Grab a Seat! Tomorrow’s the peak of the annual Leonid Meteor Shower

This map shows the sky tomorrow morning Nov. 17 facing east around 4 a.m. CST when the Leonid meteor shower peaks. Leonids can appear anywhere in the sky but all radiate back to the inside of the Leo’s Sickle. By the way, the name is pronounced LEE-uh-nids, not LAY-uh-nids. The name comes from the home constellation Leo. Stellarium

The Leonids are a tough nut this year, but that doesn’t mean you should give them the cold shoulder. While the shower returns every mid-November to toss 15 meteors per hour our way in the wee hours of the morning, this year’s full moon will halve that number. Still, they’re an enjoyable diversion. If you’re out looking for Comet ISON, keep an eye open for meteors shooting from inside the Sickle of Leo just above the star Regulus.

A magnitude -8 fireball photographed on Nov. 18, 2012 during last year’s Leonid shower. Credit: John Chumack

While fewer in number this year, the Leonids are famed for fireballs that leave bright, persistent “smoke trails” called trains. These are actually tubes of air molecules excited and ionized by the meteoroid’s passage that glow briefly as they return to their neutral or pre-excited states. Traveling at an average speed of 162,000 miles per hour (261,000 km/hr) it’s no wonder Leonids leave trains. They’re one of the fastest meteor streams around.

Comet 55P/Temple-Tuttle supplies the material that comprises the shower. Vaporizing dirty ice when the comet nears the sun leaves streams of dust particles in its wake. Every November, Earth’s path intersects that of the comet and we smack into dust and debris scattered along its orbit. Because the grit hits the upper atmosphere at high speed, it burns up in a flash of light called a meteor.

Look at all those meteors! The Leonid meteor storm photographed November 18th, 1966, from the Kitt Peak National Observatory near Tucson, Arizona. Credit: NOAO/AURA/NSF

Every 33 years, Comet Temple-Tuttle returns to the vicinity of the sun, and if the Earth happens to be near the comet’s orbit at the time, we see a massive increase in the number of Leonids. Two of the greatest showers on record with rates of around 100,000 per hour occurred in 1833 and 1966. The 2001 shower wasn’t bad either. Many of you will still remember that one and the many fireballs that whizzed across the sky. Here at my place the whole family came out to look; it was one of the few times I’ve had willing company at 4 a.m.

Comet 55P/Temple Tuttle photographed with a 19.6-inch (50-cm) reflector on Feb. 17, 1998. Copyright © 1998 by National Astronomical Observatory in Japan

You can start watching for Leonids anytime from around 1 a.m. till dawn, when the radiant or point in the sky from which the meteors will appear to originate, rises in the eastern sky. This year’s shower features two peaks, the first at 4 a.m. CST (10 UT) and a second burst at 10 a.m. CST or 6 a.m. Hawaiian Time. The earlier peak favors the eastern half of the U.S., Canada and South America; the second the central Pacific including Hawaii. But again, remember this is an off-year for the shower and numbers will probably be low.

Watching the shower is easy. Sit down in a reclining chair facing toward the south or southeast and kick back. While the Leonids are sparse except at those 33-year intervals, upticks and outbursts aren’t uncommon. In 2008 and 2009 the maximum hourly rate recorded by pro meteor observers reached the mid-70s, so who knows.

Plot of meteor counts during the peak of the 2012 Leonid meteor shower. These numbers are ZHR rates. See text for ZHR definition. Credit: IMO

You can track the pulse of the Leonids during and after the shower by visiting the live ZHR graph on the International Meteor Organization’s (IMO) website. The ZHR or Zenithal Hourly Rate is the number of meteors a single observer would see under a clear, dark sky with the radiant high in the sky near the zenith.

Another cool way to stay in touch with the shower and see quickly-posted photos is to head over to the Meteorwatch website. You can also contribute your own meteor observations there via Twitter.

Good luck and dress warmly!

