Comets

Fluttermoth

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I guess some one suggested it and it just stuck....
 

rynner2

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Probe sweeps past 'space peanut'
By Jonathan Amos, Science correspondent, BBC News

Nasa's Deep Impact probe has flown by Comet Hartley 2.

The first pictures revealed a roughly 1.5km-long, peanut-shaped object with jets of gas streaming from its surface.

The pass, which occurred about 23 million km from Earth, was only the fifth time a spacecraft had made a close approach to a comet.

Nasa said it would take many hours to retrieve all of the data recorded by Deep Impact's two visible-light imagers and one infrared sensor.

But the initial pictures to get to ground gave a fascinating view of the comet's icy body, or nucleus.

"Scientists often think of celestial bodies as roundish, and this obviously is not - it's peanut-like," commented Dr Don Yoemans, who manages Nasa's Near-Earth Object programme. "Mother Nature has once again pulled the rug out from under scientific ideas."

The information from the flyby should give scientists further insight into the diverse properties and behaviours of what are some of the Solar System's most remarkable objects.

"Every time we go to comets, they're full of surprises," said principal investigator Mike A'Hearn from the University of Maryland, College Park.

"None of them look the same, which means there must be some fundamental differences in how they all work; and that's what we're trying to figure out with the Expoxi mission."

The closest approach to Hartley 2 - a highly elongated, 2km-long object - occurred just before 1400 GMT. The probe whizzed by at a relative speed of 12.5km/s.

Deep Impact is on an extended mission, having been re-tasked to visit Hartley following its successful flyby of Comet Tempel 1 in 2005.

On that primary mission, the spacecraft released an impactor that crashed into Tempel's nucleus kicking up thousands of tonnes of icy debris.

The new venture is known by the name Epoxi. It required a series of deep-space manoeuvres, including three gravitational slingshots around Earth, to put the spacecraft in the right part of the sky to meet up with Hartley.

Comet Hartley is named after the Australian astronomer Malcolm Hartley who first identified the body in a photographic plate from a sky survey undertaken in 1986.

He was at Nasa's mission control at the Jet Propulsion Laboratory (JPL) in California to see the images of his comet come back from Deep Impact.

"It's awesome," he said. "I've been overwhelmed by everything that's happened in the last two weeks.
"There'll be enough data downloaded to keep researchers busy for the next five, 10, 15 years probably. It's proving to be very interesting."

Tim Larson, the Epoxi project manager at JPL, said: "The mission team and scientists have worked hard for this day. It's good to see Hartley 2 up close."

Comets are thought to contain materials that have remained largely unchanged since the formation of the Solar System. They incorporate compounds that are rich in carbon, hydrogen, oxygen and nitrogen.

Intriguingly these are the elements that make up nucleic and amino acids, the essential ingredients for life as we know it; and there are some who believe comet impacts in the early years of the Solar System could have seeded the Earth with the right chemical precursors for biology.

As well as Tempel 1, spacecraft have previously visited comets Borrelly, Wild 2, and Halley. All are considerably bigger than Hartley. But Hartley - it was discovered in 1986 by the Australian astronomer Malcolm Hartley - has already proved itself to be a fascinating target.

Even from a distance, scientists have seen a lot of short-term changes on the object, and it ejects twice as much gas every minute as Tempel 1.

"We're trying to find out if all the new phenomena we saw at Tempel 1 are universal across all comets or are they special to Tempel 1," said Dr A'Hearn.

"The other key goal is to separate out the primordial features which we think we saw on Tempel 1 in the layering of the cometary nucleus and see what that can tell us about the formation of the Solar System 4.5 billion years ago."

Deep Impact will keep imaging Hartley for a further 20 days.

http://www.bbc.co.uk/news/science-environment-11674694
 

rynner2

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Certainly an odd-looking object.

New image shows Nasa spacecraft flew through a mini-blizzard of ice grains to get close to distant comet
By Daily Mail Reporter
Last updated at 10:44 AM on 19th November 2010

The NASA spacecraft that flew close to a distant comet earlier this month found itself hurtling through an unexpected cosmic ice storm, scientists revealed today.
Speeding at 27,000 mph, the Deep Impact craft flew within 435 miles of comet Hartley 2 on 4th November - only the fifth time a comet had been viewed up close.

Spectacular new images from the flyby revealed a blizzard of white specks surrounding the nearly 1 1/2-mile-long peanut-shaped comet.
‘Those are not stars. Those are all chunks of ice,’ said chief investigator Michael A'Hearn of the University of Maryland.

The ice cloud surrounding Hartley 2 was driven by jets of carbon dioxide shooting out from the comet's interior, scientists said. As the carbon dioxide spewed out, it carried with it tons of ice ranging from the size of golf balls to basketballs.

Though Deep Impact was a safe distance away, it appeared it got hit nine times by icy particles weighing less than a snowflake. The craft was not damaged, said project manager Tim Larson of the NASA Jet Propulsion Laboratory, which managed the $42 million mission.

Dr Jessica Sunshine, the mission's deputy principal investigator, said: 'We know that the ice on a fundamental level can't be bigger than somewhere between one and 10 microns in size.
'That's about the thickness of our hair. What that means is that the snowballs are not what we thought to begin with - we're not seeing hail-sized particles. What we're seeing are fluffy aggregates of very small pieces of ice. They're akin more to a dandelion puff than an ice cube.'

Comets are considered time capsules of the solar system, icy leftovers from when it formed about 4.5 billion years ago. Studying comets could shed light on how Earth and the planets formed and evolved.

That that comet ice storm was created by carbon dioxide jets came as a surprise to researchers, who said it could change the way they think about these nomadic icy bodies.
Carbon dioxide ‘was never thought to be the main driver of comet activity. That role has been reserved for water,’ said astronomer David Jewitt of the University of California, Los Angeles.


Since the encounter, mission scientists have been analysing the flood of data coming down at a rate of 3,000 images a day. They have yet to determine when the ice storm began and how long it will last.

Hartley 2 is the second comet visited by Deep Impact. In 2005, it set off cosmic fireworks when it released a probe that crashed into comet Tempel 1. The $333 million collision gave scientists their first peek inside a comet.
Deep Impact will continue observing Hartley 2 until the end of the month as NASA decides whether to recycle it for a third mission. The craft does not have enough fuel to perform another flyby.

Read more: http://www.dailymail.co.uk/sciencetech/ ... z15jG4RPJO

'Dr Jessica Sunshine' - what a great name! :D
 

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Stardust spacecraft ready for comet flyby
By Jonathan Amos, Science correspondent, BBC News

Nasa's Stardust spacecraft is about to sweep past Comet Tempel 1.
The encounter early on Tuesday (GMT) will give scientists unique information on how these great balls of ice and dust change over time.

