )
and ends when the
Sun reaches the longitude of 285° (around January
5). Dōngzhì more often refers in particular to the day when the Sun
is exactly at the celestial longitude of 270°.
The solstices (as well as the equinoxes) mark the middle of the
seasons in East Asian calendars. Here, the Chinese character 至 means
"extreme", so the terms for the solstices directly signify the summits
of summer and winter.
See also: Fête St-Jean-Baptiste, Festival of San Juan, Saint Jonas
Day, St John's
Day (Estonia), Ivan Kupala Day, and Golowan
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Solstice Sunrise over Stonehenge
The term solstice can also be used in a wider sense, as the date (day)
that such a passage happens. The solstices, together with the
equinoxes, are connected with the seasons. In some languages they are
considered to start or separate the seasons; in others they are
considered to be centre points (in England, in the Northern
Hemisphere, for example, the period around the northern solstice is
known as midsummer). Midsummer's Day, defined as St. Johns
Day by the
Christian Church, is June 24, about three days after the solstice
itself). Similarly December 25 is the start of the Christmas
celebration, and is the day the
Sun begins to return to the Northern
Many cultures celebrate various combinations of the winter and summer
solstices, the equinoxes, and the midpoints between them, leading to
various holidays arising around these events. For the southern
solstice, Christmas is the most popular holiday to have arisen. In
addition, Yalda, Saturnalia, Karachun, Hanukkah,
winter solstice for more) are also celebrated around this time. For
the northern solstice, Christian cultures celebrate the feast of St.
John from June 23 to 24 (see St. John's Eve, Ivan Kupala Day,
Midsummer), while Neopagans observe Midsummer, also known as Litha.
For the vernal (spring) equinox, several spring-time festivals are
celebrated, such as the Persian Nowruz, the observance in
Passover and in most Christian churches of Easter. The autumnal
equinox has also given rise to various holidays, such as the Jewish
holiday of Sukkot. At the midpoints between these four solar events,
cross-quarter days are celebrated.
In the southern tip of South America, the
Mapuche people celebrate We
Tripantu (the New Year) a few days after the northern solstice, on
June 24. Further north, the
Atacama people formerly celebrated this
date with a noise festival, to call the
Sun back. Further east, the
Aymara people celebrate their New
Year on June 21. A celebration
occurs at sunrise, when the sun shines directly through the Gate of
Sun in Tiwanaku. Other Aymara New
Year feasts occur throughout
Bolivia, including at the site of El Fuerte de Samaipata.
In the Hindu calendar, two sidereal solstices are named Makara
Sankranti which marks the start of
Uttarayana and Karka Sankranti
which marks the start of Dakshinayana. The former occurs around
January 14 each year, while the latter occurs around July 14 each
year. These mark the movement of the
Sun along a sidereally fixed
zodiac (precession is ignored) into Makara, the zodiacal sign which
corresponds with Capricorn, and into Karkat, the zodiacal sign which
corresponds with Cancer, respectively.
South Pole Station celebrates every year on June
21 a midwinter party, to celebrate that the
Sun is at its lowest point
and coming back.
Fremont Solstice Parade
Fremont Solstice Parade takes place every summer solstice in
Fremont, Seattle, Washington
Fremont, Seattle, Washington in the United States.
Cahokia Woodhenge, a large timber circle located at
Cahokia archaeological site near
Collinsville, Illinois, is the site of annual equinox and solstice
sunrise observances. Out of respect for Native American beliefs these
events do not feature ceremonies or rituals of any kind.
Unlike the equinox, the solstice time is not easy to determine. The
changes in solar declination become smaller as the sun gets closer to
its maximum/minimum declination. The days before and after the
solstice, the declination speed is less than 30 arcseconds per day
which is less than 1⁄60 of the angular size of the sun, or the
equivalent to just 2 seconds of right ascension.
This difference is hardly detectable with indirect viewing based
devices like sextant equipped with a vernier, and impossible with more
traditional tools like a gnomon or an astrolabe. It is also hard
to detect the changes on sunrise/sunset azimuth due to the atmospheric
refraction changes. Those accuracy issues render it impossible to
determine the solstice day based on observations made within the 3 (or
even 5) days surrounding the solstice without the use of more complex
Accounts do not survive but Greek astronomers must have used an
approximation method based on interpolation, which is still used by
some amateurs. This method consists of recording the declination angle
at noon during some days before and after the solstice, trying to find
two separate days with the same declination. When those two days are
found, the halfway time between both noons is estimated solstice time.
