top of page

Messier 51 - The Whirlpool Galaxy | 255-Hour Astrophotography Collaboration

Updated: Sep 21, 2023

Messier 51, also called the Whirlpool Galaxy, is an exciting deep-sky object for both beginner and advanced astrophotographers. It is a grand-design spiral galaxy, famous for its gravitational interaction with a second galaxy, NGC 5195 (M51b). Located in Canes Venatici, M51 is a fine target for amateur astrophotographers. Below are photos and information about the galaxy - perhaps you'll try your hand at it!

Object Designation: M51

Also known as: The Whirlpool Galaxy

Constellation: Canes Venatici

Object Type: Grand-Design Spiral Galaxy

Distance: 23 million light-years away

Magnitude: 8.4

Discovered in: October 13, 1773, by Charles Messier

We spent 25 hours imaging this target from a dark site, but collaborated with 15 other astrophotographers to increase the integration time to 255 hours. The results are incredible. Learn all about this collaboration below, and watch our video on YouTube!


255 Hours on the Whirlpool Galaxy

May-August 2023

We love spending many hours on our images, our two longest integration times being 61 hours on the Seagull Nebula, and 81 hours on the Christmas Tree an Cone Nebula. The image below totals 255 hours of exposure time, and was taken by 16 astrophotographers including us! Be sure to read the information in this post to learn more about this collaboration, and how you can also join!

225 hours on the Whirlpool Galaxy astrophotography

GEAR USED (for our part of the data):

Camera: QHY600M

Telescope: Stellarvue SVX130

Mount: 10Micron GM1000 HPS

Accessories: Moonlite Nitecrawler focuser / Pegasus Astro Ultimate Powerbox

Processing: Done by William, using Pixinsight and R-C Astro plugins


Total Exposure Time: 25 hours for us, 255 hours total

Exposure Time per frame: 10 minutes

Gain: 56


We’ve always been tempted to join a group of astrophotographers and collaborate with others to go much deeper on an object and maybe be able to reveal things that were previously never seen.

We were invited by Tim Schaeffer to team up with 15 other astrophotographers on M51. Tim explained to me that they had just finished imaging M81 and M82, and that the image was incredible. He was right, the image they produced was just fantastic, and I also loved the nice write-up about it which you can read online.

393 hours on M81 and M82 astrophotography
393 hours on M81 and M82

Tim said that the Bortle 2 skies where our main telescope was hosted (Utah Desert Remote Observatories) would be a great help for the data we could gather on the next project, and we were thrilled to join the team.


Why Choose Messier 51?

So why pick M51 for this massive project?

M51 is known as the Whirlpool galaxy, and is one of the most popular targets to capture for both beginner and advanced astrophotographers, starting with Isaac Roberts on April 29th, 1889.

The First Astrophotography Picture of the Whirlpool Galaxy - 1889
The First Picture of the Whirlpool Galaxy - 1889

Drawing of M51 by William Parson - 1845
Drawing of M51 by William Parson - 1845

M51 is located 23 million light-years away in the constellation Canes Venatici, and has a size of 80.000 light-years in diameter.

The Whirlpool Galaxy has some very distinctive spiral arms which were first discovered by William Parson in 1845, who made a famous drawing of the object that same year. M51 was also the first object where spiral arms were detected.

M51 Tidal Stream
Tidal Streams annotated - A. Watkins et al.

One more unique attribute to this galaxy is the tidal stream which shows even in beginner images and at low integration times. No one really knows the full extent of that tidal stream, which is one of the reasons why the group picked this target for the project.

And this was a great pick, because we were indeed able to reveal even the faintest parts of the stream as you will see later. If you do not know, the tidal streams are visible because of the tidal interaction between the big M51a galaxy and the smaller M51b which is getting absorbed. Because yes, M51 is actually two galaxies and not just one.

M51 has been studied a lot for years, as it is a prime example as to what happens when two galaxies collide. A faint large ionized gas cloud was discovered in 2018 just north of the galaxies, and we wanted to do our best to enhance that section as much as possible as well.

M51 ionized cloud annotated - A. Watkins et al.
M51 ionized cloud annotated - A. Watkins et al.

So, our main goals for this project would be:

  1. The full extent of the tidal stream

  2. The faint ionized gas cloud

  3. The overall full details within and around M51

As a bonus, we were also able to reveal something incredibly faint, which we'll cover below!

M51, here we come!


Project Organization

How was this massive project organized, and where did everyone's raw data end up?

The “hub” for the whole project was on Discord, with different channels to keep everyone organized. Everyone was able to talk about the project, list their equipment, and see the progress on the data overall at any time.

