Comet PANSTARRS glides through the W of Cassiopeia at nightfall in late April. Look low in the northwestern sky about 1 1/2-2 hours after sunset to find it. Moonlight might render the comet invisible in binoculars, but a small telescope will still show it. This map shows the sky facing northwest around 9:30 p.m. local time. Created with Stellarium
As Comet PANSTARRS gallops off into the sunset of deep space, we anticipate the arrival of another fine binocular comet – C/2012 F6 Lemmon. Some of you might recall this comet from earlier in the year, when it reached naked eye brightness for sky watchers in the southern hemisphere and grew a long, ribbon-like tail.
After months of having it as their own, Lemmon will soon appear in the dawn sky near the Great Square of Pegasus at the end of this month in the northern hemisphere. Predictions indicate it might be visible with the naked eye from a dark, rural locale, but there’s no question we’ll see it in binoculars and small telescopes.
Comet C/2012 F6 Lemmon photographed through a 12-inch telescope from Namibia on April 21. Exposure time was 3 minutes. Notice the short dust tail and long, blue electrically-charged ion tail. Click to see more of Rhemann’s comet photos. Credit: Gerald Rhemann
Next week I’ll post a map and directions on how to find it. On May 6, a thin crescent moon will pass a short distance south of Lemmon, providing a helping hand. Comet PANSTARRS will still be out in May and though very faint in binoculars, a small telescope will show it.
I hate to go cometless for very long, so Lemmon’s arrival is welcome. Of course Comet ISON is the year’s BIGGEST celebrity. Circumstances are much better for it than PANSTARRS. ISON will pass very close to the sun in late November, be cooked into a brilliant object and develop a long tail.
Comet ISON is “rounding the corner” in Gemini the Twins this month and still very faint. It’s currently lies beyond the outer edge of the asteroid belt some 400 million miles from Earth. The Swift observation is described below. Credit: NASA
An ideal comet encounter is one where the object first passes very close to the sun then zooms by Earth soon after. This two-birds-with-one-stone trajectory allows us to see the comet near peak brightness and in its full finery. That’s exactly what will happen with ISON.
Views of Comet PANSTARRS were somewhat compromised because it receded from Earth after closest approach to the sun. It also didn’t help that the comet was more than twice as far away (101 million miles / 163 million km) when nearest Earth compared to ISON’s 40 million miles (64 million km) on Dec. 26.
On Nov. 28 Comet ISON will pass only 680,000 above the sun’s surface. Less than month later, it flys by Earth at a distance of 40 million miles. Credit: NASA
All this assumes that ISON won’t bust to bits in the intense heat it will experience during its face-to-face with the sun on Nov. 28. Back on Jan. 30, NASA’s Swift spacecraft aimed its powerful, multi-wavelength eyes at the comet when it was still near Jupiter. Even at that distance, solar heating vaporized enough ice for ISON to spew out 112,000 lbs. (51 kg) of dust a minute.
This is a tiny bit of comet dust captured by a high-flying airplane mission. The particles from ISON are similar in size – about 1/8000 of a inch across. Credit: NASA
Meteor researcher Paul Wiegert of the University of Western Ontario, who’s been using a computer to model the trajectory of dust ejected by Comet ISON, predicts that some of that dust could end up on Earth.
Less than three weeks after closest approach to our planet, Earth will pass through a flurry of the powdery stuff lofted our way by the gentle pressure of sunlight. At the same time, we’ll encounter the dust stream trailing behind ISON and headed toward the sun. Wiegert calls the double-whammy “unprecedented”.
If his forecast is correct, the dust, traveling at 125,000 mph (201,000 km/hr), will pepper Earth’s atmosphere for several days around Jan. 12, 2014. While you might expect to see a meteor shower, chances are slim; the particles are so small, they’ll slow to stop instead of getting fried as meteors by air friction. Still, you never know – maybe a few of the bigger ones will show as meteors.
Noctilucent clouds photographed from the International Space Station. Credit: NASA
As the grit drifts gently down over the months and years, it’s possible it may serve as seeds or “nuclei” for the formation of noctilucent clouds, those eerie, skeletal blue clouds visible from northern locations during the summer months. For clouds to form, water vapor needs some form of dust or grit to latch onto and grow into crystals and droplets.
For a nice visual summary of the Comet ISON dust prediction, check out this video.
Noctilucent clouds, shining in late twilight when all other clouds have gone dark, are nearly as high as the lower limit of the aurora borealis (60 miles / 96 km). While it’s only speculative, it’s possible that bits of Comet ISON may someday contribute to their formation. Wouldn’t that be just too cool?