Astronomy; Comet Ison - The Great Comet of 2013?

This image shows the first detection of Comet Ison - a seemingly unimpressive dot among many other dots - the other dots are stars or distant galaxies. But this dot moves against the backdrop of stars. That makes it different.

Hopefully as this page develops between now and the end of 2013, many more impressive images of Ison will emerge.

In September 2012, the news was broken that a new comet had been discovered. The initial projection based on its size and trajectory was that when this new comet - Comet C/2012 S1, more attractively named as Comet Ison - approaches in 2013, it might just become the greatest and most spectacular arrival in the night sky in the past 100 years. A truly memorable visitor to our local Solar neighbourhood, even brighter than the Full Moon. An apparition to spark headline news around the world. But will it? The truth is we do not yet know if Comet Ison will be as spectacular as this, or whether it will fizzle out into obscurity. But its story will be told here. This page, begun as a web page in Oct 2012, will continue as a blog as Comet Ison approaches in 2013.

On Tuesday 25th September, an e-mail was received from a website to which the author of this article subscribes. The website is called 'One Minute Astronomer', and it provides regular brief bulletins to interested parties on the latest developments in astronomy. But on this particular Tuesday, the bulletin received was of more than usual interest. It was headlined: 'Bright New Comet on the Way!' I had a compulsive need to read further:

• 'There's another comet on the way. And this might be a great one. Called Comet C/2012 S1 (ISON), this comet is about as far away as Jupiter, but it's expected to buzz the Sun late next year and, if it stays intact, may become as bright as the full Moon.'

More information was available from 'One Minute Astronomer' via a link (see later), and this only served to kindle even more enthusiasm whilst also introducing a note of caution. Some of that information and other information, is presented on this page.

Comet Ison* was discovered on 21st September 2012 by Vitali Nevski and Artyom Novichonok in Russia. At this time the comet - between the orbits of Saturn and Jupiter at a distance of 584 million miles - was too faint to be seen without powerful telescopes. However, in October 2013, it will pass very close to the Planet Mars, before crossing Earth's orbit. In November 2013, Comet Ison will pass within two million kilometres of the Sun. In late December 2013, having swept round the Sun, Ison will cross the Earth's orbit for the second time at a distance of about 60 million kilometres.

* Ison is an acronym of the institute which first reported the comet - the International Scientific Optical Network in Russia.

Eccentric human beliefs being what they are, perhaps I should make one point clear. There is no danger of Comet Ison colliding with the Earth. No doubt the doom-laden 'End Is Nigh' merchants may be out in force, predicting Armageddon yet again, but they will be wrong. Just as the Earth will not end in 2012 in accordance with the much-hyped Mayan doomsday prophesies, so it will definitely not end with Comet Ison in 2013.

In one of my pages, 'Beginner's Guide to Naked Eye and Binocular Objects', I say:

• 'Some truly spectacular comets have been recorded in history, bright and clearly visible. More commonly they appear as faint, hazy elongated smudges of light. Hopefully a great comet will visit in our life times, (but don't hold your breath)'

This was written only in May 2012. Now there is reason to hope it may come true rather sooner than anticipated.

A primary reason for the excitement generated in astronomical circles is the closeness of the approach of Comet Ison to the Sun. The closer a comet approaches to the sun, the more the Sun's light reflects, and the more the Sun's heat vapourises the hard icy shell, releasing dust and gases to form an extended glowing tail which can stretch millions of kilometres away from the comet. At this time, calculations suggest Comet Ison may possibly become so bright as to be visible in daylight. It may also develop a long tail.

However, a strong note of caution has to be aired. First of all, even if Comet Ison does become intrinsically very bright, it would be at its brightest at its closest approach to the Sun. But of course at this precise time it may be lost in the far more intense glare of the Sun itself. It would be at its most visible very low on the horizon when the Sun is just below the horizon. The comet may actually be easier to see later on as it moves away from the Sun and fades somewhat but becomes more conspicuous because it will be set against the dark night sky. At this time the closeness of its approach to Earth becomes significant.

But will Comet Ison ever be this bright anyway? Although the trajectory of Comet Ison will take it close to the Sun and reasonably close to the Earth - two of the key elements in cometary brightness, there are other factors which are not currently clear. The composition of the comet cannot be determined. A very large nucleus increases the likelihood of a great display as there is more material to reflect and fluoresce as the comet approaches the Sun. The frequency of visits to the inner Solar System also makes a difference. If this is the comet's first approach, then there will be more volatile matter in the nucleus to be stripped away into the tail. After repeated returns, the comet will gradually lose its brilliance. It is not known if this is Comet Ison's first visit to the inner Solar System, but orbital characteristics suggest that it may well be.

