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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 equation of the ellipse yields an eccentricity of 0.0549 and perigee and apogee distances of 362,600 km (225,300 mi) and 405,400 km (251,900 mi) respectively (a difference of 12%). [citation needed] Since nearer objects appear larger, the Moon's apparent size changes as it moves toward and away from an observer on Earth.
Astrophysicist Fred Espenak uses Nolle's definition but preferring the label of full Moon at perigee, and using the apogee and perigee nearest in time rather than the greatest and least of the year. [13] Wood used the definition of a full or new moon occurring within 24 hours of perigee and also used the label perigee-syzygy. [7]
This is the reason that an anomalistic month (the period the Moon moves from the perigee to the apogee and to the perigee again) is longer than the sidereal month (the period the Moon takes to complete one orbit with respect to the fixed stars).
Typically we only get one or the other, but a hybrid eclipse is different, occurring when the moon’s distance is balanced on something of a knife-edge between apogee and perigee—not too close ...
Transatmospheric orbit (TAO): geocentric orbits with an apogee above 100 km and perigee that intersects with the defined atmosphere. [4] Very low Earth orbit (VLEO) is defined as altitudes between approximately 100 - 450 km above Earth’s surface. [5] [6] Low Earth orbit (LEO): geocentric orbits with altitudes below 2,000 km (1,200 mi). [7]
The exact height of a satellite in a Tundra orbit varies between missions, but a typical orbit will have a perigee of approximately 25,000 kilometres (16,000 mi) and an apogee of 39,700 kilometres (24,700 mi), for a semi-major axis of 46,000 kilometres (29,000 mi). [7]
Semi-major axis (a) — half the distance between the apoapsis and periapsis. The portion of the semi-major axis extending from the primary at one focus to the periapsis is shown as a purple line in the diagram; the rest (from the primary/focus to the center of the orbit ellipse) is below the reference plane and not shown.