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Orbital pole

  (Redirected from Ecliptic pole)
The orbital poles of the Solar system. The yellow dot in the centre is the Sun's North pole. Jupiter's orbital pole is in orange, Mercury in pale blue, Venus in green, Earth in blue, Mars in red, Saturn in violet, Uranus in grey and Neptune in lavender. Dwarf planet Pluto is the dotless cross off in Cepheus

An orbital pole is either end of an imaginary line running through the center of an orbit perpendicular to the orbital plane, projected onto the celestial sphere. It is similar in concept to a celestial pole but based on the planet's orbit instead of the planet's rotation.

The north orbital pole of a celestial body is defined by the right-hand rule: If you curve the fingers of your right hand along the direction of orbital motion, with your thumb extended parallel to the orbital axis, the direction your thumb points is defined to be north.

The orbital pole of the earth is referred to as the Ecliptic pole.

Ecliptic poleEdit

The ecliptic poles are the points on the celestial sphere where it meets the imaginary line perpendicular to the ecliptic plane, in which the Earth travels on its orbit around the Sun.

There are two ecliptic poles:

The North Ecliptic Pole is in Draco
The South Ecliptic Pole is in Dorado

Due to precession, the celestial pole moves in a circle around the ecliptic poles once every 25,800 years.

The ecliptic poles are (as of epoch 1 January 2000) at:

  • (North) right ascension 18h 0m 0.0s (exact), declination +66° 33′ 38.55″
  • (South) right ascension 6h 0m 0.0s (exact), declination −66° 33′ 38.55″

when expressed in equatorial coordinates, as a consequence of the Earth's axial tilt.

It is not possible to have an ecliptic pole at the zenith in a dark sky. By definition, the ecliptic poles are located 90 degrees from the Sun's position. Therefore, whenever either ecliptic pole is directly overhead, the Sun must be on the horizon. The ecliptic poles can be at the zenith on the Arctic and Antarctic Circles.