 

See a lunar crater arc tonight / 4-comet tableau / Space station flybys

Tonight’s gibbous moon features a lovely arc of large craters visible in binoculars beginning with Plato on down to Clavius. Credit: Christian Legrand and Patrick Chevalley’s Virtual Moon Atlas

If you step outside tonight you’ll see a bright waxing gibbous moon below the Great Square of Pegasus. Far to the moon’s lower right shines Fomalhaut, the only bright star in the southern half of the sky during early evening hours.

The waxing gibbous moon shines high in the southern sky below the Square of Pegasus during early evening hours tonight. Stellarium

While the moon looks smooth and pasty to the naked eye, binoculars will show its biggest craters and rough, crinkly surface especially if you direct your gaze along the terminator, the curving border separating the bright, sunlit portion of the moon from the part that’s still in darkness.

Tonight’s 9-day-old moon features an arc of four prominent lunar craters just this side of the terminator: Plato, Copernicus, Tycho and Clavius. Plato, the northernmost and 68 miles across (109 km), looks like an oval swimming pool only instead of water it’s filled with dark, titanium-rich lava that solidified some 3.8 billion years ago.

Dropping south we next encounter Copernicus (58-miles / 93 km). Though smaller than Plato, it looks far more impressive because the crater sits at the center of a great corona of rays. Lunar rays form when material blasted out by an impact fall back to the surface to create long chains of secondary craters. Seen from 240,000 miles away in binoculars and telescope they look like wispy white tendrils.

Copernicus is a bowl 2.3 miles (3.75 km) deep that was blasted out in the not-to-distant past 800 million years ago. I know that sounds like a lot of years but compared to 3.84 billion years for Plato, Copernicus is a youngster. If you have a scope, look inside and around the the crater to see and appreciate how rugged and relatively fresh it is.

Continuing along the arc we meet Tycho (53 miles / 86 km), the largest fresh crater on the near side of the moon. The asteroid that excavated it struck the moon about 108 million years ago during the heyday of the dinosaurs. Sharply-defined walls and a pointed central mountain peak reflect its youth. Even without water and air, erosion happens all over the moon. The temperature extremes of the lunar day-night cycle break down the rocks, while bombardment of the surface by solar particles and radiation gradually “sandpapers” them to a powdery finish.

Like Copernicus, Tycho’s wears a crown of rays best seen around full moon.

Our last stop is Clavius, the third largest crater on the visible side of the moon. Measuring 140 miles across or about the distance between Duluth, Minn. and Minneapolis, this 4-billion-year-old scar is so huge it’s riddled with dozens of younger craters easily visible in a small telescope. Glide down the arc tonight and see all four craters.

Clockwise from top left: Comets 2P/Encke on Nov. 4, ISON (Nov. 12), C/2012X1 (Nov. 6). and Lovejoy (Nov. 10) . All four comets are visible  in 50mm and larger binoculars from a dark sky site. Comet ISON’s dust and gas tails are now very obvious. Credits: Damian Peach (Encke and X1) and Michael Jaeger (ISON and Lovejoy).

I thought I’d put together an updated tableau of the four bright morning comets Encke, ISON, Lovejoy and C/2012 X1. Encke will meet up with Mercury this weekend a few days before Comet ISON does the same on Nov. 17. Speaking of ISON, it’s developed two very clear tails the past few days – one of dust and the other gas. I’ll have a map in Friday’s blog to help you find the two. Meanwhile, Lovejoy has quietly slipped into Leo the Lion and C/2012 X1 is approaching the bright star Arcturus. There is a lot happening before sunrise!

That includes the return of the space station passes for many northern hemisphere locations. I’ve listed bright passes for the Duluth, Minn. region below. Click over to Heavens-Above or Spaceweather’s Satellite Flyby page for times for your city.

