Sky and Telescope - July 2018 - 70
Line of Lumpy Nebulosity
A softly glowing, uneven line of nebulous lumps runs northeast to southwest across M27, seemingly through its center.
This deﬁnes one side of the internal dumbbell shape. My
deep sketch (previous page) shows this feature well, and on
the best nights it forms one of the more obvious and detailed
internal portions of the Dumbbell. It's also composed of H II
and appears red in color images. The brightest area makes
up the southwest end, but the slightly less detailed northeast
end is nearly as bright. Although my brain wants to make a
connection right through the central star, I only see these
The opposing sides of the central dumbbell shape are less
obvious and are made up of the brightest areas of the central
O III nebulosity, which appears as green in the European
Southern Observatory (ESO) image on page 67, or various
shades of turquoise in other images of M27. Depending on
observing conditions, this somewhat fainter and softly contoured interior nebulosity contributes to the apparent dumbbell/rectangle shape ambiguity.
Nebula ﬁlters help boost the contrast of these features. An
Ultra High Contrast or O III ﬁlter brings out the fainter parts
of the Dumbbell, especially in my moderately light-polluted
home sky. But ﬁlters block the fainter ﬁeld stars, so I ﬁnd
the unﬁltered view more aesthetically pleasing under a dark
sky. Your preference may be different, though, so try all your
nebula ﬁlters and see for yourself.
LY R A
DELP H IN U S
A QU ILA
night under suburban skies. That's because they have more
contrast with the background sky than the interior nebulosity has with itself.
Considering that Messier saw the Dumbbell's overall oval
shape in his 6-inch Gregorian telescope from a rooftop in
smoky 1764 Paris, one night before a full Moon no less, your
chances of seeing the entire oval are quite good. Try different
magniﬁcations and ﬁlters to see which gives the best view.
And as a tribute to Monsieur Messier, have a look the next
time the nearly full Moon is in the sky, too.
Although faint, the O III wings that complete M27's oval
shape have about the same visibility as the interior nebulosity and are bright enough that they're visible on a good
Bonus Object: NSV 24959,
the Goldilocks Variable Star
Leos Ondra discovered
a variable star, NSV
24959, within the
nebulous borders of M27
in 1991. Because it's
located farther away than
M27, we view the Goldilocks Variable through the
NSV 24959 has a
magnitude range of 15.2
to 17.1 and is apparently
a Mira-type variable with
a period of approximately
213 days. And much
J U LY 2 0 1 8 * S K Y & T E L E S C O P E
like the variable stars of
Messier 5, the NSV 24959
variable is another reason
to check in on the Dumbbell
Nebula more often.
I haven't looked for this
star yet, and it doesn't
show up in any of my
sketches by accident. A
bit unlucky perhaps, but
I'll certainly be keeping a
careful eye out for it from
For more information,
The exceedingly faint outer halo of M27 is made of singly
ionized hydrogen. It was expelled from the central star while
it was ending its life as a red giant, representing the ﬁrst stage
of M27's planetary nebula formation. The H II halo is difﬁcult to see not only because it's faint, but because M27 is so
bright. Your best chance of detecting it is to keep the Dumbbell just outside your eyepiece ﬁeld of view while looking for a
nearly imperceptible glow. I've seen only the brightest, inner
parts of the halo.
The white dwarf central star was an easy catch with my
old 12.5-inch, and on nights with steady seeing a faint star
(which is not the physical companion) can be seen just to its
southwest. The white dwarf glows at magnitude 12.9 and is
much easier to see than the central star of the Ring Nebula,
so it's worth the small effort to observe simply because of its
current status as the largest-diameter white dwarf.
Even though it's the largest white dwarf found so far, it's
still rather tiny as stars go, at only 5.5% the radius of our Sun.
On the other hand, its mass is a little over half that of our
Sun, which is right in the middle of the typical mass range for
white dwarfs. This combination of small radius and relatively
high mass explains its extreme density. Quite a contrast to the
thinner-than-an-Earthly-laboratory-vacuum of M27's nebula.