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Solstices occur twice a year, when the tilt of the Earth's axis is oriented directly towards or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes. The name is derived from the Latin sol (sun) and sistere (to stand still), because at the solstices, the Sun stands still in declination; that is, its apparent movement north or south comes to a standstill. Solstice may refer to: solstice, an astronomical phenomenon, marking the seasons. ... The summer solstice also known as the summer alignment may refer to: Summer solstice Summer Solstice: Bee Stings Summer Solstice (album) or these solstice celebrations: Xiazhi (夏至), solar term in East Asia. ... ... For other uses, see Equinox (disambiguation). ... Sol redirects here. ... For other uses, see Latins and Latin (disambiguation). ... In astronomy, declination (abbrev. ...

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 English, in the Northern hemisphere, for example, the period around the June solstice is known as midsummer, and Midsummer's Day is 24 June, about three days after the solstice itself). Similarly 25 December is the start of the Christmas celebration, which was a Pagan festival in pre-Christian times, and is the day the sun begins to return back to the northern hemisphere. For other uses, see Equinox (disambiguation). ... Midsummer may refer to the period of time centered upon the summer solstice and the diverse celebrations of it around the world, but more often refers to European celebrations that accompany the summer solstice, or to Western festivals that take place in June and are usually related to Saint John... is the 175th day of the year (176th in leap years) in the Gregorian calendar. ... is the 359th day of the year (360th in leap years) in the Gregorian calendar. ... For other uses, see Christmas (disambiguation). ... Pagan may refer to: A believer in Paganism or Neopaganism Bagan, a city in Myanmar also known as Pagan Pagan (album), the 6th album by Celtic metal band Cruachan Pagan Island, of the Northern Mariana Islands Pagan Lorn, a metal band from Luxembourg, Europe (1994-1998) Pagans Mind, is...

Heliocentric view of the seasons

Illumination of Earth by Sun at the northern solstice. Download high resolution version (1560x1024, 412 KB) Illumination of Earth by Sun on the day of summer solstice on northern hemisphere. ...

Illumination of Earth by Sun at the southern solstice. Download high resolution version (1560x1024, 427 KB) Illumination of Earth by Sun on the day of winter solstice on northern hemisphere. ...

Diagram of the Earth's seasons as seen from the north. Far right: southern solstice Image File history File links Download high resolution version (2000x1100, 213 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Equinox Season ...

Diagram of the Earth's seasons as seen from the south. Far left: northern solstice Image File history File links Download high resolution version (2000x1100, 193 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Equinox Season ...

The cause of the seasons is that the Earth's axis of rotation is not perpendicular to its orbital plane (the flat plane made through the center of mass (barycenter) of the solar system (near or within the Sun) and the successive locations of Earth during the year), but currently makes an angle of about 23.44° (called the "obliquity of the ecliptic"), and that the axis keeps its orientation with respect to inertial space. As a consequence, for half the year (from around 20 March to 22 September) the northern hemisphere tips to the Sun, with the maximum around 21 June, while for the other half year the southern hemisphere has this distinction, with the maximum around 21 December. The two moments when the inclination of Earth's rotational axis has maximum effect are the solstices. In physics, the center of mass of a system of particles is a specific point at which, for many purposes, the systems mass behaves as if it was concentrated. ... The Obliquity of the ecliptic is the angle between the plane of the Earths equator and the ecliptic plane in which the Earth rotates around the Sun. ... In physics, the expression inertial space refers to the background reference that is provided by the phenomenon of inertia. ... is the 79th day of the year (80th in leap years) in the Gregorian calendar. ... is the 265th day of the year (266th in leap years) in the Gregorian calendar. ... is the 172nd day of the year (173rd in leap years) in the Gregorian calendar. ... is the 355th day of the year (356th in leap years) in the Gregorian calendar. ...

The table at the top of the article gives the instances of equinoxes and solstices over several years. Refer to the equinox article for some remarks. For other uses, see Equinox (disambiguation). ...

