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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 Earth spends less time near perihelion and more time near aphelion. This means that the lengths of the seasons vary. [ 14 ] Perihelion currently occurs around 3 January, so the Earth's greater velocity shortens winter and autumn in the northern hemisphere, and summer and spring in the southern hemisphere.
r a is the radius at apoapsis (also "apofocus", "aphelion", "apogee"), i.e., the farthest distance of the orbit to the center of mass of the system, which is a focus of the ellipse. r p is the radius at periapsis (or "perifocus" etc.), the closest distance.
Log-log plot of period T vs semi-major axis a (average of aphelion and perihelion) of some Solar System orbits (crosses denoting Kepler's values) showing that a 3 / T 2 is constant (green line) In astrodynamics the orbital period T of a small body orbiting a central body in a circular or elliptical orbit is: [1]
I would also advocate moving to this article the entire apsis sections Apsis#Perihelion and aphelion of the Earth and Apsis#Planetary perihelion and aphelion, but if you try to do that you may tread on some toes at the aphelion article. 208.50.124.65 20:09, 3 September 2014 (UTC) I think you mean the Apsis article.
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 ...
The dates of perihelion and aphelion progres through the seasons, making one complete cycle in 22,000 to 26,000 years. This is a mechanism behind one of the many Milankovitch cycles, but represents an insufficient period to cause the ice ages which occur on a period exceeding 100 million years .