periastronn.
/ˌpɛrɪˈastr(ə)n/, U.S. /ˌpɛriˈæstrən/ Astronomy.
The point in the path of a celestial object orbiting a star at which it is nearest to the star. Cf. apastron n.
ΚΠ
1862 Intellectual Observer June 374 Since that time [sc. 1720] the components have been approaching with a gradually accelerated speed, and after a most rapid perihelion, or rather periastron, passage in 1836, have been widening out again.
1876 Athenæum 16 Dec. 805/2 The small star is now at or near its periastron.
1918 R. G. Aitken Binary Stars iv. 72 T = the time of the periastron passage.
1943 Proc. Amer. Philos. Soc. 86 362/1 The longitude of periastra of fictitious ellipses invoked by the ellipticity and reflection differ by 180°.
1971 Nature 5 Feb. 395/2 To be more specific, we shall consider a planet of a few Earth masses with periastron distance 5 x 1012cm (0.35 a.u.) and orbital eccentricity e.
1993 P. Anderson Harvest of Stars (1994) 422 The air hereabouts got tricky around vernal equinox. Maybe the companion sun, approaching periastron, added something to that.
This is a new entry (OED Third Edition, December 2005; most recently modified version published online March 2022).
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