I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. I also write a daily astronomy blog called Astro Bob. My new book, "Wonders of the Night Sky You Must See Before You Die", a bucket list of essential sky sights, will publish in April. It's currently available for pre-order at Amazon and BN.
Mike Hankey of Monkton, Maryland took this photo of Comet ISON in outburst this morning Nov. 14. The tail now shows multiple streamers. Click to enlarge. Credit: Mike Hankey
After a sleepy week, Comet ISON is suddenly coming alive. Several amateur astronomers and at least one professional astronomers are reporting today that the comet has brightened at least a full magnitude overnight. Two days ago it glowed at around magnitude 7.5 and was visible weakly in 10×50 binoculars from a dark sky. Now it’s surged to around magnitude 5.5 – just above the naked eye limit – and continues to brighten. Several amateur astronomers have even seen it without optical aid.
Comet ISON on Nov. 10 before the recent outburst with well-developed dust (upper) and gas tails. Click ot enlarge. Credit: Damian Peach
ISON’s appearance has radically changed too. A week ago the comet developed a second gas or ion tail streaming alongside the wider, brighter dust tail. That new appendage has since grown like Pinocchio’s nose to nearly equal the length of the dust tail. I spotted it with averted vision Tuesday morning Nov. 12 through a 15-inch (37 cm) telescope. More exciting, the ISON’s head has been much brighter and more compact. Astronomers rate a comet’s degree of condensation or “DC” on a scale of 0 to 9 from extremely diffuse with no brightening in the center to disk-like or stellar. In recent days, Comet ISON has been packing it in at DC=6 or moderately compact and bright. Now amateurs are reporting that the comet’s head has brightened and become much more compact with a DC of 8.
Comet ISON in outburst with a completely changed tail appearance and bright, very compact coma shot this morning. Gonzalez reports the comet at magnitude 6.4. Click to enlarge. Credit: Juanjo GonzalezYou can watch Comet ISON evolve right before your eyes in this panel of photos taken by Juanjo Gonzalez. Top row left-right: Nov. 3 and Nov. 9. Bottom row left right: Nov. 12 and Nov. 14. The tail structure changes are dramatic. Click to enlarge. Credit: Juanjo Gonzalez
Backing up reports of the outburst, astronomer Emmanuel Jehin of the TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) team, noted a tenfold increase in dust production around the comet’s nucleus on Nov. 11 and 12 plus additional jets of material blasting into the coma. Jehin reports that the inner coma near the nucleus is still very sharp and shows no sign of disruption – so far, ISON’s hanging in there.
If you haven’t seen the comet yet, you can use this map to track it through the weekend as it zips quickly through Virgo. The map shows the sky facing southeast just before the start of morning twilight or about 100 minutes before sunrise. ISON should be plainly visible in binoculars in a dark sky. Created with Chris Marriott’s SkyMap program
This is all great news for comet observers. The intense heat of the sun is beginning to boil away the comet’s ice with greater fury. The heat may also be exposing new cracks or breaks in ISON’s crust. Fresh ice means even more material becomes available for the sun to vaporize and likely additional jumps in brightness in the next day or two.
Trouble finding Virgo? Use this wide-view map to get oriented. Slide from Mars toward Spica near the southeastern horizon. ISON is about halfway between Spica and Gamma Virginis. The map shows the sky around 5-5:30 a.m. CST. Stellarium
Comet ISON is making its way through the inner solar system. Visualize its unusual orbit and track its journey
around the sun with this paper model. The background image shows comet C/2001 Q4 (NEAT). Credit: NASA and T. A. Rector (Univ. of Alaska Anchorage), Z. Levay and L. Frattare (STScI) and WIYN/NOAO/AURA/NSF
Planet orbits are so easy to picture – eight nearly concentric hula hoops centered on the sun. Comets are weirder. Their orbits vary from tapered ellipses shaped like cigars to completely open-ended parabolas and even hyperbolas. Comet ISON’s highly-elongated (stretched out) orbit is best described as hyperbolic, although that’s subject to change if Jupiter gets into the act and gives the comet a gravitational nudge during its outbound journey. As the largest planet, it has a special knack for this kind of trick, having tamed many a wayward comet’s orbit into a neat ellipse.
Comets can travel in a variety of orbits from elliptical to open-ended parabolic and hyperbolic. Credit: Wikipedia
Comets in hyperbolic and parabolic orbits are typically making their first trip to the sun from the bitterly cold and distant Oort Cloud, a roughly spherical volume of space beginning about 3,000 times Earth’s distance from the sun and extending outward to 50,000 times that distance or nearly one-quarter of the way to Alpha Centauri. The Cloud is believed to hold trillions of icy comets. Think of it as the sun’s ultimate beer cave.
To help visualize Comet ISON’s travels across the solar system we can always go the Internet and search for images and video, but sometimes it’s fun to use your own hands. Building a model using a simple cardboard template can make the knowledge “stick”. Not to mention it’s an excellent classroom activity for teachers preparing students for the comet’s post-perihelion display. All you need is this color pdf file, a printer and a few minutes to assemble.
The familiar solar system with its 8 planets occupies a tiny space inside a large spherical shell containing trillions of comets – the Oort Cloud. Credit: Wikimedia Commons
Planets’ orbits are only slightly tilted to each other, but Oort Cloud comets drop in from any angle they choose. Gravitational interactions with passing stars and clouds of interstellar gas nudge them into the inner solar system, where they’re cooked by the sun into glowing and long tails composed of vaporizing ice and dust. Long ago, some passing star gave ISON a push. It’s been falling toward the sun ever since.
