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Solstice: the story on HearLore | HearLore
Solstice
The Sun does not move. At the precise moment of the solstice, the daily path of the Sun across the sky reaches its northernmost or southernmost limit and appears to pause before reversing direction. This phenomenon, which gave the word solstice its name from the Latin solstitium meaning sun and stoppage, was observed by ancient astronomers who saw the seasonal movement of the Sun's daily path reach a limit before turning back. The term entered English during the Middle English period, replacing older Germanic calques like sunstead and sunstay which fell out of use after the 17th century. For an observer at the North Pole, the Sun reaches its highest position in the sky once a year in June, while for an observer on the South Pole, the Sun reaches its highest position on the December solstice day. When it is the summer solstice at one Pole, it is the winter solstice on the other, creating a celestial dance that has defined human timekeeping for millennia. The Romans used the concept of standing to refer to a component of the relative velocity of the Sun as it is observed in the sky, a perspective that persisted through the Newtonian view of absolute space and time before Einstein's Principle of relativity redefined inertial frames of reference. Even today, the motion of the Sun across the sky is still called apparent motion in celestial navigation, a deference to the Newtonian view that remains visually verifiable despite modern physics.
The Tilted Earth's Dance
The Earth's axis of rotation is not perpendicular to its orbital plane but currently makes an angle of about 23.44 degrees, known as the obliquity of the ecliptic. This tilt causes the seasons to occur because for half the year the Northern Hemisphere is inclined toward the Sun while for the other half year the Southern Hemisphere has this distinction. At the June solstice the subsolar point is further north than any other time at latitude 23.44 degrees 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 degrees south, known as the Tropic of Capricorn. The subsolar point will cross every latitude between these two extremes exactly twice per year. During the June solstice, places on the Arctic Circle at latitude 66.56 degrees 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 at latitude 66.56 degrees 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, and this sees polar sea ice re-grow annually due to lack of sunlight on the air above and surrounding sea. The warmest and coldest periods of the year in temperate regions are offset by about one month from the solstices, delayed by the earth's thermal inertia.
What is the definition of the solstice according to the script?
The solstice is the precise moment when the daily path of the Sun across the sky reaches its northernmost or southernmost limit and appears to pause before reversing direction. This phenomenon derives its name from the Latin solstitium meaning sun and stoppage and was observed by ancient astronomers who saw the seasonal movement of the Sun's daily path reach a limit before turning back.
What is the obliquity of the ecliptic and how does it affect the solstices?
The Earth's axis of rotation makes an angle of about 23.44 degrees known as the obliquity of the ecliptic which is not perpendicular to its orbital plane. This tilt causes the seasons to occur because for half the year the Northern Hemisphere is inclined toward the Sun while for the other half year the Southern Hemisphere has this distinction.
When do the summer and winter solstices occur in the current calendar cycle?
The solstices always occur between June 20 and 22 and between December 20 and 23 in a four-year-long cycle with the 21st and 22nd being the most common dates. The dates of the solstice vary each year and may occur a day earlier or later depending on the time zone because the earth's orbit takes slightly longer than a calendar year of 365 days.
Which constellations do the solstices currently pass through due to precession?
The constellations the sun appears in at solstices are currently Taurus in June and Sagittarius in December despite the astrological signs that the sun is entering being rooted in Roman Classical period dates. The northern solstice passed from Leo into Cancer in year -1458 passed into Gemini in year -10 and passed into Taurus in December 1989.
How do different cultures celebrate the solstices according to the text?
During the southern or winter solstice Christmas is the most widespread contemporary holiday while Yalda Saturnalia Karachun Hanukkah Kwanzaa and Yule are also celebrated around this time. For the northern or summer solstice Christian cultures celebrate the feast of St. John from June 23 to 24 while Modern Pagans observe Midsummer known as Litha among Wiccans.
