Comet Ison

ISON, We’re So Over You: 73 More Comets in 2014!

For anyone who’s feeling jilted by Comet ISON’s poor showing in 2013, not to worry: 2014 will see 73 more comets (73!) looping around the Sun.

Comet Lovejoy, Dec. 31
Comet Lovejoy, Dec. 31

The Sky Live Blog lists all these comets, including the dates of their perihelion passages and expected maximum brightness, here.

According to Universe Today, four of the stand-out comets will be Comet Lovejoy (visible now), Comet PanSTARRS, Comet Oukaidmeden, and Comet Siding Spring.

Below is just a sampling of all of 2014’s comets–the names of the first 15 and the dates they’ll be closest to the Sun.

Comet 87P/Bus; Jan 7
Comet 293P/Spacewatch; Jan 9
Comet P/2007 R2 (Gibbs); Jan 11
Comet C/2013 H2 (Boattini); Jan 23      
Comet 129P/Shoemaker-Levy 3; Feb 6
Comet P/2013 N3 (PANSTARRS); Feb 11
Comet 169P/NEAT; Feb 12
Comet 292P/Li; Feb 13
Comet C/2013 P2 (PANSTARRS); Feb 17
Comet P/2013 TL117 (Lemmon); Feb 18
Comet C/2012 X1 (LINEAR); Feb 21
Comet 294P/LINEAR; Feb 26
Comet P/2007 H3 (Garradd); Mar 3
Comet 52P/Harrington-Abell; Mar 7
Comet P/2013 W1 (PANSTARRS); Mar 8

Greatest Comets of the Past 500 Years

Huffington Post has this handy recap of five of the Greatest Comets of the Past 500 Years. It’s missing some of my favorites: Donati’s Comet, the Great Comet of 1811 (featured in Tolsoy’s “War and Peace”), the phantasmagorical Great Comet of 1528, the Comet of the Black Death…

Still, there are some nice pictures. I think all of these get a mention in “The Night of the Comet.”

Greatest Comets Ever Seen In Past 500 Years
SPACE.com | By Joe Rao
Posted: 12/26/2013 9:18 am EST

When Comet ISON was discovered and a preliminary orbit for it was worked out, it was initially announced that it could be the “comet of the century.”

Of course, the 21st century is only 12 years old (from 2001) and ISON turned out to be a dud. But out there in the far recesses of space there is certainly some unknown comet worthy of such an honorific title that will ultimately put on a unique and memorable show sometime during this century.

There will always be bright and spectacular comets, but in each century there is always one that will stand above the others. Below I provide my own list of the five most spectacular comets that have appeared in each century starting from the 16th and running through the 20th century.

Take note that four of these five dazzlers appeared in the latter half of their century and that the average time between appearances amounts to 97 years. Considering that Comet Ikeya-Seki passed by in 1965, the next prospective “Comet of the Century” might not appear — according to our small sampling — until maybe 2029 at the earliest … and maybe not even until the next century (in 2103!).

Then again, stupendously bright comets are totally unpredictable and can suddenly appear at almost any time.

Greatest Comet of the 16th Century: The Great Comet of 1577

This comet passed to within 16.7 million miles (26.9 million kilometers) of the sun on Oct. 27, but was not sighted until five days later, when it was described in an account from Peru as an exceptionally brilliant object. Contemporary descriptions note that it was seen through the clouds like the moon.

o-GREAT-COMET-1577-570

The Great comet of 1577, seen over Prague on November 12. Engraving made by Jiri Daschitzky.

By Nov. 8, it was reported by Japanese observers as a “broom star,” appearing “as bright as the moon” with a white tail spanning over 60 degrees (your clenched fist held at arm’s length measures 10 degrees). The famous astronomer Tycho Brahe first saw the comet as a reflection in his garden fish pond on Nov. 13, and likened its brightness to Venus. The comet was still as bright as zero magnitude inDecember before it finally dropped below the limit of naked-eye visibility on Jan. 26, 1578. (Magnitude is a measure of a celestial object’s brightness, with smaller numbers corresponding to brighter objects.)

