Astroblog: Comet C/2012 S1 ISON Rides into the Sunrise! 22-29 November 2013

Thursday, November 21, 2013

Comet C/2012 S1 ISON Rides into the Sunrise! 22-29 November 2013


Location of comet C/2012 S1 ISON in the solar system on 23 November. Click to embiggen	Morning sky from Friday November 22 to November 22 looking north-east as seen from Adelaide at 5:30 am ACST in South Australia. Comet C/2012 S1 ISON is close to Mercury. Similar views will be seen elsewhere at the equivalent local time (click to embiggen).

Comet C/2012 S1 ISON continues to brighten, after the first outburst on November 14, it has steadily brightened and is now magnitude 4 or so from creditable reports. This week it finally reaches the Sun after a long trek that began over a thousand years ago.

The comet has survived and brightened for a week, so it is unlikely that it is breaking up, and should make its rendezvous with the Sun. On the 23rd it crosses the orbit of Mercury and may possibly jump in brightness again.

Despite the significant brightening it is difficult to see from Australian sites as it falls deeper into the twilight. Observers in New South Wales, Brisbane and places north have seen ISON in 10x50 binoculars and it has been described as having a star like appearance.Those of us south of around Sydney have little hope of seeing it in the brightening dawn unless there is a signficant increase in brightness.

Here are some nice shots from New South Wales, Brisbane and another from Brisbane.

The comet will get progressively difficult to see and may be lost to sight in Australia anywhere between the 23rd and the 25th (again, providing there isn't a significant increase in brightness in the next few days) .

The comet is to the right the bright star Spica and not far from Mercury on the 22nd, and very close to the horizon at nautical twilight, you may have to wait until after nautical twilight (an hour before sunrise) for the comet to clear the horizon sufficiently to see. There are no obvious bright stars to help guide you to the comet in the twilight, but if you can see Mercury, sweep a bit above and to the left of Mercury from the 23rd on. As the week goes on it comes closer and closer to the Sun so you have to observe closer and closer to sunrise.

We will need to watch the images from spacecraft to see it approach the Sun.

Finally on November 28 the comet is at perihelion, when it zooms just under a solar diameter above the Sun's surface, if it survives this close encounter, the northern hemisphere may see a spectacular tail. We probably won't see anything (those in the Northern Territory might see a bit of tail poking up over the horizon in the morning of the 30th).


A black and white map suitable for printing for use with binoculars and telescopes. The large circle is the approximate field of view of 10x50 binoculars.Time is civil twilight.Click to embiggen. The image is the same orientation as the horizon animation above. Click to embiggen	A high power stellarium view of the region around Porrima and Spica with ISON (expanded from the unaided eye view shown above) on November 23rd at Nautical twilight.