* Weds. morning Nov. 13 starting at 5:44 a.m. in the southwest and traveling to the northeast. Brilliant pass high in the southern sky.
*  Thurs. Nov. 14 at 6:31 a.m. Nice bright pass halfway up across the northern sky.
*  Fri. Nov. 15 at 5:45 a.m. passes almost directly overhead. Brilliant!
*  Sat. Nov. 16 at 6:31 a.m. halfway up across the northern sky.
*  Sun. Nov. 17 at 5:45 a.m. Another pass halfway up in the northern sky
*  Mon. Nov. 18 at 6:31 a.m. in the northern sky

Mercury enters early morning comet traffic jam

Mercury is now visible low in the southeastern sky below Virgo’s brightest star Spica. The planet will rise higher in the coming days and get easier to see. To find it, sweep the area to the lower left of Spica 5-10 degrees above the horizon with binoculars. This map shows the sky about 50 minutes before sunrise facing southeast. All maps: Stellarium

As the arc of dawn swelled in the eastern sky, we thought we were done observing. Jim, Eric, Greg and I had come to this dark place Sunday morning to look for comets in our telescopes. Clouds were causing trouble, but we exploited every starry hole we could find, eventually adding Jupiter, Mars and double stars to our list.

Comet ISON lines up with the planets Mercury and Saturn 5-10 degrees above the southeastern horizon on Nov. 23. Don’t take the comet’s appearance too literally. It’s hard to know how bright it will be on the date.

Then Mercury showed up. Sure enough, below Spica in Virgo, a tiny “star” winked between cloud banks barely bright enough to see with the naked eye. Binoculars made quick work of it, and through the telescope we saw a thick crescent made gooey by atmospheric turbulence.

Mercury pairs up with Saturn on the 25th and 26th. The wire-thin crescent moon joins the crew on Dec. 1.

Mercury enters a traffic jam of early dawn sights: comets ISON, Lovejoy, Encke and the planets Mars and Jupiter. Any more and I think I’ll bust.  But there will be more. Much more. As Comet ISON speeds sunward toward its close with our star on Nov. 28, it will join Mercury and the planet Saturn. Once ISON’s departed the scene, Mercury and Saturn will have a close conjunction on Nov. 25 and 26. And it’s capped off finally on December with the crescent moon passes between the two planets before sunrise. Wow! I’m out of breath and I haven’t even stepped outside yet.

Comets ISON and Encke give the gift of zodiacal light

The zodiacal light tilts upward from the southeastern horizon through the constellation Virgo toward Mars this morning Nov. 8, 2013. The green squares show the locations of two of the morning’s bright comets –  ISON and 2P/Encke. Watch for the light starting about 2 hours before sunrise. Credit: Bob King

See that big finger of light in the photo? That’s the zodiacal light, a vast cloud of mostly comet dust gathered into a thick disk in the plane of the solar system. It glows for the same reason you see sunbeams across your bedroom when you open the curtain in the morning – sunlight reflecting off specks of dust.

Sunbeams, also called crepuscular rays, are a mix of cloud shadows and sunlight reflecting off atmospheric dust. Similarly, the sun reflects off comet dust to shape the zodiacal light. Credit: Bob King

In your room we’re talking earthly dust, but in the solar system, minute motes of comet dust behave identically. From super dark locations the wedge of zodiacal light tapers and fades into a band encircling the zodiac called the zodiacal band (hence the name). The brightest part – that big finger again – is nearest the sun and visible on November mornings extending from the horizon nearly to Cancer the Crab. Take a look soon because the  glare of the moon will hide starting around the 15th.

Current comets and those from ages past deposit the dust from their tails and comas as solar heating broils their surfaces, releasing gas, bits of gravel and plenty of powdery dirt.

Comet ISON on Nov. 6 shows a glowing greenish head or coma and pretty dust tail. Notice also two new very skinny tails just up from the head. These could be the start of the comet’s gas or ion tail. Ion tails are made of gas excited by the sun’s ultraviolet light. Credit: Damian Peach

Over time much of the dust spirals in toward the sun and gets zapped, but new comets like ISON, fresh from the distant Oort Cloud, keep it replenished with new material. I wanted to share this photo because I know many of you either have been or are planning to venture outside in the cold dawn to see our current crop of bright-ish comets. If you live where the sky is very dark, the zodiacal light is easy to see. Matter of fact, the bottom half of the cone is easily as bright as the summertime Milky Way and can interfere with observing faint objects including comets.

