New Images of C/2006 P1
Check out the new images
(Jan 18-25) and
(Jan 26-Feb 05) of the comet by Rob McNaught.
Posters are available from several of these images.
Images of the comet by Gordon Garradd appear here.
What's all the Fuss About?
Every few years a comet becomes bright enough to be easily seen with the naked eye
but only every decade or so are these comparable with comets like Halley. The
recent observations of C/2006 P1 already show it to be considerably brighter
than Halley and it is likely to get much brighter still! Pictures like this one from
Hakon Dahle
in Norway on January 8 give a feel for what we might expect in Australia
after the comet swings around the Sun on January 12, moving into the
southern evening sky by January 14.
Photo: Hakon Dahle, Institute of Theoretical Astrophysics, University of Oslo.
Discovery of C/2006 P1
C/2006 P1 was a routine discovery on 2006 Aug 7, with the Uppsala Schmidt
telescope at Siding Spring Observatory, near Coonabarabran, N.S.W., Australia. It is one of 29 comets discovered by this telescope
since early 2004 in a project to systematically search the
southern skies for asteroids, or comets, that can pass close to the Earth.
The project is run by Steve Larson of the University of Arizona and
operates three telescopes;
two in Arizona
and, in collaboration with the Australian National University, the
Uppsala Schmidt at Siding Spring. This three telescope operation
discovered almost 400 Near-Earth Asteroids in 2006, over 60% of the
worldwide total. Discovery statistics are listed
here
with our group of three telescopes combined under "Catalina".
This earliest image of C/2006 P1 is from a 20sec exposure with the Uppsala Schmidt taken in moonlight on 2006 Aug. 07.
It covers 13.2 x 10.0 arcmins, a tiny part of the original 120 x 120 arcmin field of view. North is to the top and the lower
edge of the image is the bottom of the original field. Due to the moonlight, the flat fielding correction is imperfect
(our thinned CCD chip has a number of blemishes along this edge).
These four images, taken 10 minutes apart, form the sequence used in the discovery. The comet is moving in the center (see above for the location
of the comet on the first image). The background, being uneven from the imperfect flat field, appears to move around. This
"dither" pattern is a deliberate offset of the telescope so none of these cosmetic artifacts can appear to move like an
asteroid or comet and the automated detection software thus ignores them for the most part.
How Bright?
Within a week, it was clear that
this comet was unlike most others we have discovered. They have orbits that keep them
far from the Sun, such objects being of interest only to professional or amateur
astronomers. This comet was likely to pass well
within the Earth's orbit and even well within the orbit of Mercury, making it
much brighter than most, but also potentially hiding it in the Sun's glare. It
would be at its closest to the Sun in mid-January 2007. You can visualise the comet's
orbit using this very nice
NASA page.
Alternatively, cross your eyes and look at these wonderful stereo diagrams below by Paul Payne,
displaying the comet's path through the inner Solar System. Note that the planets are enlarged!
You can get larger versions here for the
top
and
bottom
images. These images may be used if credited to
Paul Payne.
If you can successfully view the images in stereo try this beautiful
Quicktime stereo animation (4.7MB)
by Paul displaying the orientation of the comet's orbit.
From August into early November the comet did brighten rapidly, but not
enough to prevent it becoming lost in the evening twilight by mid-November. Although still
brightening, it seemed that the comet might be lost to human eyes until
it reappeared in southern skies in the evening twilight of late January.
Although not visible to ground based telescopes in early December, the comet
was recorded on a number of occasions with the SWAN instrument on the SOHO satellite.
This recorded the UV halo from fluorescing gas around the comet. During the month
it was clearly brightening (see images on
Gary Kronk's Cometography
page), although just how bright this was in terms of what the human eye would see was not certain. An animation
of the latest SWAN images can be found
here
but through mid-January, C/2006 P1 will be lost to the SWAN instrument, being located in the excluded region around the Sun.
