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Thursday, November 07, 2013


Comet C/2012 S1 ISON is not dead yet, 8-15 November 2013

Location of comet C/2012 S1 ISON in the solar system on 8 November. Click to embiggenMorning sky from Friday November 8 to November 15 looking north-east as seen from Adelaide at 5:00 am ACST in South Australia. Comet C/2012 S1 ISON is to the right of  Mars. Similar views will be seen elsewhere at the equivalent local time (click to embiggen).

The rumours of ISON's demise are greatly exaggerated. The comet continues to slowly brighten, and its gas production rate has been reported to be increasing substantially. It has been imaged with DSLR cameras in the UK.

Comet C/2012 S1 ISON continues to be reported to be (just) visible in 10x50 binoculars, and has been picked up by Australian observers. Currently still somewhere around magnitude 8,  it is visible in small scopes and strong binoculars. In binoculars it should look like a faint, fuzzy dot. However,  its fuzzy, diffuse nature, its closeness to the horizon (between 7 -12 degrees depending on where you are, except Darwin and Far North Queensland, where it is more like 20 degrees above the horizon see here for charts illustrating the difference at different sites)  means that it can be difficult to spot visually in smaller scopes.

It looks like by the 8th it will still be under magnitude 7, and still a bit of a struggle to see in binoculars.

The comet is to the right of Mars, making finding it relatively easy. The best time to look for it is when it is highest in the sky and the sky is darkest.  However, especially in the Southern States, because it never gets very high, the best time to look is astronomical twilight. Astronomical twilight is an hour and a half before local sunrise.
On November 8 the comet is in the constellation of Virgo, and is between Earth's and Venus's orbits (see image above). At this time comet ISON is just under a hand span above the horizon as seen from the latitude of Melbourne, just over a hand span as seen from the latitude of Sydney, nearly two hand spans as seen from the latitude of Brisbane and almost 4 hand spans as seen from the latitude of Darwin. A hand-span is the distance across your knuckles when your hand is outstreached at the end of your arm as if making a "stop" sign.
On the 8th the comet is close to the bright star Zanijava, Beta (β) Virginis. Sweeping diagonally east about a handspan is the next brightest star Zaniah, eta (η) Virginis. From the 8th the comet heads towards Zaniah, and is closest on the 11th. Between the 8th and the 11th sweeping between and a little above these stars should reveal the comet. 
Sweeping diagonally down yet again from Zaniah is the bright star Porrima, gamma (γ) Virginis. Between the 11th and the 14th the comet is running several finger widths above an imaginary line joining these stars. On the 14th comet ISON is 4 finger widths above Porrima, and should be (just) visible to the unaided eye and easily visible in binoculars.

However, the comet is also sinking towards the horizon, so you will have to wait deeper in the twilight for the comet to get reasonably high above the horizon, as the sky brightens the comet will be more difficult to see, offsetting its own rise in brightness.

A printable PDF map is here.

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, the medium circle the approximate field of view of a 24 mm eyepiece for a reflecting telescope and the small circle a 12 mm eyepiece for a reflecting telescope.Time is astronomical twilight.Click to embiggen. The image is the same orientation as the horizon animation above. Click to embiggenA high power stellarium view of the region around Mars with ISON to go with the black and white spotters map. This view is on the 8th when the comet is close to Zaniah, eta (η) Virginis. Click to embiggen.

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