Everything seems to be in place for Comet Ison to be one of the brightest comets in recorded history, but many previous comets have been built up to high expectation only to disappoint when they finally make their approach. Some are so fragile they break up before they ever reach their closest rendevous with the Sun. We will just have to wait and see how Comet Ison eventually turns out.

I normally write web pages and publish them when they are complete. Not so this page. This page will be more of a 'blog' - a diary of the coming of Comet Ison, charting its development as it approaches the orbit of the Earth and its encounter with the Sun. As news gathers of its impending arrival in our night sky, I will update the information on an occasional basis. The page will thus become a record of the progress of Comet Ison. One hopes the story does not peter out in disappointment. One hopes the story will have a climactic ending in a blaze of glory as Comet Ison lights up the sky. If it does, then I may open up a second or third page of photos and detailed information. Please bookmark and come back from time to time to check on the Comet's progress.

Comets are usually described in the popular press as 'dirty snowballs', and consist of rock debris and various icy compounds including water ice. They may be a few kilometres in diameter. Some comets derive from the Kuiper Belt, a region of space beyond the orbit of Neptune, and these orbit the Sun with revolutions which are much more elliptical than those of planets. Such comets can take anything up to a few hundred years to complete just one revolution. Halley's Comet is the most famous example of one of these 'short-period' comets with a revolution which brings it back round the Sun every 76 years. A great many more comets however - including Comet Ison - derive from much further out, from the Oort Cloud, a vast band of debris extending out more than one light year from the Sun. Gravitational influences in outer space occasionally disturb the orbit of objects in the Oort Cloud and send them on a path through the Solar System to rendezvous with the Sun. The extreme elliptical orbit such a comet then undertakes may take many hundreds of thousands of years, or even millions of years, to complete. A comet like Ison coming from the Oort Cloud, will therefore have started its journey far in the distant past. It is only as the dirty snowball approaches the Sun that it may begin to develop a tail as the Sun vapourises icy material and a trail of dust and gas extends back from the cometary nucleus.

• EVERYTHING TO THIS POINT WAS ORIGINALLY PUBLISHED IN OCT 2012
• UPDATES TO THE PROGRESS OF THE COMET WILL BE POSTED BELOW

In this first update on the progress of Comet Ison, I have the pleasure to report that the forecast for this visitor from the outer reaches of the Solar System remains very optimistic, three months after its discovery. Striking similarities in trajectory between this comet and the so-called Great Comet of 1680 have been noted, and these similarities suggest a common origin and a possibly similar development. The Great Comet of 1680 (also known as Newton's Comet) was possibly the brightest in all of recorded history, and clearly visible in daylight. Current forecasts - which must of course always be tempered by caution - still suggest that Comet Ison may become brighter than the Full Moon in late 2013, albeit with the light concentrated into a smaller area. The comet should become visible in binoculars in September 2013, and will hopefully be visible to the naked eye by early November before brightening considerably as it approaches the Sun. Further updates will be posted shortly.

Further details of the projected path and potential brightness of Comet Ison have become clear. During October 2013, Ison theoretically will become visible to the naked eye, though how easy it is to see will depend on conditions of air pollution (both dust and also light pollution). After this, it should brighten rapidly. On 28th November, the comet will make its closest approach to the Sun - a mere 1.2 million km distant. At this stage the solar radiation could make or break Comet Ison. If it 'makes' it, then Ison should shine bright enough to be seen in daylight. Unfortunately of course, the Sun at close proximity will be shining even more intensely, making it difficult to see Ison. In December, the comet (if intact) will move away and grow dimmer, yet easier to see away from the Sun's glare. Then in the first few months of 2014, having rounded the Sun, Comet Ison begins its long journey back into outer space past and away from the Earth, and at this time it will hopefully be easily visible for many weeks throughout the hours of darkness.

Not too much to add about Comet Ison at the moment - it is still close to the orbit of Jupiter. Currently it is known to have developed a tail of dust and gas about 64,000 km (40,000 miles) long, though this is not too significant at the moment because of course the comet is still far too far away for this tail to be brightly illuminated by the light of the Sun.

Although this page is about Comet ISON, it is not the only visitor to the Inner Solar System. I would briefly mention another comet currently much closer to home. Comet Pan-STARRS has been visible in recent weeks to Southern hemisphere observers with binoculars or small telescopes. It is now becoming visible north of the equator too, and brightening as it makes its closest approach to the Sun on 10th March. By 12th March, depending on how things develop, the comet may be naked eye visible, about as bright as the Pole Star, just below and to the left of the crescent Moon in the South Western sky soon after sunset. Thereafter it will gradually dim as it moves through the Western evening constellations as shown below. Even at this late stage predicting the peak brightness of Pan-STARRS is not possible with great accuracy, though of course even the most optimistic forecasts expect it to be a mere taster for Comet Ison later in the year. Take a look and see if you can spot it.