During the northern solstice the Sun appears to be directly overhead at noon for places situated at latitude 23.44° north, known as the tropic of Cancer. Likewise during the southern solstice the same thing happens for latitude 23.44° south, known as the tropic of Capricorn. All places on Earth in between these two latitudes are known as the tropics and will see the Sun in the zenith at least two days in the year. For the novel by Henry Miller, see Tropic of Cancer (novel). ... World map showing the Tropic of Capricorn For the novel by Henry Miller, see Tropic of Capricorn (novel). ... A noontime scene from the Philippines on a day when the Sun is almost directly overhead. ... In broad terms, the zenith is the direction pointing directly above a particular location (perpendicular, orthogonal). ...

Also during the northern solstice places situated at latitude 66.56° north, known as the Arctic Circle 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 at latitude 66.56° south, known as the Antarctic Circle 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 southern solstice the effects on both hemispheres are just the opposite. For the fast food restaurant chain, see Arctic Circle Restaurants. ... The midnight sun at Nordkapp, Norway. ... Zoomable PDF of the map this is based on The Antarctic Circle is one of the five major circles of latitude that mark maps of the Earth. ... The polar night is the night lasting more than 24 hours, usually inside the polar circles. ...

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 cause of summer heat and winter cold. Image File history File links Download high-resolution version (540x635, 167 KB) [edit] Summary [edit] Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... Image File history File links Download high-resolution version (540x635, 167 KB) [edit] Summary [edit] Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... For other uses, see Watt (disambiguation). ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... For the usage in virology, see temperate (virology). ...

Further information: effect of sun angle on climate

The seasons are not caused by the varying distance of Earth to the Sun due to the orbital eccentricity of the Earth's orbit. This variation does make such a contribution, but is small compared to the effects of exposure because of Earth's tilt. Currently the Earth reaches perihelion at the beginning of January, which is during the northern winter and the southern summer. The Sun, being closer to Earth and therefore hotter, does not cause the whole planet to enter summer. Although it is true that the northern winter is somewhat warmer than the southern winter, the placement of the continents, ice-covered Antarctica in particular, may also play an important factor. In the same way, during 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 minor effects. Figure 1 This is a diagram of the seasons. ... (This page refers to eccitricity in astrodynamics. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ...

Due to Milankovitch cycles, the Earth's axial tilt and orbital eccentricity will change over thousands of years. Thus in 10,000 years one would find that Earth's northern winter occurs at aphelion and its northern summer at perihelion. The severity of seasonal change — the average temperature difference between summer and winter in location — will also change over time because the Earth's axial tilt fluctuates between 22.1 and 24.5 degrees.
Milankovitch cycles are the collective effect of changes in the Earths movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković. The eccentricity, axial tilt, and precession of the Earths orbit vary in several patterns, resulting in 100,000 year ice age cycles of the... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ...

Geocentric view of the seasons

Day arcs at 0° latitude, equator

Day arcs at 20° latitude

Day arcs at 50° latitude

Day arcs at 70° latitude

Day arcs at 90° latitude, pole

The explanation given in the previous section is useful for observers in outer space. They would see how the Earth revolves around the Sun and how the distribution of sunlight on the planet would change over the year. To observers on Earth, it is also useful to see how the Sun seems to revolve around them. These pictures show such a perspective as follows. They show the day arcs of the Sun, the paths the Sun tracks along the celestial dome in its diurnal movement. The pictures show this for every hour on both solstice days. The longer arc is always 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. Image File history File links Download high-resolution version (2000x1500, 298 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... Image File history File links Download high-resolution version (2000x1500, 298 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... Image File history File links Download high-resolution version (2000x1500, 282 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... Image File history File links Download high-resolution version (2000x1500, 282 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... Image File history File links Download high-resolution version (2000x1500, 289 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... Image File history File links Download high-resolution version (2000x1500, 289 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... Image File history File links Download high-resolution version (2000x1500, 296 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... Image File history File links Download high-resolution version (2000x1500, 296 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... Image File history File links Download high-resolution version (2000x1500, 256 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... Image File history File links Download high-resolution version (2000x1500, 256 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Solstice ... Diurnal motion is an astronomical term referring to the apparent daily motion of stars in orbit around the Earth, caused by the Earths rotation around its axis. ...

