periapsis

English

In a 2-body system in which the objects each follow an elliptical orbit around the system's centre of mass, the apsides are: the farthest point, or apoapsis, and the point of closest approach, or periapsis.

Etymology

peri- +‎ apsis.

Noun

periapsis (plural periapsides or periapsises or periapses)

1. (astronomy, astrophysics) The point of a body's (elliptical) orbit in a 2-body gravitational system such that the distance between the two bodies (measured from their respective centres of mass) is at its minimum.
   • 1983, Richard O. Fimmel, Laurence Colin, Eric Burgess, Pioneer Venus, NASA SP-461, page 109,

     Figure 5-19. Sun-Venus-Orbiter geometry illustrates how the periapsis moves around the planet during the Venusian sidereal year to sample day and night hemispheres. Because the planet rotates in a retrograde direction, it takes more than one Venusian sidereal year for periapsis to move over all longitudes of the planet (as explained in text).

   • 2001, D. A. Vallado, Fundamentals of Astrodynamics and Applications, Springer, page 325:

     We don't always want to burn near periapsis. Suppose we want to change the height at periapsis. The most efficient place to change the radius of periapsis is at apoapsis. Consider applying $\Delta v$ at some other point in the orbit. In this case both periapsis and apoapsis will change. If we apply the $\Delta v$ tangentially at apoapsis, all of the $\Delta v$ will go into changing periapsis, and vice versa.

   • 2004, R. S. Saunders, et al., Mars Odyssey Mission, C. T. Russell (editor), 2001 Mars Odyssey, Kluwer Academic Publishers, page 34,

     The main aerobraking phase began once the point of the spacecraft's periapsis had been lowered to within 110 km above the Martian surface.

2. The minimum distance between the two bodies in such a system.

Usage notes

• In the case of some particular celestial bodies, specialized terms are used. See Related terms, below, for examples.

Synonyms

• pericenter

Antonyms

• apoapsis

Hypernyms

• apsis

Derived terms

• argument of periapsis
• longitude of periapsis

Related terms

Related terms

• periareion
• periastron
• peribothron
• pericenter, pericentre
• pericynthion
• perigalacticon
• perigee
• perihelion
• perihermion
• perijove
• perikrone, perikron
• perilune
• perimelasma
• perinigricon
• periposeidon
• perisaturnium
• periselene

Translations

Translations

• Dutch: perifocus m, periapsis f
• Finnish: periapsis (fi)
• French: périapse (fr), périapside (fr) m
• Greek: περίαψη (el) f (períapsi)
• Irish: pearaipsis f
• Portuguese: periapside f

Further reading

• Apsis on Wikipedia.Wikipedia
• Apsidal precession on Wikipedia.Wikipedia

Finnish

Etymology

Internationalism (see English periapsis).

Pronunciation

• IPA^(key): /ˈperiɑpsis/, [ˈpe̞riˌɑ̝ps̠is̠]
• Rhymes: -ɑpsis
• Syllabification^(key): pe‧ri‧ap‧sis

Noun

periapsis

1. (astronomy) periapsis

Declension

Inflection of periapsis (Kotus type 39/vastaus, no gradation)
nominative		periapsis	periapsikset
genitive		periapsiksen	periapsisten periapsiksien
partitive		periapsista	periapsiksia
illative		periapsikseen	periapsiksiin
		singular	plural
nominative		periapsis	periapsikset
accusative	nom.	periapsis	periapsikset
	gen.	periapsiksen
genitive		periapsiksen	periapsisten periapsiksien
partitive		periapsista	periapsiksia
inessive		periapsiksessa	periapsiksissa
elative		periapsiksesta	periapsiksista
illative		periapsikseen	periapsiksiin
adessive		periapsiksella	periapsiksilla
ablative		periapsikselta	periapsiksilta
allative		periapsikselle	periapsiksille
essive		periapsiksena	periapsiksina
translative		periapsikseksi	periapsiksiksi
abessive		periapsiksetta	periapsiksitta
instructive		—	periapsiksin
comitative		See the possessive forms below.

