December may be the best month of 2018 when it comes to watching the sky. We’re talking about spectacles that require no sky knowledge or instrumentation.
Night comes fast and easy this month. The earliest sunset happens this very week, on December 7. I annually point this out, because everyone rightly associates maximum darkness with December 21 – when I lead a group gathering at the Mohonk Mountain House sundial at the exact moment of the solstice.
That date, which also marks the start of winter, indeed offers the longest night. Lesser-known is the fact that the darkness is then back-shifted to the post-midnight hours, since the darkest mornings don’t happen until early January. But in terms of late-afternoon brightness – which is when most people are awake and aware of light – the nadir is now rather than the solstice.
Our first naked-eye goodie is the Geminid meteor shower. These will be the year’s best meteors. Under our region’s unpolluted skies, you should see one shooting star per minute, if you observe from an open place with a big unobstructed swath of the heavens. You needn’t wait until after midnight, like with August’s Perseids; you can start observing at nightfall – as early as 5 p.m.
These meteors can appear anywhere in the sky, although the favored direction is the northeast. The Moon will be a fat crescent that won’t produce too much unwelcome brightness, but you can eliminate that small hindrance by observing after 10:30 p.m., when the Moon will be gone.
Our next naked-eye goodie is Mars, that bright-orange “star” to the left of where the Sun set. These are its final weeks as a truly brilliant zero-magnitude object. Here’s the second date to mark on your calendar: December 14. That’s when Mars hovers just above the half-Moon. It’s a worthy conjunction, and an easy sight between 5 and 7:30 p.m. Through any backyard telescope, the Moon will then be optimally illuminated to show stunning detail (though Mars will be a telescopic washout because it’s now much too small).
Our third goodie is the most unusual: Comet Wirtanen. I’ve seen eight naked-eye comets since moving here 46 years ago, and we are now overdue for a good one. Our dark, rural, unpolluted skies are ideal for comet-watching. Typically, we get a truly bright comet every 20 years or so.
We’ve had two fully spectacular comets since the mid-’70s: first, the pre-dawn mindblower Comet West on March 7, 1976; and then Hale-Bopp, which remained brilliant for almost an entire year, mostly in 1997. We’ve also had faint, barely-there-but-still-naked-eye comets in the form of Comet Kohoutek in 1973, Comet Iras-Iraki-Alcock in 1983, Halley in the autumn of 1985 and Hyakutake in 1996. The new one, which should be visible next week, is Comet Wirtanen.
This is a good news/bad news kind of deal. The bad is that it’s an unusually tiny comet whose nucleus is just a half-mile wide. The good news is that on December 15 and 16, it will pay Earth its closest-ever visit. It’ll pass just seven million miles from us. I think it will just barely be visible to the naked eye. It should be large and blobby-looking, appearing as a fuzzy glob the size of the full Moon.
My suggestion is to look halfway up the southern sky starting around 10 p.m. beginning on December 8 or so. If you can recognize the famous Seven Sisters star cluster (also known as the Pleiades), to the upper right of Orion, look far below it and sweep binoculars there, too. The comet will be brightest on the nights of December 15 and 16, when it will be located just left of the Pleiades.
If you don’t already know the Pleiades, this is a good time to make their acquaintance. At 10 p.m. any night, look south and you’ll easily see a small, tightly packed group of stars. That’s it! Sweep binoculars over them and you’ll be thrilled, since the stars in the cluster will explode from six to 100, and their blue-white diamond color will be obvious, too. It’s the very best celestial target for binoculars: a marvelous sight. And once you’ve located it, you’ll know where to look for the comet on December 15.
Want to know more? To read Bob’s previous columns, visit our Almanac Weekly website at HudsonValleyOne.com. Check out Bob’s new podcast, Astounding Universe, co-hosted by Pulse of the Planet’s Jim Metzner.