Observer’s Challenge – Mini Messier Marathon – Open Clusters

March New Moon is the traditional time for the Messier Marathon challenge – to observe all the Messier objects in one night. 

Of course there are many practical problems with a full Messier Marathon – not least that not all the Messier objects are visible from the UK, and as you head north in the country many become un-observable. 

And as there are 110 objects in the Messier catalogue, it is also quite hard to get round them all. One of the best internet resources to help with a full Messier Marathon are these pages provided by SEDS.

For this ‘mini-marathon’ we’re just going to look for Messier’s open clusters – these should be easier to find and observe, and with more time available a chance for imagers or those using electronically assisted viewing to capture them too. There is still the big challenge of the objects with a southerly declination, so those objects in Scorpius and Sagittarius will be particularly difficult – even those in the south of the UK will still need a good southern horizon.

The list below of the 27 Messier open clusters is organised in a search order recommended by Don Machholz, whose book The Messier Marathon Observer’s Guide is excellent for anyone taking up the pursuit.

We will need a good clear night from dusk to dawn, though it might be possible to have a snooze or break half way through.

If you manage to observe or image these objects in one night, or even if you just manage a few – please post your observing report or images on your Members Page. 

Good luck, happy Messier hunting!

No. Messier Constellation RA Dec Visual Mag. Size (arc-min)
1 M52 Cas 23 24.2 +61 35 7.3 13
2 M103 Cas 01 33.2 +60 42 7.4 6
3 M34 Per 02 42.0 +42 47 5.5 35
4 M45 Tau 03 47.0 +24 07 1.6 110
5 M35 Gem 06 08.9 +24 20 5.3 28
6 M37 Aur 05 52.4 +32 33 6.2 24
7 M36 Aur 05 36.1 +34 08 6.3 12
8 M38 Aur 05 28.4 +35 50 7.4 21
9 M41 CMa 06 46.0 -20 44 4.6 38
10 M93 Pup 07 44.6 -23 52 6 22
11 M47 Pup 07 36.6 -14 30 5.2 30
12 M46 Pup 07 41.8 -14 49 6 27
13 M50 Mon 07 03.2 -08 20 6.3 16
14 M48 Hya 08 13.8 -05 48 5.5 54
15 M44 Cnc 08 40.1 +19 59 3.7 95
16 M67 Cnc 08 50.4 +11 49 6.1 30
17 M29 Cyg 20 23.9 +38 32 7.1 7
18 M39 Cyg 21 32.2 +48 26 4.6 32
19 M6 Sco 17 40.1 -32 13 5.3 25
20 M7 Sco 17 53.9 -34 49 4.1 80
21 M11 Sct 18 51.1 -06 16 6.3 14
22 M26 Sct 18 45.2 -09 24 8 15
23 M16 Ser 18 18.8 -13 47 6.4 7
24 M18 Sgr 18 19.9 -17 08 7.5 9
25 M25 Sgr 18 31.6 -19 15 6.5 40
26 M23 Sgr 17 56.8 -19 01 6.9 27
27 M21 Sgr 18 04.6 -22 30 6.5 13

Cover photo M103 by David Davies

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