I don’t mind. It’s fun knowing that the very objects that create the light just happen to be winging through it right now, offering us a chance to see these flying fuzzballs’ contribution to something greater than themselves.

Morning comets ISON, Encke and Lovejoy heat up, glow green

Comet C/2013 R1 Lovejoy, discovered last month by amateur astronomer Terry Lovejoy, glows green in this photo taken with a 12-inch telescope. The comet is currently visible in 6-inch and larger scopes in the morning sky. It may show in binoculars by month’s end. Click to enlarge. Credit: Gerald Rhemann

The color green represents hope and life. It’s also a sure sign our three morning comets are heating up and becoming more active as they approach the sun. I don’t know anyone who’s noticed the green color with their eyes looking through a telescope – the comets are all still around magnitude 10-11 and too faint to fire up our color vision – but the camera records their limey appearance with ease.

2P/Encke, which orbits the sun every 3.3 years, is a large, soft puff of light in the constellation Lynx visible in the wee hours before dawn. Glowing at magnitude 10, it will show in binoculars next month. Its coma fluoresces green from molecules released from ice vaporizing in the heat of the sun. Photo taken Sept. 30. Click to enlarge. Credit: Damian Peach

In some of the pictures you can clearly see the color difference between the comet’s tail and its fluffy coma – that’s the bulbous glow surrounding the tiny and invisible comet nucleus at the center of all the activity. Comas form tenuous, temporary atmospheres tens of thousands of miles across around the icy comet nucleus.

Comet star of the year ISON shows a beautiful green coma, bright false nucleus and pale yellow tail in the photo taken Oct. 4 from Austria by astrophotographer Gerald Rhemann. Click to enlarge.

Don’t expect to ever see a bare comet nucleus through a telescope. They’re not only very tiny, typically only a few miles across, but cloaked by dust and vapors boiled away by the sun. The closest you’ll get is the bright spot in the center of the comet called the false nucleus – a compact region where the dust and volatiles are densely concentrated around the true nucleus.

Comet ISON again on the morning of Oct. 5. The green coma is approximately spherical with a short dust tail pointing northwest. Comet ISON glows at around magnitude 11 right now. Click to enlarge. Credit: Michael Jaeger

Tails glow pale yellow from sunlight reflecting off cigarette-smoke-sized dust particles released from vaporizing cometary ices. The Caribbean blue-green of the coma, pretty as it is, originates from toxic cyanogen (a compound related to cyanide) and diatomic carbon (two carbon atoms bonded to one another). When energized by ultraviolet light from the sun, the gases fluoresce an eye-appealing green.

Everyone’s got their eyes and cameras glued to Comet ISON. This photo was shot on Oct. 4 with a 12.5-inch (32 cm) telescope from Payson, Arizona. Click to enlarge. Credit: Chris Schur

In my experience, the eye can’t sense the green until the comets become bright enough to show in ordinary binoculars at around 7th magnitude. When viewed through 8-inch or larger telescopes the color is tantalizing, like the green and blue iridescence sometimes seen along the edges of high clouds.

Comets ISON, Encke and Lovejoy are all predicted to brighten into visible green territory come November. That’s only a few weeks today. We’ll take the good news that all three comets are on track and brightening steadily. Stay tuned for more updates. For the latest brightness predictions, check out Seiichi Yoshida’s Weekly Information About Bright Comets.

Check out these new photos of Comets Encke, ISON and Lovejoy

Beautiful shot of Comet ISON taken with the VATT telescope on Sept 12. The brighter nucleus – source of the comet’s ice and dust – feeds a tail that points to the northwest. Credit: Carl Hergenrother / University of Arizona / Vatican Obs

Carl Hergenrother, a professional astronomer at the University of Arizona’s Lunar and Planetary Lab, recently used the Vatican Advanced Technology Telescope (VATT) 70.8 inch (1.8-m) telescope on Mount Graham to photograph three upcoming bright comets. His images reveal personalities and details not seen in smaller scopes.

