An update on Comet ISON!

The comet had been visible in the Southern Hemisphere before passing the Sun but since the 19th November it has been very difficult to see as it has risen just before the Sun. After it had passed the Sun it would be rising just after the Sun rise and setting before the Sun set, in the southern hemisphere so hence we would not have been able to see it.

At around 6:44am our time this morning the comet reached perihelion (its closest approach to the Sun) where it broke up and then something continues on – it might just be gravel and dust or there might stay a chunk of rock big enough to stay comet like. But now only time will tell if it is big.  This goes to prove that although we certainly know a lot more about comets than we did before – there is a lot more that we do not know.  Many have pronounced Comet ISON as already being dead and it certainly will not reach the brightness and spectacular display that had been predicted – but as Mark Twain is often quoted: “Rumours of my demise are greatly exaggerated.”  Something emerged from the sun after Comet ISON made its closest approach today. Is it ISON? Both professional and amateur astronomers are analysing images from NASA satellites to learn more about comet’s fate. Northern ground based observers may have to wait until around the 9/10 of December now to see if there is anything to see. But they will not get the amazing views that we were all hoping for.

However, at every single opportunity it could find, Comet ISON has done completely the opposite of what was expected, and it certainly wouldn’t be out of character for this dynamic object to yet again do something remarkable. Even if the comet broke up, it offered a very rare opportunity to see how one of the oldest objects in the solar system interacted with the Sun’s magnetic field and its behaviour in the sun’s magnetic field will help scientists understand more about both comets and the Sun. This  was the first comet in recorded history which has come from so far away and passed so close to the sun, passing the sun at a distance of around 1.6 million kms that has been so well-studied and observed.

So we wait and see, this has been one of the most well observed, followed and commented in social media worldwide. A fleet of spacecraft watched ISON plunge toward the sun, including NASA’s STEREO satellite, the European Space Agency/NASA SOHO spacecraft and the Solar Dynamics Observatory. The Hubble Space Telescope should be able to take a close look in a couple of weeks if it did indeed survive.

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The photograph above is from the NASA SOHO Space Telescope’s LASCO C3 camera showing a fragment emerging from the other side of the Sun about 3 hours after perihelion.

The picture below is taken this at 00:42UT 1 December 2013 and shows the remnants of the comet as it leaves the SOHO LASCO C# camera’s field of view.

Comet ISON

There has been a lot of interest in the Comet 2012/S1 (ISON), more commonly known as Comet ISON. This comet has been predicted to become the comet of the century; this of course, may not eventuate. For those of us fortunate to have witnessed C/2006 P1 (McNaught) in January 2007 it will sure take a lot of beating.

The comet was discovered on 24 September, 2012, by two amateur astronomers in Belarus and Russia, using a 40-cm (16-inch) telescope. As it took them a day to confirm that the object was a comet, the organisation International Scientific Optical Network with which they are associated was credited with the discovery.

Over the past decade, hundreds of sungrazing comets have been discovered, but they are usually small, short-lived, and only seen by spacecraft designed to observe the Sun. Most sungrazing comets do not survive their trip around the Sun as they are disrupted by its intense radiation and gravity. Most of these, however, are quite small being only tens of metres across. The nucleus of Comet Ison is believed to be around 4km in diameter and hopefully its larger size will insulate the interior from the Sun’s energy.

One reason this is considered to be such an interesting comet is that it is believed to be making its first approach to the inner solar system. Along with this belief, comes the reason for all the uncertainty in the predictions as scientists can only guess at how bright it will become at the time it is closest to the Sun. There will be professional and amateur astronomers eagerly observing the comet from the ground and via the internet as a whole fleet of spacecraft have turned their cameras in its direction.

The comet has been gradually brightening as it speeds up on its journey towards the Sun. Unfortunately for us in the Southern Hemisphere just before and just after it passes behind the Sun on November 29, it will be below the horizon in both the morning and evening sky. This is the time that the comet is most likely to be at it brightest. For northern hemisphere observers, at these times, it may even be naked eye or perhaps visible in binoculars. A few weeks later the comet’s outward trajectory, providing it survives its passage around the Sun, will bring it to just 0.4 times the distance from the Earth to the Sun.

But perhaps, the greatest unknown is, in fact whether or not the comet will actually survive its passage through the corona which is the Sun’s atmosphere. At the time it passes the Sun it will only 1.1 million kms away and the nucleus of the comet will be subject to a combination of both extreme heating approximately 5000 degrees Celsius, which is hot enough to melt iron as well as constant radiation bombardment.  Add to that the fact that the Sun’s strong gravitational pull will be trying to tear it apart. Still the best guess from scientists is that the nucleus or at least a large chunk of it will manage to sweep around the Sun and start making its way out of the solar system.

Comets are believed to be the frozen left-overs from the formation of our Solar System, originating in the Oort cloud. While comets have been in a deep freeze for the past 4 billion years, planets and asteroids have changed a lot from their original compositions. Better understanding of their ices, dust, and organic matter, and how they have changed over the past billions of years, tell us about the origins of our Sun, the planets, and, possibly, life on Earth. To astronomers, every bright comet is an opportunity to learn more about our Solar System.

 NOTE that it is always dangerous to look directly at the Sun. Do not use telescopes or binoculars to search for the comet, just your unaided eyes and block the Sun with a post or other convenient object. Take extreme care!