A Comet ISON crash course and status report

A recent composite image of Comet ISON captured by the TRAPPIST telescope in La Silla, Chile.

A recent composite image of Comet ISON captured by the TRAPPIST telescope in La Silla, Chile.

Comet ISON has been lighting up the science news world for the last couple of weeks as it approaches the Sun. Today and possibly tomorrow will be the last chance to see it in South Africa before it swings around the perihelion – the closest point to the Sun in its orbit. In the next few days, it will either break up or head out of the Solar system once again, visible only in the northern hemisphere.

Comets hold a real sense of wonder for many people. Maybe it’s the centuries of portents ascribed to comets; or perhaps just the strangeness of a totally foreign object flashing through our otherwise quiet skies. Comet ISON (named after the International Scientific Optical Network, the telescope array where it was first identified) comes from the Oort Cloud, and offers new ways to understand the formation of the universe. Dr. Amanda Gulbis of the SALT telescope told me that “comets allow insights into primitive materials (ice and rock that have not been heavily altered by the Sun) which can improve our understanding of how the entire Solar System formed and evolved”. Comet ISON is particularly interesting for a few reasons – it is the first, and likely the last, time that ISON will enter our system, and it is what is called a sungrazer. Sungrazers are comets which come especially close to the sun at their perihelion. Often this results in fragmentation or complete destruction of the comet, and it seems like this might be starting to happen to comet ISON.

An image from NASA's STEREO-A spacecraft, showing ISON on the left, Mercury and Earth as two lens-flare spots, and a coronal mass ejection, or flare, from the Sun on the right

An image from NASA’s STEREO-A spacecraft, showing ISON on the left, Mercury and Earth as two lens-flare spots, and a coronal mass ejection, or flare, from the Sun on the right. The smaller comet is Encke’s Comet, a periodic comet which orbits every three years.

Uncertainty about the fate of the comet seems to be creating a lot of hype around ISON. The last few weeks has been a will-it or won’t-it game, with astronomers around the world scrutinising every image and data point to get a handle on its behaviour, and casual observers left a little confused. A few days ago, a watching astronomer at the NASA Comet ISON Observing Campaign tweeted that ISON was behaving more like a fragmenting comet than an intact one.

But more recently, it seems that the observed increase in brightness was just an outburst related to a solar flare rather than the imminent death of the comet. You can also follow the progress of ISON in real time by following that link.

So, what are our chances to see ISON before it leaves our southern skies? According to Dr. Gulbis, ISON is just visible from South Africa until today or tomorrow: “Throughout November, ISON has been very low in the morning sky, on the faint edge of what can be viewed with the naked eye. Unfortunately for South Africans, the comet makes its closest approach to the Sun today, passing just ~1.1 million km from the Sun, after which point it will be only viewable from the Northern hemisphere.” Which is some bad news for would-be comet-watchers.

On the positive side, it seems that there is some chance that ISON will survive its perihelion, and be visible on the way out, too, at least in the Northern Hemisphere. With a little luck, Comet ISON will brighten up nicely as it slings around the sun. For a few weeks, we can all wonder at this foreign visitor to our skies, before it disappears with a flourish and leaves us awestruck and humbled once again by the universe we have the privilege of inhabiting.

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