An interval of 45 days has been postulated as the best one to achieve
up to a quarter-day precision, in the solstice determination. In
2012, the journal DIO found that accuracy of one or two hours with
balanced errors can be attained by observing the sun's equal altitudes
about S = twenty degrees (or d = about 20 days) before and after the
summer solstice because the average of the two times will be early by
q arc minutes where q is (πe cosA)/3 times the square of S in degrees
(e = earth orbit eccentricity, A = earth's perihelion or sun's
apogee), and the noise in the result will be about 41 hours divided by
d if the eye's sharpness is taken as one arc minute.
Astronomical almanacs define the solstices as the moments when the sun
passes through the solstitial colure, i.e. the times when the apparent
geocentric longitude of the sun is equal to 90° (summer solstice) or
270° (winter solstice). The dates of the solstice varies each
year and may occur a day earlier or later depending on the time zone.
The solstices always occur between June 20 and 22 and between December
20 and 23 with the 21st and 22nd being the most common dates.
In the constellations
Using the current official IAU constellation boundaries – and taking
into account the variable precession speed and the rotation of the
ecliptic – the solstices shift through the constellations as
follows (expressed in astronomical year numbering in which the
year 0 = 1 BC, −1 = 2 BC, etc.):
The northern solstice passed from Leo into Cancer in year −1458,
passed into Gemini in year −10, passed into Taurus in December 1989,
and is expected to pass into Aries in year 4609.
The southern solstice passed from
Capricornus into Sagittarius in year
−130, is expected to pass into
Ophiuchus in year 2269, and is
expected to pass into
Scorpius in year 3597.
Solstices on other planets
Due to the 687-day orbit of
Mars around the
Sun (almost twice that of
the Earth), the planet experiences its summer and winter solstices at
approximately 23 month intervals.
Geocentric view of the seasons
Perihelion and aphelion
United States Naval Observatory (21 September 2015). "Earth's
Seasons: Equinoxes, Solstices, Perihelion, and Aphelion, 2000–2025".
Retrieved 9 December 2015.
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Principle of relativity
Principle of relativity was first applied to inertial frames of
reference by Albert Einstein. Before then, the concepts of absolute
space and time applied by
Isaac Newton prevailed. The motion of the
Sun across the sky is still called "apparent motion" in celestial
navigation in deference to the Newtonian view, but the reality of the
supposed "real motion" has no special laws to commend it, both are
visually verifiable and both follow the same laws of physics.
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^ For an introduction to these topics of astronomy refer to Bowditch,
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^ Strabo. The Geography. II.5.1. sphairikē ... tēs gēs epiphaneia,
spherical is the surface of the Earth
^ Strabo. The Geography. pp. II.5.2. sphairoeidēs ... ouranos,
spherical in appearance ... is heaven
Strabo II.5.2., "aplaneis asteres kata parallēlōn pherontai
kuklōn", "the fixed stars are borne in parallel circles"
Strabo II.5.2, "ho di'autēs (gē) aksōn kai tou ouranou mesou
tetagmenos", "the axis through it (the Earth) extending through the
middle of the sky"
Cleomedes (2004). Cleomedes' Lectures on Astronomy: A Translation of
The Heavens. Translated by Alan C. Bowen and Robert B. Todd. Berkeley:
University of California Press. p. 41.
ISBN 0-520-23325-5. This translation cites this passage at
the end of Book I Chapter 2 but other arrangements have it at the
start of Chapter 3. In the Greek version of
Cleomedes (1891). Ziegler,
Hermann, ed. Cleomedis De motu circulari corporum caelestium libri
duo. B. G. Teubneri. p. 32. the passage starts Chapter 4.
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^ Stewart, Alexander (1869). A Compendium of ModernGeography.
Edinburgh: Oliver & Boyd. p. 383. Retrieved December 9,
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^ Iseminger, William. "Welcome the Fall
Illinois Department of Natural Resources. Retrieved December 20,
Solstice Sunrise Observance at
Cahokia Mounds". Collinsville
Chamber of Commerce. Retrieved December 20, 2017.
Cahokia Mounds Mark Spring Equinox : The keepers of Cahokia
Mounds will host a spring gathering to celebrate the vernal equinox".
Indian Country Today. Indian Country Media Network. Retrieved December
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Solstice Determination based on
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Look up solstice in Wiktionary, the free dictionary.
Wikimedia Commons has media related to Solstice.
Equinoxes and Solstices Calculator (1600 to 2400)
"Earth's Seasons: Equinoxes, Solstices, Perihelion, and Aphelion
United States Naval Observatory, Astronomical
Applications Department. Retrieved December 9, 2015.
Weisstein, Eric (1996–2007). "Summer Solstice". Eric Weisstein's
World of Astronomy. Retrieved October 24, 2008. The above plots show
how the date of the summer solstice shifts through the Gregorian
calendar according to the insertion of leap years.
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