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Posted: 22-01-2007 12:55 Post subject:

i hadn't realised this comet was seen from UK a week or two back:
http://news.bbc.co.uk/1/hi/in_pictures/6251663.stm

Posted: 23-01-2007 12:20 Post subject:

Posted: 23-01-2007 13:20 Post subject:

Posted: 22-11-2007 22:17 Post subject:

Is Comet Holmes bigger than the Sun?

The notion that Comet Holmes is bigger than the Sun has been making the rounds on space-related websites of late. But is it true?

According to a statement on astronomer Dave Jewitt's website, it is. "Formerly, the Sun was the largest object in the Solar System," the statement reads. "Now, comet 17P/Holmes holds that distinction."

Jewitt works at the University of Hawaii, and is certainly an authority on icy denizens of the solar system, having co-discovered the first Kuiper Belt object.

But what the statement is referring to is not the "body" of the comet, called the nucleus, which is only 3.6 kilometres across, but the extended cloud of dust around the nucleus called the coma.

Comet Holmes's coma has been expanding rapidly ever since a remarkable outburst of dust and ice from its surface on 24 October that suddenly increased the comet's brightness and brought it to the world's attention. (The image above, taken by Alan Dyer, shows Comet Holmes' coma and part of its tail.)

Measurements by University of Hawaii astronomers showed the coma was 1.4 million kilometres across as of 9 November. That's slightly larger than the diameter of the Sun, which is about 1.39 million kilometres.

That's large for a comet coma, but it's not the biggest ever. Comet Hale-Bopp's coma peaked at a diameter of between 2 and 3 million kilometres in 1997.

And comet tails can get even larger. Comet Hyakutake's was measured to be more than 500 million kilometres long in 1996 by the Ulysses spacecraft and may have been longer.

Jupiter's magnetotail, a long stream of charged particles extending from the solar system's largest planet, is even larger than this. It's exact size is unknown, but it is at least 650 million kilometres long.

In any case, as far as the solid part of Comet Holmes is concerned, it is much, much smaller than the Sun. But if you include the coma, it really is larger than the Sun, and continues to grow.

David Shiga, online reporter
[links in article]

http://tinyurl.com/yvo274

Comet Holmes is now a naked-eye object:
http://www.heavens-above.com/comet.aspx?cid=17P&Session=kebgcaigmgfjpcmbfmpcndak

Posted: 05-01-2010 12:26 Post subject:

The moment comet was eaten up after orbiting too close to the sun
By Scott Warren
Last updated at 9:10 AM on 05th January 2010

A comet has been captured by Nasa being 'eaten' as it flies too close to the sun.
The space agency's solar-focused agency - Solar and Helioscopic Observatory (SOHO) - captured footage of the Kreutz Sungrazer as it made its fateful approach.
The footage has proven popular on YouTube and scientific and astronomical websites and blogs.

Kreutz Sungrazers are characterised by orbits taking them extremely close to the Sun.
They are believed to be fragments of one large comet that broke up several centuries ago and are named after German astronomer Heinrich Kreutz, who first worked out that they were related.

A SOHO spokeswoman said the agency gathered the footage using a Coronagraph, which blocks the brightest object in an image.
This allows activity around the sun - such as the comet's approach - to be viewed.
It is known as a 'false eclipse' and displays the actual footage of the comet's final seconds, presented in a way that it can be seen by the naked eye.

Hundreds of Kreutz comets, some only a few metres in diameter, have been discovered since the launch of the SOHO satellite in 1995.
Like the comet captured in these images, none have survived the section of their orbit closest to the sun.

Experts say a new cluster of Kreutz comets will approach the sun over the next few decades, treating stargazers to more spectacular shows.

