perihelion and aphelion
/ peri-HEE-lee-on, ap-HEE-lee-on /
Because most orbits are ellipses with the Sun off at one focus, a planet is not always the same distance from the Sun. There is a point where it comes closest, called perihelion, and a point where it is farthest, called aphelion. The names combine the Greek helios, meaning Sun, with peri (near) and apo (away from), so they literally mean near-Sun and far-Sun.
These two points are the ends of the ellipse's long axis, and they are where the planet's motion changes most in speed. By Kepler's second law, the planet moves fastest at perihelion and slowest at aphelion, which is really conservation of angular momentum: as it swings in closer, it must speed up, like a skater pulling in their arms. For orbits around the Earth the matching words are perigee (closest) and apogee (farthest), and the general terms for any central body are periapsis and apoapsis.
A neat fact that corrects a popular myth: Earth actually reaches perihelion, its closest approach to the Sun, in early January, during the northern hemisphere's winter. So the seasons are not caused by our distance from the Sun at all. They come from the tilt of Earth's axis, which changes how directly sunlight strikes each hemisphere through the year.
Earth's distance from the Sun ranges from about 1.47 x 10^11 m at perihelion (early January) to about 1.52 x 10^11 m at aphelion (early July), a swing of only about 3 percent, and Earth moves fastest in January.
Earth is nearest the Sun in January; the seasons come from axial tilt, not from this small change in distance.
Earth is closest to the Sun in January, so seasons are not caused by distance but by the tilt of Earth's axis; near a planet the analogous points are perigee and apogee.