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-as of [20 SEPTEMBER 2024]–
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-‘point’ of ‘greatest/least’ distance of a ‘body’ from 1 of the ‘foci’ of its ‘elliptical orbit’–
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-MEASURE [TIME CHANGE] FROM LAST YEAR’S [AP-HELION]-
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“PERI-HELION”
(nearest to ‘the sun’)
*4 JANUARY 2025*
([7:58 AM] UTC)
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“AP-HELION”
(furthest from ‘the sun’)
*3 JULY 2025*
([7:55 PM] UTC)
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(equivalent (‘further’ / ‘center’ / ‘nearest’) labels…)
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*’standard terms’* –>
(‘apocenter’ / ‘center’ / ‘pericenter’)
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(for “any orbit around a ‘star'”) –>
(‘apastron’ / ‘star’ / ‘periastron’)
(for ‘earth’s orbit around ‘the sun’ –>
‘aphelion’ / ‘sun’ / ‘perihelion”)
(for “moon’s orbit around ‘earth'”)
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(AKA ‘APSIS”)
(use ‘apogee’ when referring to ‘earth’)
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(AS OF “5 JANUARY 2019”) ==>
(‘point’ in the ‘orbit’ of a ‘celestial body’ where it is nearest to its ‘orbital focus’ (generally a ‘star’))
(an apsis (greek: ἁψίς; plural apsides /ˈæpsɪdiːz/, greek: ἁψῖδες) is an ‘extreme point’ in the ‘orbit’ of an ‘object’)
(the word comes via ‘latin’ from ‘greek’ and is ‘cognate’ with apse)
(for ‘elliptic orbits’ about a ‘larger body, there are 2 ‘apsides’:)
(named with the prefixes peri- (from περί (peri), meaning ‘near’) and ap-/apo- (from ἀπ(ό) (ap(ó)), meaning ‘away from’) added to a reference to the body being orbited)
For a body orbiting the Sun, the point of least distance is the perihelion (/ˌpɛrɪˈhiːliən/), and the point of greatest distance is the aphelion (/æpˈhiːliən/).[2]
The terms become periastron and apastron when discussing orbits around other stars.
For any satellite of Earth, including the Moon, the point of least distance is the perigee (/ˈpɛrɪdʒiː/) and greatest distance the apogee.
For objects in lunar orbit, the point of least distance is sometimes called the pericynthion (/ˌpɛrɪˈsɪnθiən/) and the greatest distance the apocynthion (/ˌæpəˈsɪnθiən/).
Perilune and apolune are also used.[3]
For an orbit around any barycenter, the terms periapsis and apoapsis (or apapsis) are used. Pericenter and apocenter are equivalent alternatives.
A straight line connecting the periapsis and apoapsis is the line of apsides.
This is the major axis of the ellipse, its greatest diameter.
The center of mass, or barycenter, of a two-body system lies on this line at one of the two foci of the ellipse.
When one body is sufficiently larger than the other, this focus may be located within the larger body.
However, whether this is the case, both bodies are in similarelliptical orbits.
Both orbits share a common focus at the system’s barycenter, with their respective lines of apsides being of length inversely proportional to their masses.
Historically, in geocentric systems, apsides were measured from the center of the Earth.
However, in the case of the Moon, the barycenter of the Earth–Moon system (or the Earth–Moon barycenter) as the common focus of both bodies’ orbits about each other, is about 75% of the way from Earth’s center to its surface.
In orbital mechanics, the apsis technically refers to the distance measured between the barycenters of the central body and orbiting body.
However, in the case of spacecraft, the family of terms are commonly used to refer to the orbital altitude of the spacecraft from the surface of the central body (assuming a constant, standard reference radius))
(point of greatest or least distance of a body from one of the foci of its elliptical orbit)
(an apsis (Greek: ἁψίς; plural apsides /ˈæpsᵻdiːz/, Greek: ἁψίδες) is an extreme point in an object’s orbit. The word comes via Latin from Greek and is cognate with apse.[1] For elliptic orbits about a larger body, there are two apsides, named with the prefixes peri- (from περί (peri), meaning “near”) and ap-, or apo- (from ἀπ(ό) (ap(ó)), meaning “away from”) added to a reference to the thing being orbited.
For a body orbiting the Sun, the point of least distance is the perihelion (/ˌpɛrᵻˈhiːliən/), and the point of greatest distance is the aphelion(/æpˈhiːliən/).[2]
The terms become periastron and apastron when discussing orbits around other stars.
For any satellite of Earth including the Moon the point of least distance is the perigee (/ˈpɛrᵻdʒiː/) and greatest distance the apogee.
For objects in Lunar orbit, the point of least distance is the pericynthion (/ˌpɛrɪˈsɪnθɪən/) and the greatest distance the apocynthion(/ˌæpəˈsɪnθɪən/).
For any orbits around a center of mass, there are the terms pericenter and apocenter. Periapsis and apoapsis (or apapsis) are equivalent alternatives.
A straight line connecting the pericenter and apocenter is the line of apsides.
This is the major axis of the ellipse, its greatest diameter.
For a two-body system the center of mass of the system lies on this line at one of the two foci of the ellipse.
When one body is sufficiently larger than the other it may be taken to be at this focus.
However whether or not this is the case, both bodies are in similar elliptical orbits each having one focus at the system’s center of mass, with their respective lines of apsides being of length inversely proportional to their masses.
Historically, in geocentric systems, apsides were measured from the center of the Earth.
However, in the case of the Moon, the center of mass of the Earth–Moon system, or Earth–Moon barycenter, as the common focus of both the Moon’s and Earth’s orbits about each other, is about 74% of the way from Earth’s center to its surface.
In orbital mechanics, the apsis technically refers to the distance measured between the centers of mass of the central and orbiting body.
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(however, in the case of [space-craft], the family of terms are commonly used to refer to the orbital altitude of the spacecraft from the surface of the central body (assuming a constant, standard ‘reference radius’))
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*👨🔬🕵️♀️🙇♀️*SKETCHES*🙇♂️👩🔬🕵️♂️*
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*🌈✨ *TABLE OF CONTENTS* ✨🌷*
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