In addition, some 'ghost' suns are indicated below the horizon, as much as 18° down. The Sun in this 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. For other uses, see Twilight (disambiguation). ...

• 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 rise 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 following special cases are depicted. In astronomy, the culmination, at a given point, of a planet, star, constellation, etc. ...

• On the equator the Sun is not overhead every day, as some people think. In fact that happens only on two days of the year, the equinoxes. The solstices are the dates that the Sun stays farthest away from the zenith, only reaching an altitude of 66.56° either to the north or the south. The only thing special about the equator is that all days of the year, solstices included, have roughly the same length of about 12 hours, so that it makes no sense to talk about summer and winter. Instead, tropical areas often have 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° means that the culmination takes place at an altitude of 86.56° in the opposite cardinal direction. For example in the southern hemisphere, the Sun remains in the north during winter, but can reach over the zenith to the south 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 does not rise more than 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. Likewise is the difference in direction of sunrise and sunset. Also note the different steepness of the daily path of the Sun above the horizon in summer and winter. It is much shallower in winter. Therefore not only is the Sun not reaching as high, it also seems not to be in a hurry to do so. But conversely this means that in summer the Sun is not in a hurry to dip deeply below 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 continues the whole night. This phenomenon is known as the white nights. And above 66° latitude, of course, one would 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, during the winter the Sun does not rise above the horizon, it is the polar night. There will be still 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. All the time the Sun is 23.44° above or below the horizon, depending on whether it is the summer or winter solstice. In the latter case, that is enough to not even have any twilight. All directions are north at the South Pole and south at the North pole. There is also no south at the South Pole, no north at the North Pole, and neither east nor west is discernible at either pole.

Due to atmospheric refraction, the Sun may already appear above the horizon when the real, geometric Sun is still below it. World map showing the equator in red For other uses, see Equator (disambiguation). ... In broad terms, the zenith is the direction pointing directly above a particular location (perpendicular, orthogonal). ... An astronomer or astrophysicist is a scientist whose area of research is astronomy or astrophysics. ... The midnight sun at Nordkapp, Norway. ... Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of altitude. ...

Cultural aspects

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 December solstice, Christmas is the most popular holiday to have arisen. In addition, Yalda, Saturnalia, Karachun, Hanukkah, Kwanzaa and Yule (see winter solstice for more) are also celebrated around this time. For the June solstice, Catholic and Nordic Protestant cultures celebrate the feast of St. John from June 23 to June 24 (see St. John's Eve, Ivan Kupala Day, Midsummer), while the Wiccan culture observes Litha or Summer Solstice. For the vernal (spring) equinox, several spring-time festivals are celebrated, such as the observance in Judaism of Passover. 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. For other uses, see Christmas (disambiguation). ... A variety of foodstuff that are consumed on Yalda Yaldā also known as Shab-e Cheleh is celebrated on the eve of the first day of the winter (December 21) in the Iranian calendar, which falls on the Winter Solstice. ... For other uses, see Saturnalia (disambiguation). ... Karachun, Korochun or Kračún is a Slavic version of Halloween as a day when the Black God and other evil spirits are most potent. ... Grand Rabbi Israel Abraham Portugal of Skulen Hasidism lighting Hanukkah lights Hanukkah (‎, alt. ... Kwanzaa (or Kwaanza) is a week-long Pan-African festival primarily honoring African-American heritage. ... For other uses, see Yule (disambiguation) and Jul (disambiguation). ... This article is about the astronomical and cultural event of winters solstice, also known as midwinter. ... For the hip-hop producer with the same name, see John the Baptist (producer). ... is the 174th day of the year (175th in leap years) in the Gregorian calendar. ... is the 175th day of the year (176th in leap years) in the Gregorian calendar. ... The evening of June 23, St. ... Night on the Eve of Ivan Kupala, by Henryk Hector Siemiradzki. ... Midsummer may refer to the period of time centered upon the summer solstice and the diverse celebrations of it around the world, but more often refers to European celebrations that accompany the summer solstice, or to Western festivals that take place in June and are usually related to Saint John... For other uses, see Wicca (disambiguation). ... Litha, the entire light half of the year, is centered upon Midsummer, with which it is easily identified, so that the summer solstice holiday is often referred to as Litha, especially in the recreated calendar used in the revived Germanic religion of Asatru. ... This article or section does not cite its references or sources. ... This article is about the Jewish holiday. ... Sukkot (Hebrew:  ; booths. ... A cross-quarter day is a day falling halfway between one of the four main solar events (two solstices and two equinoxes) and the next one. ...