Greatest Comet of the 17th Century: The Great Comet of 1680

The great excitement that accompanied the first announcement of the discovery of Comet ISON was that initially its orbit appeared strikingly similar to this spectacular 17th century comet; it was hoped that perhaps ISON was either a return of this amazing object, or at the very least a large fragment. But later calculations showed this was not so.

o-GREAT-COMET-1680-570
The Great Comet of 1680 over Rotterdam. People in the drawing are using cross-staffs which were early devices for measuring angles and a predecessor of the sextant.

The German astronomer Gottfried Kirch became the first person to ever discover a comet with a telescope when he sighted this comet on Nov. 14, 1680, when it was at fourth magnitude. By Dec. 2, it already had a 15-degree tail and had reached second magnitude (as bright as Polaris, the North Star). On Dec. 18, it was at perihelion (the closest point to the sun in its orbit) coming to within 128,000 miles (206,000 km) of the sun’s surface.

At least one report (from Albany, NY) indicates that the comet was visible in the daytime. Several days later it could be seen in the evening twilight sky with a tail stretching straight up from a second-magnitude head from the southwest horizon for 70 to 90 degrees. By Jan. 10, 1681, the tail had shrunk to 55 degrees and by the Jan. 23 it measured “only” 30 degrees, with its head having faded to fourth magnitude. It remained visible to the naked eye until early February 1681.

Greatest Comet of the 18th Century: The Great Comet of 1744

First sighted on Nov. 29, 1743, as a dim fourth-magnitude object, this comet brightened rapidly as it approached the sun. Many textbooks often cite Philippe Loys de Cheseaux, of Lausanne, Switzerland, as the discoverer, although his first sighting did not come until two weeks later.

o-GREAT-COMET-1744-570

The Great Comet of 1744, or “Comet de Cheseaux-Klinkenberg”, at 4am on March 9, 1744, showing six tails rising above the horizon.

By mid-January 1744, the comet was described as first-magnitude with a 7-degree tail. By Feb. 1, it rivaled Sirius (the brightest star in the sky) and displayed a curved tail, 15 degrees in length. By Feb.18, the comet was equal to Venus in brightness and displayed two tails.

On Feb. 27, it peaked at magnitude -7 and was reported visible in the daytime, 12 degrees from the sun. Perihelion came on March 1, at a distance of 20.5 million miles (33 million km) from the sun. On March 6, the comet appeared in the morning sky, accompanied by six brilliant tails, making it resemble a Japanese hand fan.

Greatest Comet of the 19th Century: The Great September Comet of 1882

This comet is perhaps the brightest comet that has ever been seen and was a gigantic member of the Kreutz Sungrazing Group of Comets. First spotted as a bright zero-magnitude object by a group of Italian sailors in the Southern Hemisphere on Sept. 1, this comet brightened dramatically as it approached its rendezvous with the sun.

o-GREAT-COMET-1882-570

Photograph of the Great Comet of 1882, as seen from South Africa.

By Sept. 14, it became visible in broad daylight, and when it arrived at perihelion on Dec. 17, it passed at a distance of only 264,000 miles (425,000 km) from the sun’s surface. On that day, some observers described the comet’s silvery radiance as scarcely fainter than the limb of the Sun, suggesting a magnitude somewhere between -15 and -20 (the latter magnitude would register nearly 1,000 times brighter than the full moon!). The following day, observers in Cordoba, Argentina, described the comet as a “blazing star” near the sun.

The nucleus also broke into at least four separate parts. In the days and weeks that followed, the comet became visible in the morning sky as an immense object sporting a brilliant tail. Today, some comet historians consider it a “Super Comet,” far above the run of even great comets.

Greatest Comet of the 20th Century: Comet Ikeya-Seki, 1965

This was the brightest comet of the 20th century, and was found just over a month before perihelion in the morning sky, moving rapidly toward the Sun. Like the Great Comets of 1843 and 1882, Ikeya-Seki was a Kreutz Sungrazer and on Oct. 21, swept to within 744,000 miles (1.2 million km) of the center of the sun.

o-GREAT-COMET-1965-570

This picture was captured on October 30, 1965 showing the full extent of this great comet’s tail of some 30 degrees.

