The past two decades have seen astronomers’ catalogue of planets expand over two-hundredfold, as new techniques and better telescopes have found more than 2,000 of them orbiting stars other than the sun. But in the solar system itself, the list of planets has actually shrunk — Pluto having been downgraded from that status in 2006. The number of the sun’s planetary companions has thus fallen from nine to eight.
Almost everything under the sun follows the rhythms of the sun, a 24-hour cycle hardwired from billions of years of planet Earth spinning around. Humans, animals, plants, flies, fungi, even bacteria, follow such a routine, and it’s called a circadian rhythm (circa means “around” and dies means “day”). Specifically, circadian rhythm refers to the result of constant interaction between an organism’s internal biological clocks and environmental cues — most notably, the sun, but also many other factors — a relationship that governs our behavior, hormone levels, sleep, body temperature and metabolism.