Tempel 1 was visited by another probe back in 2005. It fired a projectile at the body to disturb the surface.
Stardust's images will reveal the extent of the impact crater and any other alterations that may have occurred on the 14km-wide object.
The spacecraft is expected to get to within about 200km (120 miles) of the comet nucleus.

It will take more than 70 high-resolution images; its dust analysis instruments will also investigate the environment around the object.
The event is occurring at an enormous distance from Earth - approximately 336 million km (209 million miles) away.
Stardust will be moving past its target at about 10km/s, with the moment of closest approach timed for 0437 GMT.

"The spacecraft is currently opposite the Sun from the Earth," explained Tim Larson, the mission's project manager at Nasa's Jet Propulsion Laboratory.
"That means that when we send a command up to the spacecraft and wait for the confirmation that the command arrived and was executed properly - that round-trip light-time is about 40 minutes. So there's nothing we can do to command the spacecraft or control it real-time during a flyby like this. Therefore, everything has to be programmed ahead of time, put onboard the spacecraft and sequenced; and everything must happen autonomously."

All the data acquired during the flyby will be stored on the spacecraft until an hour after the pass.
Stardust then re-orientates itself to begin to beam back the pictures and other information.

The spacecraft is on what Nasa calls a "bonus mission". Stardust was launched back in 1999 with the primary goal of visiting another comet altogether - Wild 2. This it did in 2004, capturing dust particles from around the comet nucleus that it then returned to Earth in a capsule for study. But with sufficient fuel supplies still in its tanks, the probe was re-tasked by the US space agency to visit Tempel 1.
This extended mission has been dubbed Stardust-NExT, which is short for "New Exploration of Comet Tempel 1".

The "new" element relates to the fact that Tempel 1 has already been seen up-close by the Deep Impact spacecraft.
During that encounter in 2005, a washing-machine-sized block was fired at the comet to kick up surface material to study its composition.

But Deep Impact's swift passage across the face of the comet meant it never got to see the crater made by the projectile. Stardust will.
What is more, Stardust will be able to see what else has changed on Tempel 1 in the two trips it has since made around the Sun.

The closer a comet gets to our star, the more material it loses as ices vaporise and dust particles are carried away into space.

"Deep Impact saw only about a third of the surface and we'd like to see more," said Joe Veverka, the Stardust-NExT principal investigator from Cornell University
"And we'd like to see more of the areas that Deep Impact saw, including the smooth flows which apparently suggest that comet nuclei are not only modified by processes from the outside but also by internal processes."

Scientists observed a series [of] layered terrains on Tempel 1. They hope the new data can help explain presence of these features and whether they have something to do with the comet's original construction.

"One idea is that there were two proto-cometary bodies that collided at very low speeds and smooshed together to form a comet like a stack of pancakes," speculated Pete Schultz, a mission co-investigator from Brown University.

etc...

http://www.bbc.co.uk/news/science-environment-12433138
 

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'Exocomet' numbers nearly tripled in new study
By Jason Palmer, Science and technology reporter, BBC News, Long Beach, California

A new haul of comets around distant stars has been unveiled, more than doubling the number we know of.
The first such "exocomet" was discovered in 1987 but since then only three more had been found.
At the 221st American Astronomical Society meeting in the US, astronomer Barry Welsh gave details of seven more.
Proving that comets are common in the Universe has implications for their role in delivering water or even the building blocks of life to planets.

Comets such as Halley's Comet, which makes a long, elliptical path passing near the Sun every 75 years, make themselves known through their long "tails" of gas and debris that come off as they approach their host stars.
It is this that Dr Welsh and his collaborator Sharon Montgomery of Clarion University have measured, using the McDonald Observatory in Texas.

The exocomets' tails absorb a tiny amount of their host stars' light - and the absorption changes with time as the comets speed and slow.
With patient observation, the pair came up with seven new exocomet sightings.

In our Solar System, many comets come from the Kuiper belt, a disc of debris beyond the orbit of Neptune, and from the Oort cloud, an even larger and more distant debris disc.
Dr Welsh explained that these discs were characteristic "leftovers" of planet formation as we now understand it.
"Imagine a 'cosmic building site', where the building has already been made - the planets," he told BBC News.
"We're looking at what's left: the bricks, the mortar, the nails - the debris discs have comets, planetesimals, and asteroids."

But something must disturb the comets' orbits, putting them on a course toward their star.
While collisions between comets might do that, it is believed that the gravity of planets nearby can do the job.
In fact, in 1987 when the first exocomet was spotted around the star Beta Pictoris, it was hypothesized that a planet may have been responsible - and in 2009, a giant planet was found here.

Recent years have seen a marked focus on exoplanets, with 461 new candidates and the prospect of billions more that are Earth-sized announced on Monday.
The new study helps illuminate the interplay between those planets and the debris discs from which they came - and in turn help to explain how our own Solar System formed.

"It looks as though the planet building process is very similar in many, many cases - and in order to prove that you need to look not only at the final product and also at the things they were made from," Dr Welsh said.

The finding of more and more comets also raises the possibility that comets could play a crucial role in delivery services.
"There are two theories: one is that comets early on in our Solar System's history brought ice to the planets, the ice melted and formed oceans," Dr Welsh explained.
"And the other one, perhaps a bit more far fetched, is that the organic [molecules in comets]… were the seeds of life on planets. And if comets are so common throughout all planetary systems, then perhaps life is as well."

http://www.bbc.co.uk/news/science-environment-20954899
 

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Sky watchers ready for rare comet
A comet with a glowing tail makes a once-in-a-lifetime appearance in the evening sky this month
By Telegraph reporters
9:07AM GMT 03 Mar 2013

Comet 2011 L4 Panstarrs has taken millions of years to travel out from the Oort cloud - a huge colony of icy objects at the edge of the Solar System.

Throughout the month Panstarrs will be visible low in the west.
There could be good picture opportunities on March 12 and 13 when it brushes past the crescent moon.

However, it might be difficult to see the object without binoculars or a telescope.
"It's going to be in the twilight sky and not as bright as we had originally hoped, but comets are terribly unpredictable," said Robin Scagell, vice-president of the Society for Popular Astronomy.
Towards the end of the month the comet will fade but rise higher in the sky, possibly making it easier to see.

On around March 30 its northward path will take it close to the Andromeda galaxy.
"That could provide a good picture for sky watchers," said Mr Scagell.
Panstarrs is not expected to revisit our skies for 110,000 years. [I won't hold my breath, then.]

Another comet is expected to make a more dramatic appearance in November.
Comet Ison will fly closer to the Sun, causing it to light up. Experts say it could be bright enough to see in daylight, but from the UK it will only be visible low in the sky.
"It might be fantastic for a few days, but it's difficult to predict ahead of time," said Mr Scagell. "As ever we have to be cautious. What you might see is the tail of the comet sticking up above the horizon."

http://www.telegraph.co.uk/science/9905 ... comet.html
 

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Bright comet 'lighting sky' as it flies by Earth
By Rebecca Morelle, Science reporter, BBC World Service

Stargazers could enjoy a rare spectacle as a bright comet swings into the Northern Hemisphere.
The icy mass, called C/2011 L4 Pan-Starrs, should be visible with binoculars or a telescope from 8 March.
But in the following days, it will become even brighter and could be seen with the naked eye.
Astronomers in the Southern Hemisphere have already been treated to a fly past, with reports that the body was as bright as stars in the Plough.

