Tuesday, 28 May 2019

Into the Whirlpool

Ask someone to draw you a galaxy and chances are they'll come back with a spiral shape. Even a small telescope will show you plenty of galaxies (if you know where to look), but how large a scope do you need to see those dramatic spirals? Edge-on galaxies like M82 and NGC 4565 show lots of detail in modest-sized scopes because their light is concentrated into a smaller area, but the majority of face-on galaxies have such a low surface brightness that the slightest haze or encroaching light pollution can render their spiral arms invisible.

There are a few notable exceptions however, and for northern hemisphere observers, the consensus seems to be that Messier 51 (commonly known as the Whirlpool Galaxy) is the best of the bunch. It resides some 25 million light-years away in the constellation of Canes Venatici (the Hunting Dogs), and can be found high overhead on spring evenings near the tail of the Great Bear (Ursa Major).

Here's a photo I took (actually forty-three 90-second exposures, stacked together) in March, showing the spiral very clearly:


M51 & NGC 5195, 28 Mar 2019; Canon EOS 80D + Tele Vue-60 + Vixen Super Polaris

For a larger crop, see the version on my Flickr page.

Sixty-five minutes' worth of sensor data is one thing, but how much of that detail can you actually see with your own eyes? M51 and its interacting companion NGC 5195 are easy enough to spot through even a small scope, but it wasn't until I got the 10-inch reflector that I was able to see them as more than a pair of faint fuzzy blobs. Even then, the detail was elusive, with the dark spaces between the Whirlpool's arms often more apparent than the arms themselves.

My sketching skills are very rusty so it took me three attempts before I got something I was happy with, but here's an approximation of what M51 looks like through a medium-sized scope on a good night:




For this I used the 10-inch Orion XT10 and a Tele Vue Nagler 9mm eyepiece, giving a magnification of 133x.

Depending on the quality of your night sky, you may be able to see M51's spiral with a smaller telescope. I was never able to make it out with my 4-inch refractor (although the two galaxies themselves were obvious), and even with the XT10 I can't always see it, as demonstrated by these excerpts from my observing notes:

19 May 2018 (first night out with the new scope; sky a little hazy)
Not well placed (wrong side of meridian), but both galaxies showed bright cores. Strong hint of spiral arm structure, and a star superimposed over the face of the galaxy (not a supernova!).
10 February 2019 (cold, but not freezing; sky transparency improved considerably once the crescent moon got out of the way)
In a night of highlights, M51 was the undoubted stand-out. After staring at it for a couple of minutes I suddenly realised I could see the spiral arms quite clearly, defined by the dark space separating them. One arm curling out from core region around a foreground star. A magnificent sight at 133x, even though it was still some way from the zenith. With averted vision it started to look like a ghostly monochrome photo.
31 March 2019 (slightly chilly, windy with occasional strong gusts; transparency good, but not up to the standard set on 10 Feb)
Tonight M51 and NGC 5195 had an almost ghostly aspect about them; the spiral arms seemed to fade in and out of existence independently of averted vision. The view wasn’t substantially improved at 240x, other than highlighting some of the brighter areas with a milky glow. 
4 April 2019 (chilly, gusty evening; excellent seeing, transparency improving as night went on)
Best view of spiral structure since 10 Feb; showed particularly well in averted vision. Dark areas between arms just about visible in direct vision. Also found a faint, round little galaxy roughly south of M51 – not plotted in the Pocket Sky Atlas, but later identified as NGC 5198.

(If you're into this sort of thing and you want to read more of my observing notes, I'm in the process of putting them online at https://mskastro.blogspot.com/ )

The visibility of the spiral is very sensitive to sky conditions, so if you don't succeed on one night, try again on another (and make sure your eyes are fully dark-adapted). Patience and persistence are vital. And here's another tip: if M51's spiral still seems maddeningly faint, steer your scope to the other side of the Great Bear's tail and see what you make of the larger (and fainter) spiral galaxy M101. Trust me, when you return to M51 it will seem positively bright by comparison.

