Perihelion refers to the point nearest the sun in the orbit of a planet or other celestial body.
A story told by a hologram of Doctor Stephen Hawking referred to the perihelion of Mercury. (TNG: "Descent")
The perihelion of planets in the Chin'toka system was listed in a computer graphic display viewed by Benjamin Sisko. (DS9: "Tears of the Prophets")
The graphic reads: "perihelion 107 km".