Mark Bailey, director of the Armagh Observatory in Northern Ireland, said: "We have great hopes for this comet. Of course we are always very cautious - even now we don't know how bright it is going to get - but we are keeping out fingers crossed."

The comet was first discovered in June 2011, spotted by the Pan-Starrs telescope (hence its name) in Hawaii as a faint object more than a billion kilometres away.

Astronomers believe it originated in the Oort Cloud, a region of space packed full of comets, and has been hurtling towards the Sun for millions of years.
It is thought to be a non-periodic comet, which means this could be the first time it has ever passed through the inner Solar System, and it might not return.

On 10 March, it will make its closest approach to the Sun, passing at a distance of about 45 million kilometres.
As it heats up, the ice and dust in the Pan-Starrs' outer crust turn to gas, making it bright in the night sky. Solar wind and pressure from sunlight gives the body its characteristic double tail.
Prof Bailey said: "The closer you get to the Sun, the more of this material is ejected, and therefore the brighter the comet can be."

He said that the nucleus of the comet was estimated to be about 20-30km in diameter, but the gas and dust surrounding meant it could span more than a million kilometres.

[Map of positions during March.]
The comet will appear to move through the constellations of Pisces, Pegasus and Andromeda.
The 12 and 13 March could provide the best viewing opportunity. At this time, it will move further from the Sun, but should be easier to spot in the night sky, providing it is a clear night.

"After sunset, scan the horizon roughly in the western direction. On the 12 and 13 March, there is a nice association with the thin crescent Moon," advised Prof Bailey.
"You can use the Moon as a guide, and search just down or to the left of the Moon. Through binoculars you should be able to see the head of the comet and certainly the two types of the tail."

He added: "I would always advise people to hunt for comets with binoculars, but if you have found it with binoculars, have a good hunt around and see if you can see it with the naked eye. That's quite a challenge - but it is a wonderful thing to have seen."

After this, the comet will begin to appear later and higher up in the night sky. And then, as April draws near, it will vanish back into the depths of space where it can only be seen with large telescopes.

If the weather proves poor during this period, astronomers could be offered another chance for a celestial delight at the end of the year when comet Ison should grace our skies.
Flying four times closer to the Sun than Pan-starrs, it could prove even brighter. But there is also a chance that it could break up.

http://www.bbc.co.uk/news/science-environment-21701641
 

rynner2

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rynner2 said:
Bright comet 'lighting sky' as it flies by Earth
By Rebecca Morelle, Science reporter, BBC World Service

Stargazers could enjoy a rare spectacle as a bright comet swings into the Northern Hemisphere.
The icy mass, called C/2011 L4 Pan-Starrs, should be visible with binoculars or a telescope from 8 March.

....

It is thought to be a non-periodic comet, which means this could be the first time it has ever passed through the inner Solar System, and it might not return.

....

http://www.bbc.co.uk/news/science-environment-21701641
According to the orbital data given on Heavens Above, it is on a hyperbolic orbit. Which means it's a one-time visitor to our solar system, and will continue to recede ever more slowly, until, by chance, in billions of years time, it might encounter another star. In the icy cold of interstellar space it won't change much, and will probably outlast humanity.

All the more reason to see it now. I went out this evening, but the lie of the land is wrong, and there are too many trees and buildings. I couldn't even see the crescent moon, and Pan-Starrs would have been even lower in the sky! If it's clear tomorrow, I might try somewhere better, but my knee is bad and the evening buses are not very convenient. Ho hum...

Hey, Pan-Starrs, can I come with you?
 

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Last night and tonight I went out to Carn Marth, which promised good views. Last night was very clear, but too much cloud in the west. Tonight there was less cloud, but it still seemed likely to make a comet search unsuccessful, so I gave up and came home early.

Possibly that was a mistake, as the sky seemed to clear later, but I didn't fancy hanging around on a cold evening when the buses only run once an hour.

But the new moon (with 'the old moon in his arms') was clearly visible, although I failed to get a decent photo!

However, tomorrow we have rain forecast almost all day - it's the sunlight reflecting off the clouds to the west of Britain that gives rise to 'the new moon with the old moon in his arms'.

The good news is that the comet has crossed the ecliptic heading north, which will bring it higher above the horizon, which will help in finding it, provided it doesn't fade too fast.
 

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I'll never get on this at this late stage: :(

German airline launches comet-viewing flight
A German travel company is offering passengers a chance to view the comet Pan-STARRS on a new stargazing flight this weekend.
By Soo Kim
11:12AM GMT 13 Mar 2013

The Bonn-based tour operator, Eclipse Travel, will fly 88 passengers on an Air Berlin flight this Saturday to see the comet Pan-STARRS, the tail of which is predicted to be at its longest and most visible on March 16.

The company claims passengers on the Boeing 737-700 flight will have clearer views of the comet from 11,000 metres (36,000 feet) high, where the air is thinner and more transparent, than those seeing it from the ground. The two-hour journey will follow a zig-zag flight path to allow passengers a chance to get the best possible views.

Ticket prices range from £168 ($240) to £444 ($663) and can be booked on the Eclipse Travel website. Flyers can reserve either two adjacent seats or an entire row if they don’t wish to share a window seat. The flight will also serve a special buffet before taking off at 7.25pm.

Pan-STARRS can be viewed in the southern hemisphere and is the first of two comets to be visible to the naked eye this year. NASA scientists believe its 100 million mile trajectory from Earth could rival the constellation The Plough in brightness :?: , but also noted the comet may disappoint if it crumbles under the heat and gravitational pull of the sun.

Comet ISON is also expected to pass by the Earth this November and predicted to be one of the brightest comets to ever be seen, possibly surpassing the brightness of the moon.

http://www.telegraph.co.uk/travel/trave ... light.html
 

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A Point of View: Crowd-sourcing comets
Astronomers in the 17th Century understood the value of sharing information in order to plot the path of comets. Now modern science is using the internet to follow their example, says historian Lisa Jardine.

On three consecutive nights this week I was one of the many amateur stargazers across the northern hemisphere scanning the skies for a brand new comet, unromantically named C/2011 L4 Pan-Starrs, which has just become visible over Britain.

Judging from posts on comet Pan-Starrs' Facebook page (in 2013 a comet has its own social network complete with "likes", comments and shares), I am not alone in having been thwarted by the weather.

