One of my favorite regions of sky to image is around the constellation of Orion. Hiding within one of the most recognisable asterisms are: an ancient supernova remnant written large across ten degrees of the sky, dusty regions sculpted by stellar winds and radiation pressure and a plethora of star-forming regions.
This first image shows the constellation Orion below the Milky Way, which runs from middle left to the upper right corner. The Rosette nebula is on the left while the Hyades cluster is on the right, with the orange giant Aldebaran in front of them. It was taken with a kit lens at 18mm/f5.0 on a modded Canon 1100D camera. It's a slight crop, the field of view is about 40 by 55 degrees. The plate-solved image below shows Orion in relation to its neighbouring constellations.
A 50mm lens gives a closer view of the busiest region of Orion, including the seven bright stars recognisable to even the most casual stargazer.
The bright star at upper left is the red supergiant Betelgeuse. If placed at the centre of our solar system Mercury, Venus, Earth, Mars and perhaps Jupiter would be inside it. Yet despite its vast size its mass is only 10-15 that of the Sun, its tenuous outer layers being no more than hot near-vacuum.
The contrasting star at lower right is the blue supergiant Rigel, over 100,000 times brighter than the Sun. It is responsible for lighting up the dust cloud to its right known as the Witch's Head nebula, although in this orientation I think it looks like a leaping dolphin.
The nebula at the head of Orion is sometimes known as the Angelfish. Intense UV radiation from the star Meissa ionizes a could or largely hydrogen gas, causing it to glow a characteristic deep red colour.
Finally, the enormous nebula on the left of frame is Barnard's Loop. It's thought to be the result of a 2 million year old supernova, the explosion swept gas and dust into a roughly spherical shape. From our vantage point we see the left hand edge of the sphere because we are looking through a greater depth of materiel. The other side of the arc may be invisible because there was less material to be swept up in that direction, or because there are no hot stars in that vicinity to light it up. These superbubbles are fairly common, our own solar system is passing through one.
A 200mm lens gives a closer view of Orion's Belt and Sword, home to some of the most famous objects in the night sky.
Rotated 90 degrees anticlockwise from the other images, the bright star at lower left is Alnitak, the leftmost star of Orion's belt. Scattered across the frame are a collection of star-forming regions, in different stages of evolution.
The Flame Nebula on the left has a unique yellow colouration, I haven't been able to find an explanation of this. I suspect it has something to do with scattering of light by foreground dust. To its right lies the famous Horsehead Nebula, readily visible silhouetted against the bright emission nebula IC434. The Horsehead is at any early stage of star formation, a cloud of gas and dust is collapsing under gravity to form new stars which are obscured in visible wavelengths by the concentration of dust. Infra-red light is attenuated less, making it possible to peer inside the Horsehead and see these newly formed stars.
On the right of the image lie two bright nebulae, embedded in a wider dusty region. On the left is the Running Man, a reflection nebula. To its right is the Great Nebula in Orion, M42, the closest star-forming region to Earth and easily visible to the naked eye. (I like to think of it as a great engine of possibilities, a few hundred stars are in the process of forming inside it along with associated planetary systems. Our own Sun would have been birthed in a similar nebula about 4.5 billion years ago.) M42 is in at a much later stage of evolution than the Horsehead. Intense radiation and stellar winds from the hot young stars at its core are expelling gas and dust into space, giving it the appearance of an open rose. This will bring an end to star formation in the near future, leaving behind a bright open cluster.
These images show what is possible at the budget end of astrophotography. The first two were taken with cheap kit and 50mm lenses, a modded DSLR and a basic tracking mount. The final image was taken with a fairly expensive lens, a second hand Canon L 200mm f2.8, and a borrowed, more sturdy mount. However, similar results could have been achieved with a much cheaper optic, using a longer exposure time.
Got up at 3:30 this morning to image Comet Catalina passing close to M101 (the Pinwheel Galaxy). First light for my kit in a while due to the terrible run of whether we've been having, and first legs for my astronomical longjohns, which did their job of keeping my legs warm. The above image was taken using a vintage 135mm lens and modded Canon 1100D camera, it's 14 minutes exposure time in total.
The comet is displaying two distinct tails, a wide dust trail pointing up and a fainter, narrower ion tail to the left. The dust is left behind in the wake of the comet's orbit, while the ion tail points away from the Sun as it more strongly affected by the solar wind. M101 is a spiral galaxy similar in size to our own Milky Way. Above and to its right a faint smudge is visible. This is another galaxy, a satellite of the Pinwheel that has been disrupted by its gravity, NGC 5474.
Comet Catalina C/2013 US10 makes its closest approach to Earth tomorrow, the 17th January. By coincidence it also makes its closest pass to M101 on the same date. Hopefully the weather will be kind and some astrophotographers will be able to capture it at higher magnification than I could manage with my mid-telephoto lens. There will never be another opportunity to image this particular comet. After making its closest approach to the Sun on the 15th November it is heading back out of the solar system and will escape into interstellar space.
