The Dumbbell Nebula

For our other target, we go after another type of nebula. Like Orion, this object is a glowing cloud of gas but with a different origin. The Dumbbell Nebula (M27) named for its resemblance to a weight-lifter's equipment, is a planetary nebula. It and all its kind are the cast-off remnants of dying stars. Most stars like the Sun — average well-behaved stars — bloat up into red giants at the end of their lives. They lose weight by blowing off their outer layers of gas. As these layers expand into space they form temporary shrouds around the central star.

At a distance of 3,500 light-years, the Dumbbell is one of the closest planetaries and appears larger than most. It's worth looking for in binoculars just off the summer Milky Way. To find M27, first locate the three bright stars of the Summer Triangle. They're overhead in the evenings from July through September. They're Altair (in the south), Vega (to the west), and Deneb (to the east).

Halfway between Altair and Vega, track down Albireo, the 3rd-magnitude star that marks the head of Cygnus, the Swan. Now look halfway between Albireo and Altair for a faint but distinctive pattern that resembles a little arrow. This pattern of four 4th-magnitude stars is the constellation Sagitta. Gamma (γ) Sagittae lies at the tip of the "arrowhead."

M27 lies about half a binocular field above (due north of) this star. Look for a small puffy cloud sitting amid a rich field of stars. If skies are dark, it should be visible in most telescope finders.

A telescope of any aperture will show M27's dumbbell shape, or perhaps you might think of it as a cosmic apple core. The nebula looks brighter in larger telescopes but doesn't really show a lot more structure until you bring 12- to 20-inch scopes to bear on it.

Here's where one observing aid comes in handy — the nebula, or light-pollution filter. While not particularly useful for star clusters and galaxies, these filters really help bring out planetary nebulae. They block most of the colors of the spectrum except the prominent green light emitted by glowing oxygen atoms. Even in a dark sky, a nebula filter will boost the contrast between the nebula and its background.