Earth is farthest from the Sun in July, yet northern summers run warmer
Every early July our planet swings out to its most distant point from the Sun, catching only about 93.55 per cent of the sunlight it gets in January. Northern summer happens anyway, and is actually the warmer one. The reason lies in tilt, land and a little Greek vocabulary about orbits.
Any elliptical orbit has two extremes: a nearest point and a farthest one. Astronomers call each an apsis, from a Greek word for arch or vault, and the imaginary line joining them is the line of apsides, which is also the orbit's major axis. Names are built from a prefix and a suffix. Peri- means near and apo- means away from; tack on -gee for Earth and you get perigee and apogee, or -helion for the Sun to make perihelion and aphelion, words Johannes Kepler coined for planetary motion.
The naming game has spread wildly. Around other stars the terms become periastron and apastron. Apollo crews orbiting the Moon spoke of pericynthion, after Cynthia, another name for Artemis, whereas the Artemis program has favoured perilune. J. Frank and M. J. Rees used peribothron for black holes in a 1976 paper, crediting W. R. Stoeger and the Greek for pit; science-fiction writer Geoffrey A. Landis put perimelasma into a 1998 story before Latin-based perinigricon reached journals in 2002. Saturn's own suffix has barely appeared in half a century.
For Earth, perihelion now arrives in early January, about 14 days after the December solstice, at roughly 0.9833 astronomical units, or 147,100,000 km. Aphelion falls around 14 days after the June solstice at about 1.01664 AU. The exact date wobbles by up to 3 days year to year, as with 3 July 2025 versus 6 July 2026, because Earth's centre sits about 4,700 kilometres off the barycentre it shares with the Moon.
Seasons come from the 23.4 degree axial tilt, not distance, so one hemisphere always has summer while the other has winter. Northern summers average 2.3 °C warmer than southern ones despite coinciding with aphelion, since the north holds more land, which heats faster than sea. Distance still leaves a fingerprint: Earth moves slowest near aphelion, so northern summer stretches to 93 days while the southern version lasts 89.
Source: Apsis