Happily, a second comet - comet ISON - is set to pass between the Earth and Sun in the autumn, and astronomers expect that it will shine brightly enough to be visible even during the day. Perhaps then I will get my view of a fiercely blazing celestial body with a glowing tail.

In earlier times, a succession of comets was greeted with less equanimity than today. When two comets passed over London in quick succession in 1680-81 there were many who were more superstitiously fearful that they were harbingers of doom. Spectacular comets had appeared in the night sky in 1664 and 1665. Had not these presaged the visitation of the plague on London and the Great Fire the following year?

In early November 1680, a comet appeared, so bright that it was visible by daylight, and was tracked heading steadily in the direction of the Sun until the end of the month. In mid-December, another comet appeared in the early morning sky, this time heading away from the sun. Its tail was particularly long and spectacular.

The diarist John Evelyn held the properly scientific view that comets "appear from natural causes". "Yet", he added in his diary entry for 12 December 1680, "they may be warnings from God, as they commonly are forerunners of his animadversions."
The scientific members of the Royal Society - of whom Evelyn was one - put aside superstition and busied themselves with due professional diligence observing and plotting the trajectory of the first, and then the second comet.
Christopher Wren, Robert Hooke and Isaac Newton charted and recorded its nightly positions. Edmund Halley, on his way to Rome on Royal Society business, observed its progress across the night sky with Cassini at the Paris Observatory.

Meanwhile, astronomers across Europe also watched and plotted, collaborating with their British counterparts by sending in their calculations to the Royal Society for collation with their own results in an early example of something like crowd-sourced data collection.

At the Royal Observatory in Greenwich - established by Charles II in 1675 - the first Astronomer Royal, John Flamsteed was appointed by the king to produce better star charts to increase the accuracy of navigation at sea. He assiduously followed the progress of the comets night after night. Flamsteed would spend more than 40 years assembling meticulous records for his star catalogue, which would eventually triple the number of entries in the previously used sky atlas.

In spring 1681, after close study of the data he had compiled, Flamsteed proposed that the two comets observed in November and December of 1680 were not two comets at all, but rather one comet travelling first towards the Sun and then sharply away from it. Newton disagreed. "To make ye comets of November and December but one is to make that one paradoxical," he told Flamsteed.

Sometime between the spring of 1681 and the autumn of 1684, however, Newton changed his mind. As obstinately as he had opposed Flamsteed's suggestion, he was now convinced that it had indeed been a single comet that had rounded the sun in a tight, hairpin turn in November and December 1680. And he proposed that comets, like planets, moved around the sun in large, closed elliptical orbits under the influence of the new force he was in the process of formulating mathematically - what we now call gravity.

As the revolutionary theory of gravitational attraction took shape, the comet of 1680 became an important test case in Newton's argument. Characteristically, however, Newton refused to give Flamsteed any credit for having been the first to propose to him that comets moved under the influence of a central, attracting force.
So Flamsteed was furious when he learned in 1685 that Newton had got hold of all his data, in order "to determine ye lines described by ye comets of 1664 and 1680 according to ye principles of motion observed by ye planets".

Flamsteed's observations had been obtained by dubious means by Edmund Halley, who was once Flamsteed's assistant at the Greenwich Observatory. Halley was now a pivotal figure of the Royal Society and the fact-checker and financial backer for the preparation of Newton's ground-breaking book, Principia Mathematica.

The scientific community-wide collaborative observations of the 1680 comet, including Flamsteed's purloined data, were subsequently printed as important evidence in Newton's Principia in 1687. There Newton established (among other things) the inverse-square law of gravitational attraction.

Twenty years later, Flamsteed would again obstruct scientific progress by refusing to publish his by now huge amount of accumulated data, in the form of star charts for the use of sea captains. Declaring that he was unwilling to risk his reputation by releasing unverified data, he kept the incomplete records locked up securely at Greenwich.
Newton maintained that Flamsteed was a public servant, and therefore his work was public property, but to no avail.

So in 1712, Newton, by now president of the Royal Society, together with the indefatigable Halley, again obtained the data by subterfuge, and published a pirated edition of a new star catalogue. Undeterred, Flamsteed managed to retrieve 300 of the 400 copies printed and destroy them. His own star catalogue, the Historia Coelestis Britannica, was eventually published posthumously by his wife and co-observer at the Observatory, Margaret Flamsteed, in 1725.

The enthusiastic collaboration among the wider community of 17th Century astronomers, across nations and continents, continuing to exchange astronomical observations even when their countries were at war with one another, is in stark contrast to Flamsteed's relentless withholding. His refusal to release his valuable data, and his insistence that his work was his personal intellectual property, slowed progress on an important scientific project.

By contrast, the sharing of data among European astronomers who took part in the tracking of the 1680 comet looks surprisingly modern. It is directly comparable with the current drive, particularly within the scientific community, towards open data and data-sharing.

Elegantly echoing the activities of these early, ground-breaking astronomers, what we now refer to as "crowd-sourcing" has recently been shown to be able to determine the trajectory of a comet as spectacular as the one observed in 1680.
In October 2007, Comet 17P/Holmes briefly became the brightest object in the solar system, arousing the interest of amateur astronomers worldwide. Using search engines, Dustin Lang from Princeton University and David Hogg at the Max-Planck-Institute in Germany gathered more than 2,000 images of the comet from all kinds of online sources.

They ran the pictures through Astrometry.net, which can recognise images of the sky and measure star patterns, and identified more than 1,000 that had captured the progress of Comet Holmes. They were then able to superimpose a large number of the comet images, and to arrange them as a sequence by carefully aligning the stars.

Many of the images were time-stamped, so that when they were superimposed the comet's precise path across the sky was clearly visible. Finally, Lang and Hogg compared their orbital data with observed information from Nasa's Space Laboratory in California, and found a close match.
"You can do high-quality quantitative astrophysics with images of unknown provenance on the web," Lang and Hogg conclude. "Is it possible to build from these images a true sky survey? We expect the answer is 'yes'."

It is to be hoped that long-running, ill-tempered quarrels over data, like that between Newton and Flamsteed, are a thing of the past. And that it is the collegial and good-natured collaborations among the astronomers of Europe in the final decades of the 17th Century that will in future serve as a model for the global teamwork that underpins so much of today's scientific activity.

There is some anxiety currently in the academic community, especially in the humanities, over government insistence that publicly funded research must in future be open access. I declare myself to be a strong advocate for collaboration and sharing of data in all fields of intellectual endeavour. There may be transitional difficulties. But we are, in the end, all part of a common quest for greater knowledge and understanding.

http://www.bbc.co.uk/news/magazine-21802843

Several sidebars on page.
 

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Rosetta: Riding a ‘bucking bronco’ in space

The excitement is mounting. We're going to be talking about comets an awful lot in the coming months.
First of all, we have Comet Ison to enjoy. We hope.
This mountain of ice and dust has come hurtling in from the outer Solar System and is about to swing around the Sun.
At closest approach on 28 November, it will be no more than 1.2 million km (800,000 miles) from our star's boiling surface.