In many cultures the solstices and equinoxes traditionally determine the midpoint of the seasons, which can be seen in the celebrations called midsummer and midwinter. Along this vein, the Japanese celebrate the start of each season with an occurrence known as Setsubun. In modern western culture, the solstices and equinoxes are instead designated the beginning of each season,^{[citation needed]} as the cumulative cooling and warming that result from the tilt of the planet become most pronounced after the solstices. This article is about divisions of a year. ... Midsummer may refer to the period of time centered upon the summer solstice and the diverse celebrations of it around the world, but more often refers to European celebrations that accompany the summer solstice, or to Western festivals that take place in June and are usually related to Saint John... Illumination of Earth by Sun on the day of the northern winter solstice In astronomy, the winter solstice is the moment when the earth is at a point in its orbit where one hemisphere is most inclined away from the sun. ... Setsubun, Tokuan shrine In Japan, Setsubun (節分) is the day before the beginning of each season. ...

In the Hindu calendar, two sidereal solstices are named Uttarayana and 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 Mesha, a zodiacal sign which corresponded with Aries about 285, and into Tula, the opposite zodiacal sign which corresponded with Libra about 285. A page from the Hindu calendar 1871-72. ... For the kite-flying festival, see Makar Sankranti Uttarāyana (उत्तरायण) is the six month period between Makar Sankranti around (January 14) and Karka Sankranti around (July 14), when the Sun travels towards north on the celestial sphere. ... is the 14th day of the year in the Gregorian calendar. ... is the 195th day of the year (196th in leap years) in the Gregorian calendar. ... For other uses, see Zodiac (disambiguation). ... The precession of Earths axis of rotation with respect to inertial space is also called the precession of the equinoxes. ... Aries, the ram, is the first astrological sign of the zodiac and its origins are from the Aries constellation. ... This article is about the year. ... The golden scales Libra is the seventh astrological sign in the Zodiac, originating from the constellation of Libra. ... This article is about the year. ...

See also

• Midsummer
• Winter solstice

Midsummer may refer to the period of time centered upon the summer solstice and the diverse celebrations of it around the world, but more often refers to European celebrations that accompany the summer solstice, or to Western festivals that take place in June and are usually related to Saint John... This article is about the astronomical and cultural event of winters solstice, also known as midwinter. ...

References and external links

Look up solstice in
Wiktionary, the free dictionary.

Wikimedia Commons has media related to:

Solstices

Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 151 languages. ...

Calculations, plots and tables

• Earth's Seasons, Equinoxes, Solstices, Perihelion, and Aphelion, 2000–2020 (from the United States Naval Observatory's Astronomical Applications Department)
• Plot that shows how the date of the summer solstice shifts through the Gregorian calendar
• Solstice Dates and Times
• Solstice, Equinox & Cross-Quarter Moments for 2006 and other years, for several timezones
• Calculation of Length of Day (Formulas and Graphs)
• Calculate the Time of Solstices in Excel, CAD or your other programs. The Sun API is free and extremely accurate. For Windows Computers.

Aerial view of USNO. The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States. ...

Debate about season start

• The seasons begin at the time of the solstice or equinox (from the Bad Astronomer)
• Solstice does not signal season's start? (from The Straight Dope)

Dr. Philip Plait (a. ... Cecil Adams is the pen name of the author of The Straight Dope since 1973, a popular question and answer column published in The Chicago Reader, syndicated in thirty newspapers in the United States and Canada, and available online. ...