Read more: http://www.dailymail.co.uk/sciencetech/article-1240591/Comet-eaten-orbits-close-sun.html#ixzz0bjhKlfNF

Posted: 24-03-2010 13:58 Post subject:

Office worker stares off into space... and is the only man on Earth to see exploding comet
By Daily Mail Reporter
Last updated at 9:36 AM on 24th March 2010

An amateur stargazer has captured the moment a comet exploded in space - an event missed by the world's professional astronomers.

Musical instrument designer Nick Howes, 40, used the internet to access an online telescope as he sat at his desk in his office.

Mr Howes, of Cherhill near Calne, Wilts, logged on to a telescope in Hawaii and began staring into deep space. But he spotted a massive comet breaking up and was able to use the telescope to take photos.

Nick, who works for Yamaha, actually captured the moment the comet exploded, blowing a chunk the size of Mount Everest off one side.

He was the only person in the world to witness the dramatic event - with even American astronomers completely missing the opportunity.

The comet is known as Siding Spring after the Australian observatory where it was first spotted in 2007.

It is many times the size of Mount Everest and is travelling at a speeds of around 19 miles a second - 20 times faster than a bullet.

Nick's discovery has now been honoured by the International Astronomical Union and hailed by experts as a 'major astronomical discovery'.

Father-of-one Nick said: 'I had heard that a comet was passing so I tried to view it myself and used a telescope in Hawaii to have another look.

'But within about 10 minutes I spotted that it was blowing up. It was amazing. I contacted the International Astronomical Union and they confirmed I was the only one to make the discovery. I then made lots of frantic phone calls.'

Nick took the images from his office in London using the Faulkes Telescope Project in Hawaii last Thursday.

He used the £5million telescope to capture six images that show a chunk of ice known as a "dirty snowball" breaking away from the nucleus of the comet.

The following day a second set of images showed the new fragment is still trailing the comet, which is officially called C2007 C3. The online telescope project is run by experts at Cardiff University who say they are 'delighted' with Nick's result.

Dr Paul Roche, of Cardiff University, said: 'What this illustrates is what is achievable when amateur astronomers can get their hands on such a powerful telescope.

'As the nucleus of a comet is typically tens of kilometres across, this fragment is probably mountain-sized, and will become a small comet as it gradually separates from its parent.

'We hope this discovery will help encourage others to use the Faulkes Telescopes and lead to even more scientific discoveries.'

Nick has a small observatory himself at his home and has since been tracking the comet's progress.

It was first spotted in October and is heading away from Earth and will never been seen again.

The comet was first spotted by Donna Burton - so perhaps should have been called Donna's Comet or Burton's Comet. But it was instead named after the Siding Spring Observatory near Coonabarabran, 280 miles (500km) north-west of Sydney, Australia.

The Faulkes Telescope Project was launched in March 2004 as a way of helping to inspire school students to study science and maths.

Read more: http://www.dailymail.co.uk/sciencetech/article-1260049/Exploding-comet.html#ixzz0j6846FLI
also
http://www.cardiff.ac.uk/news/articles/a-cracked-comet.html

Posted: 02-04-2010 10:38 Post subject:

The day the Earth froze: An hour-long storm started a mini ice age, say scientists
By David Derbyshire
Last updated at 8:48 AM on 02nd April 2010

An hour-long hailstorm from space bombarded the Earth 13,000 years ago - plunging the planet into a mini-ice age, scientists claimed today.
The catastrophe was caused by a disintegrating comet and saw the planet sprayed by thousands of frozen boulders made of ice and dust.
The collisions wiped out huge numbers of animal species all over the world, disrupted the lives of our stone age ancestors and triggered a freeze that lasted more than 1,000 years.

The theory is the brainchild of Professor Bill Napier, from Cardiff University, who says it explains the mysterious period of extinction around 11,000 BC.
Scientists have long been puzzled by what caused a sudden cooling of up to 8C (14F) just as the Earth was warming up at the end of the last ice age.
The change in climate caused retreating glaciers to advance once again, and coincided with the extinction of 35 families of North American mammals.