The comet was then visible as a brilliant object within a degree or two of the sun, and wherever the sky was clear, the comet could be seen by observers merely by blocking out the sun with their hands. From Japan, the homeland of the observers who discovered it, Ikeya-Seki was described as appearing “10 times brighter than the full moon,” corresponding to a magnitude of minus 15. Also at that time, the nucleus was observed to break into two or three pieces.

Thereafter, the comet moved away in full retreat from the sun, the head fading very rapidly, but its slender, twisted tail reaching out into space for up to 75 million miles (120 million km), and dominating the eastern morning sky right on through the month of November.

Greatest Comet of the 21st Century: TBD

ISON fizzled, so we continue to wait…

Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer’s Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y. Follow us @Spacedotcom, Facebook and Google+.

Comets Kohoutek and ISON in The Baltimore Sun

Just now caught this in The Baltimore Sun, a nice review of 1973’s Comet Kohoutek, relating it to this year’s Comet ISON.

Back Story: Comet Kohoutek Was Another Flameout
Like ISON, it didn’t live up to the hype

By Frederick N. Rasmussen, The Baltimore Sun
December 5, 2013

Comet ISON

Comet ISON is pictured in this Nov. 19, 2013, handout photo by NASA, taken using a 14-inch telescope located at the Marshall Space Flight Center at 6:10 a.m. EST with a three-minute exposure. (NASA, Reuters, November 27, 2013)

 

Comets ISON and Kohoutek will forever share two things. Both were hailed as “Comets of the Century,” and both failed to live up to the hype attending their impending arrival in our solar system.

Unlike Comet Hale-Bopp, which put on a grand show in 1997 before departing the inner solar system for a 3,000-year journey through deep space, comets ISON and Kohoutek were profound flops that left thousands of disappointed stargazers across the world who had high expectations for experiencing a somewhat-rare celestial occurrence.

No one knows more about the unpredictability of comets and their fickle ways than Dr. Lubus Kohoutek, the Czechoslovakian astronomer who discovered the comet that would be named for him on March 7, 1973, while studying photographic plates at the Hamburg-Bergedorf Observatory in Germany.

News surrounding the important discovery of Kohoutek — whose formal scientific designation was C/19731 — was underscored by Dr. Brian Marsden who headed the International Clearinghouse for Astronomical Discoveries in Cambridge, Mass.

“I wouldn’t be a bit surprised if Comet Kohoutek ends up being classified as the best comet of the century,” Marsden told The Evening Sun. “An object that large should achieve unusual brightness and produce an exceptional tail.”

Anticipation of its arrival in late November was fueled by initial reports that it was larger than the famed Halley’s Comet of 1910, whose tail extended some 60 million miles, and that Kohoutek had last made a pass by the sun some 10,000 years ago.

The Evening Sun built anticipation by saying Kohoutek “wasn’t just any comet. It is a comet with a capital C,” adding that it had been “60 years since a major naked-eye comet appeared.”

The incessant drumbeat by the press kept up, even reporting that the British liner Queen Elizabeth 2 had on board 1,963 comet enthusiasts who had booked a special cruise off the coast of South Carolina in which to take in the comet.

And then the bottom began to fall out by mid-December.

“The much-publicized Comet Kohoutek is proving to be a disappointment to sky-watchers, if not a fizzle,” reported The Wall Street Journal, with the newspaper reporting two weeks later that the comet was a “celestial box-office dud because it isn’t dirty enough.”

A NASA official explained to The Wall Street Journal that “Comet Kohoutek turns out to be a comet that has much less dust than expected,” adding that gas dust is the essential component in forming spectacularly beautiful tails that can be seen by the naked eye when they are near the sun.

In early January 1974, the comet was growing fainter as it traveled away from the sun at the speed of 163,000 mph, some 85 million miles away from Earth, as it went back to where it had originated.

With the naked-eye option gone, The Washington Post lamented on Jan. 5, 1974, that the “only way to see the comet now is through a pair of binoculars or a telescope.” Astronauts aboard Skylab 4 and Soyuz 13 probably had the best view of all.

“Watergate, then the energy crisis, and now the comet,” a Boston resident said to The New York Times.

“For the first time in my life I am terribly embarrassed. At Christmas a few weeks ago, I gave all my readers a present. It was the Comet Kohoutek. … It was your comet, and it was given to you as a token of appreciation for how nice you had been to me in 1973,” wrote humorist Art Buchwald in The Washington Post.