When it comes to imaging galaxies it's natural to think that a large telescope is required, we picture of Hubble orbiting in space or giant domes on Hawaii or in the Chilean desert. And for the majority this is true due to the vast distances involved. However, there are a handful both large and close enough that they can be imaged with a small camera lens. Conveniently the two with the largest apparent size, that are visible from the northern hemisphere, are close enough in the sky that they can be imaged together.
Shown above are the Andromeda and Triangulum galaxies, our two nearest large neighbours. Andromeda is slightly larger than our own Milky Way and is thought to contain a trillion stars, while Triangulum has a relatively modest 40 billion. The bright star in the middle is Mirach, a red giant roughly a hundred times larger than out Sun. While they are relatively faint objects - the core of Andromeda can see seen through moderate light pollution while Triangulum is only visible from the darkest sites - they occupy considerable real-estate in the sky. Here's the Moon pasted in to give a sense of scale.
The image above was taken with a cheap 50mm lens at f4.5, using an entry-level DSLR camera and a simple tracking mount as shown below. It's about an hours worth of 210 seconds exposures, combined in Deep Sky Stacker and then processed in my usual erratic manner.
For a closer look at Andromeda I used a 200mm lens to take the image below, quadrupling the magnification. The image below has also been cropped for an even closer view.
The yellow core indicates a population of older stars while the bluer spiral arms are a sign of recent star formation. There are two other small galaxies in this image, M32 and M110, both satellites of Andromeda. Our own galaxy also has two prominent satellites, the Magellanic Clouds, that are visible from the Southern Hemisphere. The larger of the two has an apparent size of almost 11 by 9 degrees, twenty times the width of the full Moon. Hopefully someday I'll get a chance to image them on a trip south of the equator.
Finally, here's a wide angle shot taken with a kit lens, showing Andromeda Triangulum relative to the Milky Way. The W-shaped constellation of Cassiopeia is in the centre of the frame but it's quite difficult to spot against the dense starfield.
How does an alien go about casting a horoscope?
On a typical day this would be a trivial task for the experienced astrologer. She would ask the client for their place and date of hatching, feed the answer into her Crystal Procrastination Unit and interpret the resulting star-chart using her exceptionally well-honed sense of intuition, guided by the recorded wisdom of the sages and the ages. A Quorzok that emerged from the hatching pool while the pale light of the Stalker glitters behind the head of the Great Ruminant is surely destined to become a famous bantha-hunter – although perhaps metaphorically, especially if they happen to work in administration.
But today our astrologer has a problem. Perhaps, she reflects, if she had the foresight to consult her own horoscope this morning she would have been forewarned. For some decades ago now the Quorzoks discovered the secret of interstellar flight; the expectant client now before her hatched – not under star and sighing wind – but under blinking lights and whirring of fan blades. He is the first Quorzok to be birthed in the depths of space, far from their home world, or indeed any other. She scribbles a few words to hide her surprise.
Returning to her CPU, she enters the co-ordinates of his hatching and is dismayed. From that distant vantage many of the familiar constellations are unrecognisable. Even the mighty Great Ruminant slouches unsteadily, unwell or intoxicated. Worse still, all the home planets descend as one through the Ruminant’s bowels, indistinguishable from each other in their orbits around a dim, unremarkable star.
Troubled and adrift, the astrologer considers the problem anxiously. She turns to a familiar guide and comfort - an anthology titled The Wisdom of the Seven and a Half Sages - yet the words seem strangely empty. Perhaps, she muses, the client experienced a spiritual hatching upon his return to the Quorzok homeworld. Her enquiry meets with a discouraging response: his homecoming was a mere six seasons ago. How could he have lived the balance of his years with no destiny? Is he somehow beyond destiny? Yet she judges - by the quiver of his lower mandible and the piping of his voice - that this client would not welcome that news. An uncomfortable pressure builds in her gas bladder, brought on by stress and uncertainty.
With a deep inhalation the astrologer begins to speak, drawing upon intuition rather more than usual. The client departs eight pizeks poorer but reassured: it seems that now is an opportune time to reorganise the office filing system.
The astrologer, pressure released, relaxes and congratulates herself on a difficult job well done. Her gaze sweeps the artfully precise chamber and she rises to reward herself with lunch. On the desk lie unheeded the words of the half-sage, obscured by her discarded notes: “A seed of doubt, once planted...”
Here's an image I took of the Veil Nebula in Cygnus, using a 200mm lens. It’s a supernova remnant, the remains of a star that exploded perhaps 5,000 years ago. This event would not have escaped the notice of our ancestors, shining more brightly than Venus for a few weeks and visible during the daytime. We can only wonder what they made of it. (I can't really do the Veil justice with a camera lens, this deep hydrogen alpha image by Sara Wager shows its structure in intricate detail.)
Today the expanding nebula spans 3 degrees of the sky, six times the apparent diameter of the full Moon. The red colour is mostly hydrogen while the blue indicates an abundance of oxygen, glowing at a temperature of several thousand degrees. Most of the visible material is interstellar gas swept up by the supernova shock-wave, but mixed in is a sprinkling of heavier elements such as iron, cobalt and nickel from the core of the progenitor star. If you jangle your keys you’re handling materiel cooked up in an explosion like this.