Animation of Comet ISON’s orbit created by NASA
While it may be tough to picture Comet ISON’s orbit slicing the planetary racetrack at a 62-degree angle, the paper model will give you an intuitive understanding of ISON’s path and comet orbits in general.
P.S. In case you’re a klutz with a scissors just click on the Youtube video above.
The 20-foot (6-meter) hole punched through the ice on Chebarkul Lake by a large fragment of the Chelyabinsk meteorite. Credit: AP
Security camera video showing the impact of the largest piece of the Chelyabinsk meteorite striking Lake Chebarkul during the Feb. 15, 2013 Russian fireball. Credit: Nikolaj Mel’nikov.
When I first watched this video of the half-ton Chelyabinsk meteorite crashing into Lake Chebarkul last Feb. 15 I didn’t see anything. But once you pay close attention, what you’ll see is nothing short of amazing. You’ll recall that a 20-foot (6 meter) hole appeared in the ice immediately after the fall. While no one witnessed the impact, a security camera caught the critical moment from the other side of the lake.
The video recently appeared in an online presentation by Peter Jenniskens, noted meteorite expert and senior research scientist at the SETI Institute. It was released as part of a paper and Powerpoint on the Chelyabinsk airburst. You can listen to Jenniskens’ presentation HERE.
Frame grab from the video showing the breakdown of the impact and resulting ice and snow cloud.
When you watch the video, focus your attention just to the left of what looks like an ice fishing shack at top center and use the handy frame grab above. In the slowed-down portion of the footage you’ll see a cloud of ice and snow blow up and quickly drift to the right of the shack seconds after impact. While blurry and small, it’s amazing good fortune we have a document of this fall.
Video of the recovery of the largest piece of the Chelyabinsk meteorite
Divers ultimately fished the 1/2 ton Chelyabinsk meteorite – the largest found so far – from the lake on Oct. 16. It measured 5 feet long (1.5 meter) and broke into three pieces as scientists hoisted it into a scale to weigh it.
As a return favor, the little piece of heaven broke the scale.
Two new tail streamers are visible between Comet ISON's green coma and bright star near center. in this photo taken on Nov. 6. They're possibly the beginning of an ion tail. Click to enlarge. Credit: Damian Peach
I’m starting to get the chills about Comet ISON. I can’t help it. With practically every telescope turned the comet’s way fewer than three short weeks before perihelion, every week brings new images and developments. The latest pictures show a brand new tail feature emerging from the comet’s bulbous coma. For months, amateur and professional astronomers alike have watched ISON’s slowly growing dust tail that now stretches nearly half a degree or a full moon’s diameter. In the past two days, photos taken by amateur astronomers reveal what appears to be a nascent ion or gas tail. Damian Peach’s Nov. 6 image clearly shows two spindly streamers.
Early detection of ISON’s possible ion tail on Oct. 31 by amateur astronomer Efrain Morales Rivera in a 12-inch telescope.
The comet on Nov. 4 also shows the new tail structures extending farther from the coma. Credit: Justin Ng
Ion tails are composed of gases like carbon monoxide and carbon dioxide blown into a narrow straight tail by the solar wind and electrified to fluorescence by the sun’s ultraviolet light. Being made of ions (charged particles), they interact with the sun’s wind of charged particles. Changes in the intensity and direction of the magnetic field associated with sun’s exhalations kink and twist ion tails into strange shapes. Strong particle blasts can even snap off an ion tail. Not that a comet could care. Like a lizard, it grows a new one back a day or three later.
Comet ISON plunges sunward across Virgo in the coming days. Watch for it low in the eastern sky shortly before the start of dawn. Click to enlarge and print for outdoor use. Stellarium
A fresh forked tail isn’t ISON’s only new adornment. Its inner coma, location of the bright “false nucleus”, is becoming more compact, and the overall magnitude of the comet has been slowly but steadily rising. Two mornings ago I pointed a pair of 10×50 binoculars ISON’s way and was surprised to see it glowing at magnitude 8.5. Things happen quickly now that the comet is picking up speed While it appeared as little more than a small smudge, any comet crossing into binocular territory is cause for excitement. Other observers are reporting magnitudes as bright as 8.0. Estimates may vary among observers, but the trend is up. Seiichi Yoshida’s excellent Weekly Information about Bright Comets site predicts another half magnitude brightening over the next few days. You can use the map here to spot it in your own glass before the moon returns to the morning sky.
False color photo taken with the TRAPPIST 60-cm telescope using a narrowband CN (390 nm) filter at 8:45 Universal Time Nov. 5 shows two active jets (small double-plume) in ISON’s inner coma (right) and the dust tail at left. Field of view is 5×5 arc minutes. North is up, east to the left. Credit: Cyrielle Opitom, TRAPPIST team
But wait, there’s more. Emmanuel Jehin, a member of the TRAPPIST ( TRAnsiting Planets and PlanetesImals inSmall Telescopes) team, a group of astronomers dedicated to the detection of exoplanets and the study of comets and other small solar system bodies, reports a rapid rise in ISON’s gas production rate in the past several days. They’ve increased by a factor of two since Nov. 3. Could the spike be connected to the development of an ion tail? Jehin and team have also recorded two active jets coming from the comet’s nucleus using specialized filters. Dust production rates however have remained flat.
