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.
A Typical Assignment
The word 'hero' is bandied about a lot these days, particularly in a sporting context. A crucial tackle on the football field is more likely to be hailed as heroic than a heart bypass operation, possibly because the latter isn't typically performed in an arena of 50,000 screaming fans.
So I'm reluctant to use the term. However, every once in a while I come across an individual so bold and selfless that I'm forced to concede it's the only word that fits. One such unsung hero is Wikipedia's Scale Guy.
Untroubled by the largest carnivorous dinosaur and - with apologies to Sam Neill - star of Jurassic Park 3.
It's not simply a case of a dangerous job done well. It takes a special kind of person to confront such peril with cheery fortitude.
Unbowed before a platoon of goose-stepping tyrannosaurs.
Untrampled and ungored by triceratops both prorsus (?) and horridus.
Uneviscerated by a pack of raptors.
While mostly known for his work with dinosaurs, Scale Guy has occasionally branched out into other categories of peril.
So if you have something dangerous and no-one else is willing to stand next to it, maybe you can call - Scale Guy.
Images by wikimedia users Dropzink, Matt Martyniak, Pilcha, Ornitholestes and Kurzon.