Some geologists have argued that the world was hit by a giant asteroid - a smaller version of one which wiped out the dinosaurs 65million years ago.
The collision left behind tell tale traces in the rocks - including a black 'mat' of soot an inch thick thought to have been created by continental wide wildfires.
Microscopic 'nanodiamonds' created in massive shocks and only found in meteorites or impact craters have also been discovered dating back to the disaster.
These findings have led to claims that a 2.5mile long comet or asteroid smashed into the ice sheet covering what is now Canada and the northern US.

But other scientists say the chances of the Earth being struck by such a large object only 13,000 years ago are one thousand to one against. And they say a single impact cannot explain such widespread fires.
Professor Napier's theory suggests the devastation took place when the Earth strayed into a dense trail of fragments shed by a large comet.
Thousands of chunks of material from the comet would have rained down on Earth, each one releasing the energy of a one megaton nuclear bomb.
The impacts would have filled the atmosphere with smoke and soot and blotting out the Sun.

Prof Napier says a comet swooped into the inner solar system between 20,000 and 30,000 years ago and has been breaking apart ever since.
'A large comet has been disintegrating in the near-Earth environment for the past 20,000 to 30,000 years and running into thousands of fragments from this comet is a much more likely event than a single collision,' said Professor Napier.
His model, published in the journal Monthly Notices of the Royal Astronomical Society, suggests that the 'hailstorm' would have only lasted about an hour.
It would have caused thousands of impacts, generating global fires and depositing nanodiamonds at the 'extinction boundary' marking the point in time when many species died out.

One recent impact that may have come from the comet is known as the Tagish Lake meteorite, said Professor Napier.
The object fell on Yukon Territory in Canada in January 2000. It contained the largest amount of nanodiamonds of any meteorite studied so far.

Read more: http://www.dailymail.co.uk/sciencetech/article-1262904/Prehistoric-hailstorm-triggered-1-000-year-freeze-Earth-wiped-animal-species.html#ixzz0jvvP86zF

Prof Napier has been banging on about the "large comet [...] disintegrating in the near-Earth environment for the past 20,000 to 30,000 years" for decades - I've posted several references on this MB to Clube and Napier's books and ideas on the subject, eg: http://www.forteantimes.com/forum/viewtopic.php?p=644286#644286

Posted: 03-04-2010 02:59 Post subject:

"Prof Napier says a comet swooped into the inner solar system between 20,000 and 30,000 years ago and has been breaking apart ever since."

Surely that should be 'theorises?' Confused

Posted: 03-04-2010 11:45 Post subject:

Posted: 03-04-2010 20:50 Post subject:

Posted: 03-04-2010 23:23 Post subject:

Ah well, here I was, hoping for an intelligent debate on orbital dynamics, solar system evolution, or the chemistry of comets, and what do I get?

People wittering on about whether someone 'says' or 'theorises' something... Rolling Eyes

Posted: 10-09-2010 15:04 Post subject:

Halley's comet 'was spotted by the ancient Greeks'
By Paul Rincon, Science reporter, BBC News

A celestial event seen by the ancient Greeks may be the earliest sighting of Halley's comet, new evidence suggests.

According to ancient writers, a large meteorite smacked into northern Greece between 466BC and 467BC.

The writers also described a comet in the sky at the time the meteorite fell to Earth, but this detail has received little attention, say the researchers.

Comet Halley would have been visible for about 80 days in 466BC, researchers write in the Journal of Cosmology.

New Scientist magazine reports that, until now, the earliest probable sighting of the comet was an orbit in 240BC, an event recorded by Chinese astronomers.

If the new findings are confirmed, the researchers will have pushed back the date of the first observation of Comet Halley by 226 years.

The latest idea is based on accounts by ancient authors and concerns a meteorite that is said to have landed in the Hellespont region of northern Greece in 466-467BC.

The space rock fell during daylight hours and was about the size of "a wagon load", according to ancient sources.

