# periapsis
## English
### Etymology

From peri- +‎ apsis.

### Pronunciation

* Audio (US):(file)

### Noun

periapsis (plural periapsides or periapsises or periapses)
* (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.
* 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
* periapse

#### Antonyms

* apoapsis

#### Hypernyms

* apsis

#### Derived terms

* argument of periapsis
* longitude of periapsis

#### Related terms

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

#### Translations
### Further reading

* Apsis on Wikipedia.Wikipedia
* Apsidal precession on Wikipedia.Wikipedia

## Finnish
### Etymology

Internationalism (see English periapsis).

### Pronunciation

* IPA: /ˈperiɑpsis/, [ˈpe̞riˌɑ̝ps̠is̠]
* Rhymes: -ɑpsis
* Hyphenation: pe‧ri‧ap‧sis

### Noun

periapsis
* (astronomy) periapsis

#### Declension

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 :