Messier 21

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Open cluster M21 (NGC 6531)

Visual magnitude ~ 5.9

Dimensions ~ 16'

Distance ~ 5,400 light-years

Data Reference

The Messier Objects: 2nd Edition, Stephen James O'Meara, Cambridge University Press, New York, 2014.

Image Comparison References

1. "Imaging the Messier marathon", Alex McConahay, Sky & Telescope 125(4), April 2013, pp. 72-76.

Open cluster M23 (NGC 6494)

Visual magnitude ~ 5.5

Dimensions ~ 25'

Distance ~ 2,000 light-years

Data Reference

The Messier Objects: 2nd Edition, Stephen James O'Meara, Cambridge University Press, New York, 2014.

Image Comparison References

1. "Imaging the Messier marathon", Alex McConahay, Sky & Telescope 125(4), April 2013, pp. 72-76.

Open cluster M25 (IC 4725)

Visual magnitude ~ 4.6

Dimensions ~ 26'

Distance ~ 1,950 light-years

Data Reference

The Messier Objects: 2nd Edition, Stephen James O'Meara, Cambridge University Press, New York, 2014.

Planetary nebula M27 (Dumbbell Nebula NGC 6853)

Visual magnitude ~ 7.3

Dimensions ~ 480" x 340"

Distance ~ 1,200 light-years

Data Reference

The Messier Objects: 2nd Edition, Stephen James O'Meara, Cambridge University Press, New York, 2014.

Image Comparison References

1. "The astrophotography hit parade", Rod Mollise, Sky & Telescope 127(2), February 2014, pp. 70-74.

Open cluster M29 (NGC 6913)

Visual magnitude ~ 6.6

Dimensions ~ 10'

Distance ~ 5,500 light-years

Data Reference

The Messier Objects: 2nd Edition, Stephen James O'Meara, Cambridge University Press, New York, 2014.

Spiral galaxy M31 (Andromeda Galaxy NGC 224) and dwarf elliptical galaxy M32 (NGC 221)

Visual magnitudes ~ 3.4 (M31) and 8.2 (M32)

Dimensions ~ 3° x 1° (M31) and 11.0' x 7.3' (M32)

Distance ~ 2.5 million light-years

Data Reference

The Messier Objects: 2nd Edition, Stephen James O'Meara, Cambridge University Press, New York, 2014.

Image Comparison References

1. "Unveiling Andromeda's true nature", Ron Voller, Astronomy 53(10), October 2025, pp. 18-23.
2. "Exploring Messier 31", Alan Whitan, Sky & Telescope 126(5), November 2013, pp. 58-61.
3. "Stargazing simplified", James Mullaney, Sky & Telescope 127(4), April 2014, pp. 38-41.

Open cluster M34 (NGC 1039)

Visual magnitude ~ 5.2

Dimensions ~ 25'

Distance ~ 1,530 light-years

Data Reference

The Messier Objects: 2nd Edition, Stephen James O'Meara, Cambridge University Press, New York, 2014.

Open cluster M49 (NGC 1960)

Visual magnitude ~ 6.0

Dimensions ~ 10'

Distance ~ 4,100 light-years

Data Reference

The Messier Objects: 2nd Edition, Stephen James O'Meara, Cambridge University Press, New York, 2014.

Image Comparison References

1. "The Messier open clusters of winter", Rod Mollise, Sky & Telescope 127(1), January 2014, pp. 38-40.

Open cluster M38 (NGC 1912)

Visual magnitude ~ 6.4

Dimensions ~ 15'

Distance ~ 4,600 light-years

Data Reference

The Messier Objects: 2nd Edition, Stephen James O'Meara, Cambridge University Press, New York, 2014.

Image Comparison References

1. "The Messier open clusters of winter", Rod Mollise, Sky & Telescope 127(1), January 2014, pp. 38-40.

Double star M40 (Winnecke 4)

Visual magnitude ~ 9.0 and 9.6

Separation ~ 52.8' (Hipparcos)

Distance ~ 510 light-years (primary)

Data Reference

The Messier Objects: 2nd Edition, Stephen James O'Meara, Cambridge University Press, New York, 2014.