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Comet McNaught plunges toward the Sun


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#16    greggK

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Posted 22 January 2007 - 02:06 PM

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Been watching this every night for the last few days, sadly just went behind cloud tonight  sad.gif


Probably hiding from China.

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#17    Waspie_Dwarf

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Posted 22 January 2007 - 03:30 PM

The Great Cometary Show

The European Southern Observatory (ESO) press release 05-07 is reproduced below:

ESO 05/07 - Science Release

19 January 2007
For Immediate Release

The Great Cometary Show

Comet McNaught Over Parana

Comet McNaught, the Great Comet of 2007, is no more visible for observers in the Northern Hemisphere. It does put an impressive show in the South, however, and observers in Chile, in particular at the Paranal Observatory, were able to capture amazing images, including a display reminiscent of an aurora!

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Comet McNaught and ATs

The Comet McNaught observed in the evening of 16 January 2007 from Paranal. Two of the four VLTI Auxiliary Telescopes are seen in the foreground.

Comet C/2006 P1 was discovered in August 2006 by Robert McNaught on images taken by D. M. Burton with the 0.5-m Uppsala Schmidt telescope in the course of the Siding Spring Survey (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. At that time, the comet was only a very faint, barely diffuse object, about 50 000 times fainter than what the unaided eye can see.

However, as the comet came closer to the Sun, it brightened rapidly, in such a way as to become easily visible with the unaided eye in early January 2007, becoming brighter than Comet Hale-Bopp and Comet West, thereby earning its title of Great Comet of 2007. It even became the brightest comet in more than 40 years.

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'Old Tails'

The extended tail of Comet McNaught, seen from Paranal, observed in the evening of 18 January 2007, when the comet was setting behind the Pacific Ocean. The planet Venus is visible in the lower right of the image.



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The Comet and the Telescopes

The extended tail of Comet McNaught, seen from Paranal, observed in the evening of 18 January 2007, when the comet was setting behind the Pacific Ocean. In the foreground: one of the VLT Unit Telescope and two Auxiliary Telescopes.

Comet McNaught had its closest approach to the Sun on 12 January, being well inside the orbit of Mercury, with a minimum distance of only 17% the mean Earth-Sun distance. On January 13, it reached its maximum brightness when it was possibly brighter than Venus.

In early January, it was visible in the northern hemisphere but after passing the Sun, it only became visible from the southern hemisphere, entering the constellation Microscopium (The Microscope) on 18 January.

Astronomers in ESO's observatories in Chile are thus optimally placed to enjoy the show and certainly do not want to miss it. The comet displays a vivid coma and a lovely, sweeping tail.

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Comet McNaught

The Comet McNaught observed in the evening of 16 January 2007 from Paranal. The comet's image gets bent through the atmosphere and cloud layers.



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A Cometary 'Aurora'

The 'old tails' from Comet McNaught observed in the evening of 17 January 2007 from Paranal, when the comet had just set. The outcome resembles an aurora.

As the night deepens, and the comet had set, it revealed a sweeping fan that gives onlookers the impression they are witnessing an aurora, albeit the phenomenon is completely different. The structure in the tail is probably the fingerprint of past bursts of activity of the comet, releasing small dust particles whose paths are deflected by the solar light.

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Comet McNaught

The 'old tails' from Comet McNaught observed in the evening of 17 January 2007 from Paranal, when the comet had just set. The outcome resembles an aurora. In the foreground: one of the VLT Unit Telescope and three Auxiliary Telescopes



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Comet McNaught

The Comet McNaught observed in the evening of 17 January 2007 from Paranal.

The comet is now heading further south and should still be nicely visible for southern observers for several days.

More images of the comet are available at the McNaught ESO page.


Source: ESO Press Release pr-05-07

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#18    frogfish

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Posted 23 January 2007 - 01:17 AM

I still hate MI for making me miss this...

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#19    Waspie_Dwarf

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Posted 25 February 2007 - 02:00 AM

The Celestial Whirligig

The European Southern Observatory (ESO) press release 07-07 is reproduced below:

ESO 07/07 - Instrument Release

23 February 2007
For Immediate Release

The Celestial Whirligig

Unique Observations of Comet McNaught Reveal Sprinkling Nucleus


Comet McNaught, the Great Comet of 2007, has been delighting those who have seen it with the unaided eye as a spectacular display in the evening sky. Pushing ESO's New Technology Telescope to its limits, a team of European astronomers have obtained the first, and possibly unique, detailed observations of this object. Their images show spectacular jets of gas from the comet spiralling several thousands of kilometres into space, while the spectra reveal the presence of sodium in its atmosphere, something seen very rarely.

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Imaging of the central coma of Comet McNaught. Left: a raw image taken through a filter centred on the emission by CN gas.
Middle: the CN image processed using the Larson-Sekanina algorithm to reveal spiral jets of gas from the nucleus.
Right: A similarly processed image of the dust in the inner coma, showing a sunward plume and the dust being swept back into the tail. The
tail direction is roughly downwards in these images, which are orientated with North up and have a field of view of 2.4 arcmin on a side.


Comet C/2006 P1 (McNaught) has rightly earned the title of a 'Great Comet' - one so bright in the sky that such an occurrence could be expected just once in a generation (see ESO 05/07).

The problem for astronomers was that the comet stayed very close to the Sun and so was only visible very low on the horizon, making it impossible for most professional telescopes to study it in detail. One telescope, however, was up to the challenge: ESO's New Technology Telescope (NTT), at La Silla.

"We had previously pointed the NTT very low to observe the planet Mercury, which is very close to the Sun and is therefore only visible low in the sky just after sunset. I realised that we could take advantage of the same low pointing limit to observe the comet while it was near the Sun", said ESO astronomer Colin Snodgrass [1].