So now you have an idea of what it takes to see the spiral in M51, but what about resolving individual stars in this beautiful galaxy? For that I recommend taking a very deep dive into this image by the Hubble Space Telescope...


Tuesday, 21 May 2019

Pied Crow Tour of Britain reaches Broadstairs

Pied Crow (Corvus albus)

When I first heard about a Pied Crow being sighted in East Kent I assumed it was some kind of birders' in-joke. After all, what is a "pied crow" if not the definition of a magpie? Also, there's no such bird mentioned in either the Collins Guide or the British Birds (WILDguides) book, not even in the once-in-a-lifetime lists of obscurities tucked away at the back.

But it turns out the Pied Crow is definitely not a magpie, as I found out when I caught up with it on Broadstairs jetty last Saturday (18 May). Even from a distance the white "vest" was obvious, and the bird itself is bigger than a conventional carrion crow (though not as large as a raven).

Pied Crow (Corvus albus)

So is this smartly-dressed corvid (normally a resident of sub-Saharan Africa) a genuine wild specimen or an escapee? I won't get into the speculation on where it might have come from as there's already plenty of that online by people far more knowledgeable than me on such matters, but I will refer you to this excellent article by Sam Viles on BirdGuides. Will it fly (or hitch a ride) across the Channel or will it continue its tour of Britain's seaside resorts? Like the outcome of B****t, your guess is as good as mine.

Next stop France?

As I think I've stated before on this blog, I don't keep a count of the birds I've seen and photographed (although I do keep an index), so it makes little difference to me whether or not it gets accepted onto an official list by the powers-that-be. But I do know that this unusual and striking bird has traveled a long way to get to where I live, so I'm glad I got to see it.

See also:
Birdguides: Pied Crow
Birdforum Opus: Pied Crow

Sunday, 13 January 2019

Into the Orion Nebula

Orion Nebula (reprocessed)
M42, Orion: Tele Vue 60 + Canon 80D + Vixen Super Polaris
"An unformed fiery mist, the chaotic material of future Suns" - William Herschel, 1789 
Herschel's description (written long before spectroscopy revealed the true nature of gaseous nebulae) could hardly have been more prescient. The Great Orion Nebula (Messier 42) is indeed a cradle of new stars (at 1,300 light years, the nearest star-forming region to our own sun), visible to the naked eye as a misty patch in Orion's Sword on winter nights.

Viewing M42
I'm occasionally asked what it looks like through a telescope: a one-word answer would be "Majestic", but don't expect to see the full extent of the nebula - or indeed the vivid colours that you get in photos like the one above. As with most deep-sky objects, the Orion Nebula rewards careful and prolonged examination. Here's a sketch I made a long time ago (for GCSE Astronomy coursework!) illustrating the typical low-power view through a small telescope under suburban skies:


One telescopic feature you won't often see clearly in photographs is the Trapezium, a tight grouping of four hot young stars whose ionising radiation has helped sculpt the nebula into the shape we see today. In my 4-inch refractor the nebula is nicely framed in a 24mm Panoptic eyepiece (42x magnification) with layers of nebulosity building up to the core. Add in an Ultrablock filter to improve the contrast and the nebula takes on the appearance of a swooping bird of prey. With a 5mm Nagler (200x) under steady skies, a fifth member of the Trapezium is just visible.

So far the weather has only allowed me one opportunity to look at M42 with the XT10, but even under less than ideal viewing conditions it was immediately obvious that the extra aperture had improved the view dramatically. The core region had a strong green tint and averted vision made it so bright that the Trapezium was almost lost in the glare. Lots of finely detailed structure was visible with dark rifts cutting through the nebulosity. The Ultrablock filter wasn't really necessary for such a bright object, but it did seem to increase the overall extent of the nebula, particularly on the northern side.