The big question is: will it survive the encounter? "Sungrazers" like Ison very often just fall apart. But if it can remain intact, this "dirty snowball" will swing back out past the orbits of the inner planets, potentially throwing off huge streams of gas and dust.

The comet could appear as a great arc across the sky, no binoculars required. Then again, it might not. Comets are notoriously unreliable. ;)
Recent observations have suggested that Ison might fall short of being spectacular, but could still put on a decent show. We won't know for sure until December.

And come December, we'll all have started looking forward to the space mission of 2014: Rosetta.
This is the European Space Agency probe that was launched way back in 2004. It's spent the past nine years working its way out to the orbit of Jupiter, to chase down Comet 67-P/Churyumov-Gerasimenko.
The plan is for Rosetta to circle and track this comet as it sweeps in towards the Sun.

The big highlight, though, will be the deployment of the probe's Philae lander. It's going to try to lock down on 4km-wide 67-P and ride it.
How long Philae could withstand any outgassing as the ices heat up on approach to the Sun is anyone's guess. Will 67-P be a "bucking bronco"?

"Philae's got screws and harpoons to hold it down," says Dr Matt Taylor, the Rosetta project scientist.
"I have to be confident we'll succeed. We'll be investing a lot of time before the landing trying to find the best place to put down."

Telescopic investigations are encouraging. 67-P appears to have three main areas that produce jets, and these will be avoided. But on the whole, the comet's recent passes of the Sun have been relatively smooth - it hasn't been prone to explosive outbursts.

Rosetta is a long way from Earth currently. Probes sent out to the vicinity of Jupiter would usually use radioisotope batteries, but the European spacecraft was equipped only with solar panels.
As a consequence, it was put to sleep in 2011 to try to conserve energy.

Controllers at Europe's Space Operations Centre in Darmstadt, Germany, are not in contact with Rosetta at present.
They're keeping their fingers crossed that an internal alarm clock will rouse the probe on 20 January 2014.
Once awake, it can activate its instruments and prepare for the rendezvous. Needless to say, the alarm clock event has quite a bit of tension associated with it.

"Before turning everything off, we spun up the spacecraft to keep it stable," explains Prof Mark McCaughrean, a senior official in Esa's science directorate.
"At the moment, Rosetta's not pointing its high-gain antenna at the Earth. So, we rely now on that alarm clock going off on time, because if it doesn't we'll have great difficulty communicating with the spacecraft.
"But we do expect it to go off. And when it does, Rosetta will warm up, spin down and point to Earth again, and we will receive a signal. We don't know exactly when we'll receive that signal. It will happen in a window."


Here's a timeline for the key events:

20 January 2014: Wake-up from hibernation
Mid-March 2014: Check-out instruments
21 May 2014: Major rendezvous manoeuvre
6 August 2014: Arrive at Comet 67-P
27 August 2014: Start global mapping
11 November 2014: Philae deployment (at about 450 million km from the Sun)
13 August 2015: Perihelion - closest approach to the Sun (at about 185 million km from the Sun)
31 December 2015: Nominal end of mission (although Esa is unlikely to switch off a working Rosetta)

As you can see, it's quite drawn out. We talked of the "minutes of terror" endured waiting for Nasa's Curiosity rover to land on Mars last year. Rosetta is likely to give us months of torture.

Yes, there will be periods of relative inactivity, but there will also be moments of intense drama along the way. The wake-up, the orbit insertion, the Philae landing and the close approach to the Sun could make Rosetta one of the most remarkable missions we've ever seen.

I'm expecting the pictures to be sensational.
The main camera system onboard Rosetta is Osiris (Optical, Spectrocopic and Infrared Remote Imaging System). It has wide-angle and narrow-angle views and will be returning high-resolution perspectives of the comet's icy core, or nucleus. Osiris has already demonstrated its remarkable capability in a pass of Asteroid Lutetia in 2010.

The principal investigator is Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Katlenburg-Lindau, Germany.
"We will get thousands of images on approach," he says. "Our [best] resolution is on the order of centimetres and we will be mapping to find suitable landing sites. It is unknown whether we will catch the moment of landing - it is pure speculation right now. But it is our aim to present a movie and to get an image of Philae on the surface."

There's a lot of science to be done, of course.
Comets contain pristine materials from the formation of the Solar System. They give us insights on a time billions of years ago that we cannot get from studying planetary rocks.

"There are many very interesting questions related to comets," explains Dr Jessica Agarwal, also of MPS.
"One is to study whether they brought the water to Earth. It's thought that the water that is now on the Earth is not a remnant from the time of formation of our planet but was delivered later when it was cool enough to retain it.

"Comets are rich in water. One theory is that they may have impacted in large numbers in the past - since they would have been more numerous back then - and could have delivered enough water to fill Earth's oceans. And they may even have delivered organics. These are the things we'd like to understand with Rosetta."

http://www.bbc.co.uk/news/science-environment-24134698
 

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'Black glass' could be first comet chunk found on Earth
http://www.newscientist.com/article/dn2 ... lxkhFB4JBw
00:47 10 October 2013 by Lisa Grossman

A charred black pebble found in the Egyptian desert may be a piece of a comet that shattered near Earth about 28 million years ago. If so, the stone would offer a first close-up glimpse of rock that formed at the very edges of the solar system.

The 30-gram stone was discovered by Egyptian geologist Aly Barakat in December 1996 in a part of the Sahara desert near the border with Libya. The 6000-square-kilometre region is famous for being strewn with fragments of pale green glass, thought to have formed millions of years ago during a meteorite strike. Ancient Egyptians used a piece of this Libyan desert glass to make a scarab for King Tutankhamen's burial jewellery.

Barakat thought the darker stone might be a kind of black diamond called carbonado, so he sent a sample to Marco Andreoli at the University of the Witwatersrand in South Africa.

Years of analysis revealed that the rock may be something even rarer: the first large-scale piece of a comet. Until now, scientists had found only grains of cometary material in Earth's atmosphere and in carbon-rich dust in Antarctic ice. NASA's Stardust spacecraft also returned a few dust grains from comet Wild 2 in 2006.

"We can study material from the outermost solar system for the first time," says Jan Kramers, a member of Andreoli's team at the University of Johannesburg in South Africa. "This is actually quite exciting."

Space diamonds

Kramers and his colleagues subjected a 1-gram sample of the stone to a barrage of tests to determine its composition. They found that the rock has a high ratio of oxygen to carbon – an unearthly mix similar to that seen in the Wild 2 samples and Antarctic dust fragments. They also found that the black rock contains chunks of diamond, which could have formed when its carbon was compressed by the high pressure of an impact.

