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.

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.

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.

• SOHO images

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.

• Syuichi Nakano's polar plot

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

• Gary Kronk's Cometography

• Seiichi Yoshida's plots, analyses and pictures


The brightness predictions on this page do not include forward scatter (so are likely to be conservative).

• Spectacular images by Alessandro Dimai in Italy

• Spaceweather.com

• Michael Mattiazzo's Southern Comets Homepage

• Astronomy Picture of the Day

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.