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Comet C/2006 P1 (McNaught)
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Ulysses Spacecraft Data Reveal a Comet Biggie

Using data from the completed ESA/NASA Ulysses mission, scientists have identified a new candidate for biggest comet. Results of these findings were presented today at the Royal Astronomical Society's National Astronomy Meeting in Glasgow by Ulysses science team member Geriant Jones of University College, London.
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McNaught, is the largest comet ever seen?

The tail of the celestial sky could be more than 1.5 times the distance between Earth and Sun, according to a new measurement
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The shocking size of Comet McNaught

British scientists have identified a new candidate for the biggest comet measured to date. Dr Geraint Jones of UCL's Mullard Space Science Laboratory will be presenting the results at the RAS National Astronomy Meeting in Glasgow on Tuesday 13th April. Instead of using the length of the tail to measure the scale of the comet, the group have used data from the ESA/NASA Ulysses spacecraft to gauge the size of the region of space disturbed by the comet's presence. Analysis of magnetometer data shows evidence of a decayed shockwave surrounding the comet created when ionised gas emitted from the comet's nucleus joins the fast-flowing particles of the solar wind, causing the wind to slow down abruptly.
In January and February 2007, Comet C/2006 P1 McNaught became the brightest comet visible from Earth for 40 years. Serendipitously, Ulysses made an unexpected crossing of Comet McNaught's tail during this time, one of three unplanned encounters with comet tails during the 19-year mission. The other encounters included Comet Hyakutake in 1996, the current record-holder for the comet with the longest measured tail.

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RE: Comet 2006 P1 ( McNaught )
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Title: Comet McNaught C/2006 P1: observation of the sodium emission by the solar telescope THEMIS
Authors: F. Leblanc, M. Fulle, A. López Ariste, G. Cremonese, A. Doressoundiram, A. Sainz Dalda, and B. Gelly

Comet McNaught C/2006 P1 was the brightest comet of the last forty years when reaching its perihelion at an heliocentric distance of 0.17 AU. Two days before this perihelion, at an heliocentric distance of 0.2 AU, Themis, a French-Italian solar telescope in the Canary Islands, Spain, observed the Comet sodium emission of McNaught.
The measured maximum sodium brightness of the D2 emission line peaked at 900 Mega-Rayleigh. The spatial distribution of the sodium emission with respect to the nucleus of the comet is in agreement with previous observations. It displays a clear sunward-tailward asymmetry that suggests a dichotomy of the sodium sources between a source close to the nucleus and an extended source most probably corresponding to the dust tail. The spatial distribution along the slit of the width and speed of the Doppler Na distribution also suggests such a dichotomy. The sodium ejection rate inferred from this observation agrees with the value of the ejection rate extrapolated from comet Hale-Bopp, taking into account the heliocentric distance of comet McNaught and its significantly larger dust release.
If we suppose a similar concentration of sodium atoms in both comets, this observation suggests that the sodium ejection rate from comets McNaught and Hale-Bopp is proportional to the solar flux. Therefore the most probable ejection mechanisms are photo-sputtering, solar wind sputtering, or cometary ion sputtering, and not thermal desorption.

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Comets are made of the most primitive stuff in the solar system. As hunks of rock and ice that never coalesced into more planets, they give researchers clues to the evolution of solar systems.
So a chance encounter between spacecraft Ulysses and Comet McNaught's ion tail has scientists in the University of Michigan's College of Engineering marvelling at a stroke of luck and some surprising data.
The NASA/European Space Agency spacecraft is on a mission to study the sun's polar regions, and it carries an instrument run by U-M professors. In February, it flew through McNaught's ion tail 160 million miles from the comet's core.
Instrument readings showed there was "complex chemistry" at play, said U-M space science professor George Gloeckler, second author of a paper on the findings published Oct. 1 in Astrophysical Journal.

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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.

McNaught
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Credit ESO

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Interview with Rob McNaught
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Rob McNaught needs very little introduction - especially with the recent excitement caused worldwide by one of his many extra terrestrial discoveries – C2006 P1.
For the record, he is an astronomer at the Australian National University working on the Siding Spring Survey – whose mission it is to contribute to the inventory of near-earth objects (NEOs), or more specifically, the potentially hazardous asteroids (PHAs) and comets (PHOs) that may pose a threat of impact and thus harm to civilization.

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