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Celestial equator

 
Celestial Equator

 
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Celestial equator
 
 
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The celestial equator is a great circle
Great circle

A great circle of a sphere is a circle that runs along the surface of that sphere so as to cut it into two equal halves. The great circle therefore has both the same circumference and the same center as the sphere....
 on the imaginary celestial sphere
Celestial sphere

In astronomy and navigation, the celestial sphere is an imagination rotation sphere of "gigantic radius", concentric spheres and coaxial with the Earth....
, in the same plane as the Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
's equator
Equator

The equator is the intersection of the Earth's surface with the Plane perpendicular to the Earth's rotation and containing the Earth's center of mass....
. In other words, it is a projection of the terrestrial equator out into space. As result of the Earth's axial tilt
Axial tilt

In astronomy, axial tilt is the inclination angle of a planet axis of rotation in relation to its Orbital plane . It is also called axial inclination or obliquity....
, the celestial equator is inclined by ~23.5° with respect to the ecliptic plane
Ecliptic

The ecliptic is the apparent path that the Sun traces out in the sky during the year. As it appears to move in the sky in relation to the stars, the apparent path aligns with the planets throughout the course of the year....
.

An observer standing on the Earth's equator
Equator

The equator is the intersection of the Earth's surface with the Plane perpendicular to the Earth's rotation and containing the Earth's center of mass....
 visualizes the celestial equator as a semicircle
Semicircle

In mathematics , a semicircle is a two-dimensional geometric shape that forms half of a circle. Being half of a circle's 360?, the Arc of a semicircle always measures 180?....
 passing directly overhead through the zenith
Zenith

In broad terms, the zenith is the direction pointing directly above a particular location . Since the concept of being above is itself somewhat vague, scientists define the zenith in more rigorous terms....
. As the observer moves north (or south), the celestial equator tilts towards the southern (or northern) horizon.






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The celestial equator is a great circle
Great circle

A great circle of a sphere is a circle that runs along the surface of that sphere so as to cut it into two equal halves. The great circle therefore has both the same circumference and the same center as the sphere....
 on the imaginary celestial sphere
Celestial sphere

In astronomy and navigation, the celestial sphere is an imagination rotation sphere of "gigantic radius", concentric spheres and coaxial with the Earth....
, in the same plane as the Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
's equator
Equator

The equator is the intersection of the Earth's surface with the Plane perpendicular to the Earth's rotation and containing the Earth's center of mass....
. In other words, it is a projection of the terrestrial equator out into space. As result of the Earth's axial tilt
Axial tilt

In astronomy, axial tilt is the inclination angle of a planet axis of rotation in relation to its Orbital plane . It is also called axial inclination or obliquity....
, the celestial equator is inclined by ~23.5° with respect to the ecliptic plane
Ecliptic

The ecliptic is the apparent path that the Sun traces out in the sky during the year. As it appears to move in the sky in relation to the stars, the apparent path aligns with the planets throughout the course of the year....
.

An observer standing on the Earth's equator
Equator

The equator is the intersection of the Earth's surface with the Plane perpendicular to the Earth's rotation and containing the Earth's center of mass....
 visualizes the celestial equator as a semicircle
Semicircle

In mathematics , a semicircle is a two-dimensional geometric shape that forms half of a circle. Being half of a circle's 360?, the Arc of a semicircle always measures 180?....
 passing directly overhead through the zenith
Zenith

In broad terms, the zenith is the direction pointing directly above a particular location . Since the concept of being above is itself somewhat vague, scientists define the zenith in more rigorous terms....
. As the observer moves north (or south), the celestial equator tilts towards the southern (or northern) horizon. The celestial equator is defined to be infinitely distant (since it is on the celestial sphere); thus the observer always sees the ends of the semicircle disappear over the horizon exactly due east and due west, regardless of the observer's position on Earth. (At the poles
Geographical pole

A geographical pole , is either of two points on the surface of a spinning planet or other spinning body, at 90 degrees from its equator, at one of the two points where the Axis of rotation around which the body spins meets the surface of the body....
, though, the celestial equator would be parallel to the horizon.)

