- For objects orbiting Earth, periapsis and apoapsis are known as perigee and apogee; for objects orbiting the Sun, these locations are known as perihelion and aphelion.
- This affects the climate because the influx of solar energy to our planet would then vary between perihelion and aphelion by a larger proportion than at present.
- The radius vector is shortest when the planet is at perihelion and longest at aphelion.
- The problem involved the advance of the perihelion of the planet Mercury.
- He calculated to within a month the return in 1759 of Halley's comet to its perihelion (closest point to the Sun).