"People think of comets as a dirty snowball made of ice that evaporates in the sunshine," says Kramers. "But the heat-resistant part of comets is carbon, and if you compress it, heat it up and subject it to shock, you get some kind of glassy carbon. This appears consistent."

The team then heated other fragments of the rock to 1800?C to release gases trapped inside. They detected the noble gases neon, krypton, xenon and argon. The argon isotope ratios confirmed that the rock is not originally from Earth. The other isotope ratios look nothing like those found in known meteorites, all of which came from asteroids, rocky objects that formed inside the orbit of Jupiter.

The team thinks that a comet hit our atmosphere and exploded over the desert, akin to what happened over the Tunguska region of Siberia in 1908Movie Camera. The explosion heated and compressed the sand to create the Libyan desert glass. The black stone is a piece from the comet's solid core, which absorbed noble gases from our atmosphere on its way down and turned its carbon into diamond on impact.

"You have Libyan desert glass, which is basically molten Earth surface material, and you have a piece which is basically a shocked fragment of cometary core in the same area, so you start putting 2 and 2 together," says Kramers.

Rosetta comet

"It is definitely a strange object, different from any meteorite we have sampled so far," says Ingo Leya at the University of Bern in Switzerland, who was not involved in the analysis. But while Leya agrees that the rock probably comes from space, he is not yet convinced it is a sample of a comet. "The problem is, we have little cometary material as a standard to compare with. Therefore it is difficult to firmly conclude or exclude that this meteorite comes from a comet."

The European Space Agency's Rosetta spacecraft is heading for a rendezvous with comet 67P/Churyumov-Gerasimenko (Chury) in 2014. It will deploy a small lander that will examine that comet's core up close, perhaps helping to settle the matter. In the meantime, Kramers hopes to find more samples of the Egyptian stone for study.

"It's a very inaccessible part of the Sahara, but there must be more material lying around," he says. "To go there and try to find more, you have to spend a lot of money, but not as much as to go and capture a comet in outer space."

Journal reference: Earth and Planetary Science Letters, DOI: 10.1016/j.epsl.2013.09.003
 

rynner2

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Remember this?
rynner2 said:
Rosetta: Riding a ‘bucking bronco’ in space

The excitement is mounting. We're going to be talking about comets an awful lot in the coming months.
First of all, we have Comet Ison to enjoy. We hope.
This mountain of ice and dust has come hurtling in from the outer Solar System and is about to swing around the Sun.
At closest approach on 28 November, it will be no more than 1.2 million km (800,000 miles) from our star's boiling surface.

The big question is: will it survive the encounter? "Sungrazers" like Ison very often just fall apart. But if it can remain intact, this "dirty snowball" will swing back out past the orbits of the inner planets, potentially throwing off huge streams of gas and dust.

The comet could appear as a great arc across the sky, no binoculars required. Then again, it might not. Comets are notoriously unreliable. ;)
Recent observations have suggested that Ison might fall short of being spectacular, but could still put on a decent show. We won't know for sure until December.

http://www.bbc.co.uk/news/science-environment-24134698
I checked HeavensAbove for an update. Ison is still only about 13.5 magnitude (way below naked eye visibility), but a decent telescope or large bins might find it.

It's in Leo at the moment, as is Mars. Mars is a few degrees east of Regulus, and Ison is a little east of Mars.

But Leo, Regulus and Mars don't rise until about 0300, just north of east, so it's not worth getting excited about yet! (Especially with all the rain clouds over Britain at the moment!) But it will get a few minutes earlier each night, so fingers crossed for November...
 

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Once in a lifetime galactic fireworks display due from Comet Ison
Comet Ison, first spotted a year ago, is now visible to the naked eye and will continue to brighten as it hurtles toward the sun
By Hayley Dixon
7:41AM GMT 18 Nov 2013

A once in a lifetime galactic fireworks display appears to have begun after astronomers confirmed that Comet Ison, dubbed the “comet of the century”, has entered the Earth's orbit.
The comet has dramatically brightened with an outburst of gases in recent days as it draws ever closer to the sun, the Times reported, and if it survives it could be the greatest celestial display in more than 300 years.
It is now visible to the naked eye and is expected to continue brightening over the next few weeks until it outshines the moon.

The Comet Ison is so named because it was first spotted on photos taken by Russian’s Vitali Nevski and Artyom Novichonok using the International Scientific Optical Network telescope last September, while it was still 585 million miles from the sun.

The ball of ice and dust is thought to originate from the Oort cloud, a giant swarm of icy remnants from the creation of the solar system, which sits 93 trillion miles from Earth.
Although other comets, such as Hale-Bopp, are thought to have originated from the cloud this is the first “sungrazer” to have come from the space on the edge of the solar system in 200 years.

Ison, which is travelling at 234 miles (377km) a second, is due to come closest to the sun on November 28, when it is expected to pass 720,000 miles from the solar surface and heat up to 2,760C (5,000F).
If predictions are correct the galactic show will rival the Great Comet of 1680, which had a tail 90 million miles long and could be seen during the day because it was so bright, leading many to think it was a punishment from God.

Even if Ison breaks up before then, or fails to survive its perihelion, its closest scrape with the sun, experts believe its death throes could be spectacular and say they have already learnt a great deal from it.
Matthew Knight, an astronomer at the Lowell Observatory in Arizona and a member of Nasa's Ison observation campaign, said: “Astronomers are getting the chance to study a unique comet travelling straight from 4.5 billion years of deep freeze into a near miss with the solar furnace using the largest array of telescopes in history.
“No matter what happens, now that Ison has made it inside Earth's orbit, any or all of these scenarios are scientifically exciting
." :D

If the comet – which is best observed through a telescope or strong binoculars – survives its scrape with the sun it will reach its most brilliant in early December.

http://www.telegraph.co.uk/science/spac ... -Ison.html

3-D graphic of orbit on page - rather intrusive, actually!

I'll check Heavens Above for further details, will post them when there's a chance of clear weather. But if it does eventually outshine the moon, I won't have to bother!
 

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Ison will be in the morning sky tomorrow at about 0700, low in the SE, mag. 5.7, so a pair of 7 x 50s should find it. It should be just W of Mercury, mag, -0.5, which may be the brighest object in that part of the sky at that time, so a good chance to see Mercury too! The just-past-full moon will be near setting, so will be no problem, but Sunrise is at 0740...

The comet's moving really fast now, so everything will change in the coming days as Ison approaches the sun and becomes harder to see...
It disappears behind the sun on the 28th of the month. Will it survive? Exciting times!
 

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On the 23rd, Ison will cross the orbit of Mercury, and that morning (UK time) it will also be its closest to Mercury in our sky, although sadly much closer to the horizon than the planet.

In fact, according to the Telegraph graphic, it will be not be seen from the 21st Nov to December 5th, when it reappears on the other side of the sun, becoming an object in the evening sky. Magic!


EDIT: A periodic comet's orbit has an eccentricity of less than 1 - its orbit is elliptical.

