Finding M27

M27: The Dumbbell Nebula

Catalogues
M27; NGC 6853
Names
Dumbbell Nebula
Type
Planetary Nebula
Constellation
Vulpecula
Season Visible in Evening
Summer; June – November
Conversation Notes
Bright, easy to find planetary nebula with interesting hourglass shape.

Planetary Nebulae are fascinating objects, out of the ordinary from collections of stars, and excellent beginner targets. M27, the Dumbbell Nebula, is probably the best, as it is large, easy to find, and has an interesting shape and structure.

Warning: It looks far better in dark skies, so save your first look for a dark sky site if that is at all possible.

Planetary Nebulae are shells of gas ejected by stars in the late stages of their life. When an ordinary mass star (such as our own Sun) expends all its Hydrogen fuel, internal fusion stops. This stops the outward radiation pressure, which causes the gas to begin to collapse under its own gravity. The collapse raises the internal pressure and temperature enough to start a new fusion reaction, with the Helium gas that was the byproduct of the earlier Hydrogen fusion. The radiation from this fusion expands the star, which lowers the pressure, which stops the fusion. The gas then collapses, and fusion restarts, and so on.

This on-off cycling is called Thermal Pulsing and, each time the direction of collapse or expansion reverses, an outer layer of gas is “puffed off” into space. Successive puffs build up a structured shell of gas at some distance from the star, and this gas glows in the radiation of the inner stellar core. When we look at this shell of gas from a distance, we tend to see the edges more than the near face, since at the edges we are looking through more gas; this is why we tend to see a shape with a distinct outline (often a circle) and not a globe of gas.

Finding M27

Use the Summer Triangle to find the bright stars Vega and Altair. (Here are detailed instructions to find the Summer Triangle.)
Find the constellation Sagitta – The Arrow. It is ”inside” the Summer Triangle, between Vega and Altair, and closer to Altair.
The 3-star triangle that forms the feathered end of the arrow is easy to find, then you can find the stars that form the front of the shaft.
Practice finding it in this unenhanced sky image. (Click the image to enlarge it.)
Now, let’s observe the Sagitta area more closely. M27 is just above the pointy end of the arrow.
How far above? Note the triangle formed by the feathered end of the arrow.
Imagine that triangle standing on the point of the arrow.

Point your telescope just above and to the left of the tip of this imaginary pointer. The distance above and to the left is about the same as the separation between the stars at the feather end.

This image shows standard Telrad circles for reference.

In your magnifying finder, find and centre the small fuzzy patch of light. If you don’t have a magnifying finder, use your widest-field eyepiece.

Now choose an eyepiece in your main telescope that will give 25x to 50x magnification.

This simulation shows the size and shape of M27 in my 105 mm refractor at 25x magnification.

 


Aren’t nebulae supposed to be swirls of amazing colours? Not when viewed with your eyes – here is an explanation.

All the above images were generated with Starry Night Pro.


2 Comments

  1. I like your method of providing directions to DSO’s. Straightforward and effective. A very helpful site. Thanks!

  2. Where’s the Deneb Constellation..it is near the Altair?

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