Cold Perihelion

After a long, silent spell, Mr. H's TOE returns on perihelion, the point in Earth's elliptical orbit that we are closest to the sun for the entire year. For those of us, most anywhere in the US, it is also one of coldest starts to a morning in quite some time. With those two bits of information we can then clear up any season confusion; it's the 23.45 degree tilt of our planet that causes the seasons and has NOTHING to do with our distance from the sun. (Obviously, folks in the southern hemisphere, just 2 weeks into summer, might want to disagree with this but while they are likely not in the midst of an arctic blast the couple of million miles closer really doesn't affect things much - especially with the southern latitudes being mostly ocean, quite a heat sink.) The northern hemisphere is tilted away from the sun right now so even though we are close to our star, it's light is low in our sky, scattered and not very warm (well, it is behind a couple of layers of glass at the tire house).

Crazily, in addition to being closest to the sun today, the northern hemisphere also had the sun rise later than any other day of the year. But, the winter solstice is the shortest day...yes, but while the solstice does have a longer period of dark (or light for summer) than any other day, the rising and setting are not latest and earliest on the solstice. The earliest sunset is in early December and the latest sunrise is, again, today. This has to do with what sunrise and set really are; our rotation toward or away from the sun.  Think of a tilted ball rolling around an oval NASCAR track with you sitting in a tower in the infield. Just before the apex of the far turn (remember they go counterclockwise - a left turn) it would be hard to see the outside, right edge of the ball (early December - sunset) but as it comes out of the turn now it would be hard to see the left edge of the ball (today's sunrise). At the far point (solstice) you would see less of the top of the ball (remember, it's tipped away from you) but because it's tipped perfectly away you would see the edges equally that are a little hidden today (and back in early December for sunset).

And, thank some sky watching, math wiz for measuring things accurately enough to know all this stuff. Actually, our distant ancestors figured out the whole seasons thing, they had to know when things were going to change to stay alive (hunting and gathering and then farming requires seasonal knowledge). I'm not sure if they knew earliest and latest sunrise info because that requires some very accurate time keeping, a fairly recent phenomenon.

To wrap up this info filled, conceptual diatribe, it is cold here in central Va. but it's cold most everywhere in the US. A southern wind flow today should get temps above freezing and clouds will moderate temperatures for a day or so; drizzle, perhaps frozen, followed by rain and maybe finishing with snow will be the weather scene on Sunday into Monday morning. The cold front bringing that wet mess will clear the region Monday and temps will plummet, making today's low of 10 feel almost toasty. Tuesday should see temps at or below 0 (yes, zero, central Va.) with highs for the day only in the teens and Wednesday won't be much warmer. It will warm up some later next week but there will be no doubt that we are in winter.

With winter's still, cold air and long nights, the sky gazing will be spectacular. The moon is waxing, a thin crescent with lovely earth shine tonight but Venus, the bright beacon in the fall sky is gone. It will go between Earth and the sun on the 11th (but not directly in front of the sun, for another 103 years...) and will dominate the sky as the morning star for winter and spring. In it's place, Jupiter is at opposition tomorrow, in a line directly behind earth from the sun. That means, it's in the same position as the full moon and will rise as the sun sets (we turn away from the sun and toward Jupiter). It will be the brightest "star" in the sky, all night long. Check it with binoculars or a telescope - before the waxing moon gets too bright - and you will likely see little dots next to it. Those are the 4 Galilean moons.

Other TOE blogs will be caught up soon, so check them out, let me hear what you think, shoot me questions and bundle up and get out and enjoy today on earth.