Photographing M42
For any birders who've made it this far, the Orion Nebula is arguably to astrophotography what the kingfisher is to bird photography, the gateway drug that lures you into a lifetime hobby. (It even comes with its own fish, of a sort.) The image at the top of this post is a stack (not a mosaic) of 108 thirty-second exposures (plus 15 dark frames and 21 flat frames). As I'm still shooting unguided (for now) I've been careful not to choose targets too far away from the celestial pole, so at -5 degrees declination M42 presented the biggest test yet of my polar alignment accuracy. Fortunately the Great Nebula is a forgiving target - you can pull out a considerable amount of detail and colour even with relatively short 30-second subs. If you look closely, some slight trailing is evident, but not enough to spoil the final image.

Processing M42
As I've said before, acquiring all the light-frames (plus darks and flats) is only half the battle; there's still a lot of work to do. The image above was assembled using the freeware program Sequator. Compare it with my first attempt using the more widely-known freeware DeepSkyStacker. The samples on the Sequator website suggest it's optimised for landscape astrophotography (i.e. wide-angle shots in which the horizon is visible), but it seems to do an equally good job for deep sky photography. In terms of workflow, I certainly found it easier to process the stacked image produced by Sequator. As you can see in the mouse-over comparison below, Sequator did a much better job of retaining the detail around the Trapezium area. There's less noise too, although the DeepSkyStacker version shows more of the fainter regions of the nebula.

 

It's also worth noting that Sequator did an excellent job of identifying and removing the light pollution gradient. DeepSkyStacker doesn't cater for this so I used the Light Pollution Removal tool in Noel Carboni's Astronomy Tools Actions set (which, despite having more user control, did on this occasion leave a series of contour lines in and around the brightest parts of the nebula). The Sequator stack did contain some colour noise, but this was easily removed using the Colour Blotch Reduction tool from the same set.

Other pros and cons: Sequator was fast (less than 30 minutes processing time compared to up to an hour for DSS). However, it also left some curious purple "appendages" around some of the brighter stars, as shown in the crop below:


I've seen Sequator described as "stacking for dummies" on one popular astro-forum, but on the above evidence I think it'll be this dummy's image-stacker of choice for the foreseeable future. This is by no means a rejection of DeepSkyStacker, but more likely an indication that I still haven't learned how to get the best out of it.

I like the colours better in the Sequator version too, although that's a matter of personal taste.

Which one do you prefer?

Sunday, 30 December 2018

2018 in Pictures

I didn't think I'd be able to top the previous year, but 2018 served up a bumper crop of sightings (September in particular had enough highlights to fill a best-of list all by itself). But here for your viewing pleasure, after much vacillating, are the pick of the bunch:

January
There's nothing like a Waxwing to brighten up a dull winter's day:

Waxwing (Bombycilla garrulus)

February
I've got to include at least one Kestrel (it's the Law) and this bird was a bit special:

Kestrel (Falco tinnunculus)

March
Why go to the trouble of catching your own frog when you can steal one from a Marsh Harrier?

Buzzard vs Marsh Harrier

April
The light wasn't great that morning, but it's not every day that a Cuckoo pops up right in front of you:

Cuckoo (Cuculus canorus)

May
Here's something else you don't see every day, a Mole out in the open:

Mole (Talpa europaea)

...though it really wasn't the best day for small furry things to come out of hiding.

