Finding and Observing M39

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Apollo XX
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Finding and Observing M39

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Tuesday, September 20, 2022;

What are you doing this weekend? As of today the forecast looks favorable for some deep sky observing on both Friday and Saturday nights. Are you considering getting out with your telescope? If so, I’ve got a target suggestion for you.

Messier #39 is a large open cluster located in the constellation Cygnus, the Swan, and is a pleasant star hop from the bright star Deneb. Most of you are familiar with that giant asterism called the “Summer Triangle”, and Deneb marks the northernmost point of the triangle and also marks the tail of the Swan.

Starting at Deneb, use the attached charts to navigate your way to M39. When you put Deneb in the eyepiece of your finderscope you’ll immediately notice an arrangement of brighter stars that appear to form two “funnels” leading to the E/NE. Take one of them and you’ll land smack-dab in the North America nebula, otherwise known as NGC 7000. If it’s dark enough where you are and the sky is of high quality you may be able to make out the outline of the Gulf of Mexico in the view in your finder scope. Be sure to take some time and go there with your binos too. Just follow the funnel and check it out.

If you go down the other funnel it will take you to a path of stars leading down to 75 Cyg. From here you can drop in on the highly variable dwarf nova system SS Cyg, which when at rest shines at about 11.7 magnitude but in outburst shines as bright as 8th magnitude. The system varies frequently and is a fun one to follow because you usually don’t have to wait long for changes. It’s slightly off of the path to 75 Cyg that you’ll find M39. It’s bright enough that it stands right out in the finderscope, and in binoculars as well.

One of the best things about bright open clusters is that they show themselves well in small telescopes. If you take a look around you’ll probably note that most club members don’t own large telescopes, but many wield small scopes on the cosmic dome. For the sake of conversation, a small telescope would be one with a 6” or smaller objective lens, while a medium would have an 8” – 12” lens, and large would be in the 14”+ range. The vast majority of astronomy enthusiast’s scopes fall in the under 12” range.

M39_NOAO_AURA_NSF.jpg (155.98 KiB) Viewed 48 times
M39 as seen in an image from the National Optical Observatory

M39 is also the Observer’s Challenge object for the month of October 2022. One of the best things about participating in the challenge is that it will encourage you to spend more time analyzing an object. Personally I like to sketch them, but participants submit everything from just a few lines of notes about what they saw to high resolution images taken with very large telescopes. I’ve attached an observing log form that Astronomy Magazine formatted and distributed. If you’d like to become a participant in the Observer’s Challenge report, simply email your submission to Roger Ivester at [email protected]

M39 Robert Placenti Jr. Sketch.jpg
M39 Robert Placenti Jr. Sketch.jpg (23.65 KiB) Viewed 48 times
A sketch of M39 done by an observer looking though a 120mm telescope.

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Download this observing log form to make your own sketch of M39.

The best time to observe M39 is around the time of the New Moon, which for September happens on Sunday, the 25th. Because of its current position in the sky immediately after dark it is also observable at the highly convenient time of 8pm, and if you go out there at that time on any night between now and the middle of next week there’ll be no Moon to interfere with your observing efforts.

M39 Finder Anno.png
M39 Finder Anno.png (103.26 KiB) Viewed 48 times
When you put Deneb in the eyepiece of your finderscope you should discern two "funnels" leading towards the E/NE. They both lead to interesting objects.

M39 Finder Charts.pdf
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Download and print this chart page to use at your telescope if you're star hopping to M39.

Best of luck with finding and observing the open cluster Messier #39!

Keep Looking up!
Mike McCabe
"The purpose of life is the investigation of the Sun, the Moon, and the heavens." - Anaxagoras
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