viernes, 14 de junio de 2013

Big sun-diving Comet ISON might be spectacular in late 2013

Comet ISON might be spectacular sight in fall 2013. Or it might not. Look here for a month-by-month viewing guide.

Late in 2012, astronomers discovered a distant sungrazing comet that got many people very excited. Around the time of its perihelion – or closest approach to the sun – on November 28, 2013, Comet C/2012 S1 (ISON) has the potential to become a striking object visible to the eye alone. Will Comet ISON become a legendary comet of the century? It might. But it might not. Comet ISON will come within 800,000 miles (1.2 million km) of our sun’s surface on November 28.

That’s over 100 times closer to the sun than Earth. This close pass to the sun might cause Comet ISON to break to pieces, and, if that happens, the comet might fizzle. Or ISON might emerge from perihelion bright enough to see easily with the eye, with a long comet tail that stretches across a quarter of the sky. Comets are notoriously unpredictable. Still, this comet is one you’ll want to watch.

This comet’s orbit will bring it near the sun in November 2013. Some are predicted it’ll be briefly as bright as a full moon then, but, unfortunately, as its brightest it’ll also be near the sun’s glare. Image via NASA’s Jet Propulsion Laboratory

Comet ISON on the morning of December 10, 2013. The view is toward the east before dawn. Chart via Dave Eagle at Used with permission. View larger.

Comet ISON will be visible in both the morning and evening sky in December 2013. This view is looking west on the evening of the December 18, 2013. Chart via Dave Eagle at Used with permission.

Comet ISON month-by-month in late 2013. August 2013. As seen from Earth, Comet ISON will be behind the sun in June and July, 2013. When it returns to Earth’s sky in late August, it might be bright enough to be seen by observers using small telescopes at dark locations. September and October 2013. Comet ISON will brighten as the months pass. In September and October, amateur astronomers will surely be trying to pick it up. The comet will be sweeping in front of the constellation Leo then. It’ll pass first near Leo’s brightest star Regulus, then near the planet Mars. Maybe you can see the comet with binoculars then, and maybe these brighter objects will help you find it. November 2013. Comet ISON will continue to brighten throughout November as it nears its late November perihelion (closest point to our sun). Comet expert John Bortle wrote on June 13 that he expects the comet to reach visibility to the unaided eye about three weeks before the November 28 perihelion date. In November, ISON will pass very close to the bright star Spica and the planet Saturn, both in the constellation Virgo. These bright stars might help you find the comet. At perihelion, the comet will come within 800,000 miles – 1.2 million kilometers, or about one sun-diameter – of our sun’s surface. If all goes well, and the comet doesn’t fragment, the terrific heating Comet ISON will undergo when it’s closest to our parent star might turn the comet into a very bright object. It may also form a long comet tail around this time.

There has been some mention that Comet ISON could even become a daylight object, briefly. Remember, though, at perihelion, Comet ISON will appear close to the sun on the sky’s dome (only 4.4° north of the sun on November 28). Although the comet will be bright, it’s likely that only experts who know how to look near the sun, while blocking the sun’s glare, will see it. December 2013. This is likely to be the best month to see Comet ISON, assuming it has survived its close pass near the sun intact. The comet will be visible both in the evening sky after sunset and in the morning sky before sunrise. As ISON’s distance from the sun increases, it’ll grow dimmer. Comet expert John Bortle wrote on June 13: The crescendo of the apparition will likely occur between December 10th and 14th, when the comet will be best seen just before dawn after the moon sets. Although little or perhaps nothing of the head will remain, the huge tail will loom in the northeastern sky. Almost evenly illuminated over its length, this rapidly fading appendage could [span] almost a quarter of the heavens as seen under good, dark observing conditions. People all over Earth will be able to see it, but it’ll be best seen from the Northern Hemisphere as 2013 draws to a close. January 2014. Will ISON still be visible to the eye? Hopefully. Only time will tell. On January 8, 2014, the comet will lie only 2° from Polaris — the North Star. And here’s something else that’s fun. On January 14-15, 2014, after the comet itself has passed but when Earth is sweeping near the comet’s orbit, it might produce a meteor shower, or at least some beautiful night-shining or noctilucent clouds.

 How bright will Comet ISON be? How long will its tail be? No one can answer these questions yet, but many are excited about this comet, and many astronomers are talking about it. Some are beginning to speak of media hype that always surrounds events of this kind. In his June 13 article published at, comet expert John Bortle explained the reason we can’t know yet how bright Comet ISON will be: A close solar pass can disrupt and evaporate a comet’s nucleus completely. The intrinsically faintest sungrazer to survive its brush with the sun reasonably intact was Comet Ikeya-Seki in 1965. The long-tailed sungrazers seen in 1880 and 1887 experienced total disruption of their nuclei and dissipated completely within weeks after perihelion. The latest observations of Comet ISON suggest that it’s intrinsically about as bright as those 19th-century objects, so the survival of its head much beyond November 28 is in question. However, ISON is decidedly brighter than the recent Comet Lovejoy, which totally disrupted and, despite this or perhaps because of it, put on a spectacular long-tailed show for Southern Hemisphere observers at the end of 2011. Bortle also said that – from January through May of this year – Comet ISON did not brighten as much as astronomers had predicted it would, as it makes its way toward the inner solar system. The comet is not visible in June or July (the sun is between us and it), but it will be back in view around the end of August. You can be sure astronomers will be watching then to see how bright it appears at that time.

Who discovered Comet ISON? Eastern European and Russian astronomers announced the new comet on September 24, 2012. Discovery magnitude was 18.8 – in other words, extremely faint. Vitali Nevski of Vitebsk, Belarus and Artyom Novichonok of Kondopoga, Russia spotted the comet on CCD images obtained on September 21 with a 0.4-m f/3 Santel reflector of the International Scientific Optical Network (ISON) near Kislovodsk, Russia. Afterwards, astronomers at Remanzacco Observatory in Italy confirmed the comet’s presence with the image above.

Comet Lovejoy was a sight to behold from Earth's Southern Hemisphere in late 2011. Here the comet is reflected in the water of Mandurah Esturary near Perth on December 21, 2011. Image Credit: Colin Legg.

source and credit a earthsky