Also at Stodmarsh, a Hobby grabs an in-flight snack:

Hobby (Falco subbuteo)

June
At Foreness Housemartins collect mud for their nests:

House Martins (Delichon urbicum) 

And a Stoat pops up at Stodmarsh:

Stoat (Mustela erminea)

July
A typically quiet month for birds, but not for dragonflies such as this Norfolk Hawker:

Norfolk Hawker (Aeshna isoceles) 

August
Last ones to arrive; first ones to leave. A Swift prepares for its autumn migration at North Foreland:

Swift (Apus apus)

September
1st September at Grove Ferry was one of those rare and remarkable days where everything falls into place. It included Spotted Flycatchers and a Bullfinch (in the same tree), a Whinchat, and even a surprise Bittern. But it was the reserve's star attraction that stole the show:

Kingfisher (Alcedo atthis)

Return visits later in the month uncovered a Small Copper butterfly (the first one I can recall seeing at the reserve), plenty of Willow Emerald damselflies, Lizards, and this juvenile Green Woodpecker:

Green Woodpecker (Juvenile) 

October
Winter birds start arriving along the coast, including this handsome Brambling at North Foreland:

Brambling (Fringilla montifringilla) 

November
Not the best photo, but arguably the best bird of the year; Scott Haughie's White-billed Diver (in summer plumage!) which attracted birders and photographers from across the country:

White-billed Diver (Gavia adamsii) 

I expect I'll be frowned on in some quarters for including it, but this ESCAPED Hoopoe brought some entertainment (unless you're a grub) to an unlikely part of Thanet:

Grub's Up (again)

December
Another month, another loon; a Red-throated Diver (not in summer plumage) in Ramsgate Harbour:

Red-throated Diver (Gavia stellata)

All the photos on this page were taken with a Canon 80D DSLR and the trusty Tele Vue-60 refractor.

In the next post, I will be returning to outer space.

Wednesday, 22 August 2018

A Journey into Astrophotography

I'll say one good thing for He-Who-Must-Not-Be-Retweeted; he's encouraged me to turn my attention away from this increasingly nonsensical planet and back into deep space*. I've dabbled with astrophotography before (hand-tracking with a 50 mm lens), but mostly I've stuck to the brighter objects like the moon and Jupiter. Long-exposure astrophotography at focal lengths greater than 300 mm requires precise motorised tracking, but it was only after a trip to Astrofest 2018 (and some intensive research) that I figured out a practical and affordable way to go about it.

Here's a picture of the trusty Tele Vue-60 (the same scope I use for most of my wildlife shots) in its latest mode atop the equally trusty Vixen Super Polaris mount (fitted with Skywatcher dual-axis motor drives and an ADM dovetail plate adaptor):


With a field-flattener attached the TV-60 is roughly equivalent to a lens of 400 mm focal length. So far, this arrangement is good enough for exposures up to about two minutes duration depending on the accuracy of my polar alignment. (The Skywatcher handset does have an ST-4 port for autoguiding should I wish to attempt longer exposures in the future.) Here's another angle showing the motor drives attached to the Right Ascension and Declination axes:


Any serious astrophotographers visiting this blog might be shaking their heads at this point and muttering about vignetting and edge-of-field distortion, red sensitivity, thermal noise etc. in much the same way that serious wildlife photographers might mutter about autofocus and aperture control when they see what I'm using. But the point is, I don't get enough clear, moonless nights a year to justify spending the kind of megabucks that others spend on their gear. And, crucially, I can use the same DSLR and the same little scope for multiple purposes (which probably explains why the focuser is starting to look a little worse for wear). And (whisper it quietly) one good photo of the Orion Nebula looks very much like another good photo of the Orion Nebula, no matter where you are on the earth. Unless you have your own observatory equipped with an adaptive optics system, you're probably not breaking new ground.

That's not to say I won't be eagerly imaging the Orion Nebula when I get the chance just like every other amateur, but M42 is a spectacle of the winter sky, so for my first target I chose the globular cluster M13 (because it's big, bright, and not too far away from the north celestial pole):

M13 Globular Cluster
M13, Tele Vue-60 + Canon 80D (30 x 1 min @ ISO 800)

The long exposure times required to make an image like this turn pinprick stars into blobs of light, giving the false impression that they are almost touching each other. Although direct interactions in globular clusters do occasionally happen (the most likely origin of blue stragglers), the average distance between stars in a typical globular is actually 0.1 to 0.5 light-years, a fraction of the distance between here and Proxima Centauri (4.2 light-years), but still many times the size of our planetary system. This image from the Hubble Space Telescope resolves the core of M13, giving a better impression of the star density. Around 150 globular clusters are known to orbit our galaxy, dipping in and out of the galactic plane in highly inclined orbits. To put that in perspective, M87, the giant galaxy at the heart of the Virgo Cluster, is surrounded by 16,000 globular clusters.