“I wish I could give you something else in its place, but Kohoutek used up all my money. It was one lousy rip off and I assure you it’s going to be a long time before I buy a comet for anybody again,” he wrote.

Discoverer Kohoutek retired in 2001.

The Georgia rock band R.E.M. musically immortalized the comet with lyrics in a song aptly titled “Kohoutek” that it included in its 1985 album, “Fables of the Reconstruction.”

She carried ribbons, she wore them out

Courage built a bridge, jealousy tore it down

At least it’s something you’ve left behind

And like Kohoutek, you were gone.

fred.rasmussen@baltsun.com

Copyright © 2013, The Baltimore Sun

Songs with Astronomical Themes No. 14: “Champagne Supernova,” by Oasis

I’m still sulking about the whole Comet ISON thing. Don’t even talk to me about ISON.

To help us get over that disappointment, here’s another favorite song with an astronomical theme, Oasis’s seven-minute-long, “Champagne Supernova,” from 1996. I know I’ve posted this before, but I figure no one’s keeping track.

Break out your tie-dye and enjoy.

The Night of the Comet Featured in Country Roads Magazine

Thanks to Chris Turner-Neal for his marvelous feature story on comets and THE NIGHT OF THE COMET in December’s Country Roads Magazine. Here’s the article:

UNEXPECTED TRAJECTORIES
by Chris Turner-Neal
December 2013

Unexpected Trajectories

What an Unpredictable Comet and a Newly Published Novel Have in Common

I’m in the dark. But by the time you read this in December, you’ll already know if comet ISON is blazing beautifully across the night sky, aweing billions, or if it fizzled during the course of its great do-si-do around the sun and drove respected astronomers to the bottle. All I can do, from my cozy temporal perch in late October, is invite you to follow ISON’s unpredictable development, tell you a little about the unpredictability of comets in general, and suggest you reflect on these grand themes while reading a great new comet-themed novel, which details the unpredictability of life.

∞

The word “comet” comes from the Greek word for “long hair,” referring to the streaming tails visible comets have. These tails come from steaming ices—composed not only of water, but also frozen gases like carbon dioxide, methane, and ammonia—that generally surround a rocky, dusty core, and which vaporize as the comets approach the sun and encounter light and heat. In addition to these gases, comets can also leave tracks of solid debris; and if the Earth passes through one of these cosmic chat piles the result is a meteor shower like the Perseids—the every-August light show you always forget to get up early to look at.

Regular short-period comets, like Halley’s Comet, which famously swings by every seventy-six years or so, are thought to originate in the Kuiper Belt, the collection of small rocky bodies outside Neptune’s orbit that make up the first-tier suburb of the solar system. Longer-period and one-and-done comets probably come from the fun-to-say Oort Cloud, an even more distant group of small bodies loosely gravitationally bound to the sun. In either case, something happens—as dramatic as a collision or as gentle as a little gravity nudge from a passing neighbor—and knocks the comet-to-be off its path, sending it toward the sun.

It’s hard to predict what a new comet will do, which is why predictions for ISON are all over the map. If ISON has a lot of ices on its surface (we can’t be sure from this distance), and if it doesn’t lose them all or shatter as it makes its closest approach to the sun during November, leaving the solid debris of its body behind, then ISON might be putting on a great show by the time you read this.

ISON has invited its fair share of calamitous predictions, in good company with its historical brethren. The star of Bethlehem that sent the wise man in search of the Christ child may have been a comet, and so, possibly, was the cross in the sky seen by Emperor Constantine before he, and Christianity, became rulers of Rome. Halley’s comet by itself accounts for several dramatic omens, “announcing,” if you’re willing to be a little squishy on the dates, the Norman Conquest of England, a major invasion of Hungary by the Ottomans in 1456, and both the birth and death of Mark Twain. Even before ISON is visible to the naked eye, the usual suspects have set up websites blaming the usual suspects, with at least one connecting the word ISON to a mispronunciation of the Hebrew word “ason,” meaning “disaster,” which proves… something, apparently, probably about the United Nations and fluoridation.

