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You've probably read the quote: "Comets are like cats - they have tails, and do exactly what they want!" And it's true. Comets are famously - or should that be infamously? - unpredictable. They love nothing more than to mess us about. Sometimes comets that look as if they are going to be bright fizzle out (mentioning no names... no, not going to mention Comet ISON at all...). Other times comets that don't initially promise much put on a decent show instead, but such pleasant surprises are rare. More usually a comet that we expected to be a certain brightness falls short of it.
But sometimes, just sometimes, a comet really springs a surprise on us, by brightening unexpectedly, and then everyone gets a little bit excited, wondering what has happened to it way out there, and how bright it might actually become.
This is what's happening at the moment with Comet C/2014 S2 PanSTARRS. (Yes, another PanSTARRS, the sky is full of them! When I was looking for the comet on my phone app I turned in the "Comet names" option and the sky filled with PanSTARRS comets, it was as if they were naming snowflakes! Will a REAL person please discover a comet soon? It's nice having all these survey comets to look at and track down, but it would be nice to have a comet in the sky with a proper name for a change! Get working, SPA Comet Section members!) If it was following the rules, S2 - which was discovered almost a year ago, on September 22nd, by the Pan-STARRS 1 telescope - should be shining at around magnitude 13.7 or fainter, making it little more than a fuzzy dot in large telescopes. But for some reason it has brightened considerably, and is around magnitude 10 - still faint, still far too faint to be seen with the naked eye, but bright enough to be seen with smal telescopes and even binoculars from a dark sky site.
A quick look at where S2 is before we get down to the details. The comet is currently above the northern horizon after dark, between the stars of Cassiopeia and the Big Dipper...
I initially heard about this comet's peculiar behaviour on the popular and busy Facebook group "Comet Watch", which is run by enthusiastic comet observer Neil Norman. Neil posted a request for members to try and photograph the comet and record its unexpected brightening, so I gave it a go that night, and managed to capture its faint smudgy glow with a 300mm lens on my DSLR, taking time exposures with my iOptron tracker. The comet was in a relatively quiet patch of the sky just to the east of Cassiopeia, but being very small, and faint at magnitude 10, it took some finding. But eventually I managed to capture it...
It stands out more clearly in this image, which is a crop taken from a stack of twenty tracjed images I took using the iOptron...
Since those images were taken on September 10th, from a small, reasonably dark churchyard just outside Kendal, the comet has remained bright and appears to be getting brighter still, making it a good target for SPA Comet Section members and other skywatchers. But what's actually going on?
Perhaps the comet has brightened like this because activity on its surface has increased suddenly and dramatically after the collapse of structural material on its surface, leading to a sudden outburst - a jet or a plume spewing comet stuff out into space. Or maybe it has collided with something "out there". Or maybe it's just brightening naturally, with no ulterior motive or outside influences. We don't know. All we know is that it is brighter than expected, and is worth keeping an eye on.
And if you need any inspiration to try finding it for yourself, this beautiful photo of S2 , taken earlier today by accomplished comet photographer Rolando Ligustri, remotely, using the NM itelescope, should help...
I asked Neil what he thought. "It's DC ("DC" stands for Degree of Condensation, i.e. an indicator of how much the surface brightness of the coma increases toward the center of the coma) indicates a rapid brightening trend and not an outburst," he told me on the FB group, "because the DC would shoot up to a value of 5 or 6 if outburst. This could mean the comet could reach possibly mag 8 at perihelion in December this year, the 9th I believe..."
Magnitude 8, instead of magnitude 12.6 as originally predicted..? Now that would be very good news, and great timing too: in early December S2 will be in the constellation of Draco, and so close to Polaris that it won't set, we'll be able to follow it all through the night, while we wait to see Comet Catalina in the eastern sky before dawn.
Two comets visible in one night? We'll see...!
In the meantime, if you want to look for S2 yourself, these finder charts will help over the next week or so as it heads towards a rendezvous with Polaris early next month...
Below is a finder chart showing stars to magnitude 8.5 for September and early October, plotted using SkyMap. The circle shows a 5 degree field, typical of binoculars or an optical finder. On 6 October, the comet is very close to Polaris. Ticks show the position at midnight UT on the day in question, so for evening obserrvation look closer to the next tick along. Click to enlarge.
UPDATE: I managed to get another couple of photographs of S2 last night (Sunday 13th Sept) from a clearing in a park in the middle of light-polluted Kendal. It's that tiny greenish smudge just above the centre...
As you can see it really is a small, faint object. I think that you might see it as a faint star through a good pair of binoculars from a dark sky site, and a small telescope will pick it out, but you will have to know the sky pretty well to track it down, and this comet might remain a photographic object for a while yet. Keep checking back here for more updates.
Added by: Stuart Atkinson