Equator

Last updated
World location map (equirectangular 180).svg
Equator in the map of Earth
Nations or territories that touch the equator (red) or the Prime meridian (blue) Equator and Prime Meridian.svg
Nations or territories that touch the equator (red) or the Prime meridian (blue)

The equator of a rotating spheroid (such as a planet) is the parallel (circle of latitude) at which latitude is defined to be 0°. It is the imaginary line on the spheroid, equidistant from its poles, dividing it into northern and southern hemispheres. In other words, it is the intersection of the spheroid with the plane perpendicular to its axis of rotation and midway between its geographical poles.

Contents

On Earth, the equator is about 40,075 km (24,901 mi) long, of which 78.8% lies across water and 21.3% over land. Indonesia is the country straddling the greatest length of the equatorial line across both land and sea.

Etymology

The name is derived from medieval Latin word aequator, in the phrase circulus aequator diei et noctis, meaning ‘circle equalizing day and night’, from the Latin word aequare meaning ‘make equal’. [1]

Overview

Equator monument.jpg
Equator sign kenya.jpg
Left: A monument marking the equator near the city of Pontianak, Indonesia
Right: Road sign marking the equator near Nanyuki, Kenya

The latitude of the Earth's equator is, by definition, 0° (zero degrees) of arc. The equator is one of the five notable circles of latitude on Earth; the other four are both polar circles (the Arctic Circle and the Antarctic Circle) and both tropical circles (the Tropic of Cancer and the Tropic of Capricorn). The equator is the only line of latitude which is also a great circle—that is, one whose plane passes through the center of the globe. The plane of Earth's equator, when projected outwards to the celestial sphere, defines the celestial equator.

In the cycle of Earth's seasons, the equatorial plane runs through the Sun twice per year: on the equinoxes in March and September. To a person on Earth, the Sun appears to travel above the equator (or along the celestial equator) at these times. Light rays from the Sun's center are perpendicular to Earth's surface at the point of solar noon on the equator.

The equator marked as it crosses Ilheu das Rolas, in Sao Tome and Principe Equator Sao Tome.jpg
The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe
The Marco Zero monument marking the equator in Macapa, Brazil Equator Line Monument, Macapa city, Brazil.jpg
The Marco Zero monument marking the equator in Macapá, Brazil

Locations on the equator experience the shortest sunrises and sunsets because the Sun's daily path is nearly perpendicular to the horizon for most of the year. The length of daylight (sunrise to sunset) is almost constant throughout the year; it is about 14 minutes longer than nighttime due to atmospheric refraction and the fact that sunrise begins (or sunset ends) as the upper limb, not the center, of the Sun's disk contacts the horizon.

Earth bulges slightly at the equator; the "average" diameter of Earth is 12,750 km (7,920 mi), but the diameter at the equator is about 43 km (27 mi) greater than at the poles. [2]

Sites near the equator, such as the Guiana Space Centre in Kourou, French Guiana, are good locations for spaceports as they have a fastest rotational speed of any latitude, 460 m/s. The added velocity reduces the fuel needed to launch spacecraft eastward (in the direction of Earth's rotation) to orbit, while simultaneously avoiding costly maneuvers to flatten inclination during missions such as the Apollo moon landings. [3]

Geodesy

Precise location

The precise location of the equator is not truly fixed; the true equatorial plane is perpendicular to the Earth's spin axis, which drifts about 9 metres (30 ft) during a year. This effect must be accounted for in detailed geophysical measurements.[ citation needed ]

Exact length

The International Association of Geodesy (IAG) and the International Astronomical Union (IAU) have chosen to use an equatorial radius of 6,378.1366 kilometres (3,963.1903 mi) (codified as the IAU 2009 value). [4] This equatorial radius is also in the 2003 and 2010 IERS Conventions. [5] It is also the equatorial radius used for the IERS 2003 ellipsoid. If it were really circular, the length of the equator would then be exactly 2π times the radius, namely 40,075.0142 kilometres (24,901.4594 mi). The GRS 80 (Geodetic Reference System 1980) as approved and adopted by the IUGG at its Canberra, Australia meeting of 1979 has an equatorial radius of 6,378.137 kilometres (3,963.191 mi). The WGS 84 (World Geodetic System 1984) which is a standard for use in cartography, geodesy, and satellite navigation including GPS, also has an equatorial radius of 6,378.137 kilometres (3,963.191 mi). For both GRS 80 and WGS 84, this results in a length for the equator of 40,075.0167 km (24,901.4609 mi).