The Comet ISON Observing Campaign is both terrestrial and celestial. Nine different NASA and ESA spacecraft, eight of which are shown here, have observed comet ISON so far. Credit: NASA/ESA
Casey Lisse of the Comet ISON Observing campaign (CIOC) reports that the Chandra X-ray Observatory just became the 9th spacecraft to image the comet . More details and photos should be available soon. The campaign predicts the comet will peak in brightness between -3 to -5 magnitude when it zips closest to the sun on Nov. 28. Want to ride alongside the comet during its passage through the inner solar system? Click on this awesome, interactive simulator.
Hubble Space Telescope image of comet C/1999 S4 (LINEAR) that disintegrated around July 23, 2000. Credit: NASA/ESA
Because ISON is a fresh-faced visitor from the distant Oort Cloudthat will soon face the full fury of the sun, speculation of its fate has ranged across the spectrum. Everything from breakup and dissolution before perihelion to surviving intact trailing a spectacular dust tail. The comet is currently approaching the 0.8 A.U. mark (74.4 million miles / 120 million km) when previous comets C/1999 S4 LINEAR in 2000 and C/2010 X1 Elenin in 2011 crumbled to pieces and vaporized away. Will ISON have the internal strength to pass the test and venture further into the solar boil? Should it survive, it faces a formidable foe – the sun. Both the intense solar heat and gravitational stress on the comet’s nucleus could easily tear it apart. If this happens a few days before perihelion we’ll be left with little to see, but if ISON busts up a day or two after perihelion, watch out baby. When the comet reappears in the morning sky, it may be missing its head but make it up for the loss with a spectacular tail of fresh dust and ice many degrees in length. This is exactly what happened to Comet C/2011 W3 (Lovejoy) in December 2011. After its close graze with the home star, the nucleus disintegrated, producing a striking tail seen by skywatchers in the southern hemisphere.
Pictures of Comet C/2011 W3 Lovejoy on Dec. 22, 2011 after perihelion passage. Will ISON be a repeat? Credit: Chris Wyatt
The final scenario sees Comet ISON pushing past all barriers intact and ready to put on a splendid show. Whatever happens, I suspect we’re in for surprises ahead. For a more detailed analysis of these possibilities I invite you check out Matthew Knight’s blog on the CIOC website.
No fewer than four bright-ish comets greet skywatchers an hour before the start of dawn. From upper left counterclockwise: C/2013 R1 Lovejoy, 2P/Encke, C/2012 X1 and ISON. Credits: Gerald Rhemann, Damian Peach, Gianluca Masi and Gerald Rhemann
Get your astronomical trick-or-treat bags ready. An excursion under the Halloween morning sky will allow you fill it in a hurry — with comets! We’ve known for months that ISON and 2P/Enckewould flick their tails in the October dawn, but no one could predict they’d be joined by Terry Lovejoy’s recent comet discovery, C/2013 R1 (Lovejoy), and the obscure C/2012 X1 (LINEAR). The last surprised all of us when it suddenly brightened by more than 200 times in a matter of days. Almost overnight, a comet found on precious few observing lists became bright enough to see in binoculars. Now comet watchers the world over are losing sleep to get a glimpse of it.
Rarely are four comets this bright in the same quadrant of sky. This map shows the sky facing east about two hours before sunrise on Oct. 31. Take note of the three stars are labeled “Beta”. These are (from top) Beta Cancri, Beta Leonis and Beta Coma Berenices. We’ll use these three stars and the planet Mars to hone in on the comets’ locations in the maps below. Stellarium
Since it’s unusual to have four relatively bright comets in the same chunk of sky at the same time, you don’t want to miss this opportunity. Now that the moon has dwindled to the slightest crescent, this is THE time to hunt for these ghostly apparitions before dawn.
Detailed (updated) map showing Comet Lovejoy’s progress across Cancer in the coming days. It passes very close to the Beehive Cluster on Nov. 6-7. Click for a larger version you can print and use under the stars. All dates are at 6 a.m. CDT; north is up and west to the right and stars are shown to mag. 5. All closeup charts created with Chris Marriott’s SkyMap software
Brightest of the bunch at magnitude 8 and your best bet to see in a standard pair of 50mm binoculars is Comet Lovejoy. Using the maps, look for a round, fuzzy spot with a brighter center not far from the bright star Procyon in Canis Minor. In the coming days, Lovejoy will brighten by an additional 2 to 3 magnitudes as it trucks across Cancer headed toward the Big Dipper. This is one to watch. Lovejoy will likely reach naked eye brightness by mid-November. Small telescope users can see the comet with ease but its developing gas tail is still to faint to spot visually.
Comet Encke drops below Leo and into Virgo over the next two weeks. Your guide star Beta Leo is at upper right. Stars to mag.8. Click to enlarge.
Comet Encke treks around the sun every 3.3 years. Sometimes it’s well placed for viewing and sometimes not. Because of its short period, dedicated comet watchers meet up with it a half dozen or more times during their lives. This apparition is a favorable one with the comet well-positioned in the east at dawn near peak brightness. Current estimates place it magnitude 7.5-8 with only the wispiest of tails. Like Lovejoy, 50mm binoculars under a dark sky should nab it.
A week before Encke reaches its peak magnitude of 6 or 7 at perihelion on Nov. 21, it chases the into the glare of morning twilight. If you want to see this comet, you’ve got about 2 weeks of viewing time left. Make sure to set up in a place with an open view to the east-southeast or you’ll find it hidden by the treeline.
