Blue Saturn and Rhea Transit

As Emily points out on this post on the Planetary Society blog, it can be fun to have a look through the Recent Cassini Images page and see what’s arrived from Cassini recently. So here’s a couple of interesting images I found from today’s batch.

First, here’s a nice picture of Saturn with its satellite Rhea passing in front of it. This is actually “true colour” (actually taken with red, green and blue camera filters), though since the component images haven’t been calibrated and corrected for camera distortions yet they’re not quite what we’d see with our own eyes – but it’s close. Saturn’s a little yellowish but there’s not much colour visible. The coloured ‘afterimages’ of Rhea are caused by the fact that it moved across the field of view while each component picture was being taken (it’s moving from right to left). Below the ringplane you can see a foreshortened dark dot on Saturn – that’s a shadow of another moon passing between Saturn and the sun, so if you were in the cloud deck at that location then you’d see a solar eclipse! The component images are: 65795 (blue), 65794 (green), and 65973 (red)
This next one’s kinda fun – Saturn’s gone blue! It’s actually a false-colour image made by using a Methane2 (727nm) filter instead of a Red filter (649nm) in the red channel of the image. This filter is sensitive to infrared wavelengths, which allows us to see the details in the cloud deck more clearly (compare with the true colour image above, and you’ll notice that you can’t see the banding in the atmosphere there). Because the Methane image has more varied contrast than the Green and Blue images, it tints the planet a rather nice shade of blue as well – though it’s amazing how much of a difference that 78 nanometres makes! This is why it pays to have a variety of different filters on a spacecraft. The component images are 65788 (blue), 65789 (green), 65790 (methane2)

The neat thing is that the Cassini Images site gets updated pretty much on a daily basis, so there’s always something new to look at there!

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