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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 opposite phenomenon, an apogee syzygy or a full (or new) Moon around apogee, has been called a micromoon. [4] Definitions. The name supermoon was coined by ...
The largest possible apparent diameter of the Moon is the same 12% larger (as perigee versus apogee distances) than the smallest; the apparent area is 25% more and so is the amount of light it reflects toward Earth. The variance in the Moon's orbital distance corresponds with changes in its tangential and angular speeds, per Kepler's second law.
An inclination of 63.4° is often called a critical inclination, when describing artificial satellites orbiting the Earth, because they have zero apogee drift. [3] An inclination of exactly 90° is a polar orbit, in which the spacecraft passes over the poles of the planet. An inclination greater than 90° and less than 180° is a retrograde orbit.
Retrograde orbit: the satellite (red) orbits in the direction opposite to the rotation of its primary (blue/black) Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure).
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.
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]
Diagram showing the relationship between the zenith, the nadir, and different types of horizon. The zenith (UK: / ˈ z ɛ n ɪ θ /, US: / ˈ z iː n ɪ θ /) [1] is the imaginary point on the celestial sphere directly "above" a particular location.