The rightmost component of the Veil is often referred to as the Witch’s Broom for obvious reasons (astronomer see, astronomer say). Above it lies a dust lane, obscuring the stars behind it. The Witch’s Broom is aptly named, as the Veil expands it's sweeping this dust away and revealing - or unveiling - more stars, making it a functional as well as figurative broom.
Eventually the products of the supernova become mixed into the interstellar medium, where they can be incorporated into the next generation of stars and planets.
A simulated view of the winter constellation Orion to show the difference that observing from a dark site makes, and what long exposure photography can reveal.
From town only the seven brightest stars are visible through the murk of light pollution - if you see more in the left hand pane then your screen, like mine, could probably do with a clean. From a truly dark site a plethora of stars pop into view and the Orion Nebula is clearly visible at lower middle. The long exposure reveals thousands of stars, several nebulae and dust lanes in the Milky Way.
Another advantage of a video like this is that it gives a better sense of the relative brightness between objects. Deep images of the sky are both revealing and subtly misleading - due to the limitations of human vision objects of greatly differing luminosity must be presented at a similar level. With the video the brighter objects appear first.
The source image was taken using a 50mm lens on a modded Canon 1100D camera, with a total exposure time of roughly 75 minutes.
Here's an image of the recent Venus & Jupiter conjunction I shot with a 250mm lens. I then pasted in an image of the Moon taken previously to show their relative apparent sizes. At the time the shot was taken Jupiter was about 11 times further from Earth than Venus but being 11 times larger they appear as roughly the same size. Venus, on the left, appears as a crescent due to the angle of illumination by the Sun. Jupiter on the other hand always shows a full disc as it is outside our orbit. The only way to view Jupiter as a crescent is to go there, as the New Horizons probe did on the way to Jupiter.
Planetary imaging requires a seriously high level of magnification. If my maths is correct - something that can never be taken for granted - Jupiter is about as big as the tip of your finger from 200 feet away. The image below was taken with a 12" newtonian telescope fitted with a 4x barlow lens, giving an effective focal length of 6 metres. The mark to the left is the shadow of one of its moons, Io. The famous red spot was on the far side of the planet at the time it was taken.
DSLR cameras provide a cost-effective route into astronomical imaging, especially as the entry-level models are often just as capable as mid-level ones as far as astrophotography is concerned. However, their Achilles heel is poor sensitivity to deep reds. While not a problem when imaging galaxies and star clusters this greatly limits their ability to image emission nebula, whose light mostly comes from clouds of ionised hydrogen. The glowing hydrogen emits in a specific wavelength with a deep red colouration, and as much as 75% of this light can be blocked by the camera’s infra-red filter.
The solution is to remove or replace this filter. For the brave, there are various online guides for performing camera surgery yourself. Alternatively there are individuals who will perform this service for you. I had my Canon 1100D modded by Cheap Astrophotography and am very pleased with the result.
Here’s two images that show the difference that removal of the filter makes. The first shows Comet Jacques and the Double Cluster in Perseus, taken with the 1100D before modification, using a 135mm lens.
Comet Jacques is the green streak at the lower left, with the Double Cluster right of centre. Above and below the comet some nebulosity is faintly visible. The next image shows a very similar field of view taken using the same lens fitted to a modded camera.
Using the modded camera the Heart & Soul nebulae are clearly visible. The comparison is not an entirely fair one as the second image was taken at a site with very little light pollution, but in other experiments I've found it difficult to get much colour from an unmodded camera even from the darkest site.
While summer isn't the best time for astronomy - hindered by short nights and a lack of full astronomical darkness – there is at least one compensation. For observers at high latitudes in the northern hemisphere the season of noctilucent (night-shining) clouds is almost upon us. These tenuous ultra high-altitude clouds are only visible during deep twilight, being lit directly by the Sun while the observer stands in darkness. They are too insubstantial to be seen when standing directly underneath.
Last Summer I was lucky enough to observe and photograph this rare phenomena, only a week or two after learning of their existence. It took me some time to realise what I was seeing, at first I assumed it was a low and near cloud lit-up by light pollution, but eventually I realised it didn't appear to be moving.
This image, taken at about 1:30AM, was featured on the BBC News website. It’s an 8 second exposure taken with a Canon 1100D DSLR fitted with a 50mm lens.
I was curious as to how far away the clouds were, so I plate-solved the image to identify the visible stars and used a software planetarium to find their angles above the horizon. Noctilucent clouds form at an altitude of about 50 miles, so with a quick bit of trigonometry I was able to work out that they were several hundred miles away. From a location a few miles north of London I was looking at clouds somewhere off the west coast of Norway!
Plate-solved image shows the constellation Auriga on the horizon, with the bright star Canopus at upper right.
So if you find yourself at a dark site between June and August it’s well worth taking a moment to scan your northern horizon. A bright display like the one pictured above is clearly visible even from a moderately light-polluted site, while fainter ones may only show up on long exposure photographs.