Our April Fool’s Day imaging object of the month is Abell 1656, the Coma Galaxy Cluster!  Abell 1656 is a massive cluster of galaxies in the constellation Coma Berenices (Berenice’s Hair) and is over 2-degrees in diameter!  Nearly everything you see in the image below that is not obviously a star is actually a galaxy.  With over 650 galaxies in the cluster, Abell 1656 is one of the densest collections of galaxies in the entire sky.

The giant central elliptical galaxies, NGC 4889 on the left and NGC 4874 on the right, lie some 300 million light years away, and they are both around 250,000 light years in diameter – about two and a half times bigger than our own Milky Way.  Strangely – NGC 4874 is a strong radio source, while NGC 4889 is not.

In the Sky 90 at f#4.5 I prefer to use pretty long subs for faint fuzzies, often around 10-minutes per sub.  With the usual rule of at least 50-subs for a smooth image, this means investing around 8-9 hours total imaging time on this one – but it’s got to be worth it!  Where else are you going to get an image with so many galaxies in a single frame?  Clearly this will be more than one night’s work, and I would suggest that it is probably worth coming back to this one year after year to keep adding more data and detail to this amazing region of space.

Until May – clear skies to you all!

Our deep-sky objects for March 2011 are a pair of open clusters that sit nicely in the field of view of most imaging setups – these are M35 and close-by NGC 2158 in Gemini.  M35 (also labelled NGC 2168) has a diameter of 25′ and shines at magnitude 5.1 at a distance of 2,800 light years.  Nearby NGC 2158 looks a lot smaller at only 5′ across, but that’s due to NGC 2158 lying 6 times further away than M35.  The main stars of M35 are distinctively blue, while the stars making up NGC 2158 are clearly old and red.  This colour combination makes for a great deep-sky image if you can get both objects in the FOV.  In oder to pull out faint little NGC 2158 it is probably best to go for slightly longer sub-exposure times, I would try for at least 5-minute subs at f#3.5, and again go for at least 50-subs in total – an imaging time in excess of 4-hours is therefore required.

One of the nicest open-cluster pairings in my opinion – give M35 & NGC 2158 a go this month (weather permitting) it will make a great addition to your portfolio if you don’t already have it

Until next month – clear skies to you all!

Our imaging object for this month was discovered as recently as 1980 – yes you read that correctly – this cascade of stars was first listed by Lucian J Kemble in 1980!  Living in Alberta, Canada, Kemble came across this cascade of stars whilst observing in Camelopardalis with a pair of 7 x 50 binoculars.  Kemble wrote about his discovery to Walter Scott Houston at the Sky & Telescope magazine and Houston wrote about the discovery and named it Kemble’s Cascade – the name stuck.  There is an added bonus with Kemble’s Cascade, at the end of this string of stars is a beautiful little open cluster – NGC 1502 – which greatly adds to the “sparkle” of images taken in this region.  Kemble’s Cascade is BIG – you need a short focal length imager to get the whole thing in the field of view – I struggled to get the whole asterism in the Sky 90 diagonal where the FOV is 3.33 x 2.22 degrees – so the Cascade plus the cluster extends to over 3 degrees, which is pretty big.

Usual formula for star pictures, shortish subs, around 3-4 minutes at f#3.5 and as many of them as you can get.  For a smooth image you need at least 50 subs so we are talking about a total exposure time around 3 and a half to 4 hours, which is typical for a bright deep-sky object.

So there you have it, a deep-sky asterism discovered and named as late as 1980 – it shows you what can be done!  At this point I would like to put in my claim in for Greg’s Charm Bracelet.  Greg’s Charm Bracelet is a huge loop of stars that has the Double-Cluster hanging like a sparkly charm from the South East end of the bracelet.  What is strange about the bracelet (and this probably goes for Kemble’s Cascade as well) is that it leaps out at you in either binoculars or a low magnification telescope – but you can hardly make it out on star maps or planetarium programs.  I am not sure why the eye-brain combination makes the stars in the bracelet stand out so strongly when clearly they aren’t all that much brighter than many of the surrounding stars.  Anyway – enough of Charm Bracelet’s – Kemble’s Cascade is the imaging object for this month, and the image below got Noel and me an APOD as well, so the NASA guys like this object too.

Until March 2011 – clear skies to you all!

Happy New Year to you all – I hope the hangover from last night’s celebrations isn’t too bad

The imaging object for this month is one of the most famous supernova remnants, and the first entry in Messier’s catalogue – it is M1, the Crab nebula in the constellation Taurus.  This tiny object, only measuring 6′ x 4′ (that is arcminutes note, 1/60th of a degree) is also labelled as NGC 1952 and lies around 6,500 light years away.  Firstly, being so small, you really do need a longish focal length to do this object justice.  My 400 – 500mm using either the Sky 90 or the Hyperstar III is simply too short.  It has amazing colour and detail and would do well with narrowband imaging – the incredible Hubble image of this object is I believe one of the highest resolution images taken of any deep-sky object – and it shows!  Although we cannot possibly compete with Hubble on this one, we can get as many narrowband subs as we can at high sampling (I would suggest you sample at around your local seeing limit).  You can see from my image below that you can still get quite some impressive detail even with short focal length imagers, and you have the added bonus of seeing the Crab in context – a lonely object in a fairly barren region of space.