The geographical mile is defined as one arc-minute of the equator, so it has different values depending on which radius is assumed. For example, by WSG-84, the distance is 1,855.3248 metres (6,087.024 ft), while by IAU-2000, it is 1,855.3257 metres (6,087.027 ft). This is a difference of less than one millimetre (0.039 in) over the total distance (approximately 1.86 kilometres or 1.16 miles).

The earth is commonly modeled as a sphere flattened 0.336% along its axis. This makes the equator 0.16% longer than a meridian (a great circle passing through the two poles). The IUGG standard meridian is, to the nearest millimetre, 40,007.862917 kilometres (24,859.733480 mi), one arc-minute of which is 1,852.216 metres (6,076.82 ft), explaining the SI standardization of the nautical mile as 1,852 metres (6,076 ft), more than 3 metres (9.8 ft) less than the geographical mile.

The sea-level surface of the Earth (the geoid) is irregular, so the actual length of the equator is not so easy to determine. Aviation Week and Space Technology on 9 October 1961 reported that measurements using the Transit IV-A satellite had shown the equatorial diameter from longitude 11° West to 169° East to be 1,000 feet (300 m) greater than its diameter ninety degrees away.[ citation needed ]

Equatorial countries and territories

Map all coordinates using: OpenStreetMap  
Download coordinates as: KML  ·  GPX
GPS reading taken on the equator close to the Quitsato Sundial, at Mitad del Mundo, Ecuador ECSundialGPS.jpg
GPS reading taken on the equator close to the Quitsato Sundial, at Mitad del Mundo, Ecuador

The equator passes through the land of 11 countries. Starting at the Prime Meridian and heading eastwards, the equator passes through:

