A solstice is an astronomical occurence that happens twice every year, when the tilt of the Earth’s axis is multiple inclined toward or away from the Sun, causing the Sun’s apparent position in the sky to contact its northernmost or southernmost extreme. The and cr is derived from the Latin sol (sun) and sistere (to stand still), because at the solstices, the Sun stands still in declination; that is, the apparent movement of the Sun’s course north or southern comes to a stop before reversing direction.

The term solstice can also be used in a broader sense, as the date (day) when the current occurs. The solstices, together with the equinoxes, are connected with the seasons. In particularlly cultures they are kept in mind to start or separate the seasons, while in others properties go down nearer the middle.

Definitions and frames of reference

Of the many ways in that solstice can be defined, one of the most common (and perhaps most easily understood) is by the astronomical phenomenon for which it is named, which is readily observable by any person on Earth: a “sun-standing.” 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 high amount of times in his Natural History with the same meaning that it has today. It contains two Latin-language segments, sol, “sun”, and -stitium, “stoppage.”[2] The Romans used “standing” to refer to a element of the relative velocity of the Sun as it is seen in the sky. Relative velocity is the motion of an object based on data from the rank of view of an observer in a frame of reference. From a fixed position on the ground, the sun appears to orbit around the Earth.

To an observer in inertial space, the Earth is witnessed to rotate about an axis and revolve around the Sun in an elliptical channel with the Sun at one focus. The Earth’s axis is tilted with respect to the plane of the Earth’s orbit and this moment axis maintains a position that fluctuations little amid sympathy to the background of stars. An observer on Earth therefore sees a solar path that is the result of both rotation and revolution.

The cog of the Sun’s motion witnessed 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 diurnal 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 motion at 90° to the horizon stops and fluctuations direction by 180°. The maximum is the summer solstice and the minimum is the winter solstice. The path of the Sun, or ecliptic, sweeps north and southern between the northern and southern hemispheres. The days are longer around the summer solstice and shorter accessible the winter solstice. When the Sun’s way crosses the equator, the days and nights are of equal length; this is well&wshyp;known as an equinox. There are two solstices and two equinoxes.
Heliocentric view of the seasons

Diagram of the Earth’s seasons as observed based on the south. Far left: northern solstice

The rationale of the seasons is that the Earth’s axis of rotation is not perpendicular to its orbital plane (the flat plane made for the duration of the center of mass (barycenter) of the solar system (near or for the duration of the Sun) and the successive settings of Earth within the year), but currently causes an angle of about 23.44° (called the “obliquity of the ecliptic”), and that the axis keeps on its orientation with respect to inertial space. As a consequence, for part the year (from roughly 20 March to 22 September) the northern hemisphere is inclined toward the Sun, with the maximum accessible 21 June, while for the other half year the southern hemisphere has this distinction, with the maximum about 21 December. The two moments when the inclination of Earth’s rotational axis has maximum effect are the solstices.

The table at the top of the article gives the instances of equinoxes and solstices over multitude of years. Refer to the equinox news story for a little remarks.

At the northern solstice the subsolar point reaches to 23.44° north, renowned as the Tropic of Cancer. Likewise at the southern solstice the same thing takes place for latitude 23.44° south, known as the Tropic of Capricorn. The sub-solar point is planning to cross every latitude between these two extremes spot on twice per year.

Also during the northern solstice, places situated at latitude 66.56° north, famous as the Arctic Circle will be able to see the Sun just on the horizon during midnight, and all structures 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 opposite hand, places at latitude 66.56° south, known as the Antarctic Circle will see the Sun just on the horizon during midday, and all housing south of it should not see the Sun above horizon at any time of the day. That is the polar night. During the southern solstice the effects on both hemispheres are just the opposite.
Two images showing the amount of reflected sunlight at southern and northern summer solstices respectively (watts / m²).

At the temperate latitudes, during summer the Sun remains longer and higher above the horizon, while in winter it remains shorter and lower. This is the basis of summer heat and winter cold.
Further information: impacts of sun angle on climate

The seasons are not lead to by the varying distance of Earth based on the Sun due to the orbital eccentricity of the Earth’s orbit. This variation performs make a contribution, but is small compared providing the effects of exposure due to the fact that of Earth’s tilt. Currently the Earth reaches perihelion at the beginning of January - the arising of the northern winter and the southern summer. Although the Earth is at its closest to the Sun and therefore receiving more heat, the whole planet is not in summer. Although it is true the current the northern winter is somewhat warmer than the southern winter, the placement of the continents may also play an important factor. In the same way, within aphelion at the beginning of July, the Sun is farther away, but that still leaves the northern summer and southern winter as they are with only smaller effects.

Due to Milankovitch cycles, the Earth’s axial tilt and orbital eccentricity may change for the duration of thousands of years. Thus in 10,000 years one would find which Earth’s northern winter occurs at aphelion and its northern summer at perihelion. The severity of seasonal change-the normal temperature change between summer and winter in location-will also change over second while the Earth’s axial tilt fluctuates between 22.1 and 24.5 degrees.

