Jupiter – Captured 21st-24th May 2017
This is a set of three shots of Jupiter captured in May 2017. All consist of the best 4000 of 8000 frames captured in Firecapture with my ASI120MC planetary camera through the 8″ LX90ACF with a 2.5x Revelation Barlow (so a focal ratio of about F/25). This was my first proper attempt at planetary imaging with the LX90ACF – and what a scope it is for that. The results have been processed using AutoStakkert2. AS2 analyses the video, then orders the frames by quality (i.e how sharp they are). The best 50% of the frames are then taken and ‘stacked’, which effectively pulls out the sharpest parts of each frame and combines them into a single frame, ready to have sharpening tools applied. Stacking like this provides the best possible starting point for sharpening, as well as improving the signal to noise ratio. This means that sharpening can be pushed that little bit further before the image starts getting really grainy.
The more frames that can be collected, the better, and the more chance there is of getting a good final result. However! Jupiter rotates so quickly, that if you take more than about two minutes of video, the rotation of the planet becomes noticeable, and the stack will show evidence of ‘smearing’ – like the planetary version of motion blur! This is why a high frame rate is important – to capture as many frames as possible in the minimum time.
The stacked image is then sharpened in a program called ‘Registax’, using a tool called ‘Wavelets’, which is basically a very controllable form of sharpening algorithm, tailored to getting the best out of planetary images.
These images were taken over three separate nights, and as you can see, the position of the planet was different in each one. The Great Red Spot (a double-Earth-sized storm) can bee seen on all three, though in different positions. Also you’ll notice that the quality varies depending on the night. This is mostly down to what’s known as the astronomical ‘seeing’. This is a measure of the air stability and transparency. On nights of steady seeing, the chances of capturing more high-quality frames are much higher.
Jupiter is a fantastically dynamic planet. The storms and swirls on the gaseous ‘surface’ are constantly changing. The four largest ‘Galilean’ moons, Europa, Ganymede, Callisto and Io, often transit in front of the planet, and cast shadows which can be seen in a telescope and on images. None visible in this set – maybe next time!