Comet ISON’s moment of truth looms as it rounds Sun

Astronomers around the world are waiting with bated breath to see what is happening to Comet ISON as it swings perilously close to the Sun after its long journey from deep space. Here’s our latest report with advice on how to see it – if it survives.

Comet ISON’s track across the eastern morning sky from northern latitudes during December 2013. The number marks the date. Credit: Skymania.com

The comet is now entering the fields of view of cameras aboard space telescopes that constantly monitor the Sun. They will give us our first clues as to whether ISON is still around following its brush with a star. (Update 27 Nov: The comet has now appeared in the field of view of the ESA/NASA SOHO satellite’s LASCO C3 camera – see bottom image).

If it does survive, then everyone is still hopeful that the comet will put on a spectacular show as it draws away from the Sun again. Perhaps there will be a long bright tail visible to the East in the predawn sky during early December.

However, it has to be said that there were worrying reports about what was happening to ISON in the latter part of November in the run-up to perihelion – its closest point to the Sun – on 28 November.

Scientists said the molecular emission from the comet – basically what is producing its gas tail – had fallen dramatically, while the production of dust had grown enormously. This suggested that the solid head of the comet, the nucleus, had broken into fragments or been destroyed completely.

Update: However, on perihelion day, 28 November, ISON was still very much resembling a comet as it crossed the field of the LASCO C3 camera and had brightened to magnitude -2.

An image from STEREO on 22 November shows Comet ISON to the lower left. The second comet above and to the right of it is Comet Encke. The vertical streaks are artifacts in the image processing. Credit: Karl Battams/NRL/NASA STEREO/CIOC

NASA’s Comet ISON Observing Campaign website said of the gloomy suggestions: “. . . these reports are new, and while they are undoubtedly valid, we do still need to keep observing the comet to be sure what it happening.

“Remember: Comet ISON is a dynamically new sungrazing comet, fresh in from the Oort Cloud, and the last time we saw an object like this was never! Furthermore, a sungrazing comet just three days from perihelion has never been studied in this kind of detail – we’re breaking new ground here! When we factor in your standard “comets are unpredictable” disclaimer, what we have is a huge recipe for the unknown.”

On the positive side, the comet, which was discovered from Russia in September 2012 and is officially known as C/2012 S1, could still be seen in the fields of NASA’s twin solar observatories STEREO.

Amateur astronomers will be watching out in the first week of December to see just what there is to see. If ISON does survive perihelion, you will find it following the track indicated in our latest map produced using Carte du Ciel (Skychart).

Comet ISON appears in the field of view of SOHO’s LASCO C3 camera, just as the Sun throws of a coronal mass ejection (CME).Credit: ESA/NASA


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