Midway through the project, we all voted on a cool name for the team, which ended up being “The Deep sky collective”.

Discord worked really well to keep up to date with the project, so we’ll keep using that in the future.

Our M51 Data - Adding to the group

Refractor telescope at remote observatory
The setup we used to capture our data of M51

We personally spent 25 hours on M51 from Utah Desert Remote Observatories in RGBH. 23h20m ended up being useable for the project.

So how does everyone send their data in an easy manner? We added our data to a shared NAS, which was easily accessible by simply clicking on a link. We were able to see folders dedicated to each member of the project, and simply had to upload the registered files to the right folder under our name, and that was it!

Data gathering by everybody - Ending up with 255 hours

Because of all the different members, and the fact that not everybody is blessed with clear skies most of the year, it took a while to gather everyone’s data and finally be able to stack it all together. We joined the project in early May, and the data was all acquired around mid-July.

Discord astrophotography
Messages we sent on Discord to confirm we uploaded our data

If you plan to join a similar group, just expect that it will take some time for each target and things shouldn’t be rushed.

Each time someone added their data to the shared folder, they would notify the discord chat with the integration time, filters used, and size.

In the end, we ended up with 255 hours of usable data, which is huge and probably the longest-ever integration time for M51!

Below you can see what each master file looked like once stacked and registered:

Master files for 225 hours on M51
Red, Green, Blue, HA, and Luminance Master Files

To avoid any chaos, one person was trusted for all stacking-related tasks, Carl, and one person for actually processing the data, William. Both did amazing taking care of the massive job of stacking and processing the 255 hours of data.


So what can be seen in this 255-hour image of the Whirlpool Galaxy?

The following information was taken from our official text release, written by Tim and William. We have shortened it a bit, but be sure to check the full statement on Astrobin if you want to learn more.

The Tidal Stream

Tidal streams are diffuse, elongated structures of stars, gas, and dust, often extending beyond the boundaries of galaxies.

Examples of Tidal Streams in Galaxies
Examples of Tidal Streams in Galaxies

As M51a and M51b are currently engaged in a violent gravitational interaction, the smaller galaxy M51b (or NGC 5195) experiences tidal forces that disrupt its shape and provoke the formation of new stars. NGC 5195 also influences M51, leading to the formation of spiral arms, making this galaxy pair so unique.

Full Tidal Stream in M51

In order to get this entire stream, long integration times and dark skies are required. In the end, we had 68h 57min of Luminance which ensured nice details and a high SNR view at the stream.

The Ionised HA Cloud

The Ha cliff formation is a remarkable but rarely imaged feature found within the Whirlpool Galaxy.

This H-alpha emission, emanating from regions of intense star formation, is a crucial indicator of the presence of young, massive stars that ionize the surrounding gas, causing it to emit this distinctive wavelength of ionized Hydrogen.

Ionized HA Cloud in M51
Ionized HA Cloud in M51

Capturing this region proved to be an immense challenge. In the first stack, we had about 80h of data with relatively short exposures ranging from 300” to 600” - we quickly realized that although the integration time was high, the cliffs were barely visible and couldn’t properly be extracted in post-processing.

After some discussions, we realized that the signal is so weak that the noise floor of the sensors overpowers it. In our last attempt, we shot nearly another 40h of long exposure subs ranging from 900”-1800” to get the signal to show up, which it indeed did in the end.

The Blue Stellar stream

Similar to M82’s blue stellar stream, M51 also has one that can be found to the north of the galaxy but is rarely noticed. With nearly 20h of integration in the blue channel, we were able to get the stream to show up in great detail.

Blue Stellar Stream in M51
Blue Stellar Stream in M51

As for the cigar galaxy, the exact origin of this stream is yet to be exactly determined. The two leading explanations are that it’s either an interaction remnant or a shocked starburst stream, though most likely it is a secondary result of a galactic low-velocity shock caused by the interaction between M51a and M51b. The resulting shock heats and compresses the gas to optimal star-forming conditions, giving the stream its signature blue colour.

Lastly, many small galaxies and galaxy clusters can be seen in the background. Be sure to check the Astrobin page to learn more about this image!

List of Contributors:

M51 255 hours list of contributors

Video - 255 hours on the Whirlpool Galaxy

Learn all about this collaboration project by watching our video below!


Messier 51 Stock DSLR Astrophotography

February 2016

The photo below was taken with an 8” telescope and our unmodified DSLR camera, it is a stack of 20, 6-minute exposure photos. This was our first attempt at photographing M51, and we've learned a lot since then!