Currently, Comet Ison is about 350 million miles from the Sun (when originally detected it was about 584 million miles distant).

Comet Pan-STARRS has now faded and can only be picked up in telescopes or in good binoculars, but it is believed to have reached a maximum brightness which was comparable to some of the brighter stars in the night sky during the month of March when it was naked eye visible for several weeks. Whether Pan-STARRS proved to be a disappointment or an impressive show during its orbit round the Sun depends upon the level of expectation of those who observed it. The same, of course, may well apply to Comet Ison at the end of the year.

It's been a long time since I updated the progress of Comet Ison and that is because there has been little to report in recent months. This is due to 'line of sight' issues - since the Springtime, the orbit of the Earth has taken us to a region of space whereby the Sun is between us and the region of space occupied by the comet. Because of this line of sight problem, Ison has not been visible since early June and astronomers the world over have consequently been eagerly awaiting its return to visibility from out of the Sun's glare. Then on 12th August, amateur astronomer Bruce Gary from Arizona finally picked it up once more low in the Eastern sky before dawn, and since then, many others have been searching out Comet Ison. Unfortunately, however, the news has not been good. Comet Ison is about 6 times dimmer than had been predicted, and this has dampened predictions of the comet's ultimate brightness. It seems likely that the cometary nucleus is not so large as had been hoped - about 3 miles (5km) in diameter - and it's believed that the comet's supply of ice particles (which contributes hugely to the brightness of the light reflected by the comet from the Sun) may already be running low.

The news about Comet Ison is a little depressing at the moment. As described above, the comet has not brightened as appreciably in recent months as had been expected. Since its re-emergence on 12th August, optimism about its ultimate brightness has certainly lessened, and forecasts have ranged from those who have not yet given up hope because of the notorious unpredictability of cometary development, to those who believe that the comet may already be fizzling out and may even disintegrate before it reaches the Sun in late November. (Bear in mind that a comet is largely composed of ice, and at its closest approach to the Sun, Ison will heat up to about 2,700C. And even if this high temperature does not destroy it, gravity may). However, to remain positive, the comet can now be picked out by large amateur telescopes low in the east before dawn. It will undoubtedly brighten as it gets closer, and soon after it crosses the orbit of Mars in early October, the hope remains that Comet Ison will become binocular visible and then naked eye visible. As is to be expected, the comet is speeding up as it gets closer to the Sun from about 55,000 mph in July to about 70,000 mph in September. This velocity will then increase dramatically as closest approach to the Sun takes place in November and December.

My last two updates on the progress of Comet Ison were somewhat subdued with the news that the comet had not brightened as much as had been anticipated during the months of June and July. But today I can report that the comet has remained intact despite some fears that it might break up before now, and it has brightened appreciably in recent weeks, and with that increase in brightness comes an increase in optimism. More about the optimism in a while, but first an update on the appearance and location of Ison in the night sky, because the comet is now well within the visibility range of a good pair of binoculars, allowing it to be extensively photographed by amateur astronomers as well as the big observatories.

Today the comet, is about 120 million kms (70 million miles) from the Sun, having already passed through the orbits of Mars and Earth. In the northern hemisphere, it can be found towards the south-east just before dawn, in the southern aspect of the constellation of Virgo, passing just north of the bright star Spica on the 18th November. By then it may be naked eye visible in clear skies, albeit low on the horizon. The comet has already developed the tail characteristic of these objects as they approach the Sun, and this tail appears about a Moon's diameter in length. The nucleus is estimated to be about 3 miles across. Images of the comet as reproduced here show a greenish or cyan tint to the head, the consequence of carbon gases.

As the month of November goes on, the tail will lengthen and the comet will continue to brighten, though the comet will also drop lower in the sky around dawn as it approaches perihelion (closest approach to the Sun) on 28th November. At this time it could be brighter than the planet Venus. What happens after that remains a matter of total uncertainty, though as stated before there is some optimism based on current sightings that the comet will become - if not 'The Comet of the Century' - at least a clearly visible spectacle even for those without binoculars. If the comet survives closest approach, the comet should become visible throughout the night in mid-late December, rising higher in the sky as it moves away from the Sun, unfortunately dimming as it does so. What actually happens, we will see in the next few weeks as the comet battles the intense heat of the Sun and the solar wind.

