The Pinwheel Galaxy, also known as M101, is a spiral galaxy that we’re seeing face-on. It’s 21 million light-years from Earth.
Askar 130PHQ: April 2023
Imaging The Pinwheel Galaxy turned out to be an epic undertaking! I initially planned on gathering around 20 hours of RGB data. (I use long integration times to combat light pollution, and don’t use a filter for RGB). Then something amazing happened, as a supernova was detected in the galaxy! It was discovered during daytime hours from my observing location in the UK, but as soon as the skies were dark, my telescope was back on the target collecting more light.
This meant I was able to make a before / after comparison. I can’t claim any credit for being particularly organised; it’s just a happy coincidence that I was imaging this target every clear night around the time the supernova was detected.
The weather forecast then predicted an unusually long period of clear skies. This presented me with a dilemma: I had already gathered nearly 20 hours of data, which is what I’d initially planned. But if I kept going, would I be able to detect any noticeable change in brightness of the supernova? I decided it would be fun to try, so I just kept going every clear night for the next few weeks.
Ultimately I couldn’t really see an interesting enough change in brightness night on night, but before I knew it I was approaching 70 hours of RGB data — by far the most for any of my astro targets.
I then got thinking about my previous galaxy shoot, M81 and M82. That turned out well, but I regretted not getting any Hydrogen-alpha data to show glowing red areas of star formation. I shoot using an OSC camera and don’t have a dedicated Hydrogren-alpha filter, but I do have an Optolong L-Ultimate, which captures Hydrogen-alpha and Oxygen III. So, I gathered 30 more hours of data using this filter, then extracted the Hydrogen-alpha data (i.e. the red channel), and combined this with the 70 hours of RGB. Hey presto, a nice round 100 hours of data, resulting in an HaRGB image.
This slider comparison shows the RGB data (left) with what it looked like after I added in Hydrogen-alpha.
A vast amount of data has gone into the final image, and I followed my PixInsight Pre-Processing Guide to keep everything organised. The RGB component is made from from 2100 120-second subframes (no filter), totalling 102GB. Of course, I actually collected much more data than this, then used PixInsight’s SubframeSelector tool to remove the lowest quality subframes.
PixInsight’s WBPP was chugging away for 72 hours to produce an integrated image but then disaster struck! It failed, giving an out of memory error. C’mon PixInsight, is 48GB of RAM not enough?
Fortunately it had saved the output from the preceeding steps, so I took those files and continued more manually, using the ImageIntegration tool. In total, it took 85 hours start to finish of my PC running at full pelt to turn the 2100 RGB subframes into an integrated image!
Then it was onto the Hydrogen-alpha data, which is 900 120-second Optolong L-Ultimate subframes, totalling 43.7GB. The sky conditions weren’t as good when I was collecting this data, but I was more lenient about what went into the stack as I knew it was just going to be showing the areas of hydrogen.
Collecting such a huge amount of data was a bit nuts, but I like stretching what’s possible under city skies. I would have gotten the result faster (and probably a little better!) using a mono camera plus filters, but I certainly appreciate the simplicity in data acquisition that OSC provides.
I’ve imaged The Pinwheel Galaxy before, using my Askar FRA400 telescope (which now has gone to a new astroimager, very happily in the same city as me!) Below is a slider comparison. On the left is a tightly cropped view using that telescope, compared to the new attempt on the right.
And just for fun, this slider comparison shows my image compared to the same galaxy imaged by the Hubble Space Telescope. (To be fair, the Hubble data absolutely trashes mine when viewed at full resolution!)
* 21 April to 16 June 2023 to (8 weeks)
* Bristol, UK (Bortle 8)
* Telescope: Askar 130PHQ Flatfield Astrograph
* Camera: ZWO ASI 2600MC-PRO
* Mount: Sky-Watcher EQ6-R PRO
* Guide: William Optics 50mm Guidescope with 1.25″ RotoLock; ZWO ASI 120MM Mini
* Control: ASIAIR Plus
* Software: PixInsight, Lightroom
* Filters:
– No filter 2100 x 120 seconds (70 hours)
– Optolong L-Ultimate 900 x 120 seconds (30 hours)
Total exposure time: 100 hours
By Lee Pullen
Example source data
Askar FRA400 version 2, reprocessed December 2022
From the Reprocessing Bonanza 2022. This version uses exactly the same data as version 1, but with better processing tools and skills. BlurXTerminator was immensely useful during the reprocessing, keeping the stars tight and sharpening the galaxy nicely too.
Askar FRA400 version 1, March 2021
The Pinwheel Galaxy is definitely not suited to my wide-field telescope, and city light pollution made this imaging run an uphill struggle. But I wanted to give it a go, so set about gathering lots of data. In the end I got 20 hours, which was enough for a decent Signal-to-Noise Ratio. The shape and structure of the Pinwheel’s spiral arms are clearly evident, and there are lots of background galaxies visible too. So, not a complete bust, although darker skies and a longer focal length telescope would definitely be beneficial.
* March 2021
* Bristol, UK (Bortle 8)
* Telescope: Askar FRA400 f/5.6 Quintuplet APO Astrograph
* Camera: ZWO ASI 2600MC-PRO
* Filter: IDAS D1 Light Pollution Suppression
* Mount: Orion Sirius EQ-G
* Guide: William Optics 32mm; ZWO ASI 120MM Mini
* Software: PixInsight, Photoshop, Lightroom
* 600 x 120 seconds
Total integration time: 20 hours
By Lee Pullen
Example source data
Telescopes are expensive. Please give generously.
Wow, that’s simply amazing!
Thanks Colin!