Posted on by David Dickinson

Will Comet ISON Dazzle our Skies? An Expert Weighs In

ISON as seen by Hubble earlier this spring. (Credit: NASA/ESA/Z. Levay/STScl).

Comets are the big “question marks” of observational astronomy. Some, such as Comet Hyakutake and the Great Daylight Comet of 1910 present themselves seemingly without warning and put on memorable displays. Others, such as the infamous Comet Kohoutek or Comet Elenin, fizzle and fail to perform up to expectations after a much anticipated round of media hype.

And then there’s the case of Comet C/2012 S1 ISON. Discovered on September 21st, 2012 by Artyom Novichonok and Vitali Nevski while conducting the International Scientific Optical Network (ISON) survey, Comet ISON has captivated public interest. The media loves a good comet, or at least the promise of one.

But will Comet ISON perform up to expectations? Recently, veteran comet hunter and observer John Bortle weighed in on a Sky & Telescope post and an email interview with Universe Today on what we might expect to see this fall.

Dozens of comets are discovered every year. Most amount to nothing – a handful, like this year’s comet 2011 L4 PanSTARRS or 2012 F6 Lemmon, may become interesting binocular objects.

Part of what alerted astronomers that Comet ISON may become something special was its extreme discovery distance of 6.7 astronomical units (A.U.s) meaning it should be an intrinsically bright object, coupled with its close approach of 0.012 A.U.s (1.1 million kilometres, accounting for the solar radius) from the surface of the Sun at perihelion.

Universe Today recently caught up with Mr. Bortle, who had the following to say above tentative prospects for Comet ISON in late 2013:

“Comets coming into the near-solar neighborhood from the Oort Cloud for the very first time tend to behave rather differently from most of their other icy brethren. They often will show considerable early activity while still far from the Sun, giving a false sense of their significance. Only when they have ventured to within about 1.5-2.0 astronomical units of the Sun do they begin to reveal their true intrinsic nature in the way of brightness and development. When discovered far from the Sun, this situation has misled astronomers time and again into announcing that a grandiose display is in the offing, only to have the comet ultimately turn out to be a general disappointment. There have been exception to this, but they are rare indeed.”

Comet ISON bears similar characteristics to many of the great sungrazing comets of the past. In the last few months, word has made rounds that Comet ISON may be underperforming, stagnating around magnitude +16 (10,000 times fainter than naked eye visibility) as it crosses the expanse of the asteroid belt between Jupiter and Mars.

Bortle, however, cautioned against writing off ISON just yet in a recent message board post. “With this comet’s exceedingly small perihelion distance, the ultimate situation is less clear.” He also continues to note that the prospects for ISON are “really difficult to predict at the moment,” but estimates that Comet ISON “will not actually attain naked eye brightness until just a week or two before perihelion passage.”

Regarding naked eye visibility of Comet ISON, Mr. Bortle also told Universe Today:

“In all probability this will not occur until around early to mid-November. It will not become any sort of impressive sight before disappearing into the morning twilight only a couple of weeks thereafter.”

And that’s the big question that may make the difference between a fine binocular comet and the touted “Comet of the Century…” Will this comet survive its perihelion passage on November 28th?

Concerning the comet’s perihelion passage, Mr. Bortle told Universe Today:

“This is currently a matter of some concern to me. Basing my answer on ISON’s apparent brightness when it was last seen before disappearing into the evening twilight recently suggests that it might be close in intrinsic brightness to the survival/non-survival level for such an extremely close encounter with the Sun. We will know much better once we can view ISON again in September.”

Comet Ikeya-Seki was another sungrazing comet that went on to become a splendid naked eye comet in 1965. The late 1880’s hosted a slew of memorable comets, including two long-tailed sungrazers, one each in 1880 and 1887.

In more recent times, Comet C/2011 W3 Lovejoy survived its December 16th, 2011 perihelion passage 140,000 kilometres from the surface of the  Sun to become the surprise hit for southern hemisphere observers.

“IF” comet ISON breaks a negative magnitude, it’ll join the ranks on the top brightest comets since 1935. If it tops -10th magnitude, it’ll best Comet Ikeya-Seki at its maximum in 1965. The magic “brighter than a Full Moon” threshold sits right about at magnitude -12.5, but Bortle cautions that this peak brightness will only persist during the hours surrounding perihelion, when the comet will be very close to the Sun and difficult to see.

Mr. Bortle also voiced a concern to Universe Today that “the initial announcements by professional astronomers concerning ISON’s potential future brightness (“Brighter than the Full Moon”, etc.) were wildly excessive, as was the idea that the comet would be obvious to the general public in the daytime sky as it rounded the Sun in late November. This claim was totally unjustified from the word go.” Mr Bortle also warns that this may be  “headed us down the exact same road as the Kohoutek fisaco of 1973/74.”

We’re currently losing Comet ISON behind the Sun as it crosses through the constellation Gemini, not return to morning skies until late August. The comet will cross the orbit of Mars in early October and should also cross the +10th magnitude threshold and become visible in binoculars and small telescopes around this date.

The track of Comet ISON through the constellations Gemini, Cancer and Leo prior to perihelion. (Credit: NASA/GSFC/Axel Mellinger).
The track of Comet ISON through the constellations Gemini, Cancer and Leo prior to perihelion. (Credit: NASA/GSFC/Axel Mellinger).

From October on in, things should get really interesting. Mr. Bortle predicts that the comet will “develop more slowly in the autumn sky than initially thought,” and won’t become a naked eye object until around November 10th or so. What this sort of lag might do to the internet pundits and prognosticators might be equally interesting to watch.