Heavens Above gives Ison's orbit an Eccentricity of 1.000002. This means it is in a hyperbolic orbit, and (assuming it leaves the vicinity of the sun relatively unscathed) it will leave the solar system completely, never to return.
 

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Now I'm going to quote myself, twice!

First, from my previous post:
On the 23rd, Ison will cross the orbit of Mercury, and that morning (UK time) it will also be its closest to Mercury in our sky, although sadly much closer to the horizon than the planet.

In fact, according to the Telegraph graphic, it will be not be seen from the 21st Nov to December 5th, when it reappears on the other side of the sun, becoming an object in the evening sky. Magic!
Secondly, from another thread - this contains quotes in bold from Exodus:
Well, Professional Astronomers can play this game too!

I refer to Victor Clube and Bill Napier, who proposed (in at least a couple of books) that many of the disasters and strange events of early recorded human history were due to meteorite bombardment when a major comet broke up in the solar system.

By day the LORD went ahead of them in a pillar of cloud to guide them on their way and by night in a pillar of fire to give them light, so that they could travel by day or night. 22 Neither the pillar of cloud by day nor the pillar of fire by night left its place in front of the people.

This is a description of the comet, with its long tail, seen by night and day.

The pillar of cloud also moved from in front and stood behind them, 20 coming between the armies of Egypt and Israel. Throughout the night the cloud brought darkness to the one side and light to the other side; so neither went near the other all night long.

This is a description of the comet after it has passed perihelion (its closest approach to the sun), when it appears in the opposite part of the sky - it 'moved from in front and stood behind them'.

Now I'm not saying that Clube and Napier are right, but they do put together a very well argued and presented case.

And this is my point - stuff that happened thousands of years ago, of which we have only fragmentary remaining descriptions (many of which may have been re-interpreted in the following centuries) can have multiple 'explanations' in the light of modern science. Someday, maybe, we'll unearth sufficient evidence to work out what really happened.

In the meantime, we can only keep an open mind as we analyse any new ideas put forward.

http://www.forteantimes.com/forum/viewt ... 916#775916
And these are some of the ideas that will be in my mind in the next few weeks. Fascinating to think that we may be about to witness something similar to what may have been seen in the times of the Israelite Exodus from Egypt. 8)
 

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Mainly clear skies this morning. I did get up a couple of times hoping to see Mercury and Ison, but I couldn't be bothered to get dressed and go outside. From indoors, however, trees blocked the view to the SE, and the corridor lights were too bright anyway... :(
 

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I'm really hoping to get a good view of this comet at some point. I hit the road quite early most days to go to work, so if skies are clear, I may be lucky.

I remember Halley as being a bit disappointing, but there was a great visible comet in the mid-90s that I recall (Hale-Bopp, from memory? Yes, a quick Google confirms this). I had a photo somewhere...

Here we are - Hale-Bopp, April 1997:

 

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Peripart said:
I'm really hoping to get a good view of this comet at some point. I hit the road quite early most days to go to work, so if skies are clear, I may be lucky.
Ison has brightened to mag. 5.2, but that's still only as bright as dim naked eye stars. So as it enters the dawn twilight it will become harder to see without bins, unless there is some spectacular outburst.

No doubt some space-based telescopes will keep track of it while it's invisible to us on Earth.

Most probably now the main firework display will be after perihelion, when it will be in the evening sky.

(I also wanted to see Mercury, which is an elusive animal itself - I've only seen it twice in my life! But it passed maximum western elongation yesterday, so it too will soon drop back into the Sun's glare... :( )
 

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I managed to spot Mercury earlier this year, in the south-eastern* pre-dawn sky - that's the only time (well, I saw it on a couple of mornings in the same week, but I only count it as one occasion) I've seen it, as far as I'm aware. If I remember correctly, it as only due to a posting on this site that I knew where and when to look.


*If SE is factually incorrect, then it's my memory that's slightly amiss. I did see it, I promise, but the exact direction may not be as I recall. Just as, in my mind, that comet picture above was taken near Sutton Coldfield, though it might have been Solihull (or let's be honest, pretty much anywhere starting with an S), in the same way, I seem to recall seeing Mercury over the Belfry towards Kingsbury.

EDITED for dodgy spelling
 

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Comet Ison brightens, but without fireworks
By Paul Rincon, Science editor, BBC News website

Astronomers are getting good views of Comet Ison, but the icy object has not yet lived up to the high expectations set for it.
Ison has been brightening over the last two weeks, letting rip two giant outbursts of gas and dust.
But it has not yet produced the spectacular sky show some had predicted.

The comet is currently hurtling towards the Sun and is set for its closest approach on 28 November.
Ison might not survive its encounter with the Sun, but if it does, it could yet dazzle stargazers with a bright display.

A photo taken by astrophotographer Damian Peach on 15 November showed many separate streams inside the dusty tail. [Shown on page.]
Recent images appear to show a bifurcation, or disconnection, in the comet's tail; but this could be related to a general increase in activity.

A BBC Horizon special about the comet will be screened on Saturday.

Comet Ison was fairly quiet until 1 November 2013, when a first outburst doubled the amount of gas emitted by the nucleus.
On 13 November, a second giant outburst shook the comet, increasing its activity by a factor of 10.

This time last year, commentators were predicting that the comet would be "spectacularly bright", and visible in broad daylight. But Ison has not, as yet, lived up to those expectations.

[Another view of the comet was taken by the TRAPPIST telescope at the La Silla Observatory in Chile on 15 November]

"Most people I've spoken to don't think it's going to be that bright," said Dr Robert Massey, from the UK's Royal Astronomical Society.
"I would really like it to be bright... but it's still quite hard to see now."
He added: "I got up to see it this morning and was defeated by cloud." 8)

Not withstanding cloudy weather, the comet is bright enough to be seen with a good pair of binoculars from dark sites, and is visible in morning skies towards the East.

On 28 November, the comet swings round the Sun, approaching to a distance of just 1.2 million km from its surface, which is just a little less than the diameter of the Sun itself. :shock:

This event, known as perihelion, will cause the comet to further brighten and will make more of comet's ice sublimate (change directly from a solid to a gaseous state).

But the heat could also cause the nucleus to break up into small fragments, which would completely evaporate by the time the comet moves away from the Sun.

A Horizon special about Comet Ison will be screened on BBC Two on Saturday at 2115
[That should include the best pics to date.]

http://www.bbc.co.uk/news/science-environment-25001732
 

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Woke at about 0630 with a bright moon shining through my bedroom window. Thinking this might be my last chance to see Mercury and the comet, I flung some clothes on, added a coat and hat, grabbed my bins and went outside ...to find it had clouded over! Not thick cloud, but I know from experience that perfect visibility is necessary to see Mercury, let alone a faint comet low in the sky.

So I went back to bed, put the radio on, and some chap there was talking about Ison!

