D defs.my
Entry 1 sense Webster, 1913

Periastron

· Per·i·as·tron · IPA /pɛɹɪˈæstɹən/
01 n. That point, in the real or apparent orbit of one star revolving around another, at which the former is nearest to the latter.
  1. 1.
    That point, in the real or apparent orbit of one star revolving around another, at which the former is nearest to the latter.(Astron.)