Press Releases. You can unsubscribe anytime. Comet ISON, anticipated by skywatchers for more than a year, is brightening fast just days from its fateful hairpin swing on November 28th around the broiling surface of the Sun. The comet is now a greenish-white fuzzy "star" in binoculars, low in the east-southeast at the beginning of dawn.
Telescopic photos are showing it with a long, ribbony tail. The comet has flared with unexpected outbursts of gas and dust three times already this month. Or it might yet break up and vanish. It all depends on what happens to the comet's tiny nucleus, its only solid part. A comet's nucleus is a dirty iceball that's just a pinpoint by astronomical standards — in this case less than a mile or two across.
As it flies in from the cold outer solar system and warms in the heat of the Sun, some of its ice evaporates, releasing gas and dust that expands by thousands or even millions of miles to become the comet's glowing head "coma" and tail.
This sun-grazer comet has an orbit that's virtually parabolic, as near as we can tell. That means that its orbital path extends very far out from the sun, which, if the Oort cloud exists, would be in the region of the Oort cloud. However, more than 25 years ago the late Carl Sagan observed that there is no direct evidence that the Oort cloud exists. The situation hasn't changed since then.
Faulkner explains. Comets like ISON, in reality, are evidence for a young universe. As Dr. Faulkner recently explained , a number of things happen to efficiently kill comets like this:. In addition to gradually wearing out, two more catastrophic loss mechanisms can ravage comets. First, as comets pass close to the major planets especially the gas giant Jupiter , the gravity of those planets can alter comet orbits. When this happens, half the time the comet orbit decreases in size and orbital period, which causes the comet to wear out even faster.
But the other half of the time comets have their orbits increased. Sometimes the increase can lead to ejection from the solar system, never to return. Astronomers have observed comet ejection a number of times. Second, comets occasionally collide with planets, thus abruptly ending their existence. Scientists have observed the demise of comets, and indeed whenever over the centuries humans have observed a comet blazing away they have been observing its death, if only by degrees.
Eventually, comets run out of ice and die. So where could new comets come from? Faulkner explains :. With these efficient loss mechanisms, it is clear that we should not see any comets at all, if the solar system is billions of years old. So, for more than 60 years many astronomers have offered two hypothetical sources to replace older comets as they die. There are two types of comets: long-period comets and short-period comets. By: Monica Young January 12, By: Govert Schilling January 12, By: Monica Young January 13, This week astronomers have announced the completion of the largest 3D map of galaxies across the cosmos, plus exquisite radio observations show what happens when a stellar intruder interrupts planet formation.
By: Govert Schilling January 11, Stellar Science. By: Monica Young January 10, Astronomy in Space with David Dickinson.
By: David Dickinson January 8, By: Alan MacRobert January 7, By: Monica Young January 6, By: Joe Barry January 10, Explore the Night with Bob King. By: Bob King January 5, Sky Tour Astronomy Podcast. By: J. Kelly Beatty January 1, By then the remains will be 2. 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.
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 fairly large and obvious in binoculars and is nicely placed high in the northeast before the first trace of dawn even begins. There's no moonlight until about December 15th. See more at Lovely Comet Lovejoy. Now that's what a comet ought to be! I grew up on a small farm in Indiana. The lesson of not counting chickens until they are hatched needs to be somehow conveyed in a new saying.
Don't count on a comet being spectacular until you've actually seen it? I'll teach them to make a big deal out of one of my comets before I decide what it will do! Log in to Reply. Thanks for keeping us so well informed about the progress of the comet as it rounded the sun. The pictures from the orbiting solar observatories were spectacular. We are very fortunate to have such wonderful technology available to us at the touch of a key.
I also thought the live google-ISON party was fascinating. See the third paragraph of "Exploring the Triangulum Galaxy" - page I like the way the clock in the video slows down considerably towards the end, like the last refrain of a song that comes smoothly to a stop on its final note.
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