ISON will also track near some interesting morning objects as seen from Earth, including Mars (October 18th), Spica (November 18th), and Mercury & Saturn low in the dawn on November 26th. It will also have another famous comet nearby on November 25th (photo op!) short period Comet 2P Encke.

If Comet ISON survives perihelion, the true show could begin in early December. Comet ISON will re-emerge in the dawn skies, passing a pairing of Mercury and the very old crescent Moon on December 1st. Comet tails are even less predictable than comet magnitudes, but if Comet ISON is to unfurl a long photogenic tail, the weeks leading up to Christmas may be when it does it.

The projected view of Comet ISON from 30 degrees north latitude 30 minutes prior to local sunrise on December 1st. The orbital path of the comet and the ecliptic are also depicted. (Created by the author in Starry Night).
The projected view of Comet ISON from 30 degrees north latitude 30 minutes prior to local sunrise on December 1st. The orbital path of the comet and the ecliptic are also depicted. (Created by the author in Starry Night).

Mr. Bortle predicts a 10 to 15 degree long tail for a post-perihelion ISON as it passes through the constellation Ophiuchus into morning skies. It may become a “headless wonder” similar to the fan-shaped display put on by Comet 2011 L4 PanSTARRS earlier this spring. We’ve even seen models projecting a great fan-shaped dust tail seeming to “loop” around the Sun as seen from our Earthly vantage point!

All interesting conjecture to watch unfold as Comet ISON approaches perihelion this November. Hopefully, the hysteria that follows great cometary apparitions won’t reach a fevered pitch, though we’ve already had to put some early conspiracies to bed surrounding comet ISON.

Will ISON be the “Comet of the Century?” Watch this space… we’ll have more on the play-by-play action as it approaches!

-Read John Bortle’s predictions for Comet ISON in his recent Sky & Telescope post.

Posted on by Nancy Atkinson

New Images of Comet ISON Hurtling Towards the Sun

Images of Comet ISON obtained using the Gemini Multi-Object Spectrograph at Gemini North on February 4, March 4, April 3, and May 4, 2013 (left to right, respectively; Comet ISON at center in all images). Color composite produced by Travis Rector, University of Alaska Anchorage. Credit: Gemini Observatory/AURA

As Comet C/2012 S1 (ISON) heads closer to Earth, we’re getting a better view of what has been billed by some as the “Comet of the Century.” Astronomers say these new photos from the Gemini North telescope on Mauna Kea, Hawai‘i provide hints of how well this comet might survive one of the closest comet encounters with the Sun ever recorded, on November 28, 2013.

With astronomy enthusiasts hopeful and optimistic about having a spectacular comet visible in our skies, it’s anyone’s guess if the comet will actually survive its extremely close pass of the Sun to become early morning eye-candy in early December 2013.
The time-sequence images, spanning early February through May 2013, show that the comet is quite active, despite how distant it is from the Sun.

When Gemini obtained these images, the comet ranged between roughly 455-360 million miles (730-580 million kilometers; or 4.9-3.9 astronomical units) from the Sun, or just inside the orbital distance of Jupiter. Each image in the series, taken with the Gemini Multi-Object Spectrograph at the Gemini North telescope on Mauna Kea, Hawai‘i, shows the comet in the far red part of the optical spectrum, which emphasizes the comet’s dusty material already escaping from the nucleus. The final image in the sequence, obtained in early May, consists of three images, including data from other parts of the optical spectrum, to produce a color composite image.

Gemini astronomers say the images show the comet sporting a well-defined parabolic hood in the sunward direction that tapers into a short and stubby tail pointing away from the Sun. These features form when dust and gas escape from the comet’s icy nucleus and surround that main body to form a relatively extensive atmosphere called a coma. Solar wind and radiation pressure push the coma’s material away from the Sun to form the comet’s tail, which we see here at a slight angle (thus its stubby appearance).

“Early analysis of our models shows that ISON’s brightness through April can be reproduced by outgassing from either carbon monoxide or carbon dioxide,” said Karen Meech, at the University of Hawaii’s Institute for Astronomy (IfA) in Honolulu. “The current decrease may be because this comet is coming close to the Sun for the first time, and a “volatile frosting” of ice may be coming off revealing a less active layer beneath. It is just now getting close enough to the Sun where water will erupt from the nucleus revealing ISON’s inner secret.”

Comet ISON will come within 800,000 miles (1.3 million km) of the Sun’s surface on November 28. Shortly before that critical passage, the comet may appear bright enough for expert observers using proper care to see it close to the Sun in daylight.

“Comets may not be completely uniform in their makeup and there may be outbursts of activity as fresh material is uncovered,” added IfA astronomer Jacqueline Keane. “Our team, as well as astronomers from around the world, will be anxiously observing the development of this comet into next year, especially if it gets torn asunder, and reveals its icy interior during its exceptionally close passage to the Sun in late November.”

NASA’s Hubble Space Telescope provides a close-up look of Comet ISON (C/2012 S1), as photographed on April 10, when the comet was slightly closer than Jupiter’s orbit at a distance of 386 million miles from the sun. Credit:NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team.
NASA’s Hubble Space Telescope provides a close-up look of Comet ISON (C/2012 S1), as photographed on April 10, when the comet was slightly closer than Jupiter’s orbit at a distance of 386 million miles from the sun. Credit:NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team.