∞

New Orleans author George Bishop takes the comet’s traditional role as omen and uses it as the backdrop for his new novel, The Night of the Comet. It’s a big device, but Bishop’s able storytelling weaves it seamlessly into his book. Narrated by the fourteen-year-old son of a science teacher and amateur astronomer in small-town Louisiana in 1973, The Night of the Comet relates the story of a family reacting to the individual stresses of growing up and growing older while Comet Kohoutek approaches, eliciting promises for a spectacular show. As some readers may recall, Comet Kohoutek’s 1973 fly-by proved to be a colossal dud, barely twinkling instead of blazing, but Bishop’s novel is anything but a flop.

Bishop worries about it being billed as a coming-of-age novel, because we’ve all read enough of those to fill in the blanks ourselves: a (boy/girl) in (the Deep South/a rural Midwestern farm community/Brooklyn) learns about (death/injustice/friendship) over the course of an (unforgettable/magical) summer. Bishop ditches the formula and speaks frankly to his readers about moving through the stages of life; while Junior, the narrator, is learning how to be an adult, his parents are learning how to be middle-aged.

Once a promising young scientist and the prettiest girl in town, Junior’s father and mother are now forced to face the reality of being a high-school science teacher and a high-school science teacher’s wife. Jokes about mid-life crises staged with Ferraris and plastic surgery form a staple of open-mic nights, but the sadness of waking up one day and realizing you haven’t led the life you convinced yourself you should expect is a more rarely told, and more interesting, story.

Junior’s awkward advances toward the teenage bombshell next door and his sister’s attempts to become a hippie before it’s too late will make you smile, but their parents’ hell-for-leather efforts to Be Someone later in life will sucker-punch you right in the tear ducts. I’m hesitant to give you more of the plot, because one of the joys of reading The Night of the Comet is watching the story unfold—it has all the inexorability of a Greek tragedy, but is populated not with demigods and queens, but with the kind of people you’ve known all your life.

Bishop is a born storyteller. So many moments in The Night of the Comet just feel so true and right that you find yourself whipping through it faster than you wanted to. He even pulls off the feat of writing realistic dialogue for teenagers that’s neither corny nor “gritty”—and as a former teenage boy, I can tell you that “full frontal sex” is exactly the kind of fractured phrasing you come up with when your curiosity outstrips your knowledge.

Another great highlight is Junior’s mother’s remembered childhood encounter with Ava Gardner, who is brought so quickly and fully to life in a few short pages that you can almost smell her perfume lingering in the room.

As his parents grow more distracted and their marriage teeters, Junior continues to ask that they repeat for him the story of their engagement in exactly the same way, with every detail and plot point neatly in place, as a ritual reassurance—but also because all families have those stories that are recited, not told. The whole book rings true like this. You occasionally hear of an author who “writes women” or “does children” well; Bishop writes people well.

So, to conclude my own comet-like path through various topical orbits: good luck seeing Comet ISON; but by the time you read this, my good wishes will be either unnecessary or too little too late. Even if ISON fails to impress, I have two pieces of advice: read George Bishop’s The Night of the Comet, and take a little time on a dark, clear evening to look up at the stars. Even without ISON headlining, it’s the greatest show off Earth.

On December 19, LASM will offer a live presentation highliting Comet ISON. Weather permitting, observation of Comet ISON on the levee will follow. 7 pm at 100 South River Road, Baton Rouge. lasm.org. See page 37 of the calendar for a full description.

12 Cool Facts About Comet ISON

From Slate Magazine, here are “12 Cool Facts About Comet ISON“–maybe more than you’d ever want to know–plus photos and a video:

12 Cool Facts About Comet ISON
By Phil Plait
Nov. 21, 2013

ison_michaeljager_nov122013.jpg.CROP.original-original
[Comet ISON on Nov. 12, 2013. Photo by Michael Jäger.]

Over the years we’ve had some pretty amazing comets swing by our planet. I remember the ones I’ve seen myself: Hyakutake, Hale-Bopp, Holmes, Pan-STARRS, McNaught… they were all beautiful and amazing sights.

Now we have C/2012 S1 (ISON) passing our way, and it’s certainly grabbing attention. It’s brightened substantially in just the past few days, so now’s the time to see it! The pictures people are taking are phenomenal, and there’s plenty of science pouring in as well.