Co-ordinatesCountry, territory or seaNotes
0°N0°E / 0°N 0°E / 0; 0 (Prime Meridian) Atlantic Ocean Gulf of Guinea, "Null Island"
0°0′N6°31′E / 0.000°N 6.517°E / 0.000; 6.517 (São Tomé and Príncipe) Flag of Sao Tome and Principe.svg  São Tomé and Príncipe Passing through Pestana Equador resort on the Ilhéu das Rolas
0°0′N9°21′E / 0.000°N 9.350°E / 0.000; 9.350 (Gabon) Flag of Gabon.svg  Gabon Passing 8.9 km (5.5 mi) south of Ayem, 10.6 km (6.6 mi) north of Mayene, Booue
0°0′N13°56′E / 0.000°N 13.933°E / 0.000; 13.933 (Republic of the Congo) Flag of the Republic of the Congo.svg  Republic of the Congo Passing through the town of Makoua.
0°0′N17°46′E / 0.000°N 17.767°E / 0.000; 17.767 (Democratic Republic of the Congo) Flag of the Democratic Republic of the Congo.svg  Democratic Republic of the Congo Passing 9 km (5.6 mi) south of central Butembo
0°0′N29°43′E / 0.000°N 29.717°E / 0.000; 29.717 (Uganda) Flag of Uganda.svg  Uganda Passing 32 km (20 mi) south of central Kampala
0°0′N32°22′E / 0.000°N 32.367°E / 0.000; 32.367 (Lake Victoria) Lake Victoria Passing through some islands of Flag of Uganda.svg  Uganda in Mukono District and Namayingo District
0°0′N34°0′E / 0.000°N 34.000°E / 0.000; 34.000 (Kenya) Flag of Kenya.svg  Kenya Passing 6 km (3.7 mi) north of central Kisumu
0°0′N41°0′E / 0.000°N 41.000°E / 0.000; 41.000 (Somalia) Flag of Somalia.svg  Somalia Passing south of Jamame
0°0′N42°53′E / 0.000°N 42.883°E / 0.000; 42.883 (Indian Ocean) Indian Ocean Passing between Huvadhu Atoll and Fuvahmulah of the Flag of Maldives.svg  Maldives
0°0′N98°12′E / 0.000°N 98.200°E / 0.000; 98.200 (Indonesia) Flag of Indonesia.svg  Indonesia The Batu Islands, Sumatra and the Lingga Islands
0°0′N104°34′E / 0.000°N 104.567°E / 0.000; 104.567 (Karimata Strait) Karimata Strait
0°0′N109°9′E / 0.000°N 109.150°E / 0.000; 109.150 (Indonesia) Flag of Indonesia.svg  Indonesia Borneo (passing through Pontianak)
0°0′N117°30′E / 0.000°N 117.500°E / 0.000; 117.500 (Makassar Strait) Makassar Strait
0°0′N119°40′E / 0.000°N 119.667°E / 0.000; 119.667 (Indonesia) Flag of Indonesia.svg  Indonesia Sulawesi (Celebes)
0°0′N120°5′E / 0.000°N 120.083°E / 0.000; 120.083 (Gulf of Tomini) Gulf of Tomini
0°0′N124°0′E / 0.000°N 124.000°E / 0.000; 124.000 (Molucca Sea) Molucca Sea
0°0′N127°24′E / 0.000°N 127.400°E / 0.000; 127.400 (Indonesia) Flag of Indonesia.svg  Indonesia Kayoa and Halmahera islands
0°0′N127°53′E / 0.000°N 127.883°E / 0.000; 127.883 (Halmahera Sea) Halmahera Sea
0°0′N129°20′E / 0.000°N 129.333°E / 0.000; 129.333 (Indonesia) Flag of Indonesia.svg  Indonesia Gebe and Kawe islands
0°0′N129°21′E / 0.000°N 129.350°E / 0.000; 129.350 (Pacific Ocean) Pacific Ocean Passing between Aranuka and Nonouti atolls, Flag of Kiribati.svg  Kiribati (at 0°0′N173°40′E / 0.000°N 173.667°E / 0.000; 173.667 )
0°0′N80°6′W / 0.000°N 80.100°W / 0.000; -80.100 (Ecuador) Flag of Ecuador.svg  Ecuador Passing 24 km (15 mi) north of central Quito, near Mitad del Mundo, and precisely at the location of Catequilla, a pre-Columbian ruin. Also, Isabela Island in the Galápagos Islands
0°0′N75°32′W / 0.000°N 75.533°W / 0.000; -75.533 (Colombia) Flag of Colombia.svg  Colombia Passing 4.3 km (2.7 mi) north of the border with Peru
0°0′N70°3′W / 0.000°N 70.050°W / 0.000; -70.050 (Brazil) Flag of Brazil.svg  Brazil Amazonas, Roraima, Pará, Amapá (passing slightly south of the city center of the state capital Macapá, and precisely at the Marco Zero monument and the Avenue Equatorial)
0°0′N49°21′W / 0.000°N 49.350°W / 0.000; -49.350 (Atlantic Ocean) Atlantic Ocean At the Perigoso Canal (sv) on the mouth of the Amazon River

Despite its name, no part of Equatorial Guinea lies on the equator. However, its island of Annobón is 155 km (96 mi) south of the equator, and the rest of the country lies to the north.

Equatorial seasons and climate

Diagram of the seasons, depicting the situation at the December solstice. Regardless of the time of day (i.e. the Earth's rotation on its axis), the North Pole will be dark, and the South Pole will be illuminated; see also arctic winter. In addition to the density of incident light, the dissipation of light in the atmosphere is greater when it falls at a shallow angle. Seasons.svg

Diagram of the seasons, depicting the situation at the December solstice. Regardless of the time of day (i.e. the Earth’s rotation on its axis), the North Pole will be dark, and the South Pole will be illuminated; see also arctic winter. In addition to the density of incident light, the dissipation of light in the atmosphere is greater when it falls at a shallow angle.

Seasons result from the tilt of the Earth's axis compared to the plane of its revolution around the Sun. Throughout the year the northern and southern hemispheres are alternately turned either toward or away from the sun depending on Earth's position in its orbit. The hemisphere turned toward the sun receives more sunlight and is in summer, while the other hemisphere receives less sun and is in winter (see solstice).

At the equinoxes, the Earth's axis is perpendicular to the sun rather than tilted toward or away, meaning that day and night are both about 12 hours long across the whole of the Earth.

