Starwatch: Earth hustles for a shorter winter
January opens on the first steps in a graceful predawn dance between Venus and Jupiter. Not to be outdone, the evening sky answers with a total eclipse of a "supermoon" in mid-month.
As the sky awaits the first sunrise of 2019, we're treated to a crescent moon hanging above bright Venus, with Jupiter far below. Off to the right of Jupiter shines Antares, the red heart of Scorpius. Over the next three mornings, the moon thins as it drops past Venus and then Jupiter. On Jan. 4, look 45 minutes before sunrise to see a skinny old crescent just above the east-southeast horizon.
After Jan. 6, Venus moves slowly nearer to the rising sun. But Jupiter climbs away from it, thanks to Earth catching up to Jupiter in the orbital race. The two planets pass each other Jan. 22. Starting Jan. 30, the moon repeats its early-January performance, this time sweeping by Jupiter first. Don't miss the show on Jan. 31, when a waning crescent moon rises next to Venus. Late in the month, you may spy Saturn low in the southeast as the ringed planet, like Jupiter, begins a climb into the morning sky.
The moon celebrates its first full phase of the year by plowing through Earth's shadow in a spectacular lunar eclipse. On the night of Jan. 20, the moon will be very close and appear large and bright, hence its supermoon status. It starts to disappear into the dark inner shadow, or umbra, at 9:34 p.m., with totality beginning at 10:41 p.m. and the moon in deepest eclipse at 11:12 p.m. During or close to totality, grab some binoculars and look below and east of the moon for the lovely Beehive star cluster.
Totality ends at 11:43 p.m., when the first silver sliver peeks out from the curtain of Earth's shadow. The last vestiges of umbra drop away at 12:51 a.m. Jan. 21.
On Jan. 2 at 11:20 p.m., Earth reaches perihelion, its closest approach to the sun. We'll be 91.4 million miles away, only 1.5 million miles closer than average, so of course, we feel no extra warmth. However, if winter gets you down, you can thank the date of perihelion for the fact that winter is our shortest season.
That's because Earth's orbit is an ellipse, not a circle, and when a celestial body follows an elliptical orbit, it always moves fastest when it's closest to the body it orbits, and most slowly when it's farthest away.
Earth is farthest from the sun and slowest in early July. But it hustles through the part of its orbit it's in now. The difference in speed gives us winters that are about four and a half days shorter than our summers.
The University of Minnesota offers public viewings of the night sky at its Morris, Duluth, and Twin Cities campuses. For more information and viewing schedules in Duluth, visit the Marshall W. Alworth Planetarium at www.d.umn.edu/planet.