Everyone loves a good picture, of course, but comets are amazing well beyond just their stunning beauty. So I figured I’d take this opportunity to tell you a few things about this comet, a handful of facts to nourish the part of your brain seeking out wonder. Keep these in mind while you’re gawking at the gorgeous pictures.

1) ISON is a n00b.

Some comets are on long, elliptical orbits dropping them in to the inner solar system before sailing them back out to the depths of space. There, they slow, stop, then fall once again back into the warmth and light. Comet Halley, for example, is on a 75-year orbit that takes it out past Neptune.

But some are more extreme. If they get an extra kick on their way in — perhaps from a collision, or a boost by a planet’s gravity — their elliptical orbit gets turned into an open-ended hyperbola: they have more than enough energy to leave the solar system forever. Once they’re gone, they’re gone.

ISON is a hyperbolic comet, which means this is it: These next few weeks are our only chance to see it. After it swings back out, it ain’t coming back. This is likely its first tour of the inner solar system as well, which is why scientists are so excited about it; we’re seeing a pristine comet, billions of years old, a relic of the ancient solar system. It’s a time capsule, letting us study what conditions were like when the Sun and planets were young.

2) ISON is a sun-diver.

The orbit of ISON takes it very, very close to the Sun’s surface. Next week, on Nov. 28, it will skim a mere 1.1 million kilometers (about 700,000 miles) above the Sun’s surface. Given that the Sun is 1.4 million km across, that’s a mighty close shave! The heat it feels will be intense, and it may not survive the encounter (see #10 below).

3) When it passes the Sun, it will be moving at 360 kilometers per second.

Imagine dropping a rock. The higher you drop it, the longer the Earth’s gravity has to pull on it, and the faster it’ll be moving when it hits the ground.

The fastest a rock can hit the Earth is if you drop it from infinitely far away. When it hits it’ll be moving at escape velocity — and the physics of dropping it is reversible, so if you throw a rock at escape velocity it will continue on forever (hence the term “escape velocity”).

Comet SWAN
[Comet SWAN on a death dive into the Sun in 2012. Photo by NASA / ESA / SOHO]

The same is true for a comet rounding (or, in some cases, impacting) the Sun. Since ISON is falling from essentially infinitely far away, when it goes around the Sun it’ll be moving at the Sun’s escape velocity at that distance, or just about 360 km/sec (225 miles/sec). How fast is that? Well, it’s hundreds of times faster than rifle bullet, for example, and over 1500 times faster than a commercial jet — at that speed, the comet would cross the continental United States in about 15 seconds.

In fact, it will be moving at 0.1% the speed of light! That’s far faster than any human-made space probe has ever traveled. And the only propulsion it uses is gravity.

[CORRECTION (Nov. 22, 2013 at 16:15 UTC): I made an error in the calculation for this section, using the escape velocity for the Sun’s surface, and not for the distance ISON will be from the Sun’s center. This deserves a longer explanation, so I wrote a follow-up post about it, and simply corrected the problem here.]

4) The solid part of ISON is only about two kilometers across.

Comets are actually lumps of rock, gravel, and ice mixed together. This solid part of the comet is called the nucleus, and some are huge; Hale-Bopp had a nucleus about 30 km (20 miles) across.

ISON, though, is tiny, only about 2 km (1.2 miles) across. Heck, plop it down in the middle of the Rocky Mountains and you’d hardly notice it! The size has been estimated using images taken from the Hubble Space Telescope, which in reality only give us an upper limit. It might even be smaller.

Still, that’s enough to make the comet visible to the naked eye even from a distance of a hundred million kilometers! How can that be? Why, it’s because…

5) The coma is well over 100,000 km in size.

ison_earth_damianpeach.jpg.CROP.original-original
[A very rough comparison of the physical size of ISON’s coma and the Earth. On this scale, the solid nucleus of ISON would be about the size of a bacterium. Comet photo by Damian Peach.]

When you look at a picture of ISON (or any comet), you’re not seeing the nucleus. You’re seeing the gas surrounding it that was once frozen beneath the surface. When the comet gets near the Sun this ice warms and turns directly into a gas. It escapes the weak gravity of the nucleus, forming the fuzzy coma around it.

Since the coma isn’t solid, it doesn’t have a sharp edge. But on Nov. 15, the coma for ISON was estimated to appear about 3 arcminutes across (that’s a size on the sky; the Moon is 30 arcminutes across for comparison). Since ISON was about 140 million km (90 million miles) from Earth at the time, that would put the coma at a size of about 120,000 km (80,000 miles). That’s ten times the diameter of Earth!

6) The tail of the comet is (at least) 8 million kilometers long.

Once the gas (and ejected dust) in the coma is out in space, it can be affected by both the solar wind and the pressure of sunlight. It streams away, forming one or more long tails. Like the coma, this is extremely rarefied gas, so it doesn’t really have an edge, but the tail of ISON has been measured to be at least 8 million km (5 million miles) long. That’s 20 times the distance of the Moon from the Earth.

7) The tail is essentially a vacuum.

Weirdly, despite being bright and obvious, a comet’s tail is incredibly ethereal. The density of atoms in a typical tail can run up to about 50,000 atoms per cubic centimeter. Sound like a lot? In a cubic centimeter of air at sea level, there are 1019 (10,000,000,000,000,000,000) atoms/molecules per cc! Compared to the air we breathe, a comet’s tail is a hard vacuum. It’s only bright because it’s so big, and reflects sunlight.

8) The total mass of the comet is about 2 – 3 billion tons.

Ice isn’t terribly dense; it floats on water! If ISON is a typical mix of ice and rock, it has a density of about 600 kg per cubic meters. Assuming it’s a sphere two km across, that gives it a mass of roughly 2 – 3 billion tons. That may sounds like a lot, but remember, ice is far less dense than rock. A small rocky mountain would be far more massive.

9) ISON is shrinking.

Measurements of how much water ice is leaving the comet’s surface indicate it’s losing about 1029 molecules of water every second (bearing in mind this goes up and down all the time). Doing the math, I get that this is about three tons per second — enough to fill an Olympic pool in about ten minutes. That’s a fair amount, but given the total mass of the comet, it would take about 25 years at this rate for the comet to totally disappear. Since it’s only shedding mass for the few weeks it’s near the Sun, it’s got mass to spare. Thanks to @SungrazingComets and the Comet ISON Observing Campaign for their help with this.

10) ISON may disintegrate.

That doesn’t mean it’s safe, though! Some comets aren’t terribly solid; the ice is what holds them together. As they near the Sun and the ice starts to go away, big chunks can break off (called “calving”). In some cases the comet can disintegrate spectacularly. Even if they survive their plunge down to the Sun, some comets get so close they evaporate; we’ve seen that happen too!

It’s not clear if ISON will survive its close shave with the Sun. As of right now it seems to be OK, but who knows what the next few days will bring.

11) ISON won’t hit the Earth.

shutterstock_impactearth_no.jpg.CROP.original-original

Whenever there’s a bright comet (or near pass of an asteroid), conspiracy buffs start thinking it’ll hit us. Don’t worry about ISON. The closest it will get is on Dec. 26, 2013, when it will be about 60 million km (40 million miles) from Earth. That’s 150 times farther away than the Moon.

12) You can see it for yourself, and it may become visible in broad daylight.

Right now, ISON is bright enough to see naked eye, and easily with binoculars. It’s jumped in brightness twice just in the past week or so! As it gets near the Sun it’ll get brighter, but harder to find because, duh, it’s getting near the Sun.

However, sometimes comets like this get incredibly bright when they are close to the Sun. In 2007, I saw comet McNaught at noon. Yes, noon. It was difficult, and I had to be very careful; you don’t want to wind up looking right at the Sun, especially in binoculars, unless boiled eyeballs is something you want. Seriously, don’t just scan around with binoculars looking for the comet, because it’s very dangerous and can blind you.

There’s no way to know right now, but it’s possible that ISON will be visible in broad daylight to the naked eye for the short time it’s near the Sun. It could be possible to see it during the day if you position yourself so that the Sun is blocked behind a tree, or the edge of a house. It depends on the exact position of the comet relative to the Sun, of course.

Again, doing this is difficult and you shouldn’t attempt it unless you know what you’re doing. I’ll note that in general, glancing briefly at the Sun won’t hurt a normal eye with an undilated pupil, but it’s not a good idea to do it too much, and it’s more dangerous for kids (their lenses let through more UV light than adult eyes).

