Starting to do some science in the observatory – Jupiter, Uranian Moons and discovering asteroids

Over the past week or so I’ve been sorting out cables in the observatory and testing cameras. Still only on al alt-az mount without guiding, but a good enough setup to try a few things.

Firstly is planetary imagining. Now that I can collimate quickly and have a made a Bahtinov mask getting planetary webcam imaging is fairly straightforward. There are a couple of problems still. Firstly Jupiter doesn’t rise high enough until after Midnight, and I like my sleep. Secondly is that the focussing needs to be accurate, the mask helps immensely However the tiny webcam chip needs to be placed very accurately, and that means focussing down to around 0.5 mm. I’ve a helical focusser which allows me to focus that reasonably accurately; though it does mean touching the focuser which is connected to the camera which causes a wobble which makes focussing harder. Long term an electronic focuser will be needed. Anyway here’s another stab at Jupiter.

It’s ok. I really need to read up on wavelet processing in registax. I think I’ve got the best of the frames aligned (700/1200 in this case), but the processing introduces artifacts into the image. I’m also still experimenting with the exposure, fps, and gain on the webcam – I think I’ll have to ask someone with more experience what the raw avi should look like.

Sticking with planets I thought I’d have a stab at something I’d never managed to capture on camera before. Moons of Uranus.

It’s an easy enough shot, though care needs to be taken to get the exposure to just show the moons, and keep the brightness of the planet to a minimum. And also try and keep the noise down. This was with 4x30s exposures at 100ISO, using dark frames as well to reduce the noise. Ttania and Oberon are clearly visible. If you play with the fits image a bit you can make out something sticking out on the circle of Uranus where Ariel is supposed to be. Uranus itself is an easy target at the moment.

Lastly I wanted to see how Astronometrica works with a DSLR. Using this with an uncooled DSLR on a alt-az mount gives several challenges, not least that the signal to noise means that it has a hard time working out what exactly is a star. Nevertheless once you get the pixel size, focal length and rough centering and orientation of the image correct you can get a manual match, and once thats done it can usually automatically work out the image. Astronometrica is mostly used to look for and track asteroids and comets, you give it an image and it will map reference stars to it. Give it a few images and it will align them and you can ‘blink’ between them and you can see if one of the ‘stars’ is moving. It can also detect these moving objects and compare them to the positions of known objects. So for a first run at this I decided to give it an easy target and see if it could work it out. And it managed to automatically find the reference stars, granted after initial manual tweaking, and informed me that I had just rediscovered Pallas.

Pallas was discovered in 1802 by Heinrich Olbers, better known for Olbers Paradox – ‘Why is the sky dark at night?’, but thats a whole other topic! Pallas is bigger than Pluto, and was also initially classified as a planet.

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