So we start the New Year with an astronomical bang   The last few months of 2010 were amongst the worst (weather-wise) that I have known at the New Forest Observatory – let’s hope we get some better luck at the beginning of this New Year.

Until February – clear skies to you all!

I always have a lot of trouble with my imaging at this time of year as there are so many great objects up there to be grabbed and I can only concentrate on one at a time.  Auriga is in competition with Orion for my attention every winter as Auriga is also teeming with lots of goodies to image.  Although Cassiopeia is chock-a-block with open clusters – Auriga comes in at a pretty close second as far as I’m concerned.  This December’s Imaging Object of the Month is the beautiful open cluster M38 in Auriga.  It is pretty large with a diameter of 15 arc minutes and shines away at magnitude 6.4.  M38 lies at a distance of 4,200 light years (so it is pretty close) and it makes a great capture in a longish focal length instrument where you can nicely frame the region.

M36, M37 and M38 are all open clusters lying quite close to one another in Auriga and it is well worth bagging the lot if you get enough clear skies.

As per usual the formula for imaging this one is a resonable focal length, 3 to 5-minute subs, and as many as you can get.  In the “old” Hyperstar days I often took 100 subs of an object as my sub-exposure time was typically just one minute.  Although the images did not have great depth, they were glassy smooth, and were perfect for clusters and single bright star images.

Well – the next Imaging Object of the Month will be in a New Year.  So, Happy New Year to you all and let the long dark imaging nights continue – for just a little bit longer

For November’s Imaging Object of the Month I have chosen one of my most favourite objects of all – the open cluster NGC 7789 in Cassiopeia.  Open Cluster?  This amazing collection of stars looks pretty much like a huge globular cluster measuring a massive 25 arc minutes across and blazing away at magnitude 6.6.  This open cluster was discovered by Caroline Herschel in 1783 and it lies just 3 degrees south west of Beta Cassiopeiae.  NGC 7789 also contains an amazing object as can be seen in the image below which is an animation of 2 frames taken around a year apart.  Is it an alien interstellar beacon, or perhaps a nova?  No, it’s WY Cassiopeiae an amazingly variable, variable star undergoing a magnitude change from around 7 at its brightest to around 14-15 at its dimmest – what a contrast!

As NGC 7789 is almost the diameter of a full Moon you can get away with slightly shorter focal lengths on this one, and I have managed to grab a nice image of this region using the Takahashi Sky 90 at f#4.5 and 405mm focal length.  Usual prescription for clusters, shortish subs (from 3 to 5 minutes maximum) and lots of them to get the depth and smoothness that this object rightly deserves.  It also makes sense to take two images of this object – one at WY Cass’ maximum and one at minimum, it really is a highly impressive variable.  Or why not image every clear night you can get throughout the whole cycle for a very unique recording of this star?

We are now well into the long dark evenings, astrophotographer’s heaven – let’s just hope the weather Gods look favourably upon us and provide us with crisp, crystal clear evenings for our imaging.

Until December’s IOM – clear skies – and happy imaging to you all

This month’s imaging object is M15 [NGC7078] the Great Pegasus Cluster, a very nice Globular Cluser in the constellation Pegasus.  This is a large globular with a diameter of 18 arc minutes (M13 is 21 arc minutes) and lies at a distance of 31,000 light years.  As it is a fairly small object you do better with longer focal lengths for this one and as is usual for globulars keep the sub-exposure time down a bit so that you can resolve the core stars.  M15 contains some hidden secrets!  One of these is Pease 1, a 14th magnitude planetary nebula on its north-eastern side.  M15 also contains a large number of variable stars – nearly 100 have been logged so far.  It was discovered in 1974 that M15 was a source of X-rays, these are believed to emanate from supernova remnants.  So, for a decent image of M15 you want a reasonable focal length for an appropriate image scale, shortish subs of maybe 3-minutes duration depending on your f#, and finally, as usual, as many subs as you can get for a nice smooth finish

We are well and truly into winter imaging evenings now with long dark nights – let’s just hope we get a few clear Moonless ones as well.

Until November’s IOM – clear skies and happy imaging.

Cassiopeia as you will know is open cluster central – but do you know that there is a region THICK with open clusters (6 of them) AND it has a fantastic supernova remnant as well?  Use your scope’s GOTO to go to NGC7790 or NGC7788 in Cassiopeia – get a decent field of view – and take a very long total exposure with long subs – you won’t regret it.