Your better bet is to wait a few more days. Once ISON rounds the Sun, it’ll be visible in the west after sunset for a few weeks for those of us in the northern hemisphere, so watching it will be far easier (right now you have to get up at about 5:00 a.m., before sunrise, to see it). Here’s a finder chart (Sky and Telescope has another as well) that’ll help you spot it; planetarium software for mobile devices are great too (I like Sky Safari, but there are many to choose from). You can find plenty more finder charts online. I’ll note it’ll fade with time, but around Dec. 20 or so it should be out of the Sun’s glare, and (hopefully) easily visible with binoculars.

[UPDATE (Nov. 22, 2013 at 16:15 UTC): I’ll note that once it passes the Sun, the comet will still be visible in the east before sunrise in the morning as well as in the west after sunset in the evening. I explain this in a follow-up post.]

Seeing a good comet is a wonderful experience, and ISON gives us a chance to experience something that will only come around once, quite literally. This isn’t science fiction, or something out of a movie: This object exists, and it’s just one small part of a much grander universe that’s out there. I hope you can take a moment to drink that in.

Comet ISON Heats Up, Adds New Tail

This update on Comet ISON from Universe Today. Come on, ISON! Come on!

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Comet ISON Heats Up, Grows New Tail
by Bob King, Nov. 7, 2013

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.

Comet Ison Update

Despite dire predictions to the contrary, recent reports say that Comet ISON is still “doing just fine” and “holding it together.”

I think I’m growing to love this little comet.

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Latest Images of Comet ISON Show it is ‘Doing Just Fine’
Universe Today
October 11, 2013

As we reported yesterday, the latest data on Comet ISON indicates there is some encouraging news as far as the Comet surviving perihelion, its closest approach to the Sun. While some are all doom and gloom about the potential for Comet ISON putting on a good show, these latest images indicate that as of now, this comet is alive and doing well!

“We really do not know what comet ISON is going to do when it gets near the Sun,” wrote astronomer Karl Battams of the Comet ISON Observing Campaign website. “But what we can say for certain, right now, is that comet ISON is doing just fine! It continues to behave like a fairly typical, if somewhat smaller-than-average, Oort Cloud comet. It has given no indication that it has fragmented and while such an event can never be ruled out, we see no evidence or hint that the comet is in any imminent danger of doing so. Any reports to the contrary are just speculation.”

Hubble Confirms Comet ISON Is Holding It Together
Discovery
October 17, 2013

Despite speculation to the contrary, Comet ISON is holding its own against the sun’s heat, with its cometary nucleus apparently remaining as a solid mass.

New observations carried out by the Hubble Space Telescope on Oct. 9 have resolved the interplanetary traveler with a beautifully smooth coma (the dust and gas around the “head” of the comet) with a bright tail swept back.

The comet — which was discovered in September 2012 by the International Scientific Optical Network (ISON), near Kislovodsk, Russia — is believed to be a pristine cometary nucleus that has fallen from the hypothetical Oort Cloud — a reservoir of icy fragments left over from the birth of the solar system. It is reckoned that this “shell” of proto-comets is located around 1 light-year away from the sun.

As this is its first visit to the inner solar system, astronomers theorized that ISON’s nucleus might fragment as it becomes heated by the sun’s energy. Looking at this image, there appears to be no abnormalities in the comet’s coma that would reveal fragmentation.

Interestingly, as noted by a Space Telescope Science Institute news release, a polar jet of dust projecting from ISON’s nucleus seen in Hubble images taken in April is no longer visible and likely turned off.

ISON is due to make its closest pass to the sun on Nov. 28 and, should it survive the fiery encounter, the comet could become an impressive sight in nighttime and daytime skies when it makes closest approach with the Earth on Dec. 26.

Comet Ison Update

According to Space.com, Comet Ison, the latest “Comet of the Century,” flew past Mars last Tuesday, October 1, and is headed now for the Sun.

If it survives its skitter around the Sun, it’ll be visible with backyard binoculars later this month and visible to the naked eye in early December, just after sunset.

Don’t listen to the naysayers who believe that Comet Ison is breaking up even now. They have no romance in their hearts.

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