Possessive forms of periapsis (Kotus type 39/vastaus, no gradation)

first-person singular possessor singular plural nominative periapsikseni periapsikseni accusative nom. periapsikseni periapsikseni gen. periapsikseni genitive periapsikseni periapsisteni periapsiksieni partitive periapsistani periapsiksiani inessive periapsiksessani periapsiksissani elative periapsiksestani periapsiksistani illative periapsikseeni periapsiksiini adessive periapsiksellani periapsiksillani ablative periapsikseltani periapsiksiltani allative periapsikselleni periapsiksilleni essive periapsiksenani periapsiksinani translative periapsiksekseni periapsiksikseni abessive periapsiksettani periapsiksittani instructive — — comitative — periapsiksineni second-person singular possessor singular plural nominative periapsiksesi periapsiksesi accusative nom. periapsiksesi periapsiksesi gen. periapsiksesi genitive periapsiksesi periapsistesi periapsiksiesi partitive periapsistasi periapsiksiasi inessive periapsiksessasi periapsiksissasi elative periapsiksestasi periapsiksistasi illative periapsikseesi periapsiksiisi adessive periapsiksellasi periapsiksillasi ablative periapsikseltasi periapsiksiltasi allative periapsiksellesi periapsiksillesi essive periapsiksenasi periapsiksinasi translative periapsikseksesi periapsiksiksesi abessive periapsiksettasi periapsiksittasi instructive — — comitative — periapsiksinesi first-person plural possessor singular plural nominative periapsiksemme periapsiksemme accusative nom. periapsiksemme periapsiksemme gen. periapsiksemme genitive periapsiksemme periapsistemme periapsiksiemme partitive periapsistamme periapsiksiamme inessive periapsiksessamme periapsiksissamme elative periapsiksestamme periapsiksistamme illative periapsikseemme periapsiksiimme adessive periapsiksellamme periapsiksillamme ablative periapsikseltamme periapsiksiltamme allative periapsiksellemme periapsiksillemme essive periapsiksenamme periapsiksinamme translative periapsikseksemme periapsiksiksemme abessive periapsiksettamme periapsiksittamme instructive — — comitative — periapsiksinemme second-person plural possessor singular plural nominative periapsiksenne periapsiksenne accusative nom. periapsiksenne periapsiksenne gen. periapsiksenne genitive periapsiksenne periapsistenne periapsiksienne partitive periapsistanne periapsiksianne inessive periapsiksessanne periapsiksissanne elative periapsiksestanne periapsiksistanne illative periapsikseenne periapsiksiinne adessive periapsiksellanne periapsiksillanne ablative periapsikseltanne periapsiksiltanne allative periapsiksellenne periapsiksillenne essive periapsiksenanne periapsiksinanne translative periapsikseksenne periapsiksiksenne abessive periapsiksettanne periapsiksittanne instructive — — comitative — periapsiksinenne third-person possessor singular plural nominative periapsiksensa periapsiksensa accusative nom. periapsiksensa periapsiksensa gen. periapsiksensa genitive periapsiksensa periapsistensa periapsiksiensa partitive periapsistaan periapsistansa periapsiksiaan periapsiksiansa inessive periapsiksessaan periapsiksessansa periapsiksissaan periapsiksissansa elative periapsiksestaan periapsiksestansa periapsiksistaan periapsiksistansa illative periapsikseensa periapsiksiinsa adessive periapsiksellaan periapsiksellansa periapsiksillaan periapsiksillansa ablative periapsikseltaan periapsikseltansa periapsiksiltaan periapsiksiltansa allative periapsikselleen periapsiksellensa periapsiksilleen periapsiksillensa essive periapsiksenaan periapsiksenansa periapsiksinaan periapsiksinansa translative periapsiksekseen periapsikseksensa periapsiksikseen periapsiksiksensa abessive periapsiksettaan periapsiksettansa periapsiksittaan periapsiksittansa instructive — — comitative — periapsiksineen periapsiksinensa