The concept of the solstices was embedded in ancient Greek celestial navigation as soon as they discovered that the Earth was spherical. They devised the concept of the celestial sphere, an imaginary spherical surface rotating with the heavenly bodies fixed in it, which the modern one does not rotate but the stars in it do. As long as no assumptions are made concerning the distances of those bodies from 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 heliostasio, 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 Sun and 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 is at an oblique angle 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 degrees today, and that is why it is described by three circles: the central one is called heliacal, meaning of the sun. Other authors use Zodiac to mean ecliptic, which first appears in a gloss of unknown author in a passage of 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 the Sun is given a synonym, the ekleiptikos from ekleipsis, meaning eclipse.
Global Calendars and Festivals
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. During the southern or winter solstice, Christmas is the most widespread contemporary holiday, while Yalda, Saturnalia, Karachun, Hanukkah, Kwanzaa, and Yule are also celebrated around this time. In East Asian cultures, the Dongzhi Festival is celebrated on the winter solstice. For the northern or summer solstice, Christian cultures celebrate the feast of St. John from June 23 to 24, while Modern Pagans observe Midsummer, known as Litha among Wiccans. In the southern tip of South America, the Mapuche people celebrate We Tripantu, the New Year, a few days after the northern solstice, on the 24th of June. 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 the 21st of June. A celebration occurs at sunrise, when the sun shines directly through the Gate of the 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 the 14th of January each year, while the latter occurs around the 14th of July each year. These mark the movement of the Sun along a sidereally fixed zodiac, ignoring precession, into Makara, the zodiacal sign which corresponds with Capricorn, and into Karka, the zodiacal sign which corresponds with Cancer, respectively. The Amundsen-Scott South Pole Station celebrates every year on the 21st of June a midwinter party, to celebrate that the Sun is at its lowest point and coming back. The Fremont Solstice Parade takes place every summer solstice in Fremont, Seattle, Washington in the United States. The reconstructed Cahokia Woodhenge, a large timber circle located at the Mississippian culture 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.
Measuring the Unmeasurable
Unlike the equinox, the solstice time is not easy to determine because the changes in solar declination become smaller as the Sun gets closer to its maximum or minimum declination. The days before and after the solstice, the declination speed is less than 30 arcseconds per day which is less than 0.008 degrees 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 in 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 tools. 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 20 degrees or 20 days before and after the summer solstice. Guo Shoujing, a Chinese astronomer, found that the taller the gnomon, the more accurately the journey of the sun could be measured. He designed the gnomon constructed at Gaocheng Astronomical Observatory in 1276. The measurements from Gaocheng determined the length of the year to within one minute of the current measurement, a value in accord with the value of the Gregorian Calendar, but obtained 300 years earlier. Astronomical almanacs define the solstices as the moments when the Sun passes through the solstitial colure, the times when the apparent geocentric celestial longitude of the Sun is equal to 90 degrees for the June solstice or 270 degrees for the December solstice. The dates of the solstice varies each year and may occur a day earlier or later depending on the time zone. Because the earth's orbit takes slightly longer than a calendar year of 365 days, the solstices occur slightly later each calendar year, until a leap day re-aligns the calendar with the orbit. Thus the solstices always occur between June 20 and 22 and between December 20 and 23 in a four-year-long cycle with the 21st and 22nd being the most common dates. Currently, government organizations like USNO and IMCCE publish the date and time of the solstice.
Shifting 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 over time. 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. This precession of the equinoxes means that the constellations the sun appears in at solstices are currently Taurus in June and Sagittarius in December, despite the astrological signs that the sun is entering being rooted in Roman Classical period dates. The system of naming the solstices as the first point of Cancer and first point of Capricorn refers to the astrological signs that the sun is entering, a system that has shifted over millennia due to the slow wobble of Earth's axis. This celestial drift has no special laws to commend it, both are visually verifiable and both follow the same laws of physics, yet the names persist in cultural memory even as the stars themselves move. The solstices, together with the equinoxes, are connected with the seasons, and in some languages they are considered to start or separate the seasons, while 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, and Midsummer's Day, defined as St. Johns Day by the Christian Church, is the 24th of June, about three days after the solstice itself. Similarly the 25th of December is the start of the Christmas celebration, and is the day the Sun begins to return to the Northern Hemisphere. The traditional British and Irish main rent and meeting days of the year, the usual quarter days, were often those of the solstices and equinoxes.