Orbital pole
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An orbital pole is either point at the ends of the orbital normal, an imaginary line segment that runs through a focus of an orbit (of a revolving body like a planet, moon or satellite) and is perpendicular (or normal) to the orbital plane. Projected onto the celestial sphere, orbital poles are similar in concept to celestial poles, but are based on the body's orbit instead of its equator.
The north orbital pole of a revolving body is defined by the right-hand rule. If the fingers of the right hand are curved along the direction of orbital motion, with the thumb extended and oriented to be parallel to the orbital axis, then the direction the thumb points is defined to be the orbital north.
The poles of Earth's orbit are referred to as the ecliptic poles. For the remaining planets, the orbital pole in ecliptic coordinates is given by the longitude of the ascending node (☊Script error: No such module "Check for unknown parameters".) and inclination (Template:Mvar): ℓ = ☊ − 90° Script error: No such module "Check for unknown parameters"., b = 90° − iScript error: No such module "Check for unknown parameters". . In the following table, the planetary orbit poles are given in both celestial coordinates and the ecliptic coordinates for the Earth.
| Object | ☊Script error: No such module "Check for unknown parameters".[1] | [[inclination|Template:Mvar]][1] | Ecl.Lon. | Ecl.Lat. | [[Right ascension|RA (Template:Mvar)]] | [[Declination|Dec (Template:Mvar)]] |
|---|---|---|---|---|---|---|
| Mercury | 48.331° | 7.005° | 318.331° | 82.995° | 18h 43m 57.1s | +61° 26Template:Prime 52Template:Pprime |
| Venus | 76.678° | 3.395° | 346.678° | 86.605° | 18h 32m 01.8s | +65° 34Template:Prime 01Template:Pprime |
| Earth | 140°Template:Efn | 0.0001° | 50°Template:Efn | 89.9999° | 18h 00m 00.0s | +66° 33Template:Prime 38.84Template:Pprime |
| Mars | 49.562° | 1.850° | 319.562° | 88.150° | 18h 13m 29.7s | +65° 19Template:Prime 22Template:Pprime |
| Ceres | 80.494° | 10.583° | 350.494° | 79.417° | 19h 33m 33.1s | +62° 50Template:Prime 57Template:Pprime |
| Jupiter | 100.492° | 1.305° | 10.492° | 88.695° | 18h 13m 00.8s | +66° 45Template:Prime 53Template:Pprime |
| Saturn | 113.643° | 2.485° | 23.643° | 87.515° | 18h 23m 46.8s | +67° 26Template:Prime 55Template:Pprime |
| Uranus | 73.989° | 0.773° | 343.989° | 89.227° | 18h 07m 24.1s | +66° 20Template:Prime 12Template:Pprime |
| Neptune | 131.794° | 1.768° | 41.794° | 88.232° | 18h 13m 54.1s | +67° 42Template:Prime 08Template:Pprime |
| Pluto | 110.287° | 17.151° | 20.287° | 72.849° | 20h 56m 3.7s | +66° 32Template:Prime 31Template:Pprime |
When an artificial satellite orbits close to another large body, it can only maintain continuous observations in areas near its orbital poles. The continuous viewing zone (CVZ) of the Hubble Space Telescope lies inside roughly 24° of Hubble's orbital poles, which precess around the Earth's axis every 56 days.[2]
Ecliptic pole
The ecliptic is the plane on which Earth orbits the Sun. The ecliptic poles are the two points where the ecliptic axis, the imaginary line perpendicular to the ecliptic, intersects the celestial sphere.
The two ecliptic poles are mapped below.
| File:North ecliptic pole.png The north ecliptic pole is in Draco. |
File:South ecliptic pole.png The south ecliptic pole is in Dorado. |
Due to axial precession, either celestial pole completes a circuit around the nearer ecliptic pole every 25,800 years.
since 1 January 2000[update]Template:Dated maintenance category (articles)Script error: No such module "Check for unknown parameters"., the positions of the ecliptic poles expressed in equatorial coordinates, as a consequence of Earth's axial tilt, are the following:
- North: right ascension Template:RA (exact), declination Template:DEC
- South: right ascension Template:RA (exact), declination Template:DEC
The north ecliptic pole is located near the Cat's Eye Nebula and the south ecliptic pole is located near the Large Magellanic Cloud.
It is impossible anywhere on Earth for either ecliptic pole to be at the zenith in the night sky. By definition, the ecliptic poles are located 90° from the Sun's position. Therefore, whenever and wherever either ecliptic pole is directly overhead, the Sun must be on the horizon. The ecliptic poles can contact the zenith only within the Arctic and Antarctic circles.
The galactic coordinates of the north ecliptic pole can be calculated as ℓ = 96.38°Script error: No such module "Check for unknown parameters"., b = 29.81°Script error: No such module "Check for unknown parameters". (see celestial coordinate system).
See also
Footnotes
References
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- ↑ a b c Tabulated and mapped data obtained from Script error: No such module "citation/CS1". — Used HORIZONS input "Ephemeris Type: Orbital Elements", "Time Span: discrete time=2451545", "Center: Sun (body center)", and selected each object's barycenter. Results are instantaneous osculating values at the precise J2000 epoch, and referenced to the ecliptic.
- ↑ Script error: No such module "citation/CS1".
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