So now it's fingers crossed that Ison survives perihelion and puts on a show in December.
 

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This new BBC article has altered my understanding of Ison's orbit. I'd expected it to reappear in the west after passing the sun, but no...

Ison: The comet of the century
By Charles Colville, Producer/director, Comet of the Century: A Horizon Special

If we're lucky, then in just a few days time we could witness one of the most spectacular sights in the night sky for a generation or more.
Astronomers hope that on 3 December a comet will appear on the eastern horizon - Comet Ison.
For the whole month of December, millions of people across the northern hemisphere should be able to see its tail, which is several millions of kilometres long, stretching across the dawn sky.

Ison has come from the Oort cloud, a belt of comets on the very edge of the Solar System, where it has been for the last 4.6 billion years.
What makes Ison so special is that it is a "sungrazer". Many comets pass through the Solar System every decade, but very few go through the corona of the Sun. Ison will do just that.

Its passage through the corona, which happens on 28 November, will be watched with great interest by astronomers across the world.
It's not known exactly what effect the great heat and gravitational force of our Sun will have on the comet.
Dr Matthew Knight, from the Lowell Observatory in Arizona, has been watching the comet for the last year and has worked out three scenarios to describe what Ison might do in the coming week.

Scenario one: It could suffer the same fate as Comet Lovejoy, which went around the Sun in autumn 2011.
The gravity of the sun pulled one side of the comet's nucleus more strongly than the other, stretching it apart.

As Lovejoy emerged from the corona it exploded. Whether this will happen to Ison depends on its size. A nucleus of two kilometres or under puts it at great risk. Astronomers estimate that Ison is almost exactly two kilometres, so it's right on the borderline.

In scenario two, Ison might behave like Comet Encke. This comet has orbited the Sun about 70 times since it was first observed a few centuries ago.
It is fast using up its ice and gasses and is fizzling out. Although Ison is only going to pass the Sun once, Dr Knight fears it could suffer the same fate.

Then there is the third scenario, the one many people will be hoping for. This is what happened to Comet Ikeya-Seki in 1965.
As the comet went through the sun's corona, the heat ignited the gases deep in its nucleus and a few days after it emerged from the corona, a huge tail had developed behind it. Millions of people were thrilled by the great spectacle.

If Ison puts on a stunning display as Ikeya Seki did, then it will also help scientists answer some of the great questions about our origins. Since 1965, telescopes and imaging technology have advanced enormously.

Spectrometry will allow astrochemists to analyse the chemical composition of the ices in Ison and from that data try to work out how the Solar System formed 4.6 billion years ago.
They might even be able to study its water signature, to provide crucial data informing the argument about whether our water came to Earth on comets, or accretion from below our planet's surface.

There is even a chance that scientists will observe the chemical precursors of amino acids. These amino acids are the molecules that form the building blocks of life.
Experiments in the laboratories at Nasa Ames, in northern California, have shown that these building blocks of life can be created in the hostile environment of a comet's nucleus. Could comets be the agents that transport these building blocks across the cosmos?

Everybody can now follow the comet's progress on the internet. Here's hoping that Ison will be talked about for years to come - as the comet of the century.

Comet of the Century: A Horizon Special will be screened on BBC Two on Saturday at 2115 GMT

I had to play around with the Heavens Above Sky Chart
http://heavens-above.com/ (Click on Sky Chart)
to get my head around what's happening. When Ison disappeared into the sun's glare a few days ago, it was near the SE horizon. When it has passed behind the sun and reappeared, it will be nearer the E horizon. (Which should give me a better view! 8) )

But I will pick on another point in the article: the sun's heat will not "ignite" the comet (unless it contains oxygen to react with its hydrocarbons); nor will it set off a nuclear chain reaction, as the comet is nowhere near massive enough. But, just as heat will melt and then evaporate an ice cube, so the sun will boil off the comet's ice and dust.

Sunrise chez rynner is about 0800 on the 3rd, which is almost civilized - no getting up in the middle of the night.
;)
 

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A closer look at Ison and its orbit:
http://www.heavens-above.com/
(Cick on Comets, and then on Ison, which is at the top of the list atm.)

It approached the sun from below the ecliptic, and will recede into deep space above the ecliptic. This means it will then be more easily seen by northern hemisphere observers (assuming it hasn't disintegrated at perihelion!).
 

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Ison: Critical time for ‘comet of the century’
By Rebecca Morelle, Science reporter, BBC World Service

Astronomers are anxiously waiting to see if a comet survives its encounter with the Sun.
Comet Ison will reach its closest approach to our star at approximately 18:35 GMT on Thursday.

It has been billed as a potential "comet of the century", but the Sun's heat and gravitational tug could destroy it before it has a chance to light up the skies.
Some scientists believe it is already starting to buckle under the onslaught.

Prof Tim O'Brien, associate director of the UK's Jodrell Bank Observatory, said: "It's like throwing a snowball into fire. It's going to be tough for it to survive.
"But luckily, it's a big object and it moves fast, so it won't spend too much time close to the Sun. There is a lot of uncertainty."

Comet Ison came from the Oort Cloud, a mysterious, icy region at the furthest reaches of our Solar System.
It has been hurtling towards the Earth, travelling at more than a million kilometres an hour.
Now it is entering the most perilous stage of its epic journey.
It will pass the Sun at a distance of just 1.2 million km, effectively grazing its surface.

Prof Mark Bailey, from Armagh Observatory in Northern Ireland, said: "It's going to be exposed to the worst that the Sun can throw at it.
"It will be getting exposed to more and more intense solar heat, and that will start to sublimate the ices (turning them into gas) at an increasing rate."

The Sun's intense gravitational field produces tidal forces that will also have a major effect on the comet.
Scientists fear it could follow the path of Comet Lovejoy, which broke apart after it passed near the Sun in 2011. Or it could run out of fuel and fizzle out. It is hoped Ison's large size could protect it.

Astronomers estimate that its nucleus could be several kilometres in diameter, helping it to withstand the solar assault.
If it does remain largely intact, the heat from the Sun will excite the dust and gas in its core, allowing it to blaze a trail across the night skies. But whether it really will be a "comet of the century" is unclear.

"If it survives, the best chance of seeing it will be in early December," explained Dr Robert Massey from the Royal Astronomical Society.
"I very much doubt Ison is going to be the sort of object where you go out in the morning, just before sunrise, and see this amazingly spectacular thing across the night sky.
"It's much more likely, at the optimistic end, that it's visible with the naked eye, and with binoculars - you could see the comet's head and a nice long tail coming from that."

There has been some debate already about whether Ison is starting to break up, and telescopes such as the Esa/Nasa Soho Sun-observing satellite will be trained on the star during the approach.
"There is a lot of uncertainty, but it's going to be exciting to watch," added Prof O'Brien.

http://www.bbc.co.uk/news/science-environment-25129711
 
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