Comet 2P/Encke looks like a big powder puff with a faint, pinpoint nucleus (the tiny dot) on Sept. 12. Inset photo shows comet photographed in red light. Credit: Carl Hergenrother / University of Arizona / Vatican Obs

All three are wiggling their way across the morning sky – Comet ISON near Mars in the constellation Cancer; Encke in Auriga and high in the east at dawn and Lovejoy in Monoceros the Unicorn, a dim grouping of stars with a wonderful name east of Orion.

ISON stays within a few degrees of the planet Mars now through late October. Not only is the comet headed toward the sun from the direction of Mars as seen from Earth, it will be physically close to the Red Planet, passing just 6.5 million miles (10.5 million km) away on Oct 1. That’s 6 times closer than its flyby of Earth on Dec. 26. Mars makes a convenient marker for anyone wishing to know where to look for the comet.

Comet C/2013 R1 Lovejoy on Sept. 12 shows a bright nucleus and broader tail than ISON. Credit: Carl Hergenrother / University of Arizona / Vatican Obs

From Martian skies, Comet ISON should be easily visible to the naked eye glowing at around magnitude 2-3. NASA hopes to enlist the electronic eyes of the Mars Reconnaissance Orbiter and two rovers – Opportunity and Curiosity – to take advantage of this unprecedented opportunity.

 

Comet Encke has the shortest orbit of any known comet. When closest to the sun it swings within the orbit of Mercury then loops out nearly to Jupiter. On Nov. 18, the comet will pass only 2.3 million miles from Mercury.

Comet 2P/Encke has the shortest orbital period of all known comets, cycling around the sun once every 3.3 years. It was first seen by French astronomer Pierre Mechain in 1786 but not recognized as a returning or periodic comet until its orbit was computed by German astronomer Johann Encke in 1819. Like Halley’s Comet, Encke is named after its orbit calculator instead of the original discoverer. The “2P” refers to it being the second periodic comet with a calculated orbit

The sky facing east-southeast just before the start of dawn tomorrow morning Sept. 15. Our three featured comets form a large triangle in the east. All three require at least an 8-inch telescope to see. Created with Stellarium

Although faint and very diffuse now, Comet Encke will brighten to binocular visibility in November. Yesterday morning it was a faint, soft glow through my 15-inch telescope at low magnification. Comet ISON looked great too. It’s “pumped up the volume” compared to a week ago and now burns more brightly at magnitude 12. I noticed that its center was distinctly brighter than a week ago.

Our third morning comet, C/2013 R1 Lovejoy is brand new, discovered by Australian amateur Terry Lovejoy only a week ago. It’s also brighter than several days ago, shining now at around magnitude 12.5-13.0.

The fall is shaping up to be a good one for comet lovers. I want to thank Carl and all the other generous astronomers – amateur and professional – for freely sharing their images with us.

New Comet Lovejoy joins an exciting lineup of fall comets and planets

Comet C/2013 R1 (Lovejoy) photographed on September 8. Note the small, condensed coma (comet head) and short tail. Credit: Ernesto Guido and Nick Howes

Australian comet hunter and amateur astronomer has done it again. He discovered a brand new comet with an 8-inch telescope and camera earlier this week. It’s his 4th. You might remember the Lovejoy name; Terry’s last find was  C/2011 W3 (Lovejoy), the first Kreutz-group sungrazing comet discovered by someone on the ground (as opposed to an orbiting observatory) in over 40 years.

C/2013 R1 Lovejoy is moving slowly east and north at the moment but it will soon gather steam as it approaches Earth. Watch for it below the Bowl of the Big Dipper when closest on Nov. 23. Planet positions here shown for Sept. 10. Created with Chris Marriott’s SkyMap software

Lovejoy’s comet was spotted along the border of the familiar constellation Orion and its dim neighbor Monoceros the Unicorn. Right now it’s faint and requires dark skies and at least a 12-inch scope. I gave it a whirl in my 15-inch scope this morning around 5 a.m. shortly before dawn. C/2013 R1 Lovejoy was a small, fuzzy glow of magnitude 13.5. While I could say it appeared unremarkable, that will soon change.

