Sometimes you get lucky

A night at the cemetery
A night at the cemetery. Photo courtesy of Roman Kucharczyk.

Planetary image processing has never been my thing, as I mentioned in a recent blog entry.

There are lots of examples of amateur astronomers producing great planetary results all over the web. I like looking at planets but the processing part has always seemed tedious. And in case you haven’t noticed – I’m a Mac guy, not a Pee Cee dude. It’s a sad fact that much of the astronomical imaging software is only available on computers running Windoze. That’s just not right. The Mac is perfectly capable!

I use my Mac for just about everything – from emails and web browsing, personal finances, video editing, to electronics engineering and printed circuit design. So if I have to fire up my klunky Pee Cee just to run RegiStax, it can only mean one thing: The world has problems.

Well it does, but that’s what I’m trying to forget by looking upwards!

But now that I’ve had some success with the free, open-source, and cross-platform tool Siril running on my iMac, I’ve re-evaluated the notion of spending some more time among the planets. And with Jupiter and Saturn well-placed this time of year, I’d better collect some images!

On one recent and particularly nice night (September 4th to be exact), I was out at the cemetery with Kevin O’Neill and quite a crowd of onlookers just cruising the sky as we often do. I trained my little ASI120MCS camera and a 2.5x Power mate focal expander on Jupiter.

I soon discovered that Jupiter’s moon Io was perfectly positioned for a photo-op. Io had eclipsed Jupiter and was just emerging from the bright glare of the planet. Cool!

This is not uncommon, and easily predicted in Stellarium, but I hadn’t planned ahead that night. And what a bonus – the seeing was actually pretty decent. I started collecting frames and soon realized that I had some imagery that would be worth playing with later. And so it was.

This image is one try at processing the best 1% of the thousands of frames I collected that night:

As Io emerges from the glare of Jupiter, it’s shadow falls on the clouded surface.

Still a bit fuzzy, but yielding more than you’d see from a quick glance through the eyepiece.

Planetary imaging techniques are quite different than those used for deep-sky imaging of galaxies and nebulae. Rather than minutes-long exposures, the goal is to collect as many short exposures as you can. In this case, 10 milliseconds per frame.

The ASI120MCS is not the greatest camera. It’s used primarily as a guiding camera for deep-sky imaging, and I typically ignore it for anything else. It’s uncooled – the temperature was about 17 degrees C during this capture. And so it is somewhat noisy. But it’s inexpensive, it exists, and is easily moved from the guider scope to the primary focal plane of my CPC-800.

The planets are bright enough for short exposures to yield sufficient light while simultaneously allowing fast enough framing to occasionally catch a frame at an instant of temporary atmospheric stability – calm air!

So you collect movies and then pull out the frames later. Siril automates the process of grading the frames (roughly) for quality so that you need not sift through thousands of frames manually. This is the key to processing planets. It also has the aligning, stacking, and wavelet sharpening that’s needed to produce a still image from the small percentage of good images.

None of this is new of course, and users of Registax and other software tools have been doing this for years. And I still find the process tedious.

But this neophyte astronomer is somewhat empowered by discovering that Siril is pretty reasonable and best of all – cross platform. I – and Siril – are still rough around the edges. But it’s a start – and a lucky happenstance to see a nice view of IO that might otherwise have been missed.

Amateur astronomy is a tough hobby, but sometimes you get lucky.

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