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...

See also:
Cosmic Challenge: M51's Spiral Arms - Phil Harrington (Cloudy Nights)

Into the Orion Nebula

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?

Answer: "It's a Tele Vue."

The question being, typically: "What's that on the end of your camera?"

As the name of this blog suggests, I do most of my photography with a telescope - a Tele Vue-60 refractor to be precise. What it lacks in autofocus and aperture control it more than makes up for in sharpness and colour correction. It's compact and portable and it doesn't need to be stopped down to hit the sharpness sweet spot. Recently Tele Vue embraced the world of social media and - as part of their ongoing 40th anniversary celebration - they asked if they could feature me on their new blog, in particular why I chose the TV60 and why I've stuck with it over the years. You can read the resulting post here:

http://televue.com/notamnomen/2017/05/02/tele-vue-is-for-the-birds/#.WRC_XNQrL4Y

Three scopes in one: astro-scope, spotting scope and telephoto lens

Astronomers of course need no introduction to Tele Vue, but for those who don't know, they're a Chester, New York-based company founded in 1977 by Al Nagler. Prior to that Al designed lunar landing simulators for the Apollo missions, using his knowledge of optics to create realistic wide-field vistas to aid the astronauts' training.

Tele Vue started out making lenses for large projection-screen televisions, but they've since become renowned for their high-quality eyepieces and telescopes. If you ever get the chance to look through one of Tele Vue's wide-field eyepieces, I highly recommend it. They call it the "spacewalk" experience and with good reason: if, like me, you started out in astronomy squinting through a cheap and cheerful 0.965" eyepiece, the difference is startling. When looking through a Nagler it's as if the eyepiece "gets out of the way", leaving you immersed in the stars (or suspended above the moon if lunar observing is your thing). And if the 82-degree apparent field-of-view of a Nagler isn't enough for you, they also do an Ethos range, which goes up to a whopping 100 degrees.

In the interests of fairness and transparency I should point out that:

a) Other telescopes and eyepieces are available
b) I was not offered any incentive by Tele Vue (financial or otherwise) to contribute to their blog or write this post. I'm just a proud TV-60 owner and I wouldn't dream of parting with it.

See also:
Tele Vue home page
My TV-60 photos on Flickr