Astro Bob: Enjoy a 3-course heavenly meal tonight
Mercury, Venus and a very young crescent moon gather low in the west at dusk on Monday night (Jan. 3).
I absolutely loved the food on my recent cruise to Antarctica and the Falkland Islands. For lunch at home I usually make a salad, piling everything I can find in the fridge into a heap on a plate and topping it with dressing. On board the ship, elegantly prepared four-course lunches and dinners were the norm. After two weeks of eating like a royal, you'd think homemade food would be blasé. Not by a long shot. We eat well, but honestly, everything tastes good when you're hungry.
I hope I can whet your appetite for some eye candy Monday night (Jan. 3). Find a place with a wide-open view to the southwest and go out about half-hour after sundown . Very low to the horizon look for a super-thin lunar crescent, and above it, the planet Mercury, which will look like a tiny star. Only 4° separate them, so you should be able to fit the pair in the same binocular field of view.
A fist to the right of the moon, look for another "star." That's Venus. Two nights ago, I gazed hard at the planet to see if I could discern its crescent shape without any optical aid. At first, I thought I could. But to check myself I mentally imagined the crescent curving in the wrong direction and was able to see it that way, too. Alas, I needed glass. How I wished I'd brought binoculars. Venus is now grass-blade thin and just 1.1 percent illuminated by the sun. That makes it twice as narrow as tonight's lunar crescent.
Tuesday, Jan. 4, the waxing moon will park itself about 5° to the lower left of Saturn. I thought that was quite a leap in just one night, so I checked. Normally, the moon travels about 13° to the east (left in the northern hemisphere) each night. But between Jan. 3 and 4 it slides 14°, nearly a fist-and-a-half! What gives?
The moon's orbit isn't a circle but an ellipse with one end closer to the Earth than the other. When closest at perigee, the moon appears slightly larger and travels faster compared to apogee, when it's farthest. Perigee occurred late on Jan. 1, so the moon was (is) still relatively close to the Earth and traveling faster than normal — the reason it covered 14° instead of 13°.
Apogee happens at mid-month when the moon's daily trek slows to 12°. The difference in speed between the two extremes is significant — 2,169 miles an hour (3,492 km/hour) at apogee compared to 2,438 mph (3,924 kph) at perigee. Right now, the moon's zooming along more 100 mph faster than average. Cool.
It's fun to know that the shape of the moon's orbit is hidden within little details like its nightly motion. Its elliptical path plays out in more obvious ways, too. Like eclipses. When a lunar eclipse occurs around the time of perigee, the larger apparent size of the moon more than covers the sun, making for multiple minutes of totality. On the opposite end of its orbit at apogee, it's too small to fit over the sun and a ring or annular eclipse results.
Happy moon-watching! I've got to go make lunch.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob .