Astro Bob: Keep your eye on the crescent moon
On Nov. 3 at dawn, a stunning crescent hovers near Mercury, then it occults the planet later that afternoon. And guess what? There's more aurora in the forecast.
You can't go wrong following the moon. Like a good tour guide it will show you all the sights including those off the beaten track. On Wednesday, Nov. 3 at dawn, a leaf-thin crescent will appear about 3° above the planet Mercury. The following day the moon will be new and then return at dusk on Saturday, Nov. 7 just a few degrees to the right of brilliant Venus. Both occasions will make for delightful opportunities to see and photograph the two in each other's company.
With the sun rising so late the past couple weeks, many of us have had the pleasure of watching the moon wane outside our windows. When paired with Mercury it will be just 2.5 percent illuminated — a thin crescent indeed — and stand about 10° or one fist high in the east-southeast sky 45 minutes before sunrise. Bring binoculars to help you see the Earth-lit portion of the moon, caused by sunlight reflecting off our own planet that reflects a second time off the moon. Mercury will appear like a bright star at magnitude -0.9 and should be easy to spot.
The distance between the moon and Mercury varies from about 4° as viewed from the East Coast to just 2° from the West Coast. The reason their separation shrinks as you travel farther west is because the moon keeps moving along its orbit (to the east). When Bostonians spot it in the eastern sky, it won't be visible for another two hours for observers in San Francisco. During that time, the moon advances farther east and snugs up closer to Mercury.
The moon crosses the sky much faster than the planets because it's much closer to us. When it catches up to and passes a planet it typically inches north or south of it. But not always. Occasionally it scores a bullseye and temporarily blocks the object from view in an event called an occultation. Later Wednesday (Nov. 3), the now super-thin crescent will occult Mercury in broad daylight for up to an hour for locations across the eastern two-thirds of the U.S. and Canada.
It won't be easy to see because the moon will only be a sliver in a bright sky just 15° (1.5 fists) to the west of the sun. Although the planet might be glimpsed in daylight with binoculars, a small telescope will work best. Here are a few cities and local times when the planet "touches" the crescent's leading edge just before it disappears behind the moon. Good luck, and be careful not to look at the sun when seeking the moon.
Fargo, ND — 2:14 p.m.
Minneapolis — 2:21 p.m.
Duluth — 2:18 p.m.
Chicago — 2:33 p.m.
Cleveland — 3:38 p.m.
New York — 3:46 p.m.
Ottawa, Ont. — 3:34 p.m.
After New Moon, the crescent returns to the evening sky at dusk. Bonus! It will appear alongside Venus on Sunday evening , Nov. 7 in an eye-catching, one-night show. Since we shed Daylight Saving Time earlier that day, losing the extra hour means the sun sets an hour earlier than the night before, dipping below the horizon around 5 p.m. instead of 6. The best time to see the scintillating couple will be from about 5:30-6:15 p.m. local time.
All three of these celestial objects exhibit phases. Mercury is currently in waxing gibbous phase, while Venus is just a hair shy of half. While you're out this week, be aware that continuing solar activity may stoke more chances for auroras. We flirted with the northern lights several times the past few nights. Last night (Nov. 1), a bright arc glowed low in the northern sky for much of the evening.
A minor G1 geomagnetic storm is forecast between about 10 p.m. and 4 a.m. the night of Nov. 3-4. Should it happen, sky watchers in the northern states might see a bright arc or two dappled with faint pillars of light. With no moon at play, the timing couldn't be better.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob .