Stardust captures 7 precious pieces of cosmic dust

Weighing in at 3.1 trillionths of a gram, the “Orion” interstellar dust particle (upper right) was captured by the Stardust spacecraft. The particle contains aluminum (red), iron (green) and magnesium (blue). Credit: NASA and Anna Butterworth at the Advanced Light Source Lawrence Berkeley National Laboratory (inset)

Definition of finding a needle in a haystack? 100 million searches by over 30,000 people to find seven “probable” interstellar dust particles in debris collected by NASA’s Stardust spacecraft. These minute motes are not of this solar system but alien dust from intergalactic space.

The discoveries top a 7-plus year search by the Stardust team and thousands of volunteers to track down samples of the primordial dust wafting through interstellar space – the same stuff that long ago congealed to form the sun and planets.

I should be careful of my terms. These bits of cosmic debri, a thousandth the mass of comet dust, tear across space at nearly 10,000 mph (15,000 km/hr). They’re also incredibly sparse. Catching even one requires VERY delicate handling and a bit of luck.

Aerogel is a unique substance with a spongy, airy structure excellent for capturing high speed particles like comet  and interstellar dust without damaging them. Credit: NASA

Scientists used one of the most bizarre substances ever invented to grab the speedy dust particles without damaging them: aerogel. Sometimes called “frozen smoke”, aerogel is a pale blue, airy substance made of 99.8% empty space webbed with silica. Particles traveling thousands of miles an hour can safely speed through aerogel until they slow down and bury themselves within its porous, sponge-like texture. A high tech butterfly net as it were.

The collector tray mounted on Stardust featured many small trays filled with aerogel for collecting comet and dust between the stars. Credit: NASA

The Stardust spacecraft, launched in 1999, accomplished its main objective of collecting dust particles from the misty atmosphere or coma of comet Wild 2 and returning them in a reentry capsule when the probe passed by Earth in 2006.

That’s not all. For a total of 200 days in 2000 and 2002, Stardust stuck out its tennis racket-sized collector tray to snatch bits of interstellar dust that sifts across the solar system as the sun and planets orbit the galaxy at 4.3 miles per second.

 

A Stardust researcher examines a centimeter (about 1/2 inch) thick block of aerogel for interstellar dust particles. Credit: NASA

Problem was, there were so many pieces of aerogel to examine for tracks and possible particles, the Stardust team knew it would take ages unless they got help. So they went public and set up the Stardust@home website.

Regular folks like you and I were offered (and still have) the opportunity to examine microscopic images of aerogel slices on our computers and look for tracks left by debris from alien stars and Milky Way gas clouds. 30,714 people signed up, and after years of work doing one of the things humans do best – recognize patterns – seven possible candidates were found.

Track and possible interstellar particle captured in aerogel. Credit: NASA

Two particles weighed in at just three trillionths of a gram; another came in so fast it left only a bit of residue. Four missed the aerogel but blasted microscopic craters in the surrounding aluminum foil, leaving traces of vaporized debris within the craters.

Track and closeup of a small particle captured from Comet Wild 2 by Stardust. Credit: NASA

To confirm that the specks are truly from beyond the planets, researchers must now transfer them from the aerogel to instruments for close examination. They’re so incredibly small, great care must be taken not to lose the precious pieces.

If you’d like to learn more and become a “duster” yourself, the name given to those teasing tracks from photos, click over to Stardust@home.  Bruce Hudson of Ontario, Canada discovered the first particle and was given the privilege of naming it. He chose “Orion”, and it’s featured in the photo at the top of this article.

Rosetta’s frosty comet springs to life

Comet 67P/Churyumov-Gerasimenko photographed on February 28th, 2014, with the ESO’s Very Large Telescope in Chile. Left: The telescope tracked the comet causing the stars to trail. At right, subtracting the starry background reveals the comet more clearly. Credit: MPS/ESO

Comet 67P/Churyumov-Gerasimenko is back! The target of the European Rosetta Mission was last seen in October but too near the sun to photograph again until Feb. 28 this year. Forget about seeing the comet with your eyeballs through a telescope. It’s as far away as Jupiter and an ultra-dim 21st magnitude speck in eastern Sagittarius in the morning sky.

Comet 67P is already boiling away even at its relatively large distance from the sun. It’s located on the opposite side of the sun from Jupiter. Credit: NASA/JPL

The first sighting this year brings good news. 67P is brighter than expected which suggests that frozen ice is already beginning to vaporize and form a very thin atmosphere. Come May, the Rosetta spacecraft will begin rendezvous maneuvers with the comet and place itself into close orbit about its icy nucleus later this summer. In November, Rosetta will dispatch a small lander named Philae to 67P’s icy surface to photograph and study it up close.

67P/Churyumov-Gerasimenko is approximately 50 percent brighter than in the
last images from October 2013. While the comet has moved another 50 million miles (80 million km) closer to the sun, the increase in brightness can’t be explained by the smaller distance alone. The spike in dust and gas production tells us that 67P/Churyumov-Gerasimenko is already rousing from its slumbers with only weak sunlight to “fan the flames”.

Jupiter meets the moon / Two comets pass in the night / Space station at dusk

A 22-degree halo, formed by light refracting through the faces of hexagonal ice crystals in cirrostratus clouds, reaches almost to Jupiter (lower left) last night Feb. 8. Credit: Bob King

The moving moon keeps things interesting on a very human time scale, gliding about one outstretched fist to the east every night. Last night ice-crystally clouds made a beautiful lunar halo that nearly but not quite touched Jupiter.

The moon will lie about a bit more than a fist to Jupiter’s right tonight and below it tomorrow night. Stellarium

Tonight the moon will lie to the right of the brilliant planet, while on Monday the two will be in conjunction with the waxing gibbous moon floating just below. It’s fun to watch the moon’s travels across the sky. Because of its 5.1 degree tilted orbit, the moon follows a slightly different track through the zodiac constellations each month in a cycle lasting 18.6 years. Planets move, stars drift westward with the seasons – taken all together, the moon makes repeated visits in ever-different arrangements with the bright stars and planets it passes every month.

This wide view shows much of the sky facing south about 90 minutes before sunrise. In addition to the bright planets, two bright stars – Antares in Scorpius and Spica in Virgo – join the scene. Stellarium

Yesterday morning was clear and I went out to look at comets and planets. How convenient that the morning planets are arrayed across the southern sky, so that one might begin on one end with Mars and finish up with Venus.

Like a kid, I started with the eye-candy planet Saturn first, then jumped over to the Venusian crescent and finally hit Mars as the sky was turning blue. What a lineup – wonderful opportunities to meet our planetary neighbors as long as you’re dressed for the weather.

Comets C/2012 X1 LINEAR (top) and C/2013 R1 Lovejoy appear to be chasing each other in this photo taken with a wide field 4-inch telescope before dawn Feb. 8, 2014. They were about 2.5 degrees apart at the time. Credit: Damian Peach

Comets C/2013 R1 Lovejoy at magnitude 8 and C/2012 X1 LINEAR at 9 still shine brightly enough to show in 6-inch and larger telescopes. Both are in the constellation Ophiuchus and well-placed for observation in the eastern sky just before the start of dawn. On Feb. 6 they were in conjunction only 2 degrees apart – a rare event. Despite appearances, the two comets are unrelated and many millions of miles apart.

Although they’re slowly parting, both are still within 3 degrees of each other, making it fun to drop in on both of them with a telescope. UK astrophotographer Damian Peach captured a wonderful image of the pair on Feb. 8. For finder maps and more information on Lovejoy and XI LINEAR, click HERE.

From aboard the International Space Station, astronaut Rick Mastracchio tweeted this view of Sochi, Russia, the site of the XXII Winter Olympic Games. Credit: NASA

Out at dusk these February evenings? The International Space Station (ISS) is making passes at us just in time for Valentine’s Day. The Expedition 38 crew has been working on biomedical research and performing tests on miniature free-flying robots inside the station called Synchronized Position Hold, Engage, Reorient, Experimental Satellites or simply, SPHERES.

Bowling-ball-sized robot spheres in the space station help with routine monitoring, maintenance and data transfer. Credit: NASA

The volleyball-sized robots has been working on the station since 2006; they take photos and videos, make Wi-Fi connections and fly in formation. They’ll also be used outside the station to make repairs, conduct inspections and assist in de-orbiting malfunctioning spacecraft.

From the ground, the football-field sized space station looks like a brilliant yellow star traveling from west to east across the sky. I’ve listed a few times below when it’s visible from the Duluth, Minn. region. For times and directions for your town, go to Heavens Above or key in your zip code at Spaceweather’s Satellite Flybys link.

* Tonight Feb. 9 starting at 5:57 p.m. Low pass across the south-southeast. Max. brightness at magnitude -1.8. Second brief, brilliant appearance in the west at 7:33 p.m. Disappears into Earth’s shadow 2 minutes later. Magnitude -2.4

* Mon. Feb. 10 at 6:44 p.m. Fabulously bright, high pass across the top of the sky. Mag. -3.4!

* Tues. Feb. 11 at  5:56 p.m. high in the southern sky. Glides very close to Jupiter seconds before 6 p.m. Mag. -3.0

* Weds. Feb. 12 at 6:44 p.m. high in the northern sky. Mag. -2.7

The Unsolved Mystery of the Star of Bethlehem

The three Magi depicted in the Hortus Deliciarum by Herrad of Landsberg in 1185 AD. 

We’ll never know for sure what “star” the Magi saw when they set off from Babylon to Jerusalem seeking their newborn king, but that doesn’t stop us from wondering whether it might have had a natural cause. There are many possible explanations, a few of which we’ll explore here.

“For we have seen His star in the East (upon rising) and have come to worship him” reads the biblical account of the Three Wise Men. After meeting with King Herod, they rode south to Bethlehem:

“… and the star they had seen when it rose went ahead of them until it stopped over the place where the child was. When they saw the star, they were overjoyed.”

Precious little more was written about the star. If the Three Kings’ account had only mentioned a constellation or nearby star for reference, we could have narrowed down the possibilities. We do know the Magi’s general direction of travel and the accepted time frame of Christ’s birth between the years 7 and 2 B.C.

Bethlehem is 5.5 miles south of Jerusalem, where the Three Kings met with King Herod sometime around his death in 4 B.C.

We also know that whatever they saw moved from east to south. First visible in the east, the “star” next appeared over Bethlehem, located 5.5 miles (9 km) south of Jerusalem. As the Magi rode from Jerusalem they would have seen the apparition in the southern sky. Let’s now explore the possibilities:

* Meteors
I think we can rule out meteors or their brilliant cousins, fireballs, because they’re too brief a phenomenon, and the Kings saw the apparition on at least two occasions. Meteors also don’t “rise” but streak across the sky from any direction.

* Comets:

Woodcut showing destructive influence of a fourth century comet from Stanilaus Lubienietski’s Theatrum Cometicum (Amsterdam, 1668). Comets in the past were often described as “hanging” over a location much like the ”star” of Bethlehem, but were typically seen as augurs of doom.

Halley’s Comet would have been a bright naked eye sight in Gemini in the east before dawn in late August 12 B.C. and again in the northwestern evening sky in September. A tempting possibility but the time frame is wrong – too early for Christ’s birth.

But another comet recorded in the Book of Han was observed within the correct time frame by Chinese astronomers in 5 B.C.:

“Second year of the Chien-p’ing reign period, second month (5 B.C., March 9-April 6), a suibsing (tailed comet) appeared at Ch’ien-niu for over 70 days.”

The comet first appeared in the constellation Capricornus, which would have been visible in the eastern sky before dawn from the Middle East in early spring. Assuming it came into view just after perihelion (closest approach to the sun), it would have traveled to the west and into the southern sky roughly within the time frame required for the Wise Men to travel from the Babylon to Jerusalem and finally to Bethlehem.

Or the comet could have been seen in the east before perihelion and then crossed over into the west-southwestern evening sky as a brilliant post-perihelion sight. The Bible also mentions “shepherds abiding in the field, keeping watch over their flock by night” at the time of the birth. This points to spring as being the likely season, the same as the comet’s period of visibility.

This almost sounds like an open and shut case except for a niggling detail. Comets were generally seen in ancient cultures as omens of doom and gloom, not bringers of good news like the birth of a new king. Comets scared people because they came out of nowhere and crossed the sky in unpredictable ways. To this day a bright comet’s appearance still stirs fears of impending catastrophe in some.

* Nova or supernova

A bright nova (temporary brightening of a white dwarf in a binary star system as it “feeds” on gas from its companion) or supernova would attract the attention of many. Most remain bright for weeks or months. Credit: creekandcave.com

Exploding stars are great candidates because they fit the description of a star, and in the case of a supernova, can appear as brilliant as Jupiter or Venus. That would certainly get the attention of the oriental astrologers, who kept a vigilant eye on the heavens waiting for the ancient prophecy of a “star” in Israel to be fulfilled.

Because of Earth’s revolution around the sun it’s even possible for a “new star” to appear first in one direction and then be visible a couple months later in another, especially if you factor in time of night. Unfortunately there are no records of novas or supernovas by the super-observant Chinese or anyone else occurring during the time frame.

* Conjunctions of bright planets

The western sky at the end of evening twilight on Feb. 25, 6 B.C. would have displayed a striking gathering of the planets Jupiter, Mars and Saturn. All three were within 7 degrees of each other. Created with Chris Marriott’s SkyMap software

Conjunctions occur when two or more bright celestial objects line up closely in the sky. A conjunction of two planets is not that unusual, but a gathering of three is and may have held great symbolic value in ancient times. One such triple conjunction involving Mars, Jupiter and Saturn took place in at dusk in the constellation Pisces on February 25, 6 B.C. Could this have inspired the Magi to begin their westward journey?

On Feb. 20, five days before the symmetrical gathering of planets , a very young evening crescent moon passed through the group. Created with Chris Marriott’s SkyMap software

Five days earlier the three were nearly as close and joined by a young crescent moon, an even more auspicious sight.

Of course there are problems with this scenario. The planets appeared in the western sky and the arrangement and number of planets visible would have changed months later when the kings rode to Bethlehem.

An amazing three conjunctions of Jupiter and Saturn from late May to early December 7 B.C. Created with Chris Marriott’s SkyMap software

A recurring conjunction of Jupiter and Saturn played out between May and December in 7 B.C. when the two planets were separated by just one degree (two full moon diameters) on three occasions in the constellation Pisces. The first close pass took place in the eastern morning sky on May 29; the second on Sept. 30 (southern evening sky) and the final pairing on Dec. 5, also in the southern evening sky.

A bright planet duo over so many months rates as an eye-catcher and the directions fit the bill, but the Magi described the object as a brilliant star, not a pair of stars. Even though a degree is a relatively small distance, it would have been easy to see them as two separate objects.

Venus and Jupiter just 0.6 arc minute apart – merged into one – on June 17, 2 B.C. Created with Chris Marriott’s SkyMap software

That brings us to the dual conjunctions of the two brightest planets of all – Jupiter and Venus – in the eastern sky at dawn from the Middle East on August 12, 3 B.C. and again 10 months later on Jun 17, 2 B.C. On both occasions astrologers would have watched the two planets come so close together they would have briefly merged into one before separating again.

OK, a keen eye might have separated the pair on August 12 when they were 2/5 of a moon diameter (12 arc minutes) apart, but they would have been far too tight on June 17 – just 0.6 arc minutes – for anything but a good pair of binoculars or telescope to split them.

During the first conjunction, the Magi would have seen this brilliant pairing in the eastern sky; on June 17 the following year, they lit up the western sky.

Despite appearing as a solitary brilliant “star”, this conjunction would not have been seen in the southern sky on a journey to Bethlehem but in the west, unless we interpret the direction implied in the Bible passage more broadly.

So what’s your pleasure? My best guesses for the Bethlehem Star are the Chinese comet of 4 B.C. or the pair of Jupiter-Venus conjunctions in 3 and 2 B.C. Or it could have been a succession of events – multiple conjunctions and a comet – that led the Magi to conclude that the prophecy of Christ’s birth would soon be fulfilled.

There’s another possibility – the supernatural. But that takes us outside the realm of science. Either way, the star remains a mystery, since we’ll never know for sure what caught the eye of the Three Wise Men as they scanned the heavens looking for signs of what would come.

For more on the topic, click HERE and HERE.

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.

Hubble sees freaky asteroid P/2013 P5 sprout six tails

A fuzzy object discovered by the PanSTARRS survey turned out to be an asteroid with six dust tails. The tails flipped from one side of the comet to the other in less than two weeks. Credit: NASA/ESA

Back in August, astronomers using the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey telescope in Hawaii discovered an unusually fuzzy-looking object dubbed P/2013 P5. Later, on September 10, when the Hubble Space Telescope took a look, it revealed that the asteroid had sprouted six tails!

When Hubble returned less than two weeks later to re-photograph P/2013 P5, the entire tail structure had swung over to the other side of the asteroid. What’s going on here? Scientists think the asteroid’s rotation rate has increased to the point where it’s flinging dust from its surface into space. The pressure of sunlight pushes the dust away, forming a tail(s) just like a comet. As P/2013 P5 rotates and periodically releases dust, the tails twist about in different orientations.

P/2013 P5 isn’t the first asteroid to mimic a comet. Asteroid 596 Scheila was struck by a smaller asteroid in 2010 and developed a tail and other dust plumage. This photo by the Hubble Space Telescope. Credit: NASA/ESA

Unlike asteroids, comets are composed of dust-impregnated ice; when they’re heated by the sun, some of the ice vaporizes, liberating dust that’s then pushed back into a tail by the pressure of the solar wind. P/2013 P5 looks superficially similar to a comet but it’s smack dab in the asteroid belt and studies of the tails indicate they were released in a series of “dust-ejections” on April 15, July 18, July 24, Aug. 8, Aug. 26 and Sept. 4.

“We were literally dumbfounded when we saw it,” said lead investigator David Jewitt of the University of California at Los Angeles. “Even more amazing, its tail structures change dramatically in just 13 days as it belches out dust. That also caught us by surprise. It’s hard to believe we’re looking at an asteroid.”

The asteroid measures about 1,400 feet (427 meters) across and shines at a very dim magnitude 20, well beyond the limits of visual observing in amateur telescopes. It’s believed radiation (light and heat) pressure from the sun spun up P/2013 P5  causing it to lose dust from its equator into space – a first step in the potential breakup of the asteroid.

As of now, it’s lost only about 1,000 tons of dust, a small fraction of its mass. Astronomers plan to study the asteroid closely to see if it disintegrates. P/2013 P5′s dusty fits may shed light on how asteroids break down into ever smaller pieces, some of which are perturbed by Jupiter, end up in orbits that cross that of Earth and eventually land on our planet as meteorites.

Bright explosion on Comet C/2012 X1 – an update plus maps to help you find it

An expanding bright cloud of sunlit dust and ice particles surrounds the hidden core of comet C/2012 X1. Fresh icy materials from a large-scale event on Comet C/2012 X1 exposed to sunlight for the first time caused the comet to leap in brightness a few days ago. Photo taken today Oct. 25 by Gianluca Masi of Ceccano, Italy.

Finally got a chance to see the exploding comet C/2012 X1 (LINEAR) from my home this morning through a 10-inch telescope. You’ll recall this is the comet that went from 14th magnitude obscurity straight to binocular brightness without passing Go. The comet’s located in the dim constellation Coma Berenices not far from the handle of the Big Dipper. To see it you have to get up about two hours before sunrise and have a clear view of the northeastern sky. Even at start of dawn, X1 is only about 15 degrees or a “fist and a half” above the horizon.

Wide view of the eastern sky shortly before the start of dawn, Comet C/2012 X1 is low in the northeast near the star Beta in Coma Berenices. Position shown for Oct. 26 at dawn. See detailed chart below for use with telescopes and binoculars. Maps made with Stellarium

I was excited by what I saw. Italian amateur astronomer Gianluca Masi’s photo captures its low-power telescopic appearance well. To my eye the comet was a bright, dense, hazy ball of magnitude 7.5 with a compact knot of brighter material at its center. I could kick myself for forgetting to check it out in binoculars – even in last quarter moonlight I suspect the comet was bright enough to spot in 50mm and larger glasses.

Map covering a 5-degree chunk of sky showing C/2012 X1′s position on Oct. 26 (6 a.m. CDT) through Oct. 30. Use Beta in Coma Berenices to navigate to the comet.  Stars shown to mag. 9.5.

Now the wait is on. Once the moon gets whittled down to a crescent and becomes less of a glare bomb, we’ll soon see how well it may show in small telescopes. I encourage you to watch how the comet evolves in the coming weeks. It’s already brighter than when first seen in outburst on Oct. 21 and continues to expand. I estimated its size at 4-5 arc minutes or about 1/6 the size of the full moon. It’s amazing to see a comet this bright at the remote distance of 279 million miles.

Comet 17P/Holmes underwent a similar outburst in the fall of 2007 but brightened even more. This photo was taken on Nov. 27, 2007 a little more than a month after the explosion. Holmes remained visible for months after its outburst. Credit: Michael Jaeger

Don’t you love it? With all eyes focused on Comet ISON, here comes this upstart from deep space wanting to share a bit of the limelight. While it’s possible the comet was struck by a meteoroid, exposing fresh ices to fizz and broil in sunlight, a more likely cause for the outburst is heated gas beneath the surface breaking through and exposing fresh ice. Solar heating converts the ice directly to gas in a process called sublimation forming a tenuous glowing globe around the comet’s nucleus called a coma.

Watch this blog for more updates and finder maps for the comet in the coming weeks.

Bubble, bubble toil and trouble: Mini sungrazing comet gets zapped today

Kamikaze comet careens toward the sun early this morning. Photo from SOHO. Click to see video. Credit: NASA/ESA

Here’s something fun. Just as we’re wondering and debating whether Comet ISON will hold together in one piece during a hair-raising solar encounter on Thanksgiving Day, another sungrazing comet appeared overnight in the pictures taken with the Solar and Heliospheric Observatory’s C3 coronagraph. Like a World War II kamikaze pilot, it’s headed straight toward the sun.

The  visitor is a member of the Kreutz family (pronounced ‘Kroits’) of comets – a remnant of a much larger sungrazing comet that broke up into many smaller fragments long ago – and appears not to have survived the sun’s terrific heat. Most Kreutz sungrazers are only around 30 feet wide (10 meters) and fizz away into fine dust and gas when they get too close to the fire. SOHO comet spotters find a few dozen a year.

No sign of the little sungrazer at 12:10 p.m. CDT this afternoon. Credit: NASA/ESA

At top, you’re looking at the ‘final glory’ photo of the comet taken at 3 a.m. CDT today. The next frame (at right), made at 12:10 p.m., shows nothing. Bye, bye little guy.

ISON should fare better. With an icy nucleus measuring at least half a mile across, there’s a fair chance it will survive the battering and emerge reborn like Gandalf the White in Lord of the Rings, cloak aglow and renewed by a near brush with death.

And ready to give earthlings a fine show. The comet that is.

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.