Near the equator, this means the variation in strength of solar radiation is different relative to the time of year than it is at higher latitudes: Maximum solar radiation is received during the equinoxes, when a place at the equator is under the subsolar point at high noon, and the intermediate seasons of spring and autumn occur at higher latitudes, and the minimum occurs during both solstices, when either pole is tilted towards or away from the sun, resulting in either summer or winter in both hemispheres. This also results in a corresponding movement of the equator away from the subsolar point, which is then situated over or near the relevant tropic circle. Nevertheless, temperatures are high year round due to the earth's axial tilt of 23.5° not being enough to create a low minimum midday declination to sufficiently weaken the sun's rays even during the solstices.

Near the equator there is little temperature change throughout the year, though there may be dramatic differences in rainfall and humidity. The terms summer, autumn, winter and spring do not generally apply. Lowlands around the equator generally have a tropical rainforest climate, also known as an equatorial climate, though cold ocean currents cause some regions to have tropical monsoon climates with a dry season in the middle of the year, and the Somali Current generated by the Asian monsoon due to continental heating via the high Tibetan Plateau causes Greater Somalia to have an arid climate despite its equatorial location.

Average annual temperatures in equatorial lowlands are around 31 °C (88 °F) during the afternoon and 23 °C (73 °F) around sunrise. Rainfall is very high away from cold ocean current upwelling zones, from 2,500 to 3,500 mm (100 to 140 in) per year. There are about 200 rainy days per year and average annual sunshine hours are around 2,000. Despite high year-round sea level temperatures , some higher altitudes such as the Andes and Mount Kilimanjaro have glaciers. The highest point on the equator is at the elevation of 4,690 metres (15,387 ft), at 0°0′0″N77°59′31″W / 0.00000°N 77.99194°W / 0.00000; -77.99194 (highest point on the equator) , found on the southern slopes of Volcán Cayambe [summit 5,790 metres (18,996 ft)] in Ecuador. This is slightly above the snow line and is the only place on the equator where snow lies on the ground. At the equator the snow line is around 1,000 metres (3,300 ft)lower than on Mount Everest and as much as 2,000 metres (6,600 ft) lower than the highest snow line in the world, near the Tropic of Capricorn on Llullaillaco.