The comet went unobserved by human eyes for 40 days but was successfully reobserved in the
twilight from the northern hemisphere at the end of December. It was
becoming clear that it could be a bright object when closest to the Sun
in mid-January. Since then the comet has continued to grow in brightness
impressively! By January 6, several amateur astronomers were reporting
that the comet was visible to the naked eye in bright twilight just
a few degrees above the horizon.
Having heard of the successful daylight sighting of the comet by
the very experienced US amateur Dennis di Cicco on Jan 7,
Gordon Garradd
and Rob McNaught made the attempt on January 9 from Siding Spring
(using professional computer telescope pointing) and we were able to see
the comet. Precautions had been made to
prevent any possibility of the sun entering the telescope. With such
a bright sky, Gordon used sunglasses to cut down the glare (they would
provide no protection should you accidently look at the sun
through the telescope) and clearly saw it. Rob found it more difficult
without sunglasses, but the sun hat was appropriate wear. (Remember
"Slip, Slop, Slap"). Whilst telescopic viewing of the comet in daytime is *possible* it
is strongly recommended that nobody attempt this without considerable
prior experience. It is far too easy to accidently look at the sun and
inflict permanant eye damage or blindness.
Gordon Garradd observing the comet at midday on January 9 using the 125mm finder telescope
on the Uppsala Schmidt (the discovery telescope).
Rob McNaught observing the comet shortly after Gordon.
It seems reasonable that the baseline prediction for the peak brightness
on Jan 14 will be of -ve magnitude (brighter than the brightest stars),
but it gets better! Due to the dust
in the comet, there will be a brightness enhancement around that date
caused by the comet being located between us and the Sun. This brightening,
called forward scatter, has been estimated to increase the brightness
of the comet by around a couple of magnitudes, so an impressive brightness
might result between Jan 12 to 16. This brightening effect is
just like that of plant seeds or bugs which brighten as they drift
in front of the sun. The comet's brightness may possibly rival Venus (the
Evening star) visible in the evening twilight at the moment.
Space Telescopes
Before Jan 13, the comet is not visible in the Australian sky after sunset.
Australians will however have the chance to see the comet before this by examining
images on the web taken by space telescopes that monitor the
sky near the Sun. These record both activity on the Sun itself and in
the environment surrounding it.
From Jan 12 to 16, it would be possible to gauge its brightness
by examining images taken with the
LASCO C3 telescope on the SOHO satellite. This telescope which monitors
the Sun's atmosphere, often shows small comets passing close to the sun;
usually very small and faint objects. The following link to a NASA webpage
shows the latest SOHO images (to see the comet, choose the LASCO C3 images)
and also has a link towards the bottom of the page to Real Time Movies showing the last few day's activity.
The comet will only appear in the LASCO C3 images, which has the widest field of
view (8 degree radius) of all the SOHO telescopes. Michael Mattiazzo, a
well known Australian comet observer notes what to expect on the C3 images
and notes that the times given on the SOHO web pages are in UT:
On Jan 12 at approximately 09:00 UT (8pm NSW time), comet
C/2006 P1 McNaught appears at the 11 o'clock position in the
images. On Jan 15 at 15:55 UT (02:55am NSW time), the comet
is 40' East of Mercury. On Jan 16 at approximately 16:00 UT
(03:00am NSW time), the comet disappears at the 7 o'clock
position.
The following plot provided by Syuichi Nakano displays the path of
the comet relative to the Sun as seen from the Earth. This unusual way of plotting the path
gives the comet an apparent kink in it's motion. It is properly visualised
as the comet moving through a long loop directed towards the Earth in late-December/early-January,
but well over 100 million km distant, before it swings around the Sun and heads away from the Earth and Sun again.
Other space telescopes that monitor the Sun include a pair of telescopes called
STEREO, launched late last year. They view the Sun from different angles to
give a 3D view of the Sun's activity. The comet should move into the
field of these telescopes on Jan 10, but the images are only being updated
slowly and it may be a few days before comet images appear after this date.