The spiral arms are visible here and so is the companion object. In M51's arms are features like dust lanes, stellar nurseries, and regions of active star formation. This spiral morphology makes it an excellent example for studying the structure and dynamics of spiral galaxies.

M51 the Whirlpool Galaxy with a DSLR camera


Camera: Canon t3i

Processing: Pixinsight


Total Exposure Time: 2 hours

Exposure Time per frame: 6 minutes

20 lights - 20 Darks - 100 Bias

ISO: 800


How to Locate the Whirlpool Galaxy

How to find M51 in the sky

The Whirlpool Galaxy is very easy to find in the night sky. Despite being located in the Canes Venatici constellation, you might find it more helpful to use the Big Dipper asterism (in Ursa Major) to help you spot it. Simply find Alkaid, the star at the end of the Big Dipper’s handle, and shift 3.5 degrees southwest to land on M51.

Messier 51 can be spotted with binoculars as a gray patch of light. The core of the galaxy, as well as its companion NGC 5195, can be observed through small telescopes. Using bigger instruments will let you contemplate its halo and details within its spiral arms.

Interesting Facts

  • Discovered in 1773

  • M51 is devouring its companion galaxy

  • Three supernovas have been discovered since 1994 from the Whirlpool Galaxy


The Whirlpool Galaxy by NASA

NASA/ESA have photographed Messier 51 using space telescopes, and the results are incredible! Let's go over what the object looks like through two different billion-dollar telescopes.

M51 by the Hubble Space Telescope

Released on January 6th, 2016, this image of the Whirlpool Galaxy taken by the Hubble Space Telescope quickly became one of the most famous pictures of space around the world. Both objects (M51a and M51b) can clearly be seen here in all their glory!

M51 by the Hubble Space Telescope

In this image of Messier 51, the blue colors in the spiral arms mostly come from the hot young stars, unlike the yellow hues which represent the much older stars. The red patches all over the spiral arms are infrared light and hydrogen gasses coming from the active star-forming regions.


M51 by the James Webb Space Telescope

On August 29, 2023, the image below was released to the public and shows the Whirlpool Galaxy photographed using the JWST space telescope.

This is a composite image that combines data from both the JWST's Near-InfraRed Camera (NIRCam) and Mid-InfraRed Instrument (MIRI).

The Whirlpool Galaxy by the JWST NASA

In this picture, you can see a bright white core with swirly gasses and matter around it. The spiral arms, through the filters used, look red, orange, and yellow, and only the bright large stars are visible. There are also faint and small dark areas throughout the spiral arms.


Single Shot and Processing of Messier 51

Below is our single shot of M51 using our stock DSLR camera. It is a crisp and beautiful single frame that is promising!

M51 single shot with DSLR camera


To the right is a close-up of M51 from the Hubble Space Telescope. Notice how a stock DSLR camera without a filter does not show the reds seen in the Hubble image (ex: our image on top and the one below).

Using filters, you can extract more color and details from Messier 51. However, it doesn't mean you still can't try your hand at it.

M51 with a stock DSLR camera

The main challenge of DSLR astrophotography lies in getting enough data to make out the shape of the expelling gases from their interaction.

You may also be able to get a few tiny galaxies floating in the background of your image!

Learn how to photograph the Andromeda Galaxy in our Messier 31 tutorial post.


Final Thoughts

The Whirlpool Galaxy is a beautiful target that is a good challenge among amateur astrophotographers shooting with either DSLR or cooled astronomy cameras. Do your best to capture the spiral arms full of star-forming activity and the companion object, NGC 5195.

You do not have to spend too much time on it to get a nice photo but challenge yourself to get as crisp a photo as possible by spending at least 4 hours on it and finding the darkest skies possible.

When it comes to processing, bring out the blue color and the dark dust lanes.

Processing is easy! If you need help, we can process your image for you; or we can teach you one-on-one with a consulting session - see our astrophotography services for more info.

Clear Skies,

Galactic Hunter

14,332 views2 comments


David Hochede
David Hochede
Aug 09, 2023

This is amazing. The group should be very proud of what they've been able to do. Even 5 years ago this would have been impossible without the advances in amateur cameras, telescopes, mounts and software. Excellent article and a terrific video.


Replying to

Thank you David! Can't wait to shoot more targets with the group!

PixInsight Processing Guides

Subscribe to our newsletter and instantly receive 7 free wallpapers!

Messier Workbook 300x300px ad.jpg

Learn astrophotography with our premium online course. Get lifetime access to all types of imaging content!

Galactic Course Logo transparent.png
bottom of page