Since then, the excitement has died down somewhat. Scientists have become much more grown-up and cautious. Meanwhile, Comet ISON is still plunging blindly towards the Sun, and if there’s anyone on board I would strongly advise you to get off now.
I watched a Horizon programme about the comet last week, and it seems that there are three likely eventualities:
- Its nucleus will be pulled apart by the Sun’s gravity, causing it to explode (like Comet Lovejoy in 2011);
- The comet will fizzle out, having used up its supply of ‘fuel’ in the form of ice and gases;
- The comet will travel safely past the Sun, and the heat from the Sun’s corona will ignite the gases in its nucleus, causing it to develop a spectacular glowing tail.
Needless to say, number 3 is the hoped-for scenario. If this happens, we might find ourselves looking at something akin to ‘the Great Comet of 1965’, Comet Ikeya-Seki. This shone at magnitude -10, and reports say that it was visible in broad daylight to anyone who blocked the sun safely from their field of view. (Stars of magnitude 6 are faint to the human eye; the brightest star, Sirius, has a magnitude of -1.46, whereas the full moon has an apparent magnitude of -12.74.)
According to astronomer Stuart Clark, who writes for the Guardian, Comet ISON will be reaching perihelion (the point of closest approach to the Sun) at 1840 GMT today, 28th November.
In the days that follow, scientists will be closely monitoring the appearance – or non-appearance – of the galactic traveller, hoping for a light show of dazzling proportions. If Comet ISON survives unscathed, it will appear in the morning sky (and maybe also in the evening twilight) from the beginning of December; there’s a useful ‘finder’ image on Stuart Clark’s feature in the Guardian and also on the BBC website (links below).
Most of the comets I’ve seen, with the help of star charts and plenty of patience, have been fuzzy little blobs. This time, I’m hoping for some astronomical fireworks!
I am going to repeat Stuart Clarks’s warning: NEVER observe the sun through any form of optical instrument. Permanent blindness can result.
Update, 3rd December: According to astronomers, Comet ISON didn’t survive its encounter with the Sun. Sky and Telescope magazine reports that the ‘ghost’ of Comet ISON reappeared as a headless streak early on 1st December, but it is dimming steadily and shows no sign of cometary activity. The comet’s head had dwindled away as it passed through the corona. Sky and Telescope concludes: “Nothing will be visible by eye from Earth.” Ah, well!