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42-837: The concept of "Rinan" ( lit "South of the Sun", referring to the Southern Hemisphere) was originally astronomical: above the Tropic of Cancer , the Chinese always faced south during religious ceremonies concerning the sun. In his Records of the Grand Historian , Sima Qian claimed the Qin dynasty had expanded so far as Rinan , where the houses faced north instead of south. The Han claimed this conceptual region as early as 111 BC upon their conquest of Nanyue but did not administer an actual district under

84-507: A millennium . This wobble means that the Tropic of Cancer is currently drifting southward at a rate of almost half an arcsecond (0.468″) of latitude, or 15 m (49 ft), per year. The circle's position was at exactly 23° 27′N in 1917 and will be at 23° 26'N in 2045. The distance between the Antarctic Circle and the Tropic of Cancer is essentially constant as they move in tandem. This

126-490: A particular equinox, that is, the equinox of a particular date, known as an epoch ; the coordinates are referred to the direction of the equinox at that date. For instance, the Astronomical Almanac lists the heliocentric position of Mars at 0h Terrestrial Time , 4 January 2010 as: longitude 118°09′15.8″, latitude +1°43′16.7″, true heliocentric distance 1.6302454 AU, mean equinox and ecliptic of date. This specifies

168-556: A period of about 26,000 years, a process known as lunisolar precession , as it is due mostly to the gravitational effect of the Moon and Sun on Earth's equatorial bulge . Likewise, the ecliptic itself is not fixed. The gravitational perturbations of the other bodies of the Solar System cause a much smaller motion of the plane of Earth's orbit, and hence of the ecliptic, known as planetary precession . The combined action of these two motions

210-429: A periodic component to the position of the equinoxes; the positions of the celestial equator and (March) equinox with fully updated precession and nutation are called the true equator and equinox ; the positions without nutation are the mean equator and equinox . Obliquity of the ecliptic is the term used by astronomers for the inclination of Earth's equator with respect to the ecliptic, or of Earth's rotation axis to

252-403: A perpendicular to the ecliptic. It is about 23.4° and is currently decreasing 0.013 degrees (47 arcseconds) per hundred years because of planetary perturbations. The angular value of the obliquity is found by observation of the motions of Earth and other planets over many years. Astronomers produce new fundamental ephemerides as the accuracy of observation improves and as the understanding of

294-474: Is also used occasionally; the x -axis is directed toward the March equinox, the y -axis 90° to the east, and the z -axis toward the north ecliptic pole; the astronomical unit is the unit of measure. Symbols for ecliptic coordinates are somewhat standardized; see the table. Ecliptic coordinates are convenient for specifying positions of Solar System objects, as most of the planets' orbits have small inclinations to

336-439: Is an important reference plane and is the basis of the ecliptic coordinate system . The ecliptic is the apparent path of the Sun throughout the course of a year . Because Earth takes one year to orbit the Sun, the apparent position of the Sun takes one year to make a complete circuit of the ecliptic. With slightly more than 365 days in one year, the Sun moves a little less than 1° eastward every day. This small difference in

378-516: Is based on an assumption of a constant equator, but the precise location of the equator is not truly fixed. See: equator , axial tilt and circles of latitude for additional details. Download coordinates as: North of the tropic are the subtropics and the North Temperate Zone . The equivalent line of latitude south of the Equator is called the Tropic of Capricorn , and the region between

420-454: Is called general precession , and changes the position of the equinoxes by about 50 arc seconds (about 0.014°) per year. Once again, this is a simplification. Periodic motions of the Moon and apparent periodic motions of the Sun (actually of Earth in its orbit) cause short-term small-amplitude periodic oscillations of Earth's axis, and hence the celestial equator, known as nutation . This adds

462-486: Is divided into 12 signs of 30° longitude, each of which approximates the Sun's motion in one month. In ancient times, the signs corresponded roughly to 12 of the constellations that straddle the ecliptic. These signs are sometimes still used in modern terminology. The " First Point of Aries " was named when the March equinox Sun was actually in the constellation Aries ; it has since moved into Pisces because of precession of

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504-530: Is near an ascending or descending node at the same time it is at conjunction ( new ) or opposition ( full ). The ecliptic is so named because the ancients noted that eclipses only occur when the Moon is crossing it. The exact instants of equinoxes and solstices are the times when the apparent ecliptic longitude (including the effects of aberration and nutation ) of the Sun is 0°, 90°, 180°, and 270°. Because of perturbations of Earth's orbit and anomalies of

546-565: The Equator . Its Southern Hemisphere counterpart, marking the most southerly position at which the Sun can be seen directly overhead, is the Tropic of Capricorn . These tropics are two of the five major circles of latitude that mark maps of Earth, the others being the Arctic and Antarctic circles and the Equator . The positions of these two circles of latitude (relative to the Equator) are dictated by

588-707: The Northern Tropic , is the Earth 's northernmost circle of latitude where the Sun can be seen directly overhead . This occurs on the June solstice , when the Northern Hemisphere is tilted toward the Sun to its maximum extent. It also reaches 90 degrees below the horizon at solar midnight on the December Solstice . Using a continuously updated formula, the circle is currently 23°26′09.8″ (or 23.43605°) north of