NASA’s Swift satellite and the Hubble Space Telescope (HST) have also imaged Comet ISON recently in this region of space. Swift’s ultraviolet observations determined that the comet’s main body was spewing some 850 tons of dust per second at the beginning of the year, leading astronomers to estimate the comet’s nucleus diameter is some 3-4 miles (5-6 kilometers). HST scientists concurred with that size estimate, adding that the comet’s coma measures about 3100 miles (5000 km) across.

The comet gets brighter as the outgassing increases and pushes more dust from the surface of the comet. Scientists are using the comet’s brightness, along with information about the size of the nucleus and measurements of the production of gas and dust, to understand the composition of the ices that control the activity. Most comets brighten significantly and develop a noticeable tail at about the distance of the asteroid belt (about 3 times the Earth-Sun distance –– between the orbits of Mars and Jupiter) because this is when the warming rays of the Sun can convert the water ice inside the comet into a gas. This comet was bright and active outside the orbit of Jupiter — when it was twice as far from the Sun. This meant that some gas other than water was controlling the activity.

Meech said that Comet ISON “…could still become spectacularly bright as it gets very close to the Sun” but also added caution. “I’d be remiss, if I didn’t add that it’s still too early to predict what’s going to happen with ISON since comets are notoriously unpredictable,” she said.

Source: Gemini Observatory

Posted on by Nancy Atkinson

Astronomers Detect Dust Feature in Comet ISON’s Inner Coma

Image from May 5, 2013 of a the inner region of Comet ISON using the 2-meter Liverpool telescope at La Palma. Credit: Nick Howes and Ernesto Guido, Remanzacco Observatory; Nalin Samarasinha, Planetary Science Institute.

In April, when the Hubble Space Telescope looked out towards Jupiter’s orbit and observed what has been billed as the “Comet of the Century” – Comet C/2012 S1 ISON – the space telescope photographed a unique feature in the comet’s coma. Now, a team of ground-based astronomers have performed follow-up observations, imaging Comet ISON as it heads towards the Sun and was just outside the orbit of Mars. They, too, have seen something in the coma and suspect it’s a similar feature to what Hubble imaged. The object is thought to be a jet blasting dust particles off the sunward-facing side of the comet’s nucleus.

These very useful follow-up observations are providing more insight on this highly anticipated comet, as well as helping to predict what might happen when it makes its closest approach to the Sun in November 2013.

“The hype surrounding this comet has been extreme” said Nick Howes from the Remanzacco Observatory, “with some wildly optimistic estimates for magnitude. We’re hoping this measured scientific approach will yield results just as exciting to the science community, even if the comet doesn’t end up meeting everyone’s expectations visually, for whatever reason.”

NASA’s Hubble Space Telescope provides a close-up look of Comet ISON (C/2012 S1), as photographed on April 10, when the comet was slightly closer than Jupiter’s orbit at a distance of 386 million miles from the sun. Credit:NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team.
NASA’s Hubble Space Telescope provides a close-up look of Comet ISON (C/2012 S1), as photographed on April 10, when the comet was slightly closer than Jupiter’s orbit at a distance of 386 million miles from the sun. Credit:NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team.

Some have predicted ISON may briefly become brighter than the full Moon. But right now the comet is far below naked-eye visibility, and larger telescopes are needed to makes observations.

Howes and Ernesto Guido from the Remanzacco Observatory in Italy used a suite of Hubble-sized ground-based telescopes in Australia, Hawaii and the Canary Islands to make their observations. They are collaborating with with Nalin Samarasinha, a Senior Scientist at the Planetary Science Institute (PSI) in an attempt to get high spatial resolution data on Comet ISON.

Howes and Guido have been imaging Comet C/2012 S1 ISON since the day it was discovered and actually played a small role in its discovery. They work on a variety of programs with professional and amateur astronomers around the world, but for this comet, their focus is on the so-called Afrho, a measure of a comet’s dust production. (Learn more about Arfho here.)

Samarasinha, a specialist in comets at the Planetary Science Institute, has been looking at the detailed structure of the near-nucleus coma of comet C/2012 S1 ISON using data, which the Remanzacco team is delivering in to the PSI.

Recently, Samarasinha had looked at image comparisons for the Remanzacco team’s dataset from May 2, 5, and 7 taken with the F10 2-meter Liverpool telescope on La Palma, using an extremely sensitive camera, perfectly suited for detailed comet work.

Image from May 2, 2013 of a the inner region of Comet ISON, using the 2 meter Liverpool Telescope at La Palma. Credit: Nick Howes and Ernesto Guido, Remanzacco Observatory; Nalin Samarasinha, Planetary Science Institute.
Image from May 2, 2013 of a the inner region of Comet ISON, using the 2 meter Liverpool Telescope at La Palma. Credit: Nick Howes and Ernesto Guido, Remanzacco Observatory; Nalin Samarasinha, Planetary Science Institute.

The images shown here are 28×28 pixel crops of the inner region of the comet.

“This comparison shows that the sunward feature Nick’s team suspected from images taken on 02/05/2013 is originating slightly north of west and then the position angle of the feature (measured from north through east) increases as one moves away from the optocenter,” said Nalin.

Nalin’s interpretation is that the curvature of this feature (which the team suspected was not caused by image enhancing initially, but can now categorically state is real) is not due to any rotational effects but is due to radiation pressure pushing dust grains towards the tail. Ultimately, this feature merges in with the tail.