Climate data for Macapá, Brazil in South America
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Average high °C (°F)29.7
(85.5)
29.2
(84.6)
29.3
(84.7)
29.5
(85.1)
30.0
(86.0)
30.3
(86.5)
30.6
(87.1)
31.5
(88.7)
32.1
(89.8)
32.6
(90.7)
32.3
(90.1)
31.4
(88.5)
30.71
(87.28)
Daily mean °C (°F)26.4
(79.5)
26.2
(79.2)
26.3
(79.3)
26.5
(79.7)
26.8
(80.2)
26.8
(80.2)
26.8
(80.2)
27.4
(81.3)
27.8
(82.0)
28.1
(82.6)
27.9
(82.2)
27.4
(81.3)
27.03
(80.65)
Average low °C (°F)23.0
(73.4)
23.1
(73.6)
23.2
(73.8)
23.5
(74.3)
23.5
(74.3)
23.2
(73.8)
22.9
(73.2)
23.3
(73.9)
23.4
(74.1)
23.5
(74.3)
23.5
(74.3)
23.4
(74.1)
23.29
(73.92)
Average rainfall mm (inches)299.6
(11.80)
347.0
(13.66)
407.2
(16.03)
384.3
(15.13)
351.5
(13.84)
220.1
(8.67)
184.8
(7.28)
98.00
(3.86)
42.60
(1.68)
35.50
(1.40)
58.40
(2.30)
142.5
(5.61)
2,571.5
(101.26)
Average rainy days (≥ 0.1 mm)232224242522191365614203
Mean monthly sunshine hours 148.8113.1108.5114.0151.9189.0226.3272.8273.0282.1252.0204.62,336.1
Source: World Meteorological Organization (UN), [7] Hong Kong Observatory [8]
Climate data for Pontianak, Indonesia in Asia
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Average high °C (°F)32.4
(90.3)
32.7
(90.9)
32.9
(91.2)
33.2
(91.8)
33.0
(91.4)
33.2
(91.8)
32.9
(91.2)
33.4
(92.1)
32.6
(90.7)
32.6
(90.7)
32.2
(90.0)
32.0
(89.6)
32.7
(90.9)
Daily mean °C (°F)27.6
(81.7)
27.7
(81.9)
28.0
(82.4)
28.2
(82.8)
28.2
(82.8)
28.2
(82.8)
27.7
(81.9)
27.9
(82.2)
27.6
(81.7)
27.7
(81.9)
27.4
(81.3)
27.2
(81.0)
27.7
(81.9)
Average low °C (°F)22.7
(72.9)
22.6
(72.7)
23.0
(73.4)
23.2
(73.8)
23.4
(74.1)
23.1
(73.6)
22.5
(72.5)
22.3
(72.1)
22.6
(72.7)
22.8
(73.0)
22.6
(72.7)
22.4
(72.3)
22.7
(72.9)
Average rainfall mm (inches)260
(10.2)
215
(8.5)
254
(10.0)
292
(11.5)
256
(10.1)
212
(8.3)
201
(7.9)
180
(7.1)
295
(11.6)
329
(13.0)
400
(15.7)
302
(11.9)
3,196
(125.8)
Average rainy days (≥ 0.1 mm)151321222018162514272522238
Source: World Meteorological Organization (UN) [9]
Climate data for Libreville, Gabon in Africa
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Average high °C (°F)29.5
(85.1)
30.0
(86.0)
30.2
(86.4)
30.1
(86.2)
29.4
(84.9)
27.6
(81.7)
26.4
(79.5)
26.8
(80.2)
27.5
(81.5)
28.0
(82.4)
28.4
(83.1)
29.0
(84.2)
28.58
(83.44)
Daily mean °C (°F)26.8
(80.2)
27.0
(80.6)
27.1
(80.8)
26.6
(79.9)
26.7
(80.1)
25.4
(77.7)
24.3
(75.7)
24.3
(75.7)
25.4
(77.7)
25.7
(78.3)
25.9
(78.6)
26.2
(79.2)
25.95
(78.71)
Average low °C (°F)24.1
(75.4)
24.0
(75.2)
23.9
(75.0)
23.1
(73.6)
24.0
(75.2)
23.2
(73.8)
22.1
(71.8)
21.8
(71.2)
23.2
(73.8)
23.4
(74.1)
23.4
(74.1)
23.4
(74.1)
23.30
(73.94)
Average rainfall mm (inches)250.3
(9.85)
243.1
(9.57)
363.2
(14.30)
339.0
(13.35)
247.3
(9.74)
54.10
(2.13)
6.600
(0.26)
13.70
(0.54)
104.0
(4.09)
427.2
(16.82)
490.0
(19.29)
303.2
(11.94)
2,841.7
(111.88)
Average rainy days (≥ 0.1 mm)17.914.819.519.216.03.701.704.9014.525.022.617.6177.4
Mean monthly sunshine hours 176.7182.7176.7177.0158.1132.0117.889.9096.00111.6135.0167.41,720.9
Source: World Meteorological Organization (UN), [10] Hong Kong Observatory [11]

Line crossing ceremonies

There is a widespread maritime tradition of holding ceremonies to mark a sailor's first crossing of the equator. In the past, these ceremonies have been notorious for their brutality, especially in naval practice. [ citation needed ] Milder line-crossing ceremonies, typically featuring King Neptune, are also held for passengers' entertainment on some civilian ocean liners and cruise ships.[ citation needed ]

See also

Related Research Articles

Latitude The angle between zenith at a point and the plane of the equator

In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface. Latitude is an angle which ranges from 0° at the Equator to 90° at the poles. Lines of constant latitude, or parallels, run east–west as circles parallel to the equator. Latitude is used together with longitude to specify the precise location of features on the surface of the Earth. On its own, the term latitude should be taken to be the geodetic latitude as defined below. Briefly, geodetic latitude at a point is the angle formed by the vector perpendicular to the ellipsoidal surface from that point, and the equatorial plane. Also defined are six auxiliary latitudes which are used in special applications.

Longitude A geographic coordinate that specifies the east-west position of a point on the Earths surface

Longitude, is a geographic coordinate that specifies the east–west position of a point on the Earth's surface, or the surface of a celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians connect points with the same longitude. By convention, one of these, the Prime Meridian, which passes through the Royal Observatory, Greenwich, England, was allocated the position of 0° longitude. The longitude of other places is measured as the angle east or west from the Prime Meridian, ranging from 0° at the Prime Meridian to +180° eastward and −180° westward. Specifically, it is the angle between a plane through the Prime Meridian and a plane through both poles and the location in question.

