Looking Up

I've always been interested in astronomy and have owned a couple of telescopes, but lately it's really taken over my life. Back in March, I wound up buying a Celestron Neximage 5, which is a sort of modified webcam that you attach to your telescope to take pictures of the moon and planets. These are high-brightness objects where the main obstacle to a good picture is the state of the atmosphere. Air currents cause the image to wiggle and waver like it's at the bottom of a pan of water just on the edge of boiling. To deal with this, you take lots and lots of very short exposure pictures- perhaps as high as a hundred frames every second. Once you have your pictures, you sort through for the best and digitally stack and mess with them to bring out the sharpness. Happily, there's a lot of cheap (even free!) software that will help automate the process of taking, aligning and stacking a thousand-plus frames of video.

My first photo of the moon

Jupiter, complete with red spot. Two moons can also be seen

Mars, or possibly a space potato. The polar cap is to the upper left, the dark triangular region is Syrtis Major Planitia

Montes Caucasus region, the moon.

Saturn, with the Cassini division plainly visible in the rings

Saturn at a lower power of magnification

My first few pictures lit off something of a fire in me, so I went out and got a much better mount than the one with my telescope (a Celestron Nexstar 6se- the mount's great for visual work, but for photography, a bit wobbly and doesn't track so well)  and also a second-hand 200mm Newtonian reflecting telescope from eBay.

Next came a new camera. The neximage 5 is well suited to bright planets and the moon, but not useful for dimmer objects like star clusters, nebulas and whatnot where you don't want high framerates but long exposures of several minutes. The Neximage 5 would rapidly build up a flood of thermal noise in the picture at that kind of exposure, so I picked up a cooled astronomical CCD camera to use for deep sky work.

The problem with long exposures, though, is that it requires extremely precise tracking- if the telescope doesn't perfectly follow the motion of the stars, they will start to streak the image. Partly this can be solved by a very accurate set-up of the telescope, so that its axis points towards the celestial north pole, near where Polaris, the pole star lives. Unfortunately that's tricky for me as I don't have good visibility to the north, as the house is in the way. I have to do a bit of messing around with what's called "drift alignment", which I haven't quite mastered yet. To help with any remaining inaccuracies, most astrophotographers use auto-guiding, where they have a smaller telescope fitted to the main one, and a second camera that takes an exposure every second and feeds it to a computer that checks the star positions between frames. If there's any drift, the computer sends commands back to the telescope mount telling it to shift position slightly to line things back up.

I don't have the ability to do auto-guiding yet, what with money and stuff (maybe next pay-day...) so I hadn't tried deep-sky astrophotography until last weekend. I'd gone out to take more pictures of Saturn, but it took me longer than I expected to set up, so by the time I was ready, Saturn had ducked behind the trees. Not wanting to totally waste the night, I decided to at least try the CCD camera just to get some experience working with it.

I'd only roughly aligned the mount (the goto contoller was telling me I was out by five times the apparent diameter of the moon!), so I knew I couldn't take long exposures. I hadn't planned on doing deep-sky work, so I hadn't had the camera's cooler switched on, so long exposures would wind up with lots of thermal noise anyway. It's almost bang-on the time of year where the nights are so short they never get properly dark and I really wasn't expecting much of anything. I set the goto controller to point to Messier-57 and stared into the eyepiece at a faint grey circle that may or may not have been my imagination. Yeah, not much of anything.

I swapped the eyepiece for the camera and started up Nebulosity on my laptop. Right there in the preview window was a ghostly grey ring. I might get something out of this after all!

Exposure to 10 seconds- keep them short to avoid streaking, but switch the camera to 4x4 binned mode, where 4x4 squares of pixels in the camera are added together to make one pixel in the image, producing a lower resolution image but with sixteen times the sensitivity to light. Take a sequence of five images and let's see!

A picture! Noisy and low-res, but a picture! M57, the ring nebula, and with colours right there in the picture!

I also took some dark frames to compensate for noise and also did a set of five images at 15 seconds exposure and 2x2 binning for more resolution at the cost of less sensitivity and more trailing of the stars.

Sure, the Hubble Space Telescope may have taken far better pictures, but they had a higher budget AND ASTRONAUTS. I had a few bits of silicon and some bent glass I bought off eBay!

Is this thing still on?

It has been a while since my last post.

Things have changed in the last nearly-two-years. I changed jobs, for starters. A colleague at my last job wound up killing himself. Although I doubt it was (solely) work-related, I decided it was yet another sign I might be happier elsewhere. It hadn't helped that I'd been involved in getting the guy recruited in the first place, yet learned more about him trying to find his next of kin for the police by reading his facebook page, than I had with him sat right there in the office for months.