Animation from images taken Oct. 25 and 28 of comet C/2012 X1 (LINEAR) showing its rapidly expanding coma in the wake of an eruptive event in its icy crust. Click image to animate. Credit: Gianluca Masi
Comet C/2012 X1 would have deprived us of a unique sight had it followed the rules. Instead, an eruption of fresh, dust-laden ices from its surface blasted into space to form a gigantic glowing sphere of material that vaulted the comet’s magnitude from a wimpy 13.5 to a vol-luminous 7.5. That’s a difference of 6 magnitudes or a brightness factor of 250 times!
Outbursts of this consequence are rare; the best example of a similar blow-out happened in 2007 when Comet 17P/Holmes cut loose and brightened by half a million times from magnitude 17 to 2.8 in just under two days.
C/2012 X1 (LINEAR) hovers low in the northeast in Coma Berenices near Beta. Because it’s much further from Earth than the other three comets, it moves more slowly across the sky. It has a close conjunction with the brilliant star Arcturus in mid-November. In this map, north is at top left and west to top right. Stars to mag. 8. Click to enlarge.
As with any explosion, the cloud of debris around C/2012 X1 continues to expand. Presently measuring a healthy ~8 arc minutes in diameter (1/4 the size of the full moon), the comet will almost certainly continue to grow and fade with time. Catch it now with binoculars and small telescopes before its veil-like coma thins to invisibility. Like Encke, X1 LINEAR requires an open eastern horizon and best viewed at the start of dawn. Make it the last comet on your observing list after Lovejoy, Encke and ISON.
Mars and several other moderately bright stars in Leo will guide you to Comet ISON in the next week or two. Stars to mag. 10. Click to enlarge.
Ah, ISON. Halloween morning wouldn’t be complete without a visit to this year’s the most anticipated comet.. If it can hold itself together after a searing graze of the sun on November 28, the comet will undoubtedly become a most pleasing sight during the first three weeks of December. Right now it’s a little behind schedule on brightness, but don’t let that worry you – its best days are still ahead.
One of the finest pictures to date of Comet ISON by ace astrophotographer Damian Peach taken on Oct. 27.
Of our four morning treats, Comet ISON is currently the faintest at around magnitude 9.5. Observers with binoculars in the 70-100mm range will see it under dark skies but most of us will need a 6-inch or larger scope at least until mid-November. That’s when ISON’s expected to brighten to magnitude 6, the naked eye limit. Just before it slips into the solar glare, ISON could reach 3rd magnitude around Nov. 21, normally an easy catch with the naked eye, but low altitude will hamper the view.
So open your bag wide tomorrow before dawn and keep it open the next few mornings. Trick or treat!
Beautiful red and green aurora the night of Oct. 1-2, 2013. See below for how it appeared to the eye. Details: 20mm lens, f/2.8, ISO 1600 and 25-second exposure. Credit: Bob King
I shoot a lot of pictures of the northern lights. Just like the next photographer, I thrill to the striking colors that glow from the back of my digital camera. When preparing those images for publication, many of us lighten or brighten the images so the colors and forms stand out better. Nothing wrong with that, except most times the aurora never looked that way to our eyes.
Surprised? I took the photo above and using Photoshop adjusted color and brightness to match the naked eye view. Notice the green tinge in the bright arc at bottom. The rays were colorless. Credit: Bob King
The colors you see in aurora photos ARE real but exaggerated because the pictures are time exposures. Once the camera’s shutter opens, light accumulates on the electronic sensor, making faint and pale subjects bright and vivid. The camera can’t help it, and who would deny a photographer the chance to share the beauty? Most of us understand the magic of time exposures and factor in a mental fudge factor when looking at astronomical photos including those of the aurora.
But photos can be misleading, especially so for beginners, who might anticipate “the second coming” when they step out to watch the northern lights only to feel disappointment at the real thing. Which is too bad, because the real aurora can make your jaw drop.
A massive wall of bright purple and green rays from July 20, 2012. Details: 16mm at f/2.8, ISO 800 and 20 second exposure. Credit: Bob King
That’s why I thought it would instructive to take a few aurora photos and tone them down to what the eye normally sees. Truth in advertising you know. I’ve also started to include disclaimers in my captions when the images show striking crimson rays. Veteran aurora watchers know that some of the most memorable auroral displays glow blood-red, but most of the ruddy hues recorded by the camera are simply invisible to the eye. Our eyes evolved their greatest sensitivity to green light, the slice of the rainbow spectrum in which the sun shines most intensely. We’re slightly less sensitive to yellow and only a 1/10 as sensitive to red.
Image adjusted to better represent the visual view. Most auroras are between 60 and 150 miles high, but occasionally reach to 400 miles. Credit: Bob King
A typical aurora begins life as a pale white band low in the northern sky. If we’re lucky, the band intensifies, crosses the color threshold and glows pale green. Deeper and brighter greens are also common in active and bright auroras, but red is elusive because are eyes are far less sensitive to it than green. Often a curtain of green rays will be topped off by red, blue or purple emission recorded with sumptuous fidelity in the camera. What does the eye see? Smoky, colorless haze with hints of pink. Maybe.
Again, this doesn’t mean we only see green and white. I’ve watched brilliant (pale) green rays stretch from horizon to zenith with their bottoms bathed in rosy-purple, a most wonderful sight. Another factor to keep in mind is dark adaption – the longer you’ve been out under a dark sky, the more sensitive your eyes will be to whatever color might be present. At night, however, we’re mostly color blind, relying on our low-light-sensitive rod cells to get around. Cone cells, fine-tuned for color vision, are activated only when light intensity reaches certain thresholds. That happens often when it comes to auroral green but less so with other colors to which our cells are less responsive.