Northern Hemisphere Half of Earth that is north of the equator

The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's North Pole.

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. In many countries, the seasons of the year are determined by reference to the solstices and the equinoxes.

Celestial sphere imaginary sphere of arbitrarily large radius, concentric with the observer

In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, which may be centered on Earth or the observer. If centered on the observer, half of the sphere would resemble a hemispherical screen over the observing location.

Geographic coordinate system Coordinate system

A geographic coordinate system is a coordinate system that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are often chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position; alternatively, a geographic position may be expressed in a combined three-dimensional Cartesian vector. A common choice of coordinates is latitude, longitude and elevation. To specify a location on a plane requires a map projection.

Equatorial coordinate system celestial coordinate system used to specify the positions of celestial objects

The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects. It may be implemented in spherical or rectangular coordinates, both defined by an origin at the centre of Earth, a fundamental plane consisting of the projection of Earth's equator onto the celestial sphere, a primary direction towards the vernal equinox, and a right-handed convention.

Ecliptic coordinate system celestial coordinate system used for representing the positions of Solar System objects

The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions and orbits of Solar System objects. Because most planets and many small Solar System bodies have orbits with only slight inclinations to the ecliptic, using it as the fundamental plane is convenient. The system's origin can be the center of either the Sun or Earth, its primary direction is towards the vernal (March) equinox, and it has a right-hand convention. It may be implemented in spherical or rectangular coordinates.

Orbital inclination Angle between a reference plane and the plane of an orbit

Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object.

Tropic of Cancer Line of northernmost latitude at which the sun can be directly overhead

The Tropic of Cancer, which is also referred to as the Northern Tropic, is the most northerly circle of latitude on Earth at which the Sun can be directly overhead. This occurs on the June solstice, when the Northern Hemisphere is tilted toward the Sun to its maximum extent. It is currently 23°26′12.0″ (or 23.43668°) north of the Equator.

Tropic of Capricorn Line of southernmost latitude at which the sun can be directly overhead

The Tropic of Capricorn is the circle of latitude that contains the subsolar point on the December solstice. It is thus the southernmost latitude where the Sun can be directly overhead. Its northern equivalent is the Tropic of Cancer.

Circle of latitude Geographic notion

A circle of latitude on Earth is an abstract east–west circle connecting all locations around Earth at a given latitude.

Earth radius mean distance from the Earths center to its surface

Earth radius is the distance from the center of Earth to a point on its surface. Its value ranges from 6,378 km (3,963 mi) at the equator to 6,357 km (3,950 mi) at a pole. A nominal Earth radius is sometimes used as a unit of measurement in astronomy and geophysics, denoted in astronomy by the symbol R. In other contexts, it is denoted or sometimes .

Reference ellipsoid An ellipsoid that approximates the figure of the Earth

In geodesy, a reference ellipsoid is a mathematically defined surface that approximates the geoid, the truer figure of the Earth, or other planetary body. Because of their relative simplicity, reference ellipsoids are used as a preferred surface on which geodetic network computations are performed and point coordinates such as latitude, longitude, and elevation are defined.

Earths orbit Trajectory of Earth around the Sun

Earth orbits the Sun at an average distance of 149.60 million km, and one complete orbit takes 365.256 days, during which time Earth has traveled 940 million km. Ignoring the influence of other solar system bodies, Earth's orbit is an ellipse with the Earth-Sun barycenter as one focus and a current eccentricity of 0.0167; since this value is close to zero, the center of the orbit is close, relative to the size of the orbit, to the center of the Sun.

Heliodon

A heliodon (HEE-leo-don) is a device for adjusting the angle between a flat surface and a beam of light to match the angle between a horizontal plane at a specific latitude and the solar beam. Heliodons are used primarily by architects and students of architecture. By placing a model building on the heliodon’s flat surface and making adjustments to the light/surface angle, the investigator can see how the building would look in the three-dimensional solar beam at various dates and times of day.

A lunar standstill is the gradually varying range between the northern and the southern limits of the Moon's declination, or the lunistices, over the course of one-half a sidereal month, or 13.66 days. One major, or one minor, lunar standstill occurs every 18.6 years due to the precessional cycle of the lunar nodes at that rate.