The end is nigh! No, not for Planet Earth, but tomorrow - 28th November - Comet Ison reaches 'perihelion', its closest approach to the Sun, just 1.2 million km (720,000 miles) distant. Here the stresses on the comet caused by gravity and intense heat are incredible and so the fate of Ison will be decided in the next few days.

Just recently, the brightness of the comet has increased very significantly making it visible to the naked eye shortly before dawn, albeit very low on the horizon. And it remains intact. This has increased optimism both about its chances of surviving the Sun encounter and also about the ultimate brightness of the comet. For three or four days, Ison will now disappear, but we will know its fate soon after - perhaps on 3rd December. In the Southern Hemisphere, observing will sadly not be good, but in the Northern Hemisphere try looking to the south east before dawn in the first two weeks of the month. The comet should then be at its brightest and the tail which already stretches 13 million km (8 million miles) will hopefully be impressive. (It ought also to be visible at the end of the day, close to the setting Sun). As December progresses, the comet will rise higher in the sky and may be visible to the naked eye all night, though it will rapidly dim as the year moves to its conclusion.

But let's wait and see - after a journey which may have begun one million years ago, Comet Ison has finally reached its home star. This may well be its first ever visit, and certainly the only encounter we will ever see. Let's hope it survives ...

This video, uploaded by ktmvideodump to Youtube, is the latest NASA SOHO image of Comet Ison's orbit round the Sun. The comet is seen as a bright streak entering from below centre right. After disappearing behind the Sun, it then emerges as a fan shaped object heading towards the top of the video.

These have been an extraordinary couple of days which only serves to demonstrate just how unpredictable comets can be, and just how difficult it is to gauge what is happening to an object in close proximity to the Sun. On 28th November, Comet Ison was at perihelion, and disappeared from view. Soon afterwards, when Ison should have reappeared, one major observatory failed to detect anything at all, while two others showed a considerably faded presence, leading to disappointed reports that the comet had apparently broken up and nothing but debris and dust remained. NASA spokesmen reluctantly declared their belief that the comet had not survived, and this was the sad news which was broadcast in the international media. Subsequently however, more images were received from the European Space Agency and from NASA's Solar and Heliospheric Observatory (SOHO) which showed that this 'faded presence' had not dissipated and indeed seemed to have brightened - an indication that at least a part of the nucleus may have survived and was regrowing its tail. Whether this is really the case and whether any surviving fragment may still produce a display in December is a subject of speculation.

To sum up, I would suggest that the news is not good, because Comet Ison appears to have suffered dreadfully under the immense power of the Sun, but it may well not yet be the end of the story. Ison may yet have a display for us to witness. Excellent detailed explanations of the scientists' uncertainties are available from the NASA Comet Ison Observing Campaign, a Guardian news report and a BBC News report.

Soon after Ison - or its remnants - emerged from behind the Sun, it became clear that the comet had suffered terribly from its close approach to our star. It was still hoped that maybe something of substantial size may have survived when a fragment of the nucleus appeared to be holding together quite well and sporting a fan shaped trail of dust behind. indeed it even seemed to briefly brighten somewhat. That however, was as good as it got. Since then the fragment has faded and the trail of dust has largely dissipated. Whatever now remains is certainly not going to naked eye visible, or indeed visible in binoculars. Comet Ison has been effectively destroyed - it was just too fragile and sailed too close to the Sun. That is a colossal disappointment.

One or two further reports on this page will later review the story of its discovery, the mounting excitement as it approached, and then the ultimate failure of this would-be Comet of the Century, and they will be published in due course. But that effectively is it, I'm sorry to say. Ison is destined to follow a long list of potentially great comets which just didn't make the grade. A sorry end indeed to a journey of a million years.

This NASA video uploaded to YouTube by CoconutScienceLab shows several images of Comet Ison as it approaches the Sun and then emerges as a fan shaped structure towards the top of the screen. It is essentially an extension of the video shown earlier, but now we can clearly see - particularly in the first segment - the manner in which the remnant of the comet briefly brightens, but then fades again before disappearing from view.

This website to which I subscribe gave me the first notification of the discovery of Comet Ison. The site, published by Brian Ventrudo, posts newsworthy information about astronomy to your email inbox. It's a nice, useful way for those who have a casual interest in astronomy to learn more about the night sky in bite sized chunks, and to keep up to date with the very latest discoveries

One Minute Astronomer

Two excellent Facebook pages carry updates to Ison's progress. These are:

• Comet C/2012 S1 - ISON
• Comet Ison