The object, described as having a "burnt colour", became a tourist attraction for more than 500 years.

In his work Meteorology, Aristotle wrote about the event about a century after it occurred. He said that around the same time the meteorite fell, "a comet was visible in the west".

Astronomer Eric Hintz and philosopher Daniel Graham, both of Brigham Young University in Provo, Utah, reconstructed the likely path of Halley's comet, to see whether it agreed with the ancient observations.

They calculated that Halley's comet could have been visible for about 80 days between early June and late August in 466BC - depending on atmospheric conditions and the darkness of the sky.

"It's tough going back that far in time. It's not like an eclipse, which is really predictable," co-author Eric Hintz, from Brigham Young University in Provo, Utah, told BBC News.

"But we feel fairly good about this. If the [sighting] in 240BC is accepted, this has a fairly solid possibility."

He added: "If accepted, this would be three orbits earlier [than the Chinese sighting]."

The reconstruction of the comet's path agrees with the ancient reports, which say the comet was visible for about 75 days.

The researchers point out that while the Chinese and Babylonians kept meticulous records of heavenly phenomena for centuries, the ancient Greeks did not.

Nevertheless, the Greek accounts do provide important information, say Graham and Hintz, such as the comet's period of visibility from Earth.

Asked whether it was possible that the meteorite fall and the pass by Halley's Comet could be linked, Dr Hintz was doubtful.

"it would be really neat if they were connected - if it was a piece of Halley's that fell. My feeling is that it was just a really cool coincidence," said Dr Hintz.

The researchers say that there remains the possibility that other ancient sightings of comets could be uncovered from Chinese and Babylonian records.

http://www.bbc.co.uk/news/science-environment-11255168

Posted: 10-09-2010 17:24 Post subject:

The New Scientist article that the Beeb cribbed from also adds:

...The researchers show that Halley's comet would have been visible for a maximum of 82 days between 4 June and 25 August 466 BC. From 18 July onwards, a time of year characterised in this region by strong winds, it was in the western sky. At around this time, the Earth was moving under the comet's tail, so its debris field would have made shooting stars.

None of this proves the comet's identity, but Graham says such major comet sightings are rare, so Halley must be a "strong contender". Previously, the earliest known sighting of Halley was made by Chinese astronomers in 240 BC. If Graham and Hintz are correct, the Greeks saw it three orbits and more than two centuries earlier.

The researchers' analysis reveals this moment to be a crucial turning point in the history of astronomy. Plutarch wrote in the 1st century AD that a young astronomer called Anaxagoras predicted the meteorite's fall to Earth, which has puzzled historians because such events are essentially random occurrences.

After studying what was said about Anaxagoras, Graham concludes that he should be recognised as "the star of early Greek astronomy". Rather than predicting a particular meteorite, he reckons Anaxagoras made a general statement that rocks might fall from the sky.

At this time, says Graham, everyone thought that celestial bodies such as the moon and planets were fiery, lighter-than-air objects. But after observing a solar eclipse in 478 BC, Anaxagoras concluded that they were heavy, rocky lumps, held aloft by a centrifugal force. This implied that solar eclipses occurred when the moon blocked the light from the sun. It also meant that if knocked from position, such a rock might crash to Earth.

"When the meteorite fell, no one could deny it," says Graham. "The headline was 'Anaxagoras was right'."

Did Halley's comet play a role? It is always possible that the comet might have nudged a near-Earth asteroid from its course and sent it hurtling towards northern Greece. From that point on, the idea of rocks in the sky was accepted, and the Greeks had a new understanding of the cosmos.

http://www.newscientist.com/article/mg20727774.400-ancient-greeks-spotted-halleys-comet.html

Posted: 31-10-2010 09:27 Post subject:

Hartley 2: Nasa hopes Epoxi probe will unlock mysteries of the comets
Scientists hope that images of the orbiting bundle of dust, ice and rock known as Hartley 2 will solve some of the puzzles raised by previous missions to study comets
Robin McKie, science editor The Observer, Sunday 31 October 2010

On Thursday, a tiny US robot spacecraft will make a dramatic encounter in deep space. The probe will sweep past a comet known as Hartley 2 and take detailed measurements and photographs.