Incoming auroral electrons excite oxygen and nitrogen atoms and molecules which then shoot out photons of light at specific wavelengths when they return to their ground states. Oxygen beams light at 557.7 (green) and 603 (red) nanometers. Credit: NCAR
Auroral colors originate when electrons from the sun spiral down Earth’s magnetic field lines like firemen on a firepole and slam into oxygen and nitrogen atoms in Earth’s upper atmosphere between 60 and 150 miles (96-240 km) high. Here’s a breakdown of color, atom and altitude:
* Green – oxygen atoms 60-93 miles up (100-150 km)
* Red – oxygen atoms from 93-155 miles (150-250 km)
* Purple – molecular nitrogen up to 60 miles (100 km)
* Blue/purple – molecular nitrogen ions above 100 miles (160 km)
When an electron strikes an oxygen atom for instance, it bumps one of the oxygen’s electrons to a higher energy level. When that electron drops back down to its previous rest or ground state, it emits a photon of green light. Billions of atoms and molecules, each cranking out tiny flashes of light, make an aurora. It takes about 3/4 second for that electron to drop and the atom to release a photon before it’s given another kick from a solar electron. Most auroras are rich with oxygen emission.
The layers of our atmosphere showing the altitude of the most common auroras. Credit: Wikimedia Commons
Higher up, where the air’s so thin it’s identical to a hard vacuum, collisions between atoms happen only about every 7 seconds. With lots of time on their hands, oxygen electrons can transition down to their lowest energy level inside the atom, releasing a photon of red light instead of green. That’s why tall rays often show red tops especially in time exposure photos.
Only during very active geomagnetic storms, when electrons penetrate to low levels in the atmosphere, are they able to excite molecules of nitrogen, giving rise to the familiar purple fringes at the bottoms of bright rays. Bombarded molecular nitrogen ions at high altitude release a deep blue-purple light. Rarely visible to the eye, I did record it one night in the camera.
A striking coronal aurora in Feb. 1999 photographed on film. The red in this aurora was obvious to the naked eye but appeared more like the Photoshopped version at right. Credit: Bob King
While videos hint at how wildly dynamic auroras can be, they’re no substitute for seeing one yourself. That’s why I never seem to get to bed when that first tempting glow appears over the northern horizon. Colorful or colorless, you’ll be astonished at how the aurora constantly re-invents itself in a multitude of forms from arcs to rays to flaming patches and writhing curlicues. Don’t miss the chance to see one. If there’s one thing that looks absolutely unearthly on this green Earth, it’s the aurora borealis. Click HERE for a guide on when and where to watch for them.
Jupiter with polka dot shadows cast by Io, Europa and Callisto as depicted around 1 a.m. EDT Oct. 12. Watch for the Great Red Spot to come into view during the transit. Created with Claude Duplessis' Meridian software
Talk about a great fall lineup. Three of Jupiter’s four brightest moons plan a rare show for telescopic observers on Friday night – Saturday morning Oct. 11-12. For a span of just over an hour, Io, Europa and Callisto will simultaneously cast shadows on the planet’s cloud tops, an event that hasn’t happened since March 28, 2004.
Who doesn’t remember their first time looking at Jupiter and his entourage of dancing moons in a telescope? Because each moves at a different rate depending on its distance from the planet, they’re constantly on the move like kids in a game of musical chairs. Every night offers a different arrangement.
Jupiter and its four brightest moons seen in a small telescope. Credit: Bob King
Some nights all four of the brightest are strung out on one side of the planet, other nights only two or three are visible, the others hidden behind Jupiter’s “plus-sized” globe. Occasionally you’ll be lucky enough to catch the shadow of one of moons as it transits or crosses in front of the planet. We call the event a shadow transit, but to someone watching from Jupiter, the moon glides in front of the sun to create a total solar eclipse.
Since the sun is only 1/5 as large from Jupiter as seen from Earth, all four moons are large enough to completely cover the sun and cast inky shadows. To the eye they look like tiny black dots of varying sizes. Europa, the smallest, mimics a pinprick. The shadows of Io and Callisto are more substantial. Ganymede, the solar system’s largest moon at 3,269 miles (5,262 km), looks positively plump compared to the others. Even a small telescope magnifying around 50x will show it.
Jupiter on Sept. 24 with its moon Europa (at left) casting a pinhead black shadow on Jupiter’s clouds. Credit: John Chumack
The three inner satellites – Io, Europa and Ganymede – have shadow transits every orbit. Distant Callisto only transits when Jupiter’s tilt relative to Earth is very small, i.e. the plane of the planet’s moons is nearly edge-on from our perspective. Callisto transits occur in alternating “seasons” lasting about 3 years apiece. Three years of shadow play are followed by three years of shadowless misses. Single transits are fairly common; you can find tables of them online like this one from Project Pluto or plug in time and date into a free program like Meridian for a picture and list of times.
Because Io, Europa and Ganymede orbit in a 4:2:1 resonance (Io revolves four times around Jupiter in the time it takes Ganymede to orbit once; Europa completes two orbits for Ganymede’s one) it’s impossible for all three to line up – along with Callsto – for a “quadruple transit”. Credit: Matma Rex / Wikipedia
Seeing two shadows inch across Jupiter’s face is very uncommon, and three are as rare as a good hair day for Donald Trump. Averaged out, triple transits occur once or twice a decade. Friday night Oct. 11 each moon enters like actors in a play. Callisto appears first at 11:12 p.m. EDT followed by Europa and then Io. By 12:32 a.m. all three are in place.
Catch them while you can. Groups like these don’t last long. A little more than an hour later Callisto departs, leaving just two shadows. You’ll find the details below. All times are Eastern Daylight or EDT. Subtract one hour for Central time and add four hours for BST (British Summer Time):
* Callisto’s shadow enters the disk – 11:12 p.m. Oct. 11
* Europa – 11:24 p.m.
* Io – 12:32 a.m. ** TRIPLE TRANSIT from 12:32 – 1:37 a.m.
* Callisto departs – 1:37 a.m.
* Europa departs – 2:01 a.m.
* Io departs – 2:44 a.m.
Looking at Jupiter from high above the plane of the solar system in this diagram from more than a century ago, we can better picture how shadow transits and eclipses happen. The tiny disk of Io and the shadow of Ganymede are seen in transit; Callisto is about to be eclipsed by Jupiter’s shadow. Credit: Garrett Serviss from “Pleasures of the Telescope” (annotations: Bob King)
The triple transit will be seen across the eastern half of the U.S., Europe and western Africa. Those living on the East Coast have the best view in the U.S. with Jupiter some 20-25 degrees high in the northeastern sky around 1 a.m. local time. Things get dicier in the Midwest where Jupiter climbs to only 5-10 degrees. From the mountain states the planet won’t rise until Callisto’s shadow has left the disk, leaving a two-shadow consolation prize. If you live in the Pacific time zone and points farther west, you’ll unfortunately miss the event altogether.
From the Eastern Time Zone Jupiter will be well-placed in the eastern sky during the transit. Created with Stellarium
Key to seeing all three shadows clearly, especially if Jupiter is low in the sky, is steady air or what skywatchers call “good seeing”. The sky can be so clear you’d swear there’s a million stars up there, but a look through the telescope will sometimes show dancing, blurry images due to invisible air turbulence. That’s “bad seeing”. Unfortunately, bad seeing is more common near the horizon where we peer through a greater thickness of atmosphere. But don’t let that keep you inside Friday night. With a spell of steady air, all you need is a 4-inch or larger telescope magnifying around 100x to spot all three.
The March 28, 2004 triple transit. Shadows from left: Ganymede, Io and Callisto. You can also see the disks of Io (white dot) and Ganymede (blue dot) in this photo taken in infrared light by the Hubble Space Telescope. Credit: NASA/ESA
If bad weather blocks the view, there are two more triple transits coming up soon – a 95-minute-long event on June 3, 2014 starring Europa, Ganymede and Callisto (not visible in the Americas) and a 25-minute show on Jan. 24, 2015 featuring Io, Europa and Callisto and visible across Western Europe and the Americas. That’s it until dual triple transits in 2032.
The first photo of the lunar far side taken by the Soviet (Russian) spacecraft Luna 3 on Oct. 7, 1959. The right three-quarters of the disk is the far side. A = Mare Moscoviense, B = Tsiolkovsky Crater with central peak, C = Mare Smythii (on the near side-far side border) and D = Mare Crisium (near side). This is the wide-angle view. Credit: Roscosmos
For millennia, human eyes have seen only one face of the moon. Put a dude from the Iron Age in a time machine and whisk him to 2013 and he’d see the same pattern of light lunar highlands punctuated by dark grey spots you see. Night after night after night.
Telephoto view of the far side with Mare Smythii (Sea of Smyth) at left and bright crater Giordano Bruno at center. Credit: Roscosmos
That all changed 54 years ago today when the Soviet Union’s Luna 3 probe opened its camera shutter and snapped the first pictures of the lunar far side. Though blurry and banded with electronic noise, everyone who saw them sat up in surprise. The backside barely resembled the front. It lacked in the familiar lunar maria, the dark spots that we instinctively patch together to form the face of the “man in the moon”.
Telephoto image of Mare Moscoviense is at upper right with Tsiolkovsky and its bright central peak at lower right. You can begin to see vague outlines of many more craters in this picture. Click for more historic photos. Credit: Roscosmos
Only two dark ovals were seen, Mare Moscoviense (Sea of Moscow) and the lava-filled floor of the crater Tsiolkovsky, named for Konstantin Tsiolkovksy, the Russian rocket pioneer. The rest, which looks like dried paste, is jammed with craters and related the near side’s light-toned, cratered highlands. Both are remnants of the original lunar crust that solidified as the moon cooled after formation.
The dramatic difference between near side and far side shows up in this much more recent global map of the map made by Clementine Mission in 1994. The map is centered on the near side with its many lunar “seas” or maria. The far side trails off to the left and right of center. Mare Moscoviense is at upper right. Credit: NASA
Darker areas or “seas” are more recent basaltic lavas that welled up to fill huge impact scars left by colliding asteroids. They contain iron-rich minerals from deep beneath the crust which make them less reflective, hence darker in comparison to the highlands.
Tidal locking results in the moon rotating about its axis in about the same time it takes to orbit the Earth (left side). If the Moon didn’t spin at all, then it would alternately show its near and far sides to the Earth while moving around our planet in orbit, as shown in the figure on the right. Credit: Wikipedia
The moon hides its back or far side through a neat trick – it rotates at the same rate as it revolves around the Earth. Normally, rotation would bring new features into view, but every little bit it turns, it moves an equal amount along its orbit, hiding what would otherwise be exposed. It’s called synchronous rotation or tidal locking. Most of the larger moons in the solar system are tidally locked to their planets. Jupiter’s four biggest and brightest moons are a great example.
Luna 3 probe sent to the moon by the then Soviet Union. It held two cameras and its own film processing lab. Credit: NASA
Equipped with both wide angle (200 mm) and telephoto (500 mm) lenses, Luna 3 took 29 pictures covering about 70 percent of the far side during its loop around the moon. The first picture was shot from 39,500 miles away (63,500 km), the last taken 40 minutes later from 41,445 miles (66,700 km) distant. After the photo session was done, the probe passed over the moon’s north pole and headed back toward Earth.
Temperature and radiation-resistant film used for the photos was automatically moved to an onboard processor where it was developed, fixed and dried. A cathode ray tube then shot a beam of light through the film and onto a photoelectric multiplier, a light-sensitive device that converted the different gradations of tone into electric signals which were then transmitted to Earth. Almost sounds like a fire brigade, but hey it worked!
High resolution photo map of the moon’s far side imaged by NASA’s Lunar Reconnaissance Orbiter. Mare Moscoviense lies at upper left and Tsiolkovsky at lower left. Click for a hi res image. Credit: NASA
So what’s the reason for the moon’s split personality? We know the far side crust is 50 miles (80 km) thick versus 37 miles (60 km) for the near side. A thicker far side crust may have prevented magma from reaching and flooding the surface as they did on the near side. Heat released by the decay of radioactive elements also may play a role. NASA’s Lunar Prospector probe found more on the near side, where they may have encouraged the formation of hot magmas that eventually found their way to the surface.
What caused the fascinating asymmetry is unknown, but it may have to do with the slowing of the moon’s rotation into its present tidally-locked state under the heavy hand of Earth’s dominating gravitational influence.
At around 10 p.m. last night, the northern sky was alive with colorful auroral patches and arcs. Details: 15mm lens at f/2.8, ISO 800 and 25 second exposure. Credit: Bob King
I’m writing this at 1:30 a.m. running on what’s powering the sky over northern Minnesota right now – auroral energy. Even at this hour, rays are still sprouting in the southern sky and the entire north is milky blue-white with aurora borealis. Frankly, it’s almost impossible to resist going out again for another look.
Now updated with additional images.
An erupting filament and sharp, southward dip in the interplanetary magnetic field (IMF) was responsible for last night’s northern lights show. This image was taken with the Solar and Heliospheric Observatory’s sun-blocking coronagraph on Sept. 30. Credit: NASA/ESA
The arrival of a powerful solar wind in excess of 375 miles per second (600 km/second) from a coronal mass ejection shocked the Earth’s magnetic sheath last night beginning around 9 p.m. CDT. The sun’s magnetic field, embedded in the wind, pointed sharply southward, allowing eager electrons and protons to worm their way past our magnetic defenses and excite the atoms in the upper atmosphere to glow. Voila! Northern lights.
A classic quiet start to Tuesday night’s northern lights – a low green arc below the Big Dipper topped by a very faint red border. Credit: Bob King
Sure, it started innocently enough. A little glow low in the northern sky. But within half an hour the aurora had intensified into a dense bar of light so and green and bright it cast shadows. This bar or swath grew and grew like some atomic amoeba until it swelled beyond the zenith into the southern sky. Meanwhile, an isolated patch of aurora glowed like an green ember beneath the Pleiades in the northeastern sky. The camera captured its eerie appearance as well as spectacular curtains of red aurora dancing above the dipper-shaped cluster.
A single patch of aurora glows beneath the Pleiades star cluster at center. Beautiful red rays as seen in the time exposure were only faintly visible with the naked eye. Credit: Bob King
Soft patches, oval glows and multiple arcs lit up the north, east and west, but in the first two hours of the display I never saw a ray or feature with any definition. The camera recorded a few but all was diffuse and pillowy to the eye. Rays finally made their appearance later – after midnight and later – when they massed and surged to the zenith and beyond.
Looks a little scary. A thick wall of green aurora surges upward in the northern sky headed for the zenith. Credit: Bob King
Then came the flickering, flame-like patches and snaky shapes writhing lifelike across the constellation Pegasus during the phase called the coronal aurora. That’s when all the curtains and rays gather around the local magnetic zenith. As they flicker and flame, their shapes transform into eagle wings and snakes wriggling across the stars.
A large comet-like auroral form accented with red rays took up residence in the southeastern sky in Cetus from about 10:15 until 11 p.m. last night. around 10:30 p.m. Credit: Bob King
Funny, the space weather forecast called for quiet conditions last night and for the next two nights. But the eruption of a large filament, a tubelike region of dense hydrogen gas held aloft in the sun’s atmosphere by magnetic fields, sent a bundle of subatomic joy in Earth’s direction a bit earlier than expected. More auroras are possible tonight and tomorrow night as the effect of the shock wave continues. Despite the U.S. government shutdown, the Space Weather Prediction Center remains open.
There are so many ways to appreciate the aurora but my favorite is simply to stand there dumbfounded and try to take it all in. Few phenomena in nature are more deeply moving.
