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| Human World | Space on Dec 06, 2013

Have we seen the last of Comet ISON?

Comet ISON is now thought to be a traveling debris field, with no solid nucleus or core. Will we see the debris field from Earth? No one knows yet.

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UPDATE DECEMBER 6, 2013. As Comet ISON pulled away from its close encounter with the sun on November 28, it first brightened and then faded again. For a couple of days now, ISON has been missing in action – out of the field of view of NASA sun-observing spacecraft – and not yet visible to earthly observers, not even the Hubble Space Telescope. It is now believed that Comet ISON has become little more than a traveling field of debris in space, still following the path of the original comet.

Scientists originally said that – if it had not fragmented, if it had maintained its solid nucleus or core – Comet ISON would become visible again in Earth’s skies beginning around December 3.

That has not happened. We have not seen any post-perihelion photos of ISON taken from Earth so far. Expert amateur observers said on December 2 that we’re likely not to see any sign of Comet ISON until around December 12.

Professional observers, who gathered on December 6 at Johns Hopkins University (home of the Hubble Space Telescope), say that observations with HST are planned for late December. However, one observer wrote on December 6:

A search for ISON remnants today at IRTF came up with nothing. This brings up a problem: where do we point Hubble to look for it? There’s hope amateurs may come through.

Click here to read blog notes from the December 6 meeting of professional astronomers, talking about ISON.

Click here for more about the Hubble Space Telescope’s ISON observations, planned for late December.

For those who are asking – and, yes, people are still asking – Comet ISON will certainly NOT become visible to the unaided eye in December. Still, some remain hopeful that amateur and professional astronomers might catch sight of some remnant of the comet, in photos. Those with telescopes and good cameras will surely be attempting to aim toward the traveling debris field that is now Comet ISON.

For details on the comet’s fate after its November 30 perihelion, check out the article below, from the Comet ISON Observing Campaign: In ISON’s wake, a trail of questions

If you really want to see a comet, try Comet Lovejoy! It’s now visible to the eye in dark skies, and should remain so throughout December: How to see Comet Lovejoy in December 2013

So Comet ISON did not and will not become a comet of the century. We’re still due for one!

Comet ISON was exciting, though. It was the most exciting comet in years. We cannot see it with our eyes now, but our front row seat on its perihelion – made possible via our spacecraft – was spectacular. Plus, some very interesting comet science is bound to result, as astronomers analyze their data and publish it, in the weeks and months to come.

Comet ISON rounded the sun on November 28, 2013.  It brightened briefly after perihelion.  But, by November 30, Comet ISON had faded again.

Comet ISON rounded the sun on November 28, 2013. It brightened briefly after perihelion. But, by November 30, the comet had faded again.

Hats off to NASA Goddard’s Karl Battams, who almost singlehandedly informed the world about this comet during perihelion, both via his Twitter feed @SunGrazerComets or via NASA’s Comet ISON Observing Campaign website.

In the early evening of November 28, he posted these words: We’re calling it … you heard it here first … we believe some small part of ISON’s nucleus has survived.

But then all hopes were dashed as the comet faded again. Battams tweeted the following:

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Once again comet ISON raises our hopes and then dashes then... perhaps for the final time. It has clearly started to fade dramatically, and this does not bode well for survival.  Image and caption via ESA/NASA, annotations by Karl Battams.

Here are two images of Comet ISON taken hours apart, as the comet was nearly closest to the sun, showing a large amount of disintegration. The comet had brightened on November 27, but then it faded again shortly before perihelion on November 28, which did not bode well for its survival. Image via ESA/NASA, annotations by Karl Battams.

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In late 2012, when astronomers using large telescopes first spotted Comet ISON far, far from the sun, they could clearly see it was a large comet and a bright comet. Its size and brightness so far from the sun are what caused them to predict it might be spectacular in our sky in December 2013.

Earth’s own movement in orbit caused the comet to go behind the sun in June and July, but when it emerged from the sun’s glare in early August, it was not as bright as many had hoped. This lack of brightness caused astronomer to suggest Comet ISON would not be a comet of the century, but might still be a respectably bright comet in our night sky.

Then in November 2013, as it approached its November 28 perihelion, Comet ISON had several exciting outbursts in brightness. Many with very dark skies and good sky conditions glimpsed it with the eye. Many with ordinary cameras and/or binoculars captured it, or at least spotted it, and their photos were amazing. Click here for the best images of Comet ISON, prior to perihelion.

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This gif is pre-perihelion, but it’s one of my favorite images of Comet ISON. It’s Comet ISON (bigger and brighter) and Comet Encke from November 19-22, 2013 as seen encountering the solar wind. Image via NASA. Image via Karl Battams/NRL/NASA-CIOC.

The best time to see Comet ISON should be early December, after its November 28 perihelion - or closest point to the sun - IF the comet survives!

Here’s where ISON would be, if it did appear in our sky. The comet’s path has not changed since perihelion. Will it be bright and easy-to-see? Absolutely NOT.

If it had come back as a bright comet in earthly skies, Comet ISON would have been in the morning sky, near the place where the sun rises along your eastern horizon. Close to the sun in space = close to the sun in the sky. The rudimentary chart above shows where it would have been in our sky, as seen from the Northern Hemisphere. Now, a much better chart than this one will be needed to spot the comet.

If you still want to see Comet ISON, and you have the necessary equipment, my advice is to follow the experts at skyandtelescope.com. On December 2, senior editor and long-time night sky observer Alan MacRobert wrote in his article titled So It Ends for Comet ISON:

As I’m writing on Monday [Dec. 2], this utterly inactive ghost of ISON is 8th magnitude [far beyond visibility with the eye alone] and at least ½° wide in its brightest part, with no prospects for anything but further spreading and dimming.

By comparison, that’s about as wide as, and much dimmer than, the visual appearance of the Pinwheel Galaxy M33 in Triangulum. M33 is notorious for being wiped out even by light pollution in the night, never mind a bright sky before sunrise.

Not until about December 12 will the flying ghost of ISON climb far enough from the sun to be fairly well up in a dark sky before dawn begins (and only for northern latitudes). By then the remains will be 2.5 times farther from the sun than now, and thus 2.5 squared or 6.2 times (2 magnitudes) fainter than now. And that’s assuming the dust cloud somehow manages not to dissipate any further.

Skilled astro-imagers using today’s cameras and software work near-miracles in pulling faint things out of the darkness. We’re looking forward to seeing what they may be able to do here. And the Hubble Space Telescope will also be taking a look around mid-December, when the comet’s remains exit from Hubble’s no-pointing zone around the Sun. But Hubble cannot do wide-field imagery. The hope is for some solid, inactive fragments of the former nucleus to be large enough for Hubble to detect as tiny pinpoints.

There you have it. Adios, ISON. We’ll be watching for the farewell photos!

Bottom line: Comet C/2012 S1 (ISON)’s perihelion – closest point to the sun – was November 28, 2013 around 18:45 UTC/ 1:45 p.m. EST. It first appeared that the comet had fizzled, but later Comet ISON began showing some post-perihelion signs of life. And then it faded again. As of December 6, 2013, the comet still had not been sighted from Earth. While some are hopeful we’ll spot some remnant of the comet, it is definite that we will not get a bright comet in the predawn sky in early December, when ISON pulls far enough away from the sunrise glare to be seen again. It may be that only skilled photographers and astronomers will see it … and the rest of us will just have to enjoy their photos.