M101 – Pinwheel Galaxy
Cataloged by Charles Messier as M101, The Pinwheel Galaxy is a striking face-on spiral galaxy in the constellation Ursa Major. It can be located with your telescope by star-hopping from the bright star, Alkaid, in the handle of the Big Dipper. Through a wide field refractor like the one used to capture the image below, this deep sky object appears to be quite small from our vantage point.
However, as far a galaxies go, the apparent size of the Pinwheel Galaxy is one of the largest and brightest in the observable night sky. Over the years, I’ve captured M101 using a variety of different telescopes, cameras, and filters. My experiences should provide you with some valuable insight for those of you planning on capturing this galaxy using your own equipment. You can view my latest version of M101 and more in the photo gallery.
Above: The Pinwheel Galaxy imaged using a DSLR Camera with an iOptron Photron RC6.
M101 – The Pinwheel Galaxy
Messier 101 (also NGC 5457) lies approximately 21 million light-years from Earth and is measured at an enormous 170,000 light across. This massive grand spiral design galaxy is more than double the size of our own Milky Way Galaxy. An interesting feature of this galaxy is its high population of bright H II regions. No matter what size of telescope you use, the Pinwheel Galaxy is definitely worth a look both visually and with your digital camera.
The first time I photographed the Pinwheel Galaxy, it appeared very small. I used a Canon 450D DSLR camera through an 80mm Explore Scientific apochromatic refractor. The 480mm focal length of this compact telescope produces wide swaths of sky in a single view. The benefit of capturing M101 at this magnification is that it produces an ultra-wide field of view that reveals several surrounding smaller galaxies.
The Pinwheel Galaxy through a wide field refractor:
I tend to spend time on this particular deep-sky object during Early spring, as this is when it’s location is the most convenient for tracking. In mid-April, M101 rises high into the Northeast, swinging around the Polaris and the North celestial pole. The image below shows the location I chose to set up my telescope in the backyard to capture M101. You can take a behind-the-scenes look at the strategies I used to photograph this galaxy in my YouTube video.
Which Focal Length to Use?
In late April 2018, I began capturing more time on the Pinwheel Galaxy. This time, I had a little more focal length to play with, 1370mm to be exact. M101 was a perfect fit for the iOptron Photron RC6 telescope, with my crop sensor Canon DLSR attached. My previous attempts at this spiral galaxy produced a small DSO in the frame, as they were captured using small wide-field refractors.
The RGB data was captured under an 87% illuminated moon, which certainly held the broadband color version of M101 back. My Baader Moon and Skyglow filter helped to create contrast between the DSO and bright moonlit sky. However, much more time is required to produce a clean image with an improved signal-to-noise ratio. From the city, pouring on the overall exposure time can help make up for light polluted skies.
There is hope for DSLR imagers in the city, even if you’re using an unmodified, stock camera body. In general, photographing galaxies with a stock DLSR can turn out great, often resulting in images the capture the beautiful cool blues of the object. A modified camera will bring the ha regions of the galaxy forward, but it’s not necessary for a successful image.
M101 is bright enough to capture from your backyard, but you’ll need to focus on pulling the surface brightness of the galaxy forward during image processing. Despite my unjustified desire to collect full-color images of this galaxy using a one-shot-color camera, narrowband imaging with a monochrome camera is a smarter choice on nights like this. Capturing M101 in narrowband wavelengths will both help ignore the bright light of the moon, and isolate specific gases in the target to better reveal the structure.
M101 in Narrowband
In April 2018, I leveraged a new duo-narrowband filter to capture some interesting data on M101 in Ha and OIII. Capturing the Pinwheel Galaxy in Ha and OIII produced some sharp structures within the tendrils of the spiral arms. Usually, I reserve narrowband filters for nebulae, so I was not overly optimistic about shooting a galaxy with this filter. However, I was pleasantly surprised to see the amount of structure the Altair Hypercam 183M was able to record.
I should mention that I switched telescopes for this data. The pixel scale of the Monochrome Altair Hypercam 183M was a better fit for the glorious William Optics FLT 132 APO currently in my possession. In fact, the image scale of the iOptron RC6 with an APS-C sensor DSLR was remarkably similar to the 183M and the Fluorostar 132. This made combining the data together a lot easier!
There are several hydrogen regions in M101, which really showed up in the isolated Ha light wavelengths. Needless to say, these monochrome details added a much-needed luminance boost to my color image. To merge the images together, I simply scaled the larger color image using the DSLR to the size of the 2×2 binned monochrome version.
Astrophotography Processing Notes:
Shooting in broadband RGB during a full moon is far from ideal. The color images suffered from several issues including noise, lack of contrast, and washed out colors. The lack of overall exposure time made matters worse, which made processing these images the toughest challenge of all.
As is the case when processing all small galaxy images, a large emphasis is given to the color and balance of the background space. For my image, several iterations of gradient removal and noise reduction were applied. A layer mask was used to protect the Pinwheel Galaxy structure from losing detail and color.
The star size was reduced a great detail from the original file, to boost the contrast and depth of the image. All of the software I used to process this astrophoto can be found in the resources section of this website.
Details about the final image:
For my final image (at the top of the page), I leveraged very little narrowband data. The 4.5 hours of broadband data captured using my Canon Rebel T3i comprises 95% of the data used for the image. I stacked a grand total of 70 x 4-minute subs at ISO 1600. The final integration included 20 darks, 15 flats, and 15 bias frames.
Although I spent 2 nights capturing M101 using the Altair Hyercam 183M and the William Optics FLT 132, this data added very little value to my final color image. I’ll need to better utilize flat frames with the 183M before I can start integrating useful data into my color images using that camera.
In the end, it was the data captured on May 4th, 2018 (70 x 4-minutes) that gave me the data needed for a presentable image. The moon was 82% illuminated, which is not ideal when capturing faint deep sky objects! However, my final image of M101 is a huge improvement over my previous attempts, and a great learning experience with the new RC6 telescope.
The Pinwheel Galaxy was the subject of one of my astrophotography videos in April of 2017:
The Pinwheel Galaxy – Star Chart
In the Northern hemisphere, the months of March and April are likely the best time to capture the Pinwheel Galaxy. This is because the Ursa Major constellation swings up high overhead, putting M101 is a convenient location for imaging. No matter which obstructions you shoot over in the backyard, objects that climb overhead are presented to you in clear view.
Shooting towards the Zenith also has the benefit of avoiding the negative effects of atmospheric turbulence associated with objects that are low on the horizon. For these reasons, my camera and telescope are often pointed towards M101 in early spring.