ECEF Earth-centered, Earth-fixed reference frame

ECEF, also known as ECR, is a geographic and Cartesian coordinate system and is sometimes known as a "conventional terrestrial" system. It represents positions as X, Y, and Z coordinates. The point is defined as the center of mass of Earth, hence the term geocentric coordinates. The distance from a given point of interest to the center of Earth is called the geocentric radius or geocentric distance.

Daytime period on any given point of the planets surface during which it experiences natural illumination from sunlight

On Earth, daytime is roughly the period of the day during which any given point in the world experiences natural illumination from especially direct sunlight. Daytime occurs when the Sun appears above the local horizon, that is, anywhere on the globe's hemisphere facing the Sun. In direct sunlight the movement of the sun can be recorded and observed using a sundial that casts a shadow that slowly moves during the day. During daytime, an observer sees indirect sunlight while in the shade, which includes cloud cover. 'Day' is sometimes used instead of 'daytime', in this case 'day' will mean 'the period of light between dawn and nightfall; the interval from sunrise to sunset', which is synonymous with daytime. However, in this context, in order to be clear "daytime" should be used distinguish it from "day" which typically refers to a 24-hour period.

IERS Reference Meridian International prime meridian used for GPS and other systems

The IERS Reference Meridian (IRM), also called the International Reference Meridian, is the prime meridian maintained by the International Earth Rotation and Reference Systems Service (IERS). It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle or 102 metres (335 ft) at the latitude of the Royal Observatory, Greenwich. It is also the reference meridian of the Global Positioning System (GPS) operated by the United States Department of Defense, and of WGS84 and its two formal versions, the ideal International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF).

References

  1. "Definition of equator". OxfordDictionaries.com. Retrieved 5 May 2018.
  2. "Equator". National Geographic - Education. Retrieved 29 May 2013.
  3. William Barnaby Faherty; Charles D. Benson (1978). "Moonport: A History of Apollo Launch Facilities and Operations". NASA Special Publication-4204 in the NASA History Series. p. Chapter 1.2: A Saturn Launch Site. Archived from the original on 29 April 2019. Retrieved 8 May 2019. Equatorial launch sites offered certain advantages over facilities within the continental United States. A launching due east from a site on the equator could take advantage of the earth's maximum rotational velocity (460 meters per second) to achieve orbital speed. The more frequent overhead passage of the orbiting vehicle above an equatorial base would facilitate tracking and communications. Most important, an equatorial launch site would avoid the costly dogleg technique, a prerequisite for placing rockets into equatorial orbit from sites such as Cape Canaveral, Florida (28 degrees north latitude). The necessary correction in the space vehicle's trajectory could be very expensive - engineers estimated that doglegging a Saturn vehicle into a low-altitude equatorial orbit from Cape Canaveral used enough extra propellant to reduce the payload by as much as 80%. In higher orbits, the penalty was less severe but still involved at least a 20% loss of payload.
  4. Luzum, Brian; Capitaine, Nicole; Fienga, Agnès; Folkner, William; Fukushima, Toshio; Hilton, James; Hohenkerk, Catherine; Krasinsky, George; Petit, Gérard; Pitjeva, Elena; Soffel, Michael; Wallace, Patrick (2011). "The IAU 2009 system of astronomical constants: the report of the IAU working group on numerical standards for Fundamental Astronomy" (PDF). Celest Mech Dyn Astr. 110: 293–304. doi:10.1007/s10569-011-9352-4.
  5. "General definitions and numerical standards" (PDF). IERS Technical Note 36. Archived from the original (PDF) on 18 December 2018.
  6. Instituto Geográfico Militar de Ecuador (24 January 2005). "Memoria Técnica de la Determinación de la Latitud Cero" (in Spanish).
  7. "Weather Information for Macapa". World Weather Information Service. World Meteorological Organization.
  8. "Climatological Normals of Macapa". Hong Kong Observatory. Archived from the original on 26 October 2019.
  9. "Weather Information for Pontianak". World Weather Information Service. World Meteorological Organization.
  10. "Weather Information for Libreville". World Weather Information Service. World Meteorological Organization.
  11. "Climatological Normals of Libreville". Hong Kong Observatory. Archived from the original on 26 October 2019.

Sources