Image from May 7, 2013 of a the inner region of Comet ISON, as seen with the 2-meter Liverpool Telescope at La Palma. Credit: Nick Howes and Ernesto Guido, Remanzacco Observatory; Nalin Samarasinha, Planetary Science Institute.
Image from May 7, 2013 of a the inner region of Comet ISON, as seen with the 2-meter Liverpool Telescope at La Palma. Credit: Nick Howes and Ernesto Guido, Remanzacco Observatory; Nalin Samarasinha, Planetary Science Institute.

The team says these observations are in close agreement with features detected by the Hubble Space Telescope in April this year. As the comet comes closer to the Earth the spatial resolution will improve, and the team should get more detailed views on the coma structure.

Estimates suggest that the nucleus of ISON is no larger than 4-6 km (3-4 miles) across while the comet’s dusty coma, or head of the comet is approximately 5,000 km (3,100 miles) across, or 1.2 times the width of Australia. A dust tail extends more than 92,000 km (57,000 miles).

Ongoing observations seem to reveal this comet is ‘shedding’ quite a bit of mass, leaving astronomers to wonder if it will have enough body left to survive its perhihelion, the closest approach to the Sun on November 28, 2013.

Excitingly, Comet ISON observations are in the works for when the comet dashes past Mars, and the Curiosity rover is on tap to try imaging it from Mars’ surface with its high resolution Mastcam 100 camera, as well as on-orbit observations with the Mars Reconnaissance Orbiter (MRO).

As the comet performs a hairpin turn around the Sun in November, its ices will vaporize in the intense solar heat. Assuming it defies death by evaporation, some predict it could become as bright as the full Moon. If so, that would occur for a brief time around at perihelion when the comet would only be visible in the daytime sky very close to the Sun. When safely viewed, ISON might look like a brilliant, fuzzy star in a blue sky.

As C/2012 S1 ISON is now heading in to the evening twilight glare, Howes and Guido will turn from large aperture instrumentation on this comet for a while, and work on observations with a wider field CCD, more sensitive in the R’ band, and also imaging with the Polarimeter instrument which will allow them to create detailed maps of the inner coma region.

Howes said that these ongoing collaborations with scientists with the amateur community are delivering valuable scientific data on a hugely interesting object.

Posted on by Fraser Cain

Weekly Space Hangout – May. 3, 2013

Another busy episode of the Weekly Space Hangout, with more than a dozen space stories covered by a collection of space journalists. This week’s panel included Alan Boyle, Dr. Nicole Gugliucci, Amy Shira Teitel, David Dickinson, Dr. Matthew Francis, and Jason Major. Hosted by Fraser Cain. We discussed:

We record the Weekly Space Hangout every Friday at 12 pm Pacific / 3 pm Eastern. You can watch us live on Google+, Cosmoquest or listen after as part of the Astronomy Cast podcast feed (audio only).

Posted on by Nancy Atkinson

A New View of Comet ISON

View of Comet ISON on May 2, 2013. Credit: Ernesto Guido & Nick Howes, Remanzacco Observatory.

Update: Here’s a brand new image of Comet C/2012 S1 ISON, as seen on May 2, 2013 by Ernesto Guido and Nick Howes of the Remanzacco Observatory (their image from May 1, which we featured earlier, is below.) For this latest image, they used the 2-meter Ritchey-Chretien Liverpool Telescope. Via Facebook, Howes said they have been able to identify almost the same tail structure which was seen in the Hubble Space Telescope images of this comet from April 10.

From the May 1 observations, their initial approximation of the tail length is around 28 arcseconds, which Howes told Universe Today is bigger than some recent reports from smaller scopes.

Below is their image from May 1, using the 2 meter La Palma Telescope:

View of Comet ISON on May 1, 2013. Credit: Ernesto Guido & Nick Howes, Remanzacco Observatory.
View of Comet ISON on May 1, 2013. Credit: Ernesto Guido & Nick Howes, Remanzacco Observatory.

As of May 2, Comet ISON was approximately 3.885 AU from the Sun, which is about 581 million kilometers (361 million miles) distant from the Sun. ISON will makes its close approach to the Sun when it passes within 1.2 million km (730,000 miles) of the Sun on November 28, 2013.

Here’s a video from NASA about this comet’s path through the Solar System:

Posted on by David Dickinson

Debunking Comet ISON Conspiracy Theories (No, ISON is Not Nibiru)

ISON as seen from Hubble. (credit: NASA)

Comets always seem to bring ‘em out of the wood work.

There’s a scene from the 1998 movie Deep Impact where the president, played by Morgan Freeman, reveals a terrible truth… the U.S. government has known for over a year that a doomsday comet is headed straight towards Earth, with Hollywood CGI destruction sure to follow.

While dramatic, the scenario is also extremely implausible. On any given evening, amateur astronomers are sweeping the skies using telescopes mounted in backyard observatories that are the envy of many major universities. This effort to discover comets is collaborative and worldwide. If the “Big One” were headed our way, even the likes of Morgan Freeman couldn’t keep it secret.

Trouble is, many unfounded claims are already making their way around the internet about this years’ much anticipated “Comet of the Century,” C/2012 S1 ISON.

Many of these conspiracy theories seem to be a recycling of last years’ Nibiru nonsense. The train of thought runs something like this: Does NASA know something that they’re not telling us? Why are they so interested in this comet? We’ve even had folks ask us why certain patches of Google Earth are “blacked out!”

What ARE they hiding, man?

It’s funny how pseudoscience seems to bubble to the top on YouTube, but I won’t give these conspiracy videos the exposure of the Universe Today platform. With hundreds of thousands of hits, they certainly don’t seem to need it. A simple YouTube search of “ISON” will scare up many wacky ideas about the comet.

In any event, we’ve already fielded several questions from friends and the public on the “dangers” posed by this comet, so we can only imagine that these will grow in intensity as the comet approaches the inner solar system, especially if it performs up to expectations.

What are some of the conspiracy theories out there about Comet ISON?

One currently circulating claim states that Comet ISON has “companions” that have been imaged trailing it. While comets do indeed fragment on occasion, the culprits that can be seen in the .gif animation circulating the internet are easily identified by photography experts as hot pixels in the camera.

Another even more extravagant claim is that Comet ISON will somehow appear “as bright as the Sun.” Even if Comet ISON reaches an expected magnitude equal to that of the full Moon at -13, it will do so when it is less than a degree  from the Sun. Our Sun shines at magnitude -26.74, or over 158,000 times brighter, so it would be very difficult for this comet to compete with the Sun’s brightness in the daytime!

Others seem to worry that this comet — or particles from ISON — could impact Earth. Comet ISON will be making its inner solar system passage safely 0.426 A.U., or a little over 63 million kilometers from Earth even on its closest approach on December 26th. Scientists have defined this comet’s orbit very precisely, and it won’t hit Earth. So, no Comet ISON is not Nibiru — that ‘tenth planet’ destined to destroy Earth that conspiracy lovers can’t seem to let go of.

The debris — which might create a very nice meteor shower — is made up of extremely tiny grains of dust, no more than a few microns wide. Since they will be hitting Earth’s atmosphere at speeds up to 200,000 km/hr (125,000 miles per hour), the particles will burn up.

Here’s a video NASA released about the potential meteor shower from ISON:

Other claims focus on how this comet may cause earthquakes or wreak other untold havoc on Earth. This type of comet hysteria is nothing new. Name a bright comet in history, and you can find a historical event for a convenient tie-in. When haven’t there been earthquakes, pandemics, and wars in history? Plus, according to the US Geological Survey, on any given day there will be an average of 2,750 earthquakes around the world of which 275 are large enough to be felt by humans. But only about 100 earthquakes a year are large enough to cause any damage.

And so, its too easy to tie the “causes” of earthquakes and other events to comets in the sky. Comets have been seen before and during the Norman invasion of England in 1066, an outbreak of the Black Plague in London in 1665, and much more. Gary Kronk maintains a wacky and wonderful list of historical (and sometimes comical) comet “signs and omens” on his Cometography site.

Comet Lovejoy as seen from the International Space Station.
Another brilliant sungrazer, Comet Lovejoy as seen from the International Space Station on December, 2011. (Credit: NASA).

Halley’s Comet produced one of the first great comet hypes of the 20th century with its 1910 passage. Ironically, another comet made a brilliant passage just a few months prior, which became known as the Great Comet of 1910. In fact, many viewers in the general public actually saw this comet and confused it with Halley’s! The recent discovery of cyanogen in the comet’s spectra sparked a panic in the public as hucksters made a small fortune hawking “comet pills” and gas masks to panicked buyers. Never mind that folks ingest more toxic carcinogens from their daily environment than are ever seeded by the tenuous tails of comets.

Another curious bit of hype sprung up in 2011 around Comet Elenin, which promptly broke up and dissipated without even putting on a show. And the supposed earthquakes that conspiracy theorists predicted? Well, the evidence speaks loudly: nothing happened. And the same will be true of Comet ISON. It won’t cause any earthquakes or other disasters. As Don Yeomans from NASA said about Comet Elenin, “It will have an immeasurably miniscule influence on our planet. By comparison, my subcompact automobile exerts a greater influence on the ocean’s tides than comet Elenin ever will.”

So, what’s the harm in all the comet hysteria? Well, one only has to look at the mass suicide of the Heaven’s Gate cult in 1997 to realize that it can be no laughing matter. The suicide was sparked by the idea popularized on the late night Coast to Coast with Art Bell radio show that a spacecraft had been spotted following Comet Hale-Bopp.

Dozens of comets are discovered every year. A great majority are tiny iceballs in unfavorable orbits that never rise above magnitude +10 and are thus of little interest to backyard observers. A couple of times a year, a comet might reach magnitude +6 to +10 and become a fine binocular object.

When a discovery is made — be it by amateur or professional — the first task is to gain enough observations of the object to ascertain its orbit. Once again, we see the international collaborative methods employed by modern science. Already, the cosmic cat’s out of the bag as observatories worldwide make follow up measurements. There are no secrets about Comet ISON that hundreds of astronomers could keep quiet.

You get the idea... a 1687 leaflet depicting the havoc that a comet is sure to bring. (Wikimedia Commons image in the Public Domain).
You get the idea… a 1687 leaflet depicting the havoc that a comet is sure to bring. (Wikimedia Commons image in the Public Domain).

But here are some facts about Comet C/2012 S1 ISON. It was discovered last September by Russian amateurs Vitali Nevski and Artyom Novichonok while making observations for the International Scientific Optical Network (ISON), hence the comet’s name. At the time, it was farther than Jupiter and impossibly faint, but once ISON’s orbit was determined, astronomers realized the comet would pass only 1.1 million miles from center of the Sun (680,000 miles above its surface) on November 28, 2013.

Comet ISON belongs to a special category of comets called sungrazers. As the comet performs a hairpin turn around the Sun on that date, its ices will vaporize furiously in the intense solar heat. Assuming it defies death by evaporation, ISON is expected to become a brilliant object perhaps 10 times brighter than Venus, or maybe even brighter. But that would only occur for a brief time around at perihelion (closest approach to the Sun).

In the end, Comet ISON may put on a good show, but don’t believe the hype.

Comets are notoriously unpredictable when it comes to brightness estimations. To quote comet-hunter David Levy, “Comets are like cats… they have tails, and they do exactly what they want.” But they cannot, however, violate the laws of orbital mechanics!

The orbit and orientation of Comet ISON the day after Christmas 2013 on closest approach to the Earth. (Credit: NASA/JPL's Small-Body Database Browser).
The orbit and orientation of Comet ISON the day after Christmas 2013 on it closest approach to the Earth. (Credit: NASA/JPL’s Small-Body Database Browser).
Posted on by Fraser Cain

Weekly Space Hangout – April 26, 2013

We had an action packed Weekly Space Hangout on Friday, with a vast collection of different stories in astronomy and spaceflight. This week’s panel included Alan Boyle, Dr. Nicole Gugliucci, Scott Lewis, Jason Major, and Dr. Matthew Francis. Hosted by Fraser Cain.

Some of the stories we covered included: Pulsar Provides Confirmation of General Relativity, Meteorites Crashing into Saturn’s Rings, Radio Observations of Betelgeuse, Progress Docks with the ISS, Hubble Observes Comet ISON, Grasshopper Jumps 250 Meters, April 25th Lunar Eclipse, and the Mars One Reality Show.

We record the Weekly Space Hangout every Friday at 12 pm Pacific / 3 pm Eastern. You can watch us live on Google+, Cosmoquest or listen after as part of the Astronomy Cast podcast feed (audio only).

Posted on by Nancy Atkinson

Hubble Telescope Captures Image of Comet ISON

Comet ISON was used in a search for time travelers. NASA’s Hubble Space Telescope provides a close-up look of Comet ISON (C/2012 S1), as photographed on April 10. Credit: NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team.

Here’s our first good look at Comet (C/2012 S1) ISON. The Hubble Space Telescope captured this shot on April 10, when the comet was slightly closer than Jupiter’s orbit at a distance of 634 million kilometers (394 million miles) from Earth. Later this year, this comet could become a brilliant object in the sky, perhaps 10 times brighter than Venus.

Astronomers say preliminary measurements from the Hubble images suggest that the nucleus of ISON is no larger than 4-6 km (3-4 miles) across.


The astronomers said this is remarkably small considering the high level of activity observed in the comet so far. Astronomers are using these images to measure the activity level of this comet and constrain the size of the nucleus, in order to predict the comet’s activity when it will come with 1.1 million km (700,000 miles) of the Sun on November 28, 2013.

Even though Comet ISON was 620 million km from the Sun when this image was taken, the comet is already active as sunlight warms the surface and causes frozen volatiles to sublimate. A detailed analysis of the dust coma surrounding the solid, icy nucleus reveals a strong, jet blasting dust particles off the sunward-facing side of the comet’s nucleus.

The comet’s dusty coma, or head of the comet, is approximately 5,000 km (3,100 miles) across, or 1.2 times the width of Australia. A dust tail extends more than 92,000 km (57,000 miles), far beyond Hubble’s field of view.

Comet ISON belongs to a special category of comets called sungrazers. As the comet performs a hairpin turn around the Sun in November, its ices will vaporize in the intense solar heat. Assuming it defies death by evaporation, some predict it could become as bright as the full Moon. If so, that would occur for a brief time around at perihelion (closest approach to the Sun) when the comet would only be visible in the daytime sky very close to the Sun. When safely viewed, ISON might look like a brilliant, fuzzy star in a blue sky.

More careful analysis is currently underway to improve these measurements and to predict the possible outcome of the sungrazing perihelion passage of this comet.

ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences.

Source: NASA

Posted on by David Dickinson

Was the Repeating Passage of Halley’s Comet Known of in Ancient Times?

Comet P/Halley as seen on its last inner solar system passage on March 8th, 1986. (Credit: W. Liller/NASA GSFC/ International Halley Watch Large Scale Phenomena Network).

An interesting and largely unknown tale of ancient astronomy recently came our way while reading author and astrophysicist Mario Livio’s blog. The story involves the passage of the most famous of all comets.  

It’s fascinating to consider ancient knowledge of the skies. While our knowledge of ancient astronomy is often sparse, we know that cultures lived and perished by carefully monitoring the passage of the heavens.  A heliacal rising of Sirius might coincide with the impending flooding of the life-giving waters of the Nile, or the tracking of the solstices and equinoxes might mark the start of the seasons.

To the ancients, comets were “hairy stars” which appeared unpredictably in the sky. We generally attribute the first realization that comets are periodic to Sir Edmond Halley, who successfully utilized Newton’s laws of gravity and Kepler’s laws of planetary motion to predict the return of Halley’s Comet in 1758. Such a prediction was a vindication of science.

But an interesting tale comes to us from the 1st century CE that Rabbi & Jewish Scholar Yehoshua Ben Hananiah may have known something of “a star that appears every 70 years.” The tale, as told in the Horayoth (rulings) of the Talmud and described in Mr. Livio’s blog is intriguing:

Rabbi Gamliel and Rabbi Yehoshua went together on a voyage at sea. Rabbi Gamliel carried a supply of bread. Rabbi Yehoshua carried a similar amount of bread and in addition a reserve of flour. At sea, they used up the entire supply of bread and had to utilize Rabbi Yehoshua’s flour reserve. Rabbi Gamliel then asked Rabbi Yehoshua: “Did you know that this trip would be longer than usual, when you decided to carry this flour reserve?” Rabbi Yehoshua answered: “There is a star that appears every 70 years and induces navigation errors. I thought it might appear and cause us to go astray.”   

The Rabbi’s assertion is a fascinating one. There aren’t a whole lot of astronomical phenomena on 70 cycles that would have been noticeable to ancient astronomers. With an orbital period of 75.3 years, Halley’s Comet seems to fit the bill the best. The earliest confirmed description of Halley’s comes from Chinese astronomers during its 240 BCE passage. Later subsequent passages of the comet through the inner solar system were noted by the Babylonians in 164 & 87 BCE.

Of course, there’s no further evidence that ancient scholars identified those passages as the same comet. Some great comets such as Hale-Bopp seen in 1997 and this year’s anticipated Comet C/2012 S1 ISON are on orbits spanning thousands of years that outlast most Earthly civilizations.

Mr. Livio also notes that historical knowledge of ancient apparitions of Halley’s may have been accessible to the Great Knesset scholars during the Babylonian exile of the 6th century BCE.

One of the chief objections raised to the Halley hypothesis is the circumstances of the appearance of Halley’s Comet in the Rabbi’s lifetime. Remember, most folks didn’t live for 70 years in the 1st century. Any tales of a periodic comet would have been handed down by generations. You would be lucky to see Halley’s Comet once in your lifetime. Plus, not all apparitions of Halley’s Comet are favorable. For example, Halley’s was bright enough to induce “comet hysteria” with the public in 1910. In contrast, few northern hemisphere members of the general public got a good view of it during its 1986 passage.

Medieval woodcut depicting the supposed destructive influence of a 4th century comet. (Credit: Stanilaus Lubienietski's Theatrum Cometicum, Amsterdam 1668).
Medieval woodcut depicting the supposed destructive influence of a 4th century comet. (Credit: Stanilaus Lubienietski’s Theatrum Cometicum, Amsterdam 1668).

Halley’s Comet was visible on and around January 25th, 66 CE during the Rabbi’s lifetime. However, the Rabbi would have been in his 20’s and have been a student (and not yet a Rabbi) himself. One can imagine that if he was fearful of a “false star” leading them astray, he must’ve known that the 70 year period was just about neigh.

The 66 CE apparition of Halley’s Comet would have appeared around the time of the Jewish Rebellion and just four years before the destruction of the Second Temple in Jerusalem by the Romans in 70 CE.

One other possible astronomical culprit has been cited over the years. The classic variable star Mira (Omicron Ceti) currently has a 332 day cycle which ranges from magnitude +3.5 to below naked eye visibility at +8.6 to +10.1. The variability of Mira was first discovered by astronomer David Fabricius on August 3rd 1596. There are suggestions that ancient Chinese and Babylonian astronomers may have known of this “vanishing star”.

The variable star Mira as imaged by the Hubble Space Telescope. (Credit: NASA/STScl/Margarita Karovska at the Harvard-Smithsonian Center for Astrophysics).
The variable star Mira as imaged by the Hubble Space Telescope. (Credit: NASA/STScl/Margarita Karovska at the Harvard-Smithsonian Center for Astrophysics).

Mira is expected to reach maximum for 2013 from July 21st to 31st.

Not all maxima for Mira are of equal brightness. Mira can peak anywhere from magnitude +2.0 to +4.9 (a 15-fold difference) and there’s evidence to suggest it may have been brighter in the past. Astronomer Philippe Veron noted in 1982 that a larger oscillation period of 60 years for the peak maxima of Mira falls just a decade short of Rabbi Yehoshua’s mention of an errant star.

Whatever the case, its fascinating to consider what celestial object might’ve been referred to, and how many other astronomical tales might be awaiting discovery in ancient texts. We’ve got lots of comets to ponder this year as Comet PanSTARRS, Lemmon, and ISON grace our skies in 2013. Halley’s will make its next visit to the inner solar system in 2061. I’ll open it up to you, the astute Universe Today reading public; was the Rabbi’s Star a comet, a variable star, a meteor storm, or none of the above?

Halley's Comet as seen from latitude 30 north on the morning of July 31st, 2061. (Created by the author using Starry Night software).
Halley’s Comet as seen from latitude 30 north on the morning of July 31st, 2061. (Created by the author using Starry Night software).

-Dr. Mario Livio blogs at A Curious Mind. Be sure to check out his new book Brilliant Blunders: From Darwin to Einstein – Colossal Mistakes by Great Scientists That Changed Our Understanding of Life in the Universe out on May 14th!

 

Posted on by David Dickinson

Comet Lemmon: A Preview Guide for April

Comet C/2012 F6 Lemmon as imaged by Luis Argerich as from near Buenos Aires, Argentina on March (Credit: Nightscape photography. Used with permission).

As Comet 2011 L4 PanSTARRS moves out of the inner solar system, we’ve got another comet coming into view this month for northern hemisphere observers. 

Comet C/2012 F6 Lemmon is set to become a binocular object low to the southeast at dawn for low northern latitudes in the first week of April. And no, this isn’t an April Fools’ Day hoax, despite the comet’s name. Comet Lemmon (with two m’s) was discovered by the Mount Lemmon Sky Survey (MLSS) based outside of Tucson, Arizona on March 23, 2012. MLSS is part of the Catalina Sky Survey which searches for Near Earth Asteroids. We’ve got another comet coming into view this month for northern hemisphere observers as Comet 2011 L4 PanSTARRS moves out of the inner solar system.

The comet is on an extremely long elliptical orbit, with a period of over 11,000 years. Comet Lemmon just passed perihelion at 0.74 astronomical units from the Sun on March 24th.

Animation of Comet Lemmon as it passes the star Gamma Crucis on January 17th. (Courtesy of Luis Argerich. Used with permission).
Animation of Comet Lemmon as it passes the star Gamma Crucis on January 17th. (Courtesy of Luis Argerich. Used with permission).

Southern hemisphere observers have been getting some great views of Comet Lemmon since the beginning of this year. It passed only three degrees from the south celestial pole on February 5th, and since that time has been racing up the “0 Hour” line in right ascension. If that location sounds familiar, that’s because another notable comet, 2011 L4 PanSTARRS has been doing the same. In fact, astrophotographers in the southern hemisphere were able to catch both comets in the same field of view last month.

Another celestial body occupies 0 Hour neighborhood this time of year. The Sun just passed the vernal equinox marking the start of Spring in the northern hemisphere and Fall in the southern on March 19th.

And like PanSTARRS, Comet Lemmon has a very steep orbit inclined 82.6° relative to the ecliptic.

The steep path and current position of Comet Lemmon. (Credit: NASA/JPL' Small-Body Database Browser).
The steep path and current position of Comet Lemmon. (Credit: NASA/JPL’ Small-Body Database Browser).

Comet Lemmon broke naked-eye visibility reaching +6th magnitude in late February and has thus far closely matched expectations. Current reports place it at magnitude +4 to +5 as it crosses northward through the constellation Cetus. Predictions place the maximum post-perihelion brightness between magnitudes +3 and +5 in early April, and thus far, Comet Lemmon seems to be performing right down the middle of this range.

Brightness graph for Comet Lemmon for the months surrounding perihelion. (Created by author).
Brightness graph for Comet Lemmon for the months surrounding perihelion. (Created by author).

Southern observers have caught a diffuse greenish 30” in diameter nucleus on time exposures accompanied by a short, spikey tail. Keep in mind, the quoted brightness of a comet is extended over its entire surface area. Thus, while a +4th magnitude star may be easily visible in the dawn, a 3rd or even 2nd magnitude comet may be invisible to the unaided eye. Anyone who attempted to spot Comet PanSTARRS in the dusk last month knows how notoriously fickle it actually was. Binoculars are your friend in this endeavor. Begin slowly sweeping the southeast horizon about an hour before local sunrise looking for a fuzzy “star” that refuses to reach focus. Comet Lemmon will get progressively easier in the dawn sky for latitudes successively farther north as the month of April progresses.

The apparent path of Comet Lemmon for April looking southeast about an hour before local sunrise from latitude 30 degrees north. (Created by the Author using Starry Night).
The apparent path of Comet Lemmon for April 10th through the 30th looking east about an hour before local sunrise from latitude 30 degrees north. (Created by the Author using Starry Night).

Comet Lemmon will continue to gain elevation as it crosses from Cetus into the constellation Pisces on April 13th. An interesting grouping occurs as the planet Mercury passes only a few degrees from the comet from April 15th to April 17th. Having just past greatest elongation on March 31st, Mercury will shine at magnitude -0.1 and make a good guide to locate the comet in brightening dawn skies. The pair is joined by the waning crescent Moon on the mornings of April 7th and 8th which may also provide for the first sighting opportunities from low north latitudes around these dates.

The apparent path of Comet Lemmon for April looking southeast about an hour before local sunrise from latitude 30 degrees north. (Created by the Author using Starry Night).
Mercury meets Comet Lemmon on April 15th as seen about an hour before local sunrise from latitude 30 degrees north. (Created by the Author using Starry Night).

The Moon reaches New phase on Wednesday, April 10th at 5:35AM EDT/9:35 UT. It will be out of the morning sky for the next couple of weeks until it reaches Full on April 25th, at which point it will undergo the first eclipse of 2013, a very shallow partial. (More on that later this month!)

Comet Lemmon will then slide across the celestial equator on April 20th and cross the plane of the ecliptic on April 22nd as it heads up into the constellation Andromeda in mid-May. We’re expecting Comet Lemmon to be a fine binocular object for late April, but perhaps not as widely observed due to its morning position as PanSTARRS was in the dusk.

By mid-May, Comet Lemmon will have dipped back down below +6th magnitude and faded out of interest to all but a few deep sky enthusiasts. Comet Lemmon will pass within 10° of the north celestial pole on August 9th, headed back out into the icy depths of the solar system not to return for another 11,000-odd years.

It’s interesting to see how these two springtime comets will effect observers expectations for the passage of Comet C/2012 S1 ISON. Will this in fact be the touted “Comet of the Century?” Much hinges on whether ISON survives its November 28th perihelion only 1,166,000 kilometers from the center of our Sun (that’s 0.68 solar-radii or about 3 times the Earth-Moon distance from the surface of the Sun). If so, we could be in for a fine “Christmas Comet” rivaling the passage of Comet Lovejoy in late 2011. On the other hand, a disintegration of Comet ISON would be more akin to the fizzle of Comet Elenin earlier in 2011.

In the meantime, enjoy Comet Lemmon as an Act 2 in the 2013 Three Act “Year of the Comet!”