Well, don't say we didn't warn you. As we hoped all along wouldn't happen, Comet ISON turned into a dud not a dazzle — a speck not a spectacle — a complete, unmitigated flop in terms of any kind of visual display for the world in the December dawn sky.
But it sure was exciting while it lasted, and never more so than on November 27th and 28th as it approached and then passed through perihelion while spacecraft watched. Our web traffic spiked through the roof as we posted the ever-changing news to our ISON Updates page. Real-time science is incredibly thrilling in the internet age. Especially when a scientific team as dedicated as the Comet ISON Observing Campaign makes so much effort to keep the world abreast of developments as they happen.
To recap: Comet ISON thwarted predictions at every turn. It spent much of 2013 underperforming compared to astronomers' original expectations. Then as it neared the Sun in mid- to late November it livened up, resulting in such exciting (enhanced) imagery as this, this, and this.
Then, as it disappeared down into the glare of sunrise for viewers on Earth, spacecraft took over. In the hours before the comet's fateful Thanksgiving Day roasting at perihelion, its starlike head brightened rapidly to dazzle the SOHO cameras at an estimated magnitude –2, and then just as rapidly the head dwindled away to insignificance compared to the tail, as seen in the movie at the top of this page. Watch a later, fuller version of the fateful four days.
At perihelion, less than one solar diameter from the Sun's surface, the extreme-ultraviolet cameras on the Solar Dynamics Observatory — the only craft able to look so close to the Sun — saw nothing whatsoever. The comet seemed to have evaporated totally.
Scientists glumly pronounced near-obituaries on a live NASA webcast. I was on the verge of titling an update "ISON Now ISOFF."
Then out the other side came a headless dust-and-rubble stream. It regrouped somewhat (as would be expected for a stream decelerating away from the Sun) while hinting at further cometary activity. A brief encounter with a plume of solar wind may have boosted its apparent brightness for a bit. Would ISON live to greet our telescopes and binoculars, at least, after all?
And then the dust cloud did nothing further, other than gradually expand and steadily fade in the lessening illumination as it left the Sun behind.
As I'm writing on Monday, this utterly inactive "ghost of ISON" is 8th magnitude 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 12th 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.
Oh well. That's comets for you.
Let's hope for better luck next time.
P. S.: The consolation prize. By the way, don't forget that a beautiful comet has been hanging high in the morning sky all along! At least for binoculars and telescopes. It's Comet Lovejoy C/2013 R1, now glowing at about magnitude 4.5 or 5. It's fairly large and obvious in binoculars and is nicely placed high in the northeast before the first trace of dawn even begins. Here's our latest finder chart as Lovejoy crosses Bootes, Corona Borealis, and Hercules in December. There's no moonlight until about December 15th. See more at Lovely Comet Lovejoy. And here's a fantastic image of it taken by Michael Jäger on December 1st. Now that's what a comet ought to be!