M3 Globular Cluster

19. Apr. 2025

Gear used

• Telescope: ASKAR 103APO with 1x flattener
• Camera: ZWO ASI2600MC pro
• Guidescope: Uniguide 32
• Guidecamera: ZWO ASI220MM Mini
• Mount: ZWO AM5N
• Controls: ASIAIR Plus

Data collected

• Sky: Bortle 4 to 5
• Lights: 33 x 180s
• Biases: 30
• Darks: 30
• Flats: 24

More Reach, Little Time

I recently acquired the 1x field flattener for my ASKAR 103APO, giving me even more reach than I ever had before. With this new setup, I now have an image scale of just over 1 arcsecond per pixel, borderline limited by atmospheric seeing conditions. Unfortunately, I didn’t have much time to test it extensivly, so I figured a globular cluster would make the perfect target. These clusters have a relatively high surface brightness, allowing for stunning images even with minimal data. Since a globular cluster is made up entirely of stars, it’s also a great way to test the optical performance of this gear combination.

With that in mind, I fired up Stellarium, found the largest globular cluster decently high in the sky, and planned the shot. I ended up choosing M3, as it was the only suitable globular cluster high enough during my available imaging window.

While processing the image, I was amazed at just how many stars are packed into such a cluster. I had never taken a close look at one before, but seeing the over 500'000 stars in M3, each showing wonderful colors, was far more beautiful than I expected.