[BAA-ebulletin 00770] Comet C/2012 S1 (ISON)

[BAA electronic bulletins service]

This comet is now only 15 days from perihelion and it is currently 0.66 
AU from the Sun. In recent days it has been seen to brighten as expected 
and it is now around magnitude 7. There has also been a noticeable 
increase in the level of activity within the tail. The rather bland and 
uniform dust tail has been supplemented by a number of straight gas 
streamers which are now relatively easy to image.

The main dust tail has broadened and is now around 1 degree long and 
today's observations show that the gas tail has undergone a 
disconnection event due to its interaction with the solar wind. This is 
clearly visible in images obtained by BAA observer Tony Angel:

http://britastro.org/baa/index.php?view=detail&id=1908&option=com_joomgallery&Itemid=200

The comet is currently a morning object low in the eastern dawn sky with 
a very short observing window before the onset of twilight. Despite the 
difficult conditions it would be very worthwhile to make an attempt to 
observe this object. We cannot reliably predict what will happen in the 
coming weeks since we have never before seen a comet with these 
characteristics pass so close to the sun. Only continued observations 
will help us to tell the final tale.

It is worth noting that due to the comet's brightness and tail length 
the most suitable imaging instruments are now the very popular (and 
fairly common) 80mm apochromatic refractors coupled to CCDs or DSLRs. 
This type of instrument tends to be portable so it can be taken to a 
site with a clear eastern horizon.

Drawings, images, written accounts and visual magnitude estimates are 
welcome and can be posted via email to cometobs at britastro.org. It would 
help greatly if you could conform to the file naming convention 
documented here:

http://www.ast.cam.ac.uk/~jds/cimgname.htm

Images of this comet taken by BAA observers and others up the present 
date can be seen on the BAA Comet Gallery:

http://britastro.org/baa/index.php?view=category&catid=74&option=com_joomgallery&Itemid=200

The increase in activity during the past week could be a sign that the 
comet may become a naked eye object at some point around perihelion or 
just after. Of course, at the time of perihelion the comet will not be 
observable using basic observing techniques due to its close proximity 
to the sun.

The best source of information about the comet during the next few weeks 
can be found at the NASA CIOC website:

http://www.isoncampaign.org/Present

There is another naked eye comet currently available in the night sky. 
This is C/2013 R1 (Lovejoy). This comet is best seen around midnight and 
onwards. It is presently in Leo and images of this comet taken by BAA 
observers can be found on the BAA Comet Gallery:

http://britastro.org/baa/index.php?view=category&catid=133&option=com_joomgallery&Itemid=200

Denis Buczynski
Secretary Comet Section
British Astronomical Association