The explanation given in the previous section is useful for observers in outer space. They may see how the Earth revolves around the Sun and how the distribution of light on the country would tweak over the year. To observers on Earth, it is too useful to see how the Sun turns out to revolve around them. These pictures show such a perspective as follows. They verify the day arcs of the Sun, the paths the Sun tracks along the celestial dome in its diurnal movement. The pictures show presently for any hour on both solstice days. The longer arc is constantly the summer track and the shorter one the winter track. The two tracks are at a distance of 46.88° (2 × 23.44°) away from each other.

In addition, some ‘ghost’ suns are implied below the horizon, as much as 18° down. The Sun in such a area causes twilight. The pictures can be used for both the northern and southern hemispheres. The observer is supposed to sit near the tree on the island in the middle of the ocean. The green arrows give the cardinal directions.

* On the northern hemisphere the north is to the left, the Sun rises in the east (far arrow), culminates in the south (to the right) while moving to the right and sets in the west (near arrow). Both appreciation and set positions are displaced towards the north in summer, and towards the south for the winter track.
* On the southern hemisphere the south is to the left, the Sun rises in the east (near arrow), culminates in the north (to the right) while moving to the left and sets in the west (far arrow). Both rise and set positions are displaced towards the south in summer, and towards the north for the winter track.

The approaching special cases are depicted.

* On the equator the Sun is not overhead every day, as selected lendees think. In fact that happens clearly on two days of the year, the equinoxes. The solstices are the dates that the Sun stays farthest away from the zenith, one and only reaching an altitude of 66.56° either to the north or the south. The only thing special up the equator is that all days of the year, solstices included, have roughly the same length of about 12 hours, so the current it instigates no sense to talk about summer and winter. Instead, tropical cities often experience wet and dry seasons.
* The day arcs at 20° latitude. The Sun culminates at 46.56° altitude in winter and 93.44° altitude in summer. In this case an angle larger than 90° signals the current the culmination takes place at an altitude of 86.56° in the converse cardinal direction. For example in the southern hemisphere, the Sun remains in the north throughout winter, but can reach over the zenith to the southern in midsummer. Summer days are longer than winter days, but the difference is no more than two or three hours. The daily path of the Sun is steep at the horizon the whole year round, resulting in a twilight of only about one hour.
* The day arcs at 50° latitude. The winter Sun performs not appreciation more as opposed to 16.56° above the horizon at midday, and 63.44° in summer above the same horizon direction. The difference in the length of the day between summer and winter is striking - faintly less than 8 hours at midwinter, to slightly a larger number of than 16 hours in midsummer. Likewise is the difference in direction of sunrise and sunset. Also note the steepness of the daily path of the Sun above the horizon. It is much shallower than at 20° latitude. Therefore not just is the Sun not reaching as high, it furthermore seems not to be in a hurry to do so. But conversely this means that the Sun is not in a hurry to dip deeply short of the horizon at night. At this latitude at midnight the summer sun is only 16.56° below the horizon, which means that astronomical twilight continues the whole night. This phenomenon is known as the grey nights, nights when it does not get dark enough for astronomers to do their observations. Above 60° latitude the Sun would be even closer to the horizon, only 6.56° away from it. Then civil twilight keeps on the whole night. This phenomenon is famed as the white nights. And above 66.56° latitude, of course, one ought to get the midnight sun.
* The day arcs at 70° latitude. At local noon the winter Sun culminates at -3.44°, and the summer Sun at 43.44°. Said another way, within the winter the Sun does not rise above the horizon, it is the polar night. There will be significantly a strong twilight though. At local midnight the summer Sun culminates at 3.44°, said another way, it does not set, it is the polar day.
* The day arcs at the pole. At the time of the summer or winter solstices, the Sun is 23.44° degrees above or below the horizon respectively, irrespective of time of day. Whilst the Sun is up (during summer months) it am able to circle approximately the huge sky, appearing to stay at the same angle from the horizon, therefore the concept of day or night is meaningless. The angle of elevation might gradually change on an annual cycle, with the Sun reaching its most massive point at the summer Solstice, and rising or setting at the Equinox, provided extended periods of twilight lasting a good amount of days after the autumn equinox and before the spring equinox.

Cultural aspects

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[5] properties devised the notion of the celestial sphere,[6] an imaginary spherical surface rotating with the heavenly bodies (ouranioi) set in it (the modern one does not rotate, but the stars in it do). As long as no assumptions are came up with concerning the distances of those bodies from Earth or from each other, the sphere can be accepted as real and is in happening still in use.

The stars move across the inner surface of the celestial sphere along the circumferences of circles in parallel planes[7] perpendicular to the Earth’s axis long indefinitely into the heavens and intersecting the celestial sphere in a celestial pole.[8] The Sun and the planets do not move in these parallel paths but along an additional 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.*

Cleomedes states:

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 every of the tropical circles at one rate … This Zodiac has a determinable width (set at 8° today) … that is why it is illustrated by 3 circles: the central one is identified “heliacal” (hÄ“liakos, “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 Zodiac to make for ecliptic, which first appears in a gloss of unknown author in a passage of Cleomedes where he is explaining who the Moon is in the zodiacal circle as well and periodically crosses the path of the Sun. As some of such crossings speak on the behalf of eclipses of the Moon, the path of the Sun is given a synonym, the ekleiptikos (kuklos) from what i read in ekleipsis, “eclipse.”