Come November the comet will be much closer and perhaps shine as brightly as 8th magnitude, making for a nice show in small telescopes. Closest approach of 38.1 million miles (61.3 million km) happens on Nov. 23  when the comet will peel across Ursa Major the Great Bear at a clip of more than a degree per night. With Lovejoy cruising the northern constellations, northern hemisphere skywatchers will be favored when comet’s at its best.

Perihelion or closest approach to the sun (81 million miles / 130.3 million km) happens on Christmas Day.after which the comet begins its slow departure back into deep space.

This map shows the sky facing southeast on the morning of Nov. 9, 2013. All three comets should be visible in binoculars or small telescopes. Mars and Jupiter add planetary bling to the comet-rich scene. Comet locations are accurate but appearances are for illustration only.  Stellarium

Now it just so happens there are two other comets sharing the morning sky at the same time as Lovejoy – comets 2P/Encke (EN-kee) and our good friend Comet ISON. Throw in the bright planets Mars and Jupiter and you’ve got one amazing morning sky show in early November. Check it out. All five objects form a wiggly line stretching across the southeastern sky before dawn.

On and around Nov. 9 will be the best time to ride the comet train. Lovejoy is expected to be mag. 9.5 on that date and visible in a 4-6-inch telescope; Encke at mag. 7 and Comet ISON at 6 should show up plainly in 35mm and 50mm  binoculars. Observers with very dark skies might glimpse ISON with the naked eye. Telescopic views will show more details including longer tails than binoculars.

I’m getting excited thinking about all the fun we’ll have early that month. Sure hope the weather’s good.

 

Comet Lemmon’s back plus Earth may get peppered with Comet ISON dust

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?

Comets Panstarrs and Lemmon share a Kodak moment

Two for the price of one! Comet L4 PANSTARRS is bright dot lower left with a short tail; Comet F6 Lemmon and its skinny tail are visible at right next to the Small Magellanic Cloud, a satellite galaxy of the Milky Way. Click to enlarge. Photo taken on Feb. 17, 2013 from Australia. Credit: Justin Tilbrook

Justin Tilbrook of Australia took a marvelous image earlier this week showing our two current comet celebs F6 Lemmon and L4 PANSTARRS together in the same picture.It’s not often you’ll see two tail-toting comets captured with a wide-angle lens at the same time.

To bring you up to date, Panstarrs is still visible very low above the horizon in morning twilight from far southern latitudes. This week it’s brightened to 4th magnitude and appears like a fuzzy pearl with a short tail. One observer noted a yellow color to the comet’s head caused by dust reflecting the ever-intensifying sunlight as PANSTARRS barrels sunward toward its March 10 perihelion.

Comet Lemmon photographed on Feb. 20, 2013 through a 19.6 inch telescope. Click to enlarge Credit: Martin Mobberley

Lemmon is higher up in the sky but fainter at magnitude 5.5. Right now it might be difficult to see with the naked eye because of moonlight. Binoculars show a bright head and a  1/2-degree-long tail.

You might be interested in a recent study on brightness predictions for comets L4 PANSTARRS and ISON by Ignacio Ferrin of the University of Antioquia in Medellin, Colombia. Here are the main points:

* C/2011 L4 Panstarrs will be less bright than Halley’s Comet was in 1986. It will show
a tail easily detectable with the naked eye.

* There’s a 75% chance that  C/2012 S1 ISON will continue to brighten and put on a great show late this fall. Ferrin predicts it could become as bright as the full moon (magnitude -12.6) when nearest the sun. But his prediction comes with a caution: ISON will pass within the Roche Limit when it swings around the sun in late November. This is the minimum distance a smaller body can hold together in one piece while orbiting a larger body without being torn to bits by the larger body’s overwhelming gravity.

