Speeding Through Winter
Would you believe it’s our shortest season?
Thursday brings two celestial milestones: it marks the latest sunrise of the year and it marks perihelion, earth’s closest point to the sun.
Intuitively, you might expect the closer to the sun we are the warmer the weather. However, the three million miles difference between perihelion and aphelion — our farthest point from the sun in July — is not near enough to account for the changing seasons. Instead, earth’s 231⁄2-degree tilted axis brings about our seasons, as one hemisphere faces the sun for more hours than not.
While our proximity to the sun isn’t responsible for the seasons, it certainly does influence them. The earth orbits the sun not in a circle but in an egg-shaped ellipse. With perihelion, we’re at the pointed tip of that egg. Being closer to the sun, its gravitational pull on us is all the stronger, propelling us around the bend roughly five percent faster than when we’re at the wider, more shallow end of our orbit. As a result, the time it takes earth to travel from the point of our winter solstice to vernal equinox is several days less than the time it takes to travel from the point of our summer solstice to autumnal equinox. In short, our winter is almost five days shorter than our summer.
Sunday’s full moon, the Old Moon, rises in the east around sunset, climbs highest in the sky around midnight and sets in the west around sunrise. Its bright face bleaches out all but the brightest stars this week. Of those, many belong to the Great Winter Circle, surrounding the familiar shape of Orion. Start at the hunter’s foot with Rigel and move clockwise to Sirius in Canis Major, Procyon in Canis Minor, Pollux and Castor of Gemini and finally to Aldebaran, the red heart of Leo the lion. While nearly at the center of the circle, Orion’s shoulder Betelgeuse is not part of it.