STEREO images
Note that the images are in FITS format requiring a suitable astronomical image viewer.
Visibility from Australia
I'll concentrate my comments on the latitude of Sydney, which will be
reasonably accurate for most of the Australian population.
The first possibility to see the comet will be at sunset on Jan 13
when the comet would be a *very* difficult object some 6 degrees
north of the azimuth of the just set sun. The comet will set only
7 minutes after the top edge of the sun has set. You would need a
very good horizon and beautifully clear skies to see it, but given
the possible brightness it is not an impossibility. The tail would
lie almost flat along the horizon to the comet's right.
The first real chance will be at sunset on Jan 14 with the comet about
5 degrees from the just set sun, up at 45 degrees to the right (and
gas tail continuing away from the sun in that direction). The head
of the comet will set about 23 mins after the sun, still in the bright
twilight, but as the sky darkens it is probable that the tail will
become visible at greater distances from the comet. It is
close to sunset on the 14th that the comet will reach its theoretical
brightest.
At sunset on Jan 14, the comet will be located only 1.2 deg due right
of Mercury which will then be mag. -1, and some 14 deg from Venus
which at mag. -4 lies up to the right of the comet. [The magnitude scale
is used by astronomers to measure brightness. The Sun is mag. -26, the full moon
mag. -12 and the faintest stars you see on a dark night are about mag. +6.]
The best geometry occurs on Jan 15, with the comet starting to move
away from the sun (now 7 degrees) and almost directly above the
position of the sun at sunset. The head will set about 39 mins after
the sun, although the azimuth at which it sets will be 5.0 degrees to
the left of the sunset point. It is quite reasonable to expect the tail
to remain visible up to an hour after sunset, so it may be seen in a
dark sky.
On Jan 15 the comet is already 3 degrees from Mercury, up to the left.
By Jan 16, the effect of forward scattering will have dropped back to
about zero and the comet will already be heading away from the Sun and Earth;
back to the obscurity of the Oort cloud. Although now clearly fading,
it will be moving higher into the southern sky away from the sun. At
sunset on the 16th, the comet will be about 10 degrees from the sun and
just left of directly above the Sun at sunset. It will set 54 mins
after the sun, 9 degrees to the left of the sunset point.
From Jan 17 onwards, the comet, although fainter, should be well visible
in the darker skies. It then moves into the SW sky at roughly
a 45 deg angle up to the left of the sunset point.
The angular distance of the comet from sun at the time of sunset from
Sydney then increases on a daily basis:
Jan 17 12deg
18 15deg
19 17deg
after which date the head of the comet will set when the sun has already
passed more than 18 degrees below the horizon (astronomical darkness).
This diagram by
Steve Quirk
shows the WSW sky just after sunset for NSW. Venus
will be an obvious bright object up to the right, but Mercury will
be difficult to see except in binoculars (do not try to look for it
or the comet before the Sun has fully set). The
position of the comet on seven nights from Jan 13 to 19 is given.
Although technically visible on the 13th, the comet sets just after
the sun, so it is on the 14th and 15th before the comet is likely to be
easily seen. The tail is plotted as a general indication of
what might be seen. The outer parts of the tail will only be
visible after the sun, and the comet's head, have set much lower
below the horizon.
This diagram
(and a b+w version)
can be freely used in
any publication if credited (c) Steve Quirk (2007). Note however the diagram is only really
applicable to the southern states of Australia.
The Comet's Tail
A note of the appearance of the tail is necessary. Any
prediction of the length and brightness of the tail is likely to be
more difficult than the brightness of the comet; comet brightness
prediction being difficult enough in itself. It is likely that the
blue gas tail will be narrow, pointing away from the sun, with a broad
diffuse and strongly curved yellow dust tail to it's right. The reason
for this geometry is that the gas moves very quickly away from the head
so tends to point directly away from the sun. The dust however is
heavier and once ejected, follows a wider and slower orbital path
around the sun moving relatively more slowly as its distance from the
comet increases.