At top, an object like a comet has crossed the Roche Limit and starts to disintegrate into pieces. Below, the individual pieces spread out according to distance. Particles closer to the sun (left) move more quickly (red arrows) than those farther away. Credit: Wikipedia

Ferrin writes: “Any object within this limit  has a large probability of disintegrating due to differential gravitational forces from the Sun. The combinations of Roche’s Limit, plus solar radiation plus very high temperature, suggest that the comet may not survive its encounter with the Sun, disintegrating into several pieces. Or it may survive, if its internal cohesion is
sufficient to endure those conditions.”

If you’d like to learn more, please check out the complete study.

Mid-February bright comet update: Panstarrs, Lemmon, Bressi, Ison

Comet Panstarrs on Feb. 8, 2013 photographed with a 300mm telephoto lens from Castlemaine, Victoria, Australia. Observers describe very bright head and broad tail. Click to see more comet photos. Credit: Michael Mattiazzo.

There are a lot of icy mudballs , ie. comets, flying around up there at the moment, so let’s take a look at what’s happening. We’ll start with C/2011 L4 PANSTARRS, better known as Comet Panstarrs. It’s been slowly brightening to within naked eye range, hovering now right on the edge of visibility under dark skies. Recent observations by amateur comet observers put the comet a smidge above the naked eye limit at magnitude 5.5-5.7. It’s a snap to see in binoculars in morning twilight in the southern hemisphere. As you can tell from the photo, it has an intensely bright, almost star-like head and wide, dusty tail that’s about 1/2 degree long. It should be a most excellent sight in binoculars for both northern and southern hemisphere sky watchers when it emerges at dusk in the western sky next month. We’re only four weeks away!

What a comet! This is Comet Lemmon shot through a 5-inch widefield telescope on Feb. 8, 2013 from Possum Observatory Complex in Gisborne, New Zealand. Click for large version. Credit: John Drummond

Meanwhile, another comet has temporarily stolen the show. C/2012 F6 Lemmon has swelled into a huge, green leek of a thing, Like Panstarrs, it too is faintly visible with the naked eye (mag. 5.8) under dark skies for southern hemisphere skywatchers. How come they get all the fun?

A long, thin exclamation point of a tail shoots from Lemmon’s giant, whipped-up coma or cometary atmosphere. Good news is, the comet is still brightening and may reach 3rd magnitude, making it an easy sight even from the suburbs.

We northerners will have to be patient if we want a glimpse of this comet. Not until early May, when it swings around the sun and enters the morning sky at about magnitude 5, will we get our chance.

You can see the fading of Comet Bressi in this sequence of photos made by Rob Kaufman of Bright, Victoria, Australia.

Then there’s C/2012 T5 Bressi, a modest, unassuming comet that experienced a bright outburst in late January. In a matter of days it became 10 times brighter than expected. On Feb. 4, Bressi glowed at 9.2 magnitude and then slid to 10.5 the very next day.

Sad to say, this is a bad omen for a comet and usually means the beginning of the end. They are crumbly things after all and subject to breakup as their ices volatilize under the relentless sun. Unfortunately, the nail might get hammered into Bressi’s coffin on Feb. 24, when it reaches perihelion or closest distance from the sun (28 million miles). Some comet observers predict it will disintegrate around that time.

Reversed (negaitve) image of Comet ISON on Feb. 3. At the time, the comet was 4 times Earth’s distance from the sun. Credit: Rolando Ligustri / CARA Project

Finally we come to this year’s best hope for a brilliant comet – C/2012 S1 ISON. It’s still slowly cruising through northern Gemini and beautifully placed for telescopic observation every clear night for observers in the northern hemisphere. Would that it were a tad brighter. You still need a 12-inch or larger telescope to see this 15th magnitude fuzzy blotch. I shouldn’t be so offhanded. Ison has developed a short tail of late, lending it enough character to whet our appetite for things to come.

By late fall, ISON should be an easy binocular object in the morning sky. Come Christmas it’s likely to be a glorious sight at dusk. Tag along with me and I’ll let you know how it goes as the clocks ticks cometward.