Celestial objects near the celestial equator are visible worldwide, but they culminate
Culmination

In astronomy, the culmination, at a given point, of a planet, star, constellation, etc. is the time within the diurnal motion when it appears on an observer's meridian ....
 the highest in the sky in the tropics. The celestial equator passes through these constellation
Constellation

A constellation is a group of stars that appear to have a physical proximity in the sky. The stars in a constellation are often vastly distant from each other, but they appear close to each other from the perspective of Earth....
s:

  • Pisces
    Pisces (constellation)

    Pisces is a constellation of the zodiac. Its name is the Latin plural for fish, and its symbol is . It lies between Aquarius to the west and Aries to the east....
  • Cetus
    Cetus

    Cetus is a constellation in the northern sky. Its name refers to Cetus , a sea monster in Greek mythology, although it is often called 'the whale' today....
  • Taurus
    Taurus (constellation)

    Taurus is one of the constellations of the zodiac. Its name is Latin for cattle, and its symbol is , a stylized bull's head. Taurus is a large and prominent constellation in the northern hemisphere's winter sky, between Aries to the west and Gemini to the east; to the north lie Perseus and Auriga , to the southeast Orion , to the south E...
  • Eridanus
    Eridanus (constellation)

    Eridanus is a constellation. It is represented as a river; its name is the Greek language name for the Po River. It was one of the 48 constellations listed by the 1st century astronomer Ptolemy, and it remains one of the 88 modern constellations....
  • Orion
    Orion (constellation)

    Orion , often referred to as "The Hunter," is a prominent constellation ? one of the largest, most conspicuous, and most recognizable in the night sky....
  • Monoceros
    Monoceros

    Monoceros is a faint constellation in the northern sky. Its name is Greek for unicorn. Its creation is attributed to the 17th-century Dutch cartographer Petrus Plancius....
  • Canis Minor
    Canis Minor

    Canis Minor is a small constellation. It was included in the 1st century astronomer Ptolemy's 48 constellations, and is still included among the 88 modern constellations....
  • Hydra
    Hydra (constellation)

    Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees. It has a long history, having been included among the 48 constellations listed by the 1st century astronomer Ptolemy....
  • Sextans
    Sextans

    Sextans is a minor celestial equator constellation which was introduced in the 17th century by Johannes Hevelius. Its name is Latin for the sextant , an instrument that Hevelius made frequent use of in his observations....
  • Leo
    Leo (constellation)

    Leo is one of the constellations of the zodiac. Its name is Latin for lion. Its symbol is , a corruption of the initial letter of ?e?? . Leo lies between dim Cancer to the west and Virgo to the east....
  • Virgo
    Virgo (constellation)

    Virgo is one of the constellations of the zodiac. Its name is Latin for virgin, and its symbol is . Lying between Leo to the west and Libra to the east, it is the second largest constellation in the sky....
  • Serpens
    Serpens

    Serpens is a constellation. Its name is Latin for snake, and it is unique among the modern constellations in being split into two separate sections, Serpens Caput to the west and Serpens Cauda to the east....
  • Ophiuchus
    Ophiuchus

    Ophiuchus is a large constellation located around the celestial equator. Its name is Greek language for 'snake-holder', and it is commonly represented as a man grasping the snake that is represented by the constellation Serpens....
  • Aquila
    Aquila (constellation)

    Aquila is a constellation. Its name is Latin for 'eagle' and it is commonly represented as such. It lies roughly at the celestial equator. The alpha star, Altair, is a vertex of the Summer Triangle asterism ....
  • Aquarius
    Aquarius (constellation)

    Aquarius Aquarius is one of the oldest of the recognized constellations along the zodiac . It is found in a region often called the Sea due to its profusion of constellations with watery associations such as Cetus the whale, Pisces the fish and Eridanus the river....


    • See also

    • Celestial pole
      Celestial pole

      The north and south celestial poles are the two imaginary points in the sky where the Earth axis of rotation, "infinitely extended", intersects the imaginary rotating sphere of stars called the celestial sphere....
    • Celestial sphere
      Celestial sphere

      In astronomy and navigation, the celestial sphere is an imagination rotation sphere of "gigantic radius", concentric spheres and coaxial with the Earth....