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Sun, 23 Aug 2015 - A Tale of Two Comets - amateurs hunting down 67P and Catalina

Unless you've been living out in the Oort Cloud for the past year or so you'll know that an unmanned European Space Agency probe, Rosetta, has spent the last twelve months or so flying alongside a comet called Churyumov–Gerasimenko, or "67P" for short. As is the case with most comets, 67P is named after its discoverers, in this case a pair of Soviet astronomers, Klim Ivanovych Churyumov and Svetlana Ivanovna Gerasimenko. But this wasn't a recent discovery - they spotted the comet way back in 1969. 

Since Rosetta arrived at 67P last August it has sent back thousands of thrilling images, allowing us to see a comet in stunning detail. It was assumed for a long time that comets were basically just dirty snowballs, without much in the way of surface features. Then we started flying spaceprobes past comets, and it became clear that comets, like other small solar system bodies, have craters, hills, and other landscape features. Now, thanks to Rosetta, for the first time we have seen a cometary nucleus in all its glory. Rosetta images have shown us crumbling cliffs, plains strewn with boulders, deep pits and meandering cracks and valleys. It's been a true revelation, and the mission has fascinated millions of people around the world, not just amateur astronomers like us!

For the past year Rosetta has kept pace with 67P as it approached the Sun, and its cameras and instruments have seen the comet waking up slowly. Now, having passed perihelion, 67P is really "waking up", and becoming very active, as this latest image from Rosetta shows...

ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

Looking at that beautiful image (and the full size version is here, if you want to drool over it!) you can clearly see jets and plumes of gas and dust shooting out of the nucleus.

So... now 67P is showing more activity, naturally amateurs are keen to see it for themselves, through their own telescopes, instead of just looking at pretty Rosetta pictures of it.

In fact, amateurs have been observing 67P for quite a while now. It has been bright enough to see through large telescopes, and many experienced amateurs around the world have been supporting ESA by observing and photographing the comet and sharing their work online and through social media. There's a very active Facebook group dedicated to the study of 67P, and for several weeks now its members have been posting observing reports and photographs.

Because of its position in the sky, and its low brightness, until now the comet has remained out of reach of less experienced amateurs, but that is finally starting to change. And now, finally, 67P can be seen and photographed through medium and small telescopes - and can even be photographed with just a sky-tracking camera, if you know how to stack multiple images together.

Yesterday the SPA's very own Paul Sutherland posted an image on social media of 67P that he had taken through his own very modest equiment, and although the comet just looks like a small, faint, fuzzy blob - which is, let's be honest, what most comets look like! - it's a great picture because it shows what can be achieved with dedication, hard work, and trust in the abilities of yourself and your equipment.

Paul wrote to me:

As I have a clear and dark view to the east, over the sea, with nothing between me and Belgium, I realised that I had a good vantage point to try for Comet 67P in the shortish spell between Gemini rising and the start of twilight. I also wanted to see whether I could capture it with my new 66mm Lightwave refractor, which functions as an excellent telephoto camera lens.

Without a guiding facility, I had to trust my mount’s drive, and I took 25 one-minute exposures with my Canon 600D SLR camera at a fast 3200 ISO, and hoped for the best. My shots were taken from my seaside balcony in Walmer, Kent, between 01.52 and 02.36 UT on the morning of 22 August. Having randomly stacked many of them, I was trying to identify which bit of noise was the comet when I noticed a more obvious smudge a short distance away and wondered what nebula that was. It was then that I realised that the American chart I had been using was giving times as PDT instead of UT, and the "nebula" was my comet! And though I have nothing more than misshapen stars and a faint splodge, I was thrilled to have caught Rosetta’s comet!

And here's his image...



67P is dead centre, but this crop of Paul's shows it more clearly...



Yep, there it is, great work Paul! Brilliant that an SPA member, with very modest equipment, was able to take a photograph of the same comet Rosetta is studying from rather closer...!

If you want to find 67P and maybe even try photographing it too, these finder charts will help you track it down.

First of all, let's look at just where it is in the sky. Basically it's an early morning object, visible after 3am or so, low in the east as seen from the UK. Here's where it was a few days ago, and it hasn't really moved much since then. Please click on all the charts to enlarge them.




Here's where it will be in the weeks ahead...




Those charts - produced using the freeware Stellarium planetarium program - show the area of the sky the comet will be in. For a closer view, to see where it will be in the crowded starfields of that part of the sky, you can use these charts kindly produced using SkyMap by Robin Scagell – click to enlarge each one...


Chart A: 23 August – 3 September

Chart B: 4–16 September

Chart C: 10–22 September


Many thanks to Robin for making those charts for us.

At the moment 67P is shining (if you can call it that!) at magnitude 12, but it should start to brighten as it warms up and becomes more active post-perihelion. So, good luck tracking it down. You won't see the dramatic views Rosetta is enjoying, but you'll be able to say that you saw the actual comet with your own eyes, not just photographs of it.

Another comet

The title of this post refers to two comets, so which – and where – is the second one? Well, although it can't be seen in the northern sky yet, Comet C/2013 US10 Catalina is currently wowing observers in the southern hemisphere (how many times do we hear or read that???) and some really pretty photographs are being taken of it; those taken by one of the most successful comet photographers working today, Damian Peach, show its beautiful green colour and wispy tail. The good news is that Comet Catalina is already shining at a respectable magnitude 7.1 or so, meaning it is easily visible in binoculars... and the better news is, it's heading north, and will be visible in our northern skies at the end of the year. Comet experts are hoping it will reach magnitude five, or maybe even magnitude 4, by then, which would make it a pretty naked eye comet. But we'll see... comets are the Lokis of the solar system, and love to play tricks on us, getting our hopes up before dashing them cruelly. So let's look ahead to where Catalina will be, and forget for now any talk of how bright it will be.

Here are some charts showing where it will be later in the year - and you'll see that it will offer some very interesting photo opportunities for us, as it slowly makes its way towards and then up a parade of planets in the pre-dawn sky...





If you look at the times of those charts you'll see that Catalina is going to be visible in the hours before dawn, but it should be worth it. If it keeps behaving like it is, in early December we might be treated to the sight of a naked eye comet close to Venus before dawn. And even if it isn't a naked eye object, it should be a nice sight in binoculars and small telescopes, so something to look forward to there.

In the meantime, give tracking down Comet 67P a go. Yes, it will be challenging, but as I've told the members of my astronomical society for years, "If you don't look you're guaranteed to see nothing"!

Thanks to Neil Norman for his help with this report.


Added by: Stuart Atkinson