The results that will be sent back by Nasa's Epoxi spaceship are keenly awaited – previously scientists have found that the more they learn about comets the more baffling and mysterious they appear to be. They hope that this time round, some of those mysteries may be resolved.

In recent years, space scientists have discovered one comet that contains minerals created at extremely high temperatures, another that belches gases containing cyanides, one that has a surface fluffier than snow and another that has a firm surface peppered with craters.

"Comets were once thought to be roughly similar in shape and structure," said Dr Mark Bailey, of Armagh Observatory, in Northern Ireland. "But the more probes that we fly past them, the more differences we find. Goodness knows what we are going to find this time at Hartley 2."

Comets are formed from space rubble – dust, ice and small pieces of rock – left over from the making of our solar system billions of years ago and vary in size from a few hundred metres in diameter to tens of kilometres. Most orbit the Sun at the very edge of the solar system and only occasionally sweep close to Earth. When they do, radiation from the Sun causes their surfaces to heat up and release gas and dust. This material forms the comet's tail and gives these visitors to the night sky their distinctive appearance.

Scientists believe that water and complex organic materials detected on comets may have played a key role in the evolution of life on Earth. Hence their interest in studying them close up.

To do this, four space probes – one European and three American – have been sent on missions to rendezvous with comets. The first mission took place in 1986 when Europe's Giotto probe passed close to Halley's comet and sent back photographs of a dark surface from which jets of glowing material were emerging. Fifteen years later, Nasa's Deep Space 1 probe swooped close to Borrelly's comet and revealed a much smaller object with a more varied surface that appeared to be warm and dry.

Then in 2004, Nasa's Stardust probe flew past the comet Wild 2 and returned to Earth with particles it had collected from its tail. These were found to include crystalline silicates that are only formed at high temperatures. For an astronomical body that is generally thought to orbit in deep, cold space, these compounds are a puzzle, scientists admit.

And finally, a comet called Tempel 1 was visited by Nasa's Deep Impact probe in 2005. The spacecraft fired a copper projectile into the comet to study the debris thrown up. It also carried out a detailed photographic survey of the comet which showed it was littered with craters that must have been caused by smaller objects striking it in the past.

Given that a comet's surface is supposed to change every time it orbits close to the Sun, as radiation drives material from it, the existence of these old craters is also a puzzle. Only an unchanging surface could preserve craters, scientists have pointed out. "It seems like every time we go to a new comet, we discover new phenomena," said Dr Lori Feaga, an astronomer at the University of Maryland, and a member of the Epoxi science team.

Now astronomers have a new comet to target, though they are using an old probe to study it. After Deep Impact swept past its first target, the mission was given a new name, Epoxi, and sent on an orbit that will bring it to within 430 miles of Harley 2 this week. Already the mission has revealed fresh surprises. Last month, its instruments showed that the comet was emitting a toxic gas called cyanogen whose output increased fivefold over an eight-day period before slowly decreasing again. Mission scientists are still arguing over interpretations of this data.

"Comets have more than one source," said Bailey. "Some are found at the very edge of the solar system in a great band known as the Oort cloud. Others are found in a belt closer to the Sun known as the Kuiper belt. And then others can be created by asteroid collisions or some other violent event. So we should perhaps not be too surprised if they are turning out to be very different from each other."

Many of these new mysteries may be solved in 2014 when the European Space Agency's Rosetta probe reaches the comet Churyumov-Gerasimenko in 2014 and follows it, for more than a year, as it passes near the Sun. On the other hand, added Bailey, the mission may simply throw up even more puzzles.

http://www.guardian.co.uk/science/2010/oct/31/hartley-2-nasa-epoxi-probe