The rich and gauzy star fields along the Milky Way towards the constellations Sagittarius and Scorpius constitute what’s arguably the most beautiful part of the night sky. Northern observers can see these constellations well over the southern horizon in the mid-to-late evening hours in August and September, while southern-hemisphere observers see this glorious region nearly overhead. Aim binoculars or a telescope towards this part of the sky, or simply gaze in this direction on a dark night with your unaided eyes, and you will see something good. The trick is figuring out which sight is which. To help you sort it all out, here’s a step-by-step tour of a small selection of the more prominent sights of the deep sky towards the center of the Milky Way.
First, get oriented by looking southward to find the “teapot” shape of the constellation Sagittarius. It’s about as big as your fist held at arm’s length. The “handle” is on the east side, the “lid” to the north, and the “spout” to the west. Let’s begin there and follow a stream of deep-sky sights of staggering beauty that rise like steam northwards from the spout.
Look for a small thickening of the Milky Way right above the spout. This is the Large Sagittarius Star Cloud, a bright clot of unresolved stars in the Sagittarius Arm of the Milky Way, the next-nearest spiral arm of our galaxy towards the center. Just west of this star cloud, unmarked by any visual fanfare, lies the direction of the nucleus of the Milky Way. Interstellar dust obscures what must be a grand spectacle, but radio astronomers can detect and map intense emissions here. In fact it was this part of the sky that Karl Jansky detected in the 1930s with his “merry-go-round” radio antenna at Bell Labs.
Turn your gaze upwards slightly to a pair of nebulae that appear as small, hazy blisters to the unaided eye. More aperture and magnification will only make these two nebulae more beautiful and complex. The brighter of the pair is the Lagoon Nebula, Messier 8, one of the brightest emission nebulae in the sky and an active region of new star formation. The fainter is the Trifid Nebula, Messier 20, another star forming region that reveals, in larger-scale images, a collection of reddish-pink emission nebulae, blue-white reflection nebulae, and dark nebulae that split the whole assembly into three. You won’t see any color visually through a telescope, but they are still lovely sights worthy of many nights of inspection. Here’s an image of what a camera can see of these two nebulae through a telescope. In binoculars or wide-field telescope, you can see both the Lagoon and the Trifid in the same field of view.
Keep moving north now to take in the icy glow of the modest open star cluster Messier 23. In any other part of the sky, this group of new stars would be a fine sight, if not a showpiece object. But M23 is completely overshadowed by the stunning rectangle of starlight to its east. This patch, about 4ºx5º wide, is the Small Sagittarius Star Cloud or Messier 24. This is not a cluster or cloud of associated stars. It’s an astonishing window through the pervasive interstellar dust, about 600 light years wide, that gives us a view into the inner parts of the Milky Way. To the unaided eye, it looks like a small silver rectangle that’s clearly brighter than the surrounding Milky Way. As you look into this patch, you are seeing a column of stars between 10,000 and 16,000 light years away, nearly a quarter of the way to the center of the galaxy. M24 is best viewed with binoculars or a wide-field telescope. Nowhere else in the sky can you see as many stars in one field of view with such an instrument.
Northwards now to two more blisters of star formation, the Swan Nebula (M17) and the Eagle Nebula (M16). Like the Lagoon Nebula, the Swan Nebula is one of a handful of emission nebulae bright enough to see with the unaided eye. It is a remarkably beautiful object, especially in dark sky or even in suburban skies with a good light pollution filter and a small telescope. This star forming region lies about 4,900 light year from Earth.
The Eagle Nebula is only slightly fainter and lies at about the same distance. It surrounds a young star cluster that’s emerging from the nebula itself. In a telescope, this whole assembly does indeed resemble the wings of an eagle in flight. At the core of M16 lie finger-like dark nebulae known as the “Pillars of Creation” where new stars are coalescing. A telescope of modest aperture, perhaps 6″ or larger, will give you a glimpse of these remarkable light-years-long structures.
Again, a camera shows more than you will ever see visually in a telescope. But here’s a look at the Swan and Eagle Nebulae through a camera and wide-field telescope.
Look now above the “lid” of the Sagittarius Teapot, just to the east, for the magnificent globular cluster Messier 22. To the unaided eye, the cluster looks like a fuzzy star. In binoculars, the size and extent of the cluster become apparent: the whole assembly, including stars in the outer halo of this giant sphere of stars, is nearly as large as the full Moon. In a telescope of 3″ aperture or larger, