In this Hubble Space Telescope composite image taken in April 2013, the sun-approaching Comet ISON floats against a seemingly infinite backdrop of numerous galaxies and a handful of foreground stars. The icy visitor, with its long gossamer tail, appears to be swimming like a tadpole through a deep pond of celestial wonders. In this composite image, background stars and galaxies were separately photographed in red and yellow-green light. Because the comet moved between exposures relative to the background objects, its appearance was blurred. The blurred comet photo was replaced with a single, black-and-white exposure. The images were taken with the Wide Field Camera 3 on April 30, 2013. UPI/NASA | License Photo
Comet of the century. Super comet. Hyped by the media and the subject of a couple of drum-beating TV documentaries, a dusty cosmic snowball named Comet ISON has a lot to live up to.
While it has brightened considerably in the last few days as it nears its Nov. 28 close encounter with the sun, and has managed to shine enough to be spotted by the naked eye -- if you know when and where to look -- it is not expected to live up to its advance publicity of providing something for the history books, blazing across the sky and visible at, say, high noon.
Wanting to witness such a sight is understandable, of course; who wouldn't want to be able to tell their grandchildren some day and say they saw the "comet of the century" with a tail that spanned half the daytime sky?
Thus the TV documentaries and breathless media headlines, but the truth is almost certain to be a little less dramatic.
While ISON has brightened enough to be visible to the human eye, so far that's only been as a faint smudge in the predawn sky before full daylight overcomes it.
If it survives its flyby of the sun -- not a sure thing, as the sun's heat, radiation and gravity could cause it to disintegrate -- there may be more chances to see it as it moves away from the sun, back toward where it came from in the distant Oort cloud far beyond the limits of our solar system.
Comets have long fascinated -- and sometimes terrorized -- humankind, with ancient comets seen as harbingers of war, famine or some other imminent disaster.
Or, some thought, they were messages from the gods, if mere mortals could just figure out what the gods were trying to say.
As scientific knowledge of what comets were and from where they came improved, the fear abated, replaced by wonder and curiosity.
Although that hasn't always been the case, even in the 20th century: In 1997 a group in San Diego calling itself Heaven's Gate was convinced Comet Hale-Bopp signaled the end of the Earth but that a spacecraft hidden in the comet's tail would take their souls away to safety.
In "preparation" for their expected rescue, 39 members of the group committed suicide in their rented mansion.
Comet ISON will, hopefully, be the center of attention for just scientific reasons, and astronomers say there are good reasons for the attention.
While many comets have long elliptical orbits that bring them back toward the sun at regular, if sometimes long, intervals -- Halley's comet visits Earth's vicinity every 75 years -- Comet ISON, once it leaves, isn't coming back.
That's because it's on what is knows as a hyperbolic orbit, which will take it back out of the solar system never to return.
That also suggests its appearance in the inner solar system is probably its first and only such trip, astronomers say.
That's significant because it suggests ISON is a pristine comet, unaffected by any previous visits to the sun's vicinity and unchanged since its creation billions of years ago at the time of the formation of the solar system, with the possibility of providing clues to conditions when the sun and its orbiting planets -- including Earth -- were in the bloom of youth.
So forget the hype. There's enough about Comet ISON to merit our attention -- and fascination. It doesn't need to be the Comet of the Century. It just needs to be its cosmically intriguing self.