Friday night at the Whirlpool

I can never seem to get enough of M51, the beautiful, the fantastic Whirlpool Galaxy. It was irresistible on another Friday night impromptu stargazing session. Friday was the warmest night so far with nice conditions for spring stargazing, with a light breeze, no bugs, and decent transparency and seeing.

I grabbed a new set of 3-minute exposures, about 26 of them (it would have been 31, see below!).

The Whirlpool Galaxy is a beautiful pair of interacting galaxies that are located just a bit off from the Big Dipper, and about 31 million light-years from Earth.

Here’s a pro tip though for deep sky photographers from a neophyte astronomer – don’t forget to remove your Bahtinov mask! A Bahtinov mask is a focusing aid that you place in front of the telescope while fine-focusing on a bright star. It’s a deceptively simple yet terrific tool, one that I cut from a sheet of poster board using a craft knife. The mask produces a distinctive spiked diffraction pattern which becomes symmetrical when your point-source (star) is in perfect focus. Great!

Diffraction pattern, the result of focusing on a bright star while using a Bahtinov mask.

But this wouldn’t be the first time I forgot to remove it after focusing! Returning the telescope to M51 yielded a muted picture of the galaxy that didn’t look too bad at first. But I neglected to realize for the first five exposures that it wasn’t quite right, as I was still shooting through the mask! Oh well! I had to toss those exposures, but I took 26 more of the three-minute shots @ 1600 ISO through my DSLR camera:

M51 – The Whirlpool Galaxy taken on April 14, 2023. 26 sub-exposures of three minutes each, processed with the newest version of Siril – 1.0.2b2.

It was still great fun as I killed time walking around the cemetery, listening to owls and coyotes while watching for meteors. Cool!

The image served as a nice test subject for trying out the Generalized Hyperbolic Stretch transformation, a nice addition to latest version of Siril. I’m quite happy with the results, although I must admit I spent quite a few hours reading tutorials while pulling and stretching the image in different directions – and it wasn’t always fun! There’s always more for this neophyte astronomer to learn!

Siril is the free astrophotography image processing software that I’ve been using for the past couple of years. I’m gradually getting better at it, but I won’t say that it’s been quick. It takes a lot of messing around to learn tricks of the software. But I think that Siril is getting quite good. Hat’s off to the developers of this free and open-source software! That’s right – free – open-source! Way to go!

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