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The ancient Greek astronomer Hipparchus noted the apsidal precession of the Moon's orbit (as the revolution of the Moon's apogee with a period of approximately 8.85 years); [4] it is corrected for in the Antikythera Mechanism (circa 80 BCE) (with the supposed value of 8.88 years per full cycle, correct to within 0.34% of current measurements). [5]
The apsides refer to the farthest (2) and nearest (3) points reached by an orbiting planetary body (2 and 3) with respect to a primary, or host, body (1). An apsis (from Ancient Greek ἁψίς (hapsís) 'arch, vault'; pl. apsides / ˈ æ p s ɪ ˌ d iː z / AP-sih-deez) [1] [2] is the farthest or nearest point in the orbit of a planetary body about its primary body.
The red curve crosses zero at perihelion and aphelion. The 2:3 resonance between the two bodies is highly stable and has been preserved over millions of years. [ 96 ] This prevents their orbits from changing relative to one another, so the two bodies can never pass near each other.
Near-Earth asteroids are divided into groups based on their semi-major axis (a), perihelion distance (q), and aphelion distance (Q): [2] [26] The Atiras or Apoheles have orbits strictly inside Earth's orbit: an Atira asteroid's aphelion distance (Q) is smaller than Earth's perihelion distance (0.983 AU).
Centaurs have unstable orbits in which the perihelion (q) is well inside of Neptune's orbit but the farthest point (aphelion, Q) is very distant. The first TNO to be discovered was Pluto in 1930. It became the namesake of a larger group of resonant objects called plutinos (another such resonant subgroup are the twotinos).
Although Mercury is farthest from Earth when it is full, ... Mercury's separation from the Sun ranges anywhere from 17.9° at perihelion to 27.8° at aphelion. [144] ...
An object with an e of between 0 and 1 will have an elliptical orbit, with, for instance, an object with an e of 0.5 having a perihelion twice as close to the Sun as its aphelion. As an object's e approaches 1, its orbit will be more and more elongated before, and at e =1, the object's orbit will be parabolic and unbound to the Solar System (i ...
One particularly distant body is 90377 Sedna, which was discovered in November 2003.It has an extremely eccentric orbit that takes it to an aphelion of 937 AU. [2] It takes over 10,000 years to orbit, and during the next 50 years it will slowly move closer to the Sun as it comes to perihelion at a distance of 76 AU from the Sun. [3] Sedna is the largest known sednoid, a class of objects that ...