Pictures and videos

• NASA picture of day, winter solstice
• Video of Winter Solstices Celebration at Stonehenge

v • d • e Time measurement and standards Major subjects Time · Chronometry · Orders of magnitude · Units of time · Metrology Time Portal International standards UTC · UT · TAI · ISO 31-1 · Second · DUT1 · Leap second · IERS Terrestrial Time · Geocentric Coordinate Time · Barycentric Coordinate Time A time scale specifies divisions of time. ... This article is about the concept of time. ... Wikipedia does not yet have an article with this exact name. ... // The pages linked in the right-hand column contain lists of times that are of the same order of magnitude (power of ten). ... Metrology (from Greek metron (measure), and -logy) is the science of measurement. ... Image File history File links Portal. ... UTC redirects here. ... Universal Time (UT) is a timescale based on the rotation of the Earth. ... International Atomic Time (TAI, from the French name Temps Atomique International) is a high-precision atomic time standard that tracks proper time on Earths geoid. ... ISO 31-1 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to space and time. ... This article is about the unit of time. ... The time correction DUT1 is the difference between the Universal Time scale UT1 (which corresponds to the Earths rotation) and the Coordinated Universal Time (UTC) (which corresponds, except for a constant offset, to International Atomic Time (TAI)). DUT1 = UT1 - UTC DUT1 is maintained in the range -0. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... The International Earth Rotation and Reference Systems Service is the body responsible for maintaining global time and reference frame standards, notably through its Earth Orientation Parameter (EOP) and International Celestial Reference System (ICRS) groups. ... Terrestrial Time (TT) is the modern time standard for time on the surface of the Earth. ... Geocentric Coordinate Time (TCG) is a coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to precession, nutation, the Moon, and artificial satellites of the Earth. ... Barycentric Coordinate Time (TCB) was defined in 1991 by the International Astronomical Union as one of the replacements for the ill-defined Barycentric Dynamical Time (TDB). ... Civil time · Minute · Hour · 12-hour clock · 24-hour clock · ISO 8601 Civil time is another name for mean solar time reckoned from midnight. ... This article is about the unit of time, angle and right ascension. ... The hour (symbol: h) is a unit of time. ... The 12-hour clock is a timekeeping convention in which the 24 hours of the day are divided into two periods called ante meridiem (a. ... The 24-hour clock is a convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, numbered from 0 to 23. ... ISO 8601 is an international standard for date and time representations issued by the International Organization for Standardization (ISO). ... International Date Line · Solar time · Time zone · Daylight saving time · Time offset · Annum Obsolete standards Ephemeris time · Barycentric Dynamical Time · Greenwich Mean Time · Prime Meridian Time in physics Spacetime · Chronon · Cosmological decade · Planck epoch · Planck time · T-symmetry Theory of relativity · Time dilation · Gravitational time dilation · Coordinate time · Proper time “Date line” redirects here. ... Solar time is based on the idea that when the sun reaches its highest point in the sky, it is noon. ... Timezone and TimeZone redirect here. ... Although DST is common in Europe and North America, most of the worlds people do not use it. ... A time offset is defined by international convention as a number of hours and minutes from Coordinated Universal Time in Greenwich, England. ... Annum is a Latin noun meaning year. ... Ephemeris Time (ET) is a now obsolete time scale used in ephemerides of celestial bodies, in particular the Sun (as observed from the Earth), Moon, planets, and other members of the solar system. ... Barycentric Dynamical Time (TDB) was defined by the International Astronomical Union (IAU) in 1976 to be used as the relativistic replacement for the non-relativistic Ephemeris Time which had been used in the ephemerides starting in 1960. ... GMT redirects here. ... Location of the Prime Meridian Image:Prime Meridian. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... For other uses of this term, see Spacetime (disambiguation). ... A chronon is a hypothetical concept in theoretical physics intended to describe a quantum of time. ... A cosmological decade ( CÐ ) is a division of the lifetime of the cosmos. ... Named after Max Planck, in cosmology the Planck epoch (or Planck Era) is the earliest period of time in the history of the universe, from zero to 10-43 seconds (one Planck time), during which all four fundamental forces were unified and elementary particles did not yet exist. ... In physics, the Planck time (tP), is the unit of time in the system of natural units known as Planck units. ... T-symmetry is the symmetry of physical laws under a time-reversal transformation— The universe is not symmetric under time reversal, although in restricted contexts one may find this symmetry. ... -1... Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... Gravitational time dilation is a consequence of Albert Einsteins theories of relativity and related theories which causes time to pass at different rates in regions of a different gravitational potential; the higher the local distortion of spacetime due to gravity, the slower time passes. ... Coordinate time is the interval of time independent of relativistic time dilation. ... In relativity, proper time is time measured by a single clock between events that occur at the same place as the clock. ... Time domain · Continuous time · Discrete time · Absolute time and space Horology Clock · Astrarium · Atomic clock · Hourglass · Marine chronometer · Radio clock · Sundial · Watch · Water clock History of timekeeping devices · Equation of time · Complication Calendar Day · Week · Month · Year · Decade · Century · Millennium Astronomical · Julian · Gregorian · Islamic · Lunisolar · Solar · Lunar · Epact · Intercalation · Leap year Time-domain is a term used to describe the analysis of mathematical functions, or real-life signals, with respect to time. ... A continuous signal or a continuous time signal is a varying quantity (a signal) that can be, or is expressed, as a continuous function of an independent variable, usually time. ... Discrete time is non-continuous time. ... In physics, the concept of absolute time and absolute space are hypothetical models in which time either runs at the same rate for all the observers in the universe or the rate of time of each observer can be scaled to the absolute time by multiplying the rate by a... Horology is the study of the science and art of timekeeping devices. ... For other uses, see Clock (disambiguation). ... An astrarium, also called a planetarium, is the mechanical representation of the cyclic nature of astronomical objects in one timepiece. ... “Nuclear Clock” redirects here. ... For other uses, see Hourglass (disambiguation). ... A marine chronometer is a timekeeper precise enough to be used as a portable time standard, used to determine longitude by means of celestial navigation. ... A radio clock A radio clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock. ... For other uses, see Sundial (disambiguation). ... For other uses, see Watch (disambiguation). ... A water clock or clepsydra is a device for measuring time by letting water regularly flow out of a container usually by a tiny aperture. ... The equation of time is the difference, over the course of a year, between time as read from a sundial and a clock. ... In horology terms, a complication in a mechanical timepiece is any feature beyond that of a simple hours, minutes, and seconds movement. ... For other uses, see Calendar (disambiguation) A page from the Hindu calendar 1871–1872. ... Look up day in Wiktionary, the free dictionary. ... For more details on each day of the week, see days of the week. ... Look up Month in Wiktionary, the free dictionary. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... For other senses of this word, see decade (disambiguation). ... A century (From the Latin cent, one hundred) is one hundred consecutive years. ... A millennium (pl. ... Astronomical year numbering is based on BCE/CE (or BC/AD) year numbering, but follows normal decimal integer numbering more strictly. ... The Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). ... For the calendar of religious holidays and periods, see liturgical year. ... The Islamic calendar or Muslim calendar (Arabic: التقويم الهجري; at-taqwÄ«m al-hijrÄ«; Persian: تقویم هجري قمری ‎ taqwÄ«m-e hejri-ye qamari; also called the Hijri calendar) is the calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate... A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. ... A solar calendar is a calendar whose dates indicate the position of the earth on its revolution around the sun (or equivalently the apparent position of the sun moving on the celestial sphere). ... A lunar calendar is a calendar that is based on cycles of the moon phase. ... The epact (from Greek: epaktai hèmerai = added days) is, as the second Canon of the Gregorian Calendar reform puts it, nothing else than the number of days which the common solar year of 365 days surpasses the common lunar year of 354 days (Latin: Epacta nihil aliud est quam... Intercalation is the insertioffn of an extra day, week or month into some calendar years to make the calendar follow the seasons. ... For the 1921 film starring Fatty Arbuckle, see Leap Year (film). ... 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