I recently had the pleasure of looking at M13 through a 10-inch telescope and the result was breath-taking (so much so that I completely forgot to look for NGC 6207 - the "little" galaxy visible towards the bottom-left of the image above).

In my 4-inch achromat M13 takes on the appearance of a "grainy snowball thrown against a pane of glass", always on the brink of being resolved but never quite making it, except when averted vision is employed. In the 10-inch scope (at 133x magnification with a 9mm Nagler eyepiece) it was transformed into a vast three-dimensional city of stars, its brighter members glinting like crushed diamonds right across the face of the cluster, with hundreds - perhaps thousands - more revealing themselves in averted vision. The longer I looked, the more impressive it became, as I began to discern chains of stars arcing out from the centre.

M13 is arguably the most spectacular globular cluster visible from UK latitudes, but there are several others which run it close, such as M3 in the constellation Canes Venatici:

Messier 3
M3, Tele Vue-60 + Canon 80D (31 x 1 min @ ISO 800)

Of course, acquiring the images is only half the battle; processing them is an art-form in itself. I'll leave those details for another time as I'm still very much a beginner at this, but if you want to know what software I used, the links are here.

In the meantime, if you ever get the opportunity to look at M13 or any of the other showpiece globulars through a medium to large-sized telescope, I strongly recommend it. Drink in the spectacle, contemplate what you're seeing, and then look at it again. Photographs just can't do it justice.

See more of my TV-60 deep-sky photos on Flickr.


*Famous last words... While I was drafting this post, He-Who-Must-Not-Be-Retweeted announced the creation of SPACE FORCE (I swear I can hear the echo as I'm typing it). It seems there really is no escape from the Tangerine Nightmare.

Sunday, 13 May 2018

Birds of East Kent: Kestrel

Latest in an occasional series of posts discussing the different birds that can be found in East Kent and how easy (or not) it is to get a decent picture of them.

Kestrel (Falco tinnunculus)

I don't usually bother with top-ten lists or stuff like that, but if I had to choose a favourite bird it would undoubtedly be the Kestrel. It's not the biggest (or smallest) bird of prey; nor is it the most colourful. It's not even the only British bird that hovers, though the other contenders can't hope to match its precision or its tenacity. But, more than any other bird, it's always been a small part of my life in some shape or form. It was there on the striking red badge I received when I joined the YOC:


It was there in Ken Loach's famous film (adapted from the novel by Barry Hines) that I saw in my early teens. And it was there at the start and end of the summer holidays, glimpsed from the side window of a car; a bird that seemed to defy not just gravity but time itself as it hovered above the roadside verges while the twentieth century flowed around it.

Kestrel (Falco tinnunculus)

I've had the privilege of seeing a wild kestrel up close on a couple of occasions, most recently in February of this year when I encountered one perched in a small tree by the North Foreland golf course. I took some photos and continued on to Botany Bay to see if there was anything interesting on the shore. When I turned around to walk back I was surprised to see the same kestrel standing on a fence post. Naturally, I couldn't pass up the opportunity to take some more photos:

Kestrel (Falco tinnunculus)

From badges to films to poetry (see: The Windhover by Gerard Manley Hopkins) there is something about the kestrel that seems ingrained in the British psyche. A good example of this can be found in Powell and Pressburger's 1944 wartime classic A Canterbury Tale. In the film's prologue, a group of medieval pilgrims make their way towards Canterbury while a voiceover narrates a passage from Chaucer's text. A falconer stops to release a kestrel into the sky. The bird dips and soars ... and transforms into a Spitfire flying above the English countryside. Four hundred years of history spanned in a single cut.