This special area was first brought to my attention by Eddie Guscott in his Practical Astronomer magazine [August 2008, pages 22-24] in a great little article called “Six little clusters, all in a row….”  The six little clusters comprise King 12, Harvard 21, Frolov 1, NGC7788, NGC7789 and Berkely 58 moving from north to south through this region.  It wasn’t however the “Six little clusters, all in a row” that caught my attention in the black and white image on page 23, what was that amazing object just making an appearance at the top of the page??  There was a semi-circular region of nebulosity, obviously part of a great circle of nebulosity – but what was it?  A little detective work showed that this was CTB1, a beautiful supernova remnant, brilliantly imaged by Steve Cannistra – I wanted this one!!  No problem – I have the Hyperstar – I can image ANYTHING – especially faint stuff, not actually true.  Even though I took very long sub exposures, and extremely long total exposures – I just couldn’t pull out CTB1 – even with Noel’s superb processing skills.  Why?  Because this one is getting close to my skyglow limiting background.  O.K. no problem – stick in an H-alpha filter and have another go.  Yes I did this, and found the problem with narrowband filters and low f# optical systems – they don’t go together!  O.K. no problem again – just get one of those wideband H-alpha filters and go for it again.  Well yes but the huge increase in bandwidth means you sacrifice a lot of contrast – and to be honest, you don’t actually gain a lot by going down this route with the Hyperstar system.  So what is to be done?  The only answer I have is to one day put the f#4.5 Sky 90 back on with a narrowband H-alpha filter and do the thing properly, but that may be a LONG time off.  Until then, just look at this rich region of open clusters – and better still – get imaging them.

The accompanying image is a mosaic of 3 Hyperstar III/SXVF-M25C frames and measures something like 3.5 x 24 degrees.  Sub-exposure times with the Hyperstar III went to over 10-minutes (!!!!) equivalent to over an hour with the Sky 90 – and total imaging time would be in excess of 20-hours.  One of my more impressive deep-sky imaging failures.  Why not see if you can do better and grab a really nice image of the little-known and rarely-imaged CTB1?

Until October – clear skies and happy imaging!!!

Imaging conditions steadily improve as we proceed through August and once again reasonably dark skies can be had in the late evening – the only problem being if you have a day job to get up early for the next morning!!  Day jobs notwithstanding August sees the real beginning of the new imaging season and as we’re still in summer it’s the summer constellations that we’ll still be interested in.  Cygnus again (same as last month) but this time a beautiful nebula rather than the open cluster we saw last month – this time we’ll look in some detail at the Cocoon nebula [IC5146].

The Cocoon nebula itself is a beautiful little emission nebula some 10′ x 10′ in size at a distance of around 3,300 light years.  But it is not just the nebula that is interesting – look at its surroundings!!  This one lies in the rich Milky Way and there’s yet another bonus – look at those dark nebula streamers billowing out from behind the Cocoon – it looks like the Cocoon has blundered its way into this Milky Way region of stars from the right, pushing stars out of its way as it travelled through and finally came to rest.  This amazing dark nebula is Barnard 168 [B168] and is one of the northern sky’s most visually stunning dark nebulae when viewed through a low-power instrument.  It is also large!  The accompanying image is a two-frame Hyperstar III mosaic measuring some 4 degrees across – and it still wasn’t a big enough FOV to capture the full extent of B168!

Now go back to the Cocoon nebula again – and look at that amazing stream of stars coming out the top of the nebula looking like some celestial whale head blowing sea water out of its blow-hole – incredible!

This region demands a LOT of exposure time AND a huge field of view as well.  It is well worth the time and effort to put together a nice mosaic of this area to capture the full richness of the region.  For my Hyperstar III/SXVF-M25C setup I recommend 5-minute subs to get some real depth to the Milky Way stars, and as per usual, at least 4-hours per frame, preferably 5-hours to give around 60 subs for a decent stacking and good signal to noise.

I will almost certainly go back to this one to get the third frame off to the right to get a little more of the amazing B168 into the final image.

Until September, when we WILL be getting those darker skies – clear skies and happy imaging!!

With virtually no imaging for the last 6-8 weeks we enter July where at least the skies start to get a little darker in the late evening.  It is still not great conditions for imaging though and you will note a slight degradation of image quality during July compared to the pitch-black skies we get over the winter.  Never mind!!  Dust of the telescope, fire up the mount and let’s get some imaging underway.

This month’s object is open cluster M39 in Cygnus.  Not too surprising we are looking at a Cygnus object in July, but M39 is pretty much overlooked by imagers – perhaps because it is noted as being a “very large, very poor cluster, very little compressed, of 7th – to 10th- magnitude stars” – not exactly a great advert for M39 is it?  But then you put some imaging time on this one and get a little depth and you realise that although large and sparse it is a very colourful cluster.  Being large [30' diameter] you need a decent field of view, and the Hyperstar III with the SXVF-M25C camera with its 2.4 x 1.6 degree field of view is almost ideal for imaging this object.  Clusters as we know need less sub-exposure time, and we have the bonus that we can also work on them when the Moon is about.  For the Hyperstar III at f#2 I typically use 3-minute subs on clusters, and for the Sky 90 at f#4.5 I often used 4-5 minute subs.  However, as with any object things simply improve with total exposure time and I always like to get an absolute minimum of 4-hours on an object – even a cluster.

Give M39 a try – open clusters in general are often overlooked by imagers, yet they have so much to offer.

Until August – Clear Skies, and happy imaging!