630-405: The dynamics increases, and from these ephemerides various astronomical values, including the obliquity, are derived. Until 1983 the obliquity for any date was calculated from work of Newcomb , who analyzed positions of the planets until about 1895: ε = 23°27′08.26″ − 46.845″ T − 0.0059″ T + 0.00181″ T where ε is the obliquity and T is tropical centuries from B1900.0 to

672-407: The mean equinox of 4 January 2010 0h TT as above , without the addition of nutation. Because the orbit of the Moon is inclined only about 5.145° to the ecliptic and the Sun is always very near the ecliptic, eclipses always occur on or near it. Because of the inclination of the Moon's orbit, eclipses do not occur at every conjunction and opposition of the Sun and Moon, but only when the Moon

714-526: The Earth–Moon center of mass , the apparent path of the Sun wobbles slightly, with a period of about one month . Because of further perturbations by the other planets of the Solar System , the Earth–Moon barycenter wobbles slightly around a mean position in a complex fashion. Because Earth's rotational axis is not perpendicular to its orbital plane , Earth's equatorial plane is not coplanar with

756-421: The Solar System orbit the Sun in nearly the same plane. This is likely due to the way in which the Solar System formed from a protoplanetary disk . Probably the closest current representation of the disk is known as the invariable plane of the Solar System . Earth's orbit, and hence, the ecliptic, is inclined a little more than 1° to the invariable plane, Jupiter's orbit is within a little more than ½° of it, and

798-423: The Sun's position against the stars causes any particular spot on Earth's surface to catch up with (and stand directly north or south of) the Sun about four minutes later each day than it would if Earth did not orbit; a day on Earth is therefore 24 hours long rather than the approximately 23-hour 56-minute sidereal day . Again, this is a simplification, based on a hypothetical Earth that orbits at uniform speed around

840-412: The Sun. The actual speed with which Earth orbits the Sun varies slightly during the year, so the speed with which the Sun seems to move along the ecliptic also varies. For example, the Sun is north of the celestial equator for about 185 days of each year, and south of it for about 180 days. The variation of orbital speed accounts for part of the equation of time . Because of the movement of Earth around

882-456: The Tropic of Cancer experience two distinct seasons: an extremely hot summer with temperatures often reaching 45 °C (113 °F) and a warm winter with maxima around 22 °C (72 °F). Much land on or near the Tropic of Cancer is part of the Sahara Desert , while to the east, the climate is torrid monsoonal with a short wet season from June to September, and very little rainfall for

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924-461: The calendar , the dates of these are not fixed. The ecliptic currently passes through the following thirteen constellations : There are twelve constellations that are not on the ecliptic, but are close enough that the Moon and planets can occasionally appear in them. The ecliptic forms the center of the zodiac , a celestial belt about 20° wide in latitude through which the Sun, Moon, and planets always appear to move. Traditionally, this region

966-410: The celestial equator. Spherical coordinates , known as ecliptic longitude and latitude or celestial longitude and latitude, are used to specify positions of bodies on the celestial sphere with respect to the ecliptic. Longitude is measured positively eastward 0° to 360° along the ecliptic from the March equinox, the same direction in which the Sun appears to move. Latitude is measured perpendicular to

1008-718: The date in question. From 1984, the Jet Propulsion Laboratory's DE series of computer-generated ephemerides took over as the fundamental ephemeris of the Astronomical Almanac . Obliquity based on DE200, which analyzed observations from 1911 to 1979, was calculated: ε = 23°26′21.45″ − 46.815″ T − 0.0006″ T + 0.00181″ T where hereafter T is Julian centuries from J2000.0 . JPL's fundamental ephemerides have been continually updated. The Astronomical Almanac for 2010 specifies: ε = 23°26′21.406″ − 46.836769″ T − 0.0001831″ T + 0.00200340″ T − 0.576×10 ″ T − 4.34×10 ″ T These expressions for

1050-404: The distance is set to a rounded value of at least 36,770 kilometres (22,850 mi). Ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth around the Sun . From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic against the background of stars . The ecliptic

1092-405: The ecliptic plane, but is inclined to it by an angle of about 23.4°, which is known as the obliquity of the ecliptic . If the equator is projected outward to the celestial sphere , forming the celestial equator , it crosses the ecliptic at two points known as the equinoxes . The Sun, in its apparent motion along the ecliptic, crosses the celestial equator at these points, one from south to north,

1134-412: The ecliptic, and therefore always appear relatively close to it on the sky. Because Earth's orbit, and hence the ecliptic, moves very little, it is a relatively fixed reference with respect to the stars. Because of the precessional motion of the equinox , the ecliptic coordinates of objects on the celestial sphere are continuously changing. Specifying a position in ecliptic coordinates requires specifying

1176-436: The ecliptic, to +90° northward or −90° southward to the poles of the ecliptic, the ecliptic itself being 0° latitude. For a complete spherical position, a distance parameter is also necessary. Different distance units are used for different objects. Within the Solar System, astronomical units are used, and for objects near Earth , Earth radii or kilometers are used. A corresponding right-handed rectangular coordinate system

