January weather in North America seems counter-intuitive. Some of the coldest temperatures of the year occur around the early part of this month. If we reckoned temperatures by our distance from the Sun, our winter temperatures should be less severe in early January. I’ve often puzzled over this oddity ever since my high school science teacher taught the class about Perihelion.
Actually we learned about Earth’s Perihelion the same day we found out about Aphelion. (I blogged about Aphelion last summer on July 3rd.) We have both of these because our planet’s orbit around the Sun is elliptical. This also leads to the counter-intuitive nature of July weather. Aphelion is when our planet is furthest from the Sun, but North America has some of its most uncomfortably hot days then.
If you live south of the Equator, these phenomenon are flipped around and the climate varies from the north in sometimes opposite ways. In either instance this business of Aphelion and Perihelion is interesting and all of us experience it whether we know it or not.
Not only are we closer or farther away from the Sun in winter and summer, but the dates when Aphelion and Perihelion occur are drifting towards later on the calendar. Way back in 1246, astronomers might have noticed that the December Solstice happened on the same day as Perihelion. Meantime astronomers estimate that over 4,000 years from now in 6430 that the March Equinox will coincide with Perihelion.
Maybe you remember this fact from your high school science class regarding celestial terms: Apogee is the farthest distance a celestial object is from the object around which it orbits and Perigee is the closest. Sometimes Apogee and Aphelion along with Perigee and Perihelion are used interchangeably when discussing planetary motion around the Sun.
This year, Perihelion happens at 05:34 UTC. That’s tomorrow morning at Greenwich, England, and tonight in the Americas. This means that in Norfolk, Nebraska the time of the event is 11:34 PM CST. If you don’t live in the USA Central Time Zone just add or subtract hours as needed for your own time.
Perihelion only happens once each year, so it should be celebrated. Unfortunately neither Perihelion nor Aphelion are red-number days on the calendar. I’m not aware of any official proclamations. Perhaps astronomers covertly hold Perihelion parties at observatories. It seems sad that an event that affects the entire planet goes by with such widespread indifference.
Oh well, if Perihelion means something special to you, now is the time to indulge in a small celebration. Maybe you just want to count down the minutes and seconds until 05:34 UTC for a cheap thrill.
The Blue Jay of Happiness likes this thought from Carl Sagan: “It’s been said that astronomy is a humbling and, I might add, a character-building experience.”