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Title: Comet Lovejoy Survives Brush With the Sun
Source:
PC Magazine
URL Source: http://www.pcmag.com/article2/0,2817,2397756,00.asp
Published: Dec 16, 2011
Author: Tony Hoffman
Post Date: 2011-12-16 23:45:14 by A K A Stone
Keywords: None
Views: 547
On Wednesday, I reported on the approach to the Sun by Comet Lovejoy, the first "sungrazing" comet to be discovered by a ground-based observer in over 40 years. Most comet experts had predicted that the comet, officially known as C/2011 W3 (Lovejoy), would disintegrate on Friday, vaporized by its passage just a fraction of a solar radius from our star. Clearly, the comet had other ideas. To the delight of astronomers, it survived its close encounter with the Sun, retaining much of its brilliance as seen in images from spaceborne observatories. It’s now receding from the Sun and should become visible in the night sky within days for observers at southerly latitudes. Yesterday, as seen in images from the Solar and Heliospheric Observatory (SOHO), Comet Lovejoy rapidly closed in on the Sun, brightening (as evidenced by the "wings" on either side of the comet’s head—an artifact due to "pixel blooming" as the camera’s CCD censors became oversaturated by the comet’s brilliance, flooding adjacent pixels with brightness) and then fading in its final approach to the Sun. It’s not unusual for comets approaching the Sun to be totally melted by our star’s fierce heat; that has been the fate of all of the nearly 1,500 Kreutz comets discovered in SOHO’s images. In a couple of cases, traces of the comet’s tail persisted after perihelion (the comet’s closest approach to the Sun), but in no case did the comet’s head survive this encounter. Lovejoy was brighter (and presumably larger) than any of the Kreutz comets found by SOHO, but the laws of orbital dynamics seemed to be working against it. The comet was due to pass a mere 50,000 km from our star, and many comet experts expected Lovejoy to be totally vaporized by the fierce heat of our star. But as American comet discoverer David H. Levy once said, “Comets are like cats; they have tails, and they do precisely what they want.” When animations came in from the extreme ultraviolet camera of the Solar Dynamics Observatory (SDO), a spacecraft that takes hi-res images of the Sun, they showed a streak emerging from behind the solar limb and speeding off into space. Whether this was the comet itself or a debris cloud remained uncertain until this morning, when new images from SOHO’s LASCO wide-field telescope were posted, and showed the comet shining with renewed brilliance (as evidenced by the pixel blooming that causes the comet to look like a line with a bright node in the middle). If comets are like cats, Lovejoy looked decidedly Manx-like as it re-emerged from its encounter with our star, having becoming detached from its tail—which lingered for a while on the other side of the Sun—in the comet’s hairpin arc around our star. (Once again, pixel blooming, a saturation effect caused by the comet’s brilliance, gave the comet the appearance of having wings to either side.) Lovejoy is already developing a new tail and within a few days it will emerge into the predawn sky, where visibility will strongly favor Southern Hemisphere viewers. Comet Lovejoy has already defied the astronomical pundits by re-emerging, phoenix-like, from the searing fires of the Sun. Let’s hope it provides other surprises before it retreats to the outer solar system, not to return for some 400 years. In the meantime other, undiscovered comets are inbound, some of which are sure to put on splendid shows in the years to come.
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