If the description of that scene rings a bell it's because Stanley Kubrick used the same trick in the famous bone-to-spacecraft transition in 2001: A Space Odyssey. Coincidence, homage or blatant rip-off? It's a question that's been debated for fifty years, and will probably be debated for fifty more. In the meantime, the kestrel continues to soar above fields, along cliff-tops, and across marshes - hovering, observing, sometimes descending for prey, and then moving on, seeing colours that no human eye can see as it patiently constructs its daily map of the world.

Effortlessly at height hangs his still eye.
His wings hold all creation in a weightless quiet,
Steady as a hallucination in the streaming air. 
Ted Hughes, The Hawk in the Rain (1957)


See also:
More of my Kestrel photos on Flickr
Kestrel (RSPB)
Kestrel (Birdforum)
Kestrel (Birdguides)

Sunday, 24 December 2017

2017 in Pictures

I normally leave end-of-year round-ups to the more prolific bloggers, but this year I've taken a lot more photos that usual, partly because I bought a new camera, and also to serve as a welcome distraction from the daily hourly news maelstrom generated by Brexit and He-Who-Must-Not-Be-Retweeted. It's reassuring to know that there are still some quiet corners of the world where wagtails still wag, kingfishers still fish, and kestrels still hover, unconcerned by the sound and fury of angry old men who never stop to listen.

But enough of all that; here are some highlights.

January
Photographers often rhapsodise about the "golden hour" just before sunset, and it doesn't get much more golden than this:

White on Gold

February
A Water Rail breaks from cover at Grove Ferry:

Water Rail (Rallus aquaticus)

March
This colourful Pheasant took it upon himself to greet visitors to the Stodmarsh car park:

Pheasant (Phasianus colchicus) 

April
A smart Shelduck flies overhead at North Foreland:

Shelduck (Tadorna tadorna)

May
A dull and drizzly May Day at Grove Ferry was livened up by this magnificent Kingfisher (one dive, one fish caught, one lucky photographer):

Dive!

Later in the month, a decent view (for a change) of a Cuckoo:

Cuckoo (Cuculus canorus)

June
The dragonflies at Grove Ferry / Stodmarsh attracted lots of visitors, including this dashing Red-footed Falcon:

Red-footed Falcon (Falco vespertinus)

July
Fortunately there were still plenty of dragonflies left after the Red-footed Falcon departed, including this Norfolk Hawker (aka the Green-eyed Hawker):

Norfolk Hawker (Aeshna isoceles)

August
Lots to see in North Yorkshire, including Red Grouse:

Red Grouse (Lagopus lagopus)

...and the famous Gannets of Bempton Cliffs:

The Gannets of Bempton Cliffs

Back in Kent, a relative newcomer to Grove Ferry, a Willow Emerald Damselfly:

Willow Emerald Damselfly

September
Some drastic Photoshopping saved this image from the bin. The Marsh Harrier changed direction so suddenly I cut off half of the upper wing and had to clone it from the other one. I wouldn't normally do this much work to an image, but I think in this case it was worth it:

Marsh Harrier

October
Fortunately my reflexes were a little better when this Kestrel made a quick getaway:

Flight of the Kestrel

November
After seeing a Red-throated Diver in 2014 and a Great Northern Diver in 2015, I wondered how many years I'd have to wait to see a Black-throated Diver in Ramsgate Harbour. Turns out it was only two:

Black-throated Diver (Gavia arctica)

December
Another new visitor to Ramsgate Harbour, an Iceland Gull:

Iceland Gull (Larus glaucoides)

The year started with a Little Egret against a golden backdrop, so it seems fitting to end it with its larger cousin, a Great White Egret, looking for fish in front of the golden reeds of Grove Ferry:

Great White on Gold


No autofocus was used in the making of these pictures.