Shooting stars

The night sky can be a glorious sight on a clear night. If you have ever seen it in a part of the country unaffected by local street lights or the light pollution from a nearby city, a sky full of stars is a thing of wonder. 

In my part of Sussex, there is always the orange glow of Brighton on the southern horizon. The city itself is hidden behind the South Downs, but nevertheless signals its presence after dark and lightens the sky somewhat in that direction. When there is no moon, the southern sky can still look good, but it's a compromised view. 

If I look northwards from my house, the sky is darker, but still nothing like the intense blackness one can find out in sparsely-populated countryside, a blackness in which thousands of visible stars can be seen, some of them coloured red, yellow or blue, depending on how hot they are, how large they are, and how near they are. To the unaided eye, they are all just points of light, being far too distant to show a disc, as the Moon and the other planets in the Solar System can. Even so, fascinating to observe, although sometimes hard on the neck, and an occupation to chill you to the bone on winter nights.  

I don't possess a telescope, nor even a pair of binoculars, but now and then I attempt to take photos of the night sky, which I can then study at high magnification on my laptop. I had another go earlier in the week. I popped Lili on my tripod, setting the focus to infinity, and setting the shutter speed for an automatic time exposure, meaning that I was letting the camera work out the appropriate ISO, and to time the exposure accordingly. The focal length was of course fixed at 23mm (equivalent to 35mm in full-frame terms).

As it happened, Lili's shutter opened for 1 second with all three of my shots. The ISO however was 1,000 for one, and 3,200 for the other two. Why this variation? After all, the shot using an ISO of only 1,000 was aimed at the darker sky to the north-west. Well, the other two shots, taken with an ISO of 3,200, included bits of Jackie and Kevin's house next door and I think that Lili was trying hard to get their roof and the top of their campervan properly exposed in preference to the night sky. So she upped the ISO sensitivity. 

I should have chosen the ISO manually, and not left it on automatic. A high ISO value is like increasing the volume on a TV or radio or speaker - the higher you make it, the greater the likelihood of output distortion. In photo terms, this means 'noise' - speckles and patterns in the background of the picture which progressively smudge the detail captured, and alter the colour fidelity. 

All this said, I wasn't disappointed with Lili's first foray into celestial photography. It was a casual, spur-of-the-moment affair that turned out rather well. 

Next time I'll take more pains, and also do it later in the evening (my shots were grabbed around 8.00pm). I may live in a village, but there is still too much light pollution from nearby street lamps. But these are turned off after midnight, and that's the better time to get out the tripod and have a go. Although (a) even in summer it might be damned cold; and (b) it's very creepy out of doors, standing around in the darkness! I might in fact leave the next attempt to my first caravan holiday, on my usual farms in the West County. I should get much better results in those deep-countryside locations, and for some reason won't feel so exposed to the kind of midnight prowlers you think of in Sussex, whether they are hedgehogs or foxes or mad axemen. The moos and baas of cows and sheep on farms are much more reassuring!

Anyway, what did I get?

First up, a shot of the constellation Cassiopeia, unmistakably W-shaped. This was the shot taken facing north-west at only ISO 1,000, which in theory should make it a better-quality shot. (Click on any of the following to enlarge them - they are much clearer that way)

Zooming in:

Hmm. All the brighter stars are there. And they do look pretty distinct. And the ISO 'noise' is very subdued. ISO 1,000 looks about right.

Next, the two shots taken at ISO 3,200. These show a distracting background texture or patterning that wasn't there in reality. It's just a sign that Lili's APS-C sensor from 2016 struggles a bit with this kind of photography. A larger, modern sensor would give me better results. (But I have no money left for a newer camera, and must make do with what I have)

The first of these sub-standard shots is of the constellation Taurus, with the star-cluster called the Pleiades off to the right:

Zooming in, here's a close-up of the distinctive V-shaped formation in Taurus at left centre:

And here's Pleiades, right centre, very much enlarged:

Ah, this illustrates two problems with star-photography. The stars look like little globes, but this is spurious and is just the effect of setting Lili's lens at infinity: very distant points of light have become small discs that seem to have a measurable diameter. But it's simply a product of how the camera lens has been focused, and its own optical limitations. I'm not going further into the theory: read up on Circles of Confusion if especially interested. 

The other problem is that the stars look elongated. This is what happens if the exposure is long enough to record the rotation of the earth. And at this magnification, one second is quite long enough to show the effect. Ideally, the camera needed to be edged slowly sideways to counteract the earth's movement. Keen amateur astronomers and national observatories have mechanisms to achieve that. Me, I'll have to make do without, and just come out with endless excuses!

The third shot was of the constellation Orion:

And here are two enlargements, the top one showing the huge star Betelgeuse in the bottom left. and the lower one showing the 'belt' of Orion and the 'sword':

Even at ISO 3,200, it's a decent result, showing all the main stars and nebulae. The super-hot blue stars show up well, but nearly all the red hues have been suppressed. In actuality Betelgeuse is distinctly orange-red, even to the naked eye.

I'm rather pleased with these off-the-cuff shots, taken in sub-optimal outdoor lighting conditions, with in two out of three cases higher ISOs than I'd wish. And despite these defects, they are surely best night-sky pictures I've yet taken. 

I'll set Lili up better in future, and be more picky about the background lighting conditions. 

I must remember to take my tripod with me on holiday!