[A very crude analogy would be of spinning around holding a garden hose.
If the hose was on high, the stream of water would be fast and fairly
straight (we are talking of the appearance as seen from above). As you
slow the speed of the stream, still spinning at the same rate, the
curvature of the stream is much more marked].
Other Bright Comets
Until the modern era of automated surveys and space telescopes,
it was not uncommon for a comet to suddenly appear in the bright twilight
as an already impressive object. Without the survey telescope at Siding Spring, or
space telescopes, the current naked-eye sightings could have really been the
first anyone would have known about the comet. This is bourne out
by a report by
Hakon Dahle
of the Institute of Theoretical Astrophysics at the University of
Oslo. Responding to a query as to how the comet would compare with
some famous recent comets like Bennett, West, Halley, Hyakutake and Hale-Bopp,
he replied:
I already consider the comet to be in that league.
Yesterday (Jan. 8) I found it the most striking object
in the evening twilight sky, and our department had
been getting a lot of phone calls throughout the day
(particularly from northern Norway, where the sun is
still below the horizon at noon) from the general
public. The typical story was from people who had
"discovered" the comet while going to/from work,
waiting for the bus etc.
It is most unlikely that this comet will approach the spectacular
brightness of comet Ikeya-Seki in 1965, but it should turn out to be the
brightest comet for over 40 years.
Where to Look
For those using astronomical telescopes, below is an ephemeris for
09:30 UT (8:30pm NSW time) for Sydney (or any location in eastern
Australia at around 35S latitude for 12 mins after sunset). Delta is
the distance of the comet from the Earth and r of the comet from the
Sun (in AU, 1AU = ~150 million km). Elong. is angular distance from
the Sun in degrees.
UT R.A. (J2000) Dec. Delta r Elong.
YYYY MM DD HHMM HH MM.mm DD MM.m AU AU deg
2007 01 13 0930 19 58.79 -18 06.7 0.839 0.172 5.9
2007 01 14 0930 20 06.15 -21 36.6 0.822 0.183 5.5
2007 01 15 0930 20 12.70 -25 11.0 0.817 0.201 7.2
2007 01 16 0930 20 18.46 -28 35.3 0.820 0.224 9.8
2007 01 17 0930 20 23.56 -31 42.1 0.830 0.251 12.6
2007 01 18 0930 20 28.13 -34 29.0 0.845 0.279 15.3
2007 01 19 0930 20 32.31 -36 56.8 0.863 0.308 17.7
2007 01 20 0930 20 36.18 -39 07.2 0.883 0.337 19.9
2007 01 21 0930 20 39.81 -41 02.3 0.904 0.367 21.9
2007 01 22 0930 20 43.25 -42 44.2 0.926 0.396 23.7
2007 01 23 0930 20 46.54 -44 14.9 0.949 0.425 25.3
2007 01 24 0930 20 49.70 -45 35.9 0.971 0.454 26.8
2007 01 25 0930 20 52.76 -46 48.6 0.994 0.482 28.2
2007 01 26 0930 20 55.74 -47 54.1 1.017 0.510 29.5
2007 01 27 0930 20 58.65 -48 53.6 1.039 0.538 30.7
2007 01 28 0930 21 01.50 -49 47.7 1.061 0.565 31.8
2007 01 29 0930 21 04.29 -50 37.2 1.083 0.592 32.8
2007 01 30 0930 21 07.04 -51 22.7 1.104 0.618 33.8
2007 01 31 0930 21 09.74 -52 04.7 1.125 0.644 34.8
2007 02 01 0930 21 12.42 -52 43.6 1.146 0.670 35.7
Webpages about C/2006 P1
Disclaimer
A telescope has been marketed in Germany under the name "McNaught Comet Catcher". Rob McNaught was not contacted by the company, does not endorse it
and has no knowledge of its quality.
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