From the 29th January onwards, the comet was thus observed with the NTT, revealing in detail the heart of the comet. This was no easy feat as even with the NTT it was only observable for half an hour after sunset. Luckily, the NTT has another major advantage: it is equipped with the versatile ESO Multi Mode Instrument (EMMI), which can provide both imaging and spectroscopic observations across the visible wavelength range. This meant that the maximum amount of scientific data could be taken during the limited time available for observations.

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ESO's New Technology Telescope at La Silla is unique in that it can observe very low
on the horizon. The telescope is not housed in a traditional dome with a slot in the roof
to look at the sky, but in an innovative enclosure design with a sliding roof and wall that
open up to leave a view of the sky which goes all the way to the ground. The whole
building then rotates with the telescope to track objects on the sky. Inside the building
the telescope can swing up or down, and was built to be able to swing down far further
than normal telescopes: the NTT can point at objects only 10 degrees above the horizon


The unique images reveal three clear jets of gas, which are seen to spiral away from the nucleus as it rotates, like a Catherine Wheel firework.

"These jets are produced when sunlight heats ices on the surface of the comet, causing them to evaporate into space and create 'geyser' like jets of gas and small dust particles, which stretch over 13,000 km into space - greater than the diameter of the Earth - despite the fact that the nucleus of the comet is probably less than 25 km in diameter," explained Snodgrass.

By comparing images like this taken at different times, astronomers should be able to calculate how fast the nucleus rotates from the changing pattern of jets.

Other images also reveal that while the gas forms spiral jets, the large dust particles released from the comet follow a different pattern, as they are thrown off the comet's surface on the brightly lit side towards the Sun, producing a bright fan, which is then blown back by the pressure of sunlight itself.

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Long slit medium resolution spectrum taken on 3 February 2007 and covering the spectral range 450-650nm (the spectral direction is along
the horizontal axis, blue side to the left and red to the right). The spatial direction is along the vertical axis and covers about 80,000 km
on the sky. The nucleus has been centred in the 1" (800 km) slit, and is located at the position of the solar continuum in the spectrum.
The Sun direction is up and the tail direction is toward the bottom of the image. The many emission lines from the gaseous coma are
spatially extended by several thousands kilometres and grouped in so-called molecular bands. The sodium (NaI D) emission is visible as
the sharp and very extended line. In fact the sodium doublet (NaI D1 and D2 lines) is just resolved. On 3 February the flux that this line
had in the inner coma dropped by a factor of 10 in only a few days. For sake of clarity only some of the most conspicuous features are
annotated.


As well as taking images, the astronomers were able to investigate which gases were present in the comet's atmosphere [2] using spectroscopy. The usual gaseous species have been detected, such as cyanide, carbon, and ammonia, whose analysis will help the astronomers to determine the activity level of the comet and its chemical type.

But already in the first high resolution spectrum obtained on 29 January, the astronomers noted something quite unusual.

"We detected two very bright lines - the brightest of the whole spectrum taken on this day as a matter of fact - close to 589 nm and quickly identified them as belonging to neutral sodium atoms," said Emmanuël Jehin (ESO). "Further measurements showed this sodium emission to be extending over more than 100,000 km in the tail direction and fading rapidly with time."

Such lines have only been detected in the greatest comets of the past century like C/Ikeya-Seki in 1965, C/West in 1976 and C/Hale-Bopp in 1997, for which a very narrow sodium tail was even photographed. This straight neutral tail appears in addition to the dust and ionised gas tails when the comet is close to the Sun.

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Photograph of the comet tail from Paranal, after the comet
itself had set, with the laser guide star system above Yepun
(Unit Telescope 4) in the foreground. The laser is used to
produce a fake 'star' on the sky to allow the changing
atmosphere to be corrected. It works by making sodium
atoms high in the atmosphere glow - these atoms may
have originally come from comets like McNaught.
Photo by Emmanuel Jehin, ESO


"Its origin lies most probably in the dissociation of the cometary dust grains," said Jehin. "In very active comets, which are also usually the ones which pass closer to the Sun, the dust grains are vaporised under the intense heat and start releasing sodium atoms which then react to the solar radiation and emit light—at the very same yellow-orange wavelength of the lamps on our streets."

Sodium has also been observed around Mercury and the Moon forming a very tenuous atmosphere. But closer to us, at 90 km altitude in our atmosphere, there is the so-called 'sodium layer'. The origin of that layer is not well known but might be coming from the ablation of meteoroids that are burning (due to their high entry speed in the atmosphere) at the same altitude. As most shooting stars (or meteors) originate from comets (annual showers like the Eta Aquarids and Orionids originate from comet P/Halley, the Leonids come from comet P/Tempel-Tuttle, and the Perseids from comet P/Swift-Tuttle), the sodium in those dust particles might just be the same. As a kind of gift to the astronomers that layer is used by observatories like Paranal to produce with a laser an artificial star that allows for the correction of atmospheric turbulence!

Notes

[1] The team is composed of Colin Snodgrass, Emmanuël Jehin, and Olivier Hainaut (ESO), Alan Fitzsimmons (Queen's University, Belfast, UK), and Jean Manfroid and Damien Hutsemékers (Université de Liège, Belgium). These results were presented in a Circular Telegram to the International Astronomical Union (IAU CBET 832).

[2] When a comet is approaching the Sun, the ices trapped in the small nucleus sublimate, sometimes in the form of very strong gaseous jets, dragging in the process a lot of dust particles into space and forming a dusty atmosphere - called the coma - of several thousands of kilometers around the nucleus. All those molecules and dust particles are then pushed in the direction opposite to the Sun (by the solar radiation pressure), creating the gaseous and dust tails of the comet.


Source: ESO Press Release pr-07-07

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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