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Dalriada n:
Kingdom of the Scots,
home of the residents

Jupiter’s moons are in the frame

I have been struggling to get a decent image of Jupiter in a wide enough field of view to include a few of its Galilean moons.

Here is the Stellarium screenshot as usual:

Screenshot_2016-05-11_20-41-21

Also, I discovered a great site at http://www.shallowsky.com/jupiter/ which plots the positions of Jupiter’s Galilean moons at any specified date/time. Here is its screenshot (although I think Europa is behind Jupiter, not in front of it, at Tue May 10 2016 22:37:20 GMT+0100) :

moons

But it is quite difficult to reproduce anything quite like that using a camera and a telescope. The problem for astrophotographers is that the planet is so bright and its moons are so dim that it is very difficult to get a reasonable image of the planet which includes some of its Galilean moons. My SkyWatcher 200mm Newtonian ‘scope (which has a bigger field of view, less magnification, than the 150mm Maksutov) was already set up in the garden, from Mercury in transit, so I decided to have another go. I produced these with my ZWO ASI224MC camera:

22_38_37_g3_ap1_conv

original image shows Jupiter’s bands – but no moons are visible

22_38_37_g3_ap1_conv_01

increase the exposure to see the moons, but now the planet is way over-exposed

We have to ‘cheat’ a bit and use some image processing software. I used a program called Darktable to draw a mask round Jupiter so that I could selectively increase the exposure of the rest of the image, until I could see three Galilean moons. Then I used GIMP ( the free Linux equivalent of Photoshop) to rotate the image to match the Stellarium screenshot – and add a bit of annotation.

jupitersmoonsviagimpanddarktable3