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Wednesday, 13 November 2013

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

BAA electronic bulletin
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:

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 It
would help greatly if you could conform to the file naming convention
documented here:

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

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:

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:

Denis Buczynski
Secretary Comet Section
British Astronomical Association
BAA-ebulletin mailing list visit:
(c) 2013 British Astronomical Association

Good Clear Skies
Colin James Watling
Various Voluntary work-Litter Picking for Parish Council (Daytime) and
also a friend of Kessingland Beach (Watchman)
Lyra Website:
Real Astronomer and head of the Comet section for LYRA (Lowestoft and
Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland
Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)

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