1218-496: The fact that the Sun appears to "turn back" at the solstices. The Tropic of Cancer's position is not fixed, but constantly changes because of a slight wobble in the Earth's longitudinal alignment relative to the ecliptic , the plane in which the Earth orbits around the Sun. Earth's axial tilt varies over a 41,000-year period from about 22.1 to 24.5 degrees, and as of 2000 is about 23.4 degrees, which will continue to remain valid for about

1260-479: The following 17 countries (including two disputed territories) and 8 water bodies, starting at the prime meridian and heading eastward: The climate at the Tropic of Cancer is generally hot and dry, except for cooler highland regions in China, marine environments such as Hawaii, and easterly coastal areas, where orographic rainfall can be very heavy, in some places reaching 4 metres (160 in) annually. Most regions on

1302-572: The name until 48 BC. Under the Western Han , it was recorded as having 14,000 households or about 69,000 people. Several embassies from Rome ( Da Qin ) during the 1st and 2nd centuries – including one from Marcus Aurelius in AD 166 – are recorded as having come via Rinan, presumably by sea via India . In AD 264, during the division of Jiaozhou by the Emperor Jing of Wu , Rinan

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1344-408: The obliquity are intended for high precision over a relatively short time span, perhaps several centuries. J. Laskar computed an expression to order T good to 0.04″ /1000 years over 10,000 years. All of these expressions are for the mean obliquity, that is, without the nutation of the equator included. The true or instantaneous obliquity includes the nutation. Most of the major bodies of

1386-463: The other from north to south. The crossing from south to north is known as the March equinox , also known as the first point of Aries and the ascending node of the ecliptic on the celestial equator. The crossing from north to south is the September equinox or descending node . The orientation of Earth's axis and equator are not fixed in space, but rotate about the poles of the ecliptic with

1428-457: The other major planets are all within about 6°. Because of this, most Solar System bodies appear very close to the ecliptic in the sky. The invariable plane is defined by the angular momentum of the entire Solar System, essentially the vector sum of all of the orbital and rotational angular momenta of all the bodies of the system; more than 60% of the total comes from the orbit of Jupiter. That sum requires precise knowledge of every object in

1470-678: The rest of the year. The highest mountain on or adjacent to the Tropic of Cancer is Yu Shan in Taiwan . It had glaciers descending as low as 2,800 metres (9,190 ft) during the Last Glacial Maximum . At present glaciers still exist around the Tropic. The nearest currently surviving are the Minyong and Baishui in the Himalayas to the north and on Iztaccíhuatl in Mexico to the south. According to

1512-488: The rules of the Fédération Aéronautique Internationale , for a flight to compete for a round-the-world speed record, it must cover a distance no less than the length of the Tropic of Cancer, cross all meridians , and end on the same airfield where it started. The length of the Tropic of Cancer is 36,788 km (22,859 mi): For an ordinary circumnavigation the rules are somewhat relaxed and

1554-468: The sky's distant background. The ecliptic forms one of the two fundamental planes used as reference for positions on the celestial sphere, the other being the celestial equator . Perpendicular to the ecliptic are the ecliptic poles , the north ecliptic pole being the pole north of the equator. Of the two fundamental planes, the ecliptic is closer to unmoving against the background stars, its motion due to planetary precession being roughly 1/100 that of

1596-460: The system, making it a somewhat uncertain value. Because of the uncertainty regarding the exact location of the invariable plane, and because the ecliptic is well defined by the apparent motion of the Sun, the ecliptic is used as the reference plane of the Solar System both for precision and convenience. The only drawback of using the ecliptic instead of the invariable plane is that over geologic time scales, it will move against fixed reference points in

1638-402: The tilt of Earth's axis of rotation relative to the plane of its orbit , and since the tilt changes, the location of these two circles also changes. In geopolitics , it is known for being the southern limitation on the mutual defence obligation of NATO , as member states of NATO are not obligated to come to the defence of territory south of the Tropic of Cancer. When this line of latitude

1680-401: The two, centered on the Equator, is the tropics . In the year 2000, more than half of the world's population lived north of the Tropic of Cancer. On the Tropic of Cancer there are approximately 13 hours, 35 minutes of daylight during the summer solstice. During the winter solstice, there are 10 hours, 41 minutes of daylight. Using 23°26'N for the Tropic of Cancer, the tropic passes through

1722-522: Was named in the last centuries BCE , the Sun was in the constellation Cancer ( Latin : Crab ) at the June solstice (90° ecliptic longitude ). Due to the precession of the equinoxes , this is no longer the case; today the Sun is in constellation Taurus at the June solstice. The word "tropic" itself comes from the Greek "trope (τροπή)", meaning turn (change of direction or circumstance), inclination, referring to

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1764-437: Was placed under the new Jiaozhou. This article related to the history of China is a stub . You can help Misplaced Pages by expanding it . This Vietnam -related article is a stub . You can help Misplaced Pages by expanding it . Tropic of Cancer 23°26′12.5″N 0°0′0″W  /  23.436806°N -0.00000°E  / 23.436806; -0.00000  ( Prime Meridian ) The Tropic of Cancer , also known as

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