Opposite Cetus in the Aquila Milky Way, a huge ghostly patch resembling breath on a mirror lingered for some 20 minutes before fading away. Credit: Bob KingThis comet-like wisp next to Alpha Andromeda east of the Square of Pegasus appeared to flutter in the wind as it constantly dimmed, brightened and shape-shifted. Click photo to learn more about when to expect the next auroral display. Credit: Bob KingFinally – a mighty show of rays around 3 a.m. this morning. What you don’t see in the photo are the rhythmic pulsations fluttering through the entire display, a phenomenon known as “flaming”. Credit: Bob King
Magnetic and auroral activity indicators shot up to high levels last night and this morning. Left image from the POES satellite shows the extent of the auroral oval shortly after midnight CDT. At right, the Kp index shot up to 6 – a G2 or moderate geomagnetic storm – by the early morning. Click to see the current oval. Credit: NOAA
UPDATE: Other astrophotographers in the US also were able to capture some aurora images. John Chumack, whose images we frequently feature here on UT got this shot early on the morning of October 2:
Aurora Borealis, ‘The Northern Lights, as seen near Dayton, Ohio on October 2, 2013. Credit and copyright: John Chumack/Galactic Images.
And Alan Dyer in Canada got this amazing “fiery” shot:
A red and green aurora, from southern Alberta, Canada on Oct 1, 2013. Credit and copyright: Alan Dyer/Amazing Sky Photography.
This timelapse from Arthur, Ontario was shot on Oct. 2 as well:
Comet ISON, photographed with a 3-inch (80mm) telescope on this morning Sept. 28 shows a circular green coma and short dust tail pointing northwest. Click to enlarge. Credit: Michael Jaeger
As NASA and the European Space Agency prepare their remote photojournalists – Mars Express, Mars Reconnaissance Orbiter and the Curiosity and Opportunity rovers – to capture photos of Comet ISON’s flyby of Mars early next week, amateur astronomers continue to monitor and photograph the comet from backyard observatories across the blue Earth. Several recent color photos show ISON’s bright head or nucleus at the center of a puffy, green coma. Green’s a good omen – a sign the comet’s getting more active as it enters the realm of the inner solar system and sun’s embrace.
Another great photo of the “greening” of Comet ISON taken on Sept. 24 with a 17-inch (43-cm) telescope. Click to enlarge. Credit: Damian Peach
Sunlight beating down on the comet’s nucleus (core) vaporizes dust-impregnated ice to form a cloud or coma, a temporary atmosphere of water vapor, dust, carbon dioxide, ammonia and other gases. Once liberated , the tenuous haze of comet stuff rapidly expands into a huge spherical cloud centered on the nucleus. Comas are typically hundreds of thousands of miles across but are so rarified you could wave your hand through one and not feel a thing. The Great Comet of 1811 sported one some 864,000 miles (1.4 million km) across, nearly the same diameter as the sun!
Among the materials released by solar heating are cyanogenand diatomic carbon. Both are colorless gases that fluoresce a delicious candy-apple green when excited by energetic ultraviolet light in sunlight.
Sounds like a plan. Newspaper clipping from 1910.
Cyanogen smells pleasantly of almonds, but it’s a poisonous gas composed of one atom each of carbon and nitrogen. Diatomic carbon or C2 is equally unpleasant. It’s a strong, corrosive acid found not only in comets but also created as a vapor in high-energy electric arcs. But nature has a way of taking the most unlikely things and fashioning them into something beautiful. If you’re concerned about the effects of cometary gas and dust on people, rest easy. They’re spread too thinly to touch us here on Earth. That didn’t stop swindlers from selling “comet pills” and gas masks to protect the public from poisoning during the 1910 return of Halley’s Comet. Earth passed through the tail for six hours on May 19 that year. Amazingly, those who took the pills survived … as did everyone else.
Comet ISON’s location and approximate appearance on October 1 seen from the Curiosity Rover. ISON will pass only 6.7 million miles (10.8 million km) from Mars on Tuesday Oct. 1. Stellarium
While Comet ISON is still too faint for visual observers to discern its Caribbean glow, that will change as it beelines for the sun and brightens. If you could somehow wish yourself to Mars in the next few days, I suspect you’d easily see the green coma through a telescope. The comet – a naked eye object at magnitude 2.5-3 – glows low in the northern sky from the Curiosity rover’s vantage point 4.5 degrees south of the Martian equator.
Comet Hale-Bopp shows off its bright dust tail and fainter, blue ion tail in early spring 1997. Credit: Bob King
I’ve noticed that when a comet reaches about 7th magnitude, the green coloration becomes apparent in 8-inch (20 cm) and larger telescopes. Bright naked eye comets often display multiple subtle colors that change chameleon-like over time. Dust tails, formed when sunlight pushes dust particles downwind from the coma, glow pale yellow. Gusty solar winds sweep back molecules from the coma into a second “ion” tail that glows pale blue from jazzed up carbon monoxide ions fluorescing in solar UV.
One of the highlights of seeing Comet L4 PANSTARRS through a small telescope was its brilliant, pea-like false nucleus glowing yellow from sunlit dust. The real comet nucleus – the actual comet – lies within the false nucleus and hidden by dust. Drawing: Bob King
During close encounters with the sun, millions of pounds of dust per day boil off a comet’s nucleus, forming a small, intensely bright, yellow-orange disk in the center of the coma called a false nucleus. Earlier this year, when Comet C/2011 L4 PANSTARRS emerged into the evening sky after perihelion, not only was its yellow tail apparent to binocular users but the brilliant false nucleus glowed a lovely shade of lemon in small telescopes.
With ISON diving much closer to the sun than L4 PANSTARRS, expect a full color palette in the coming weeks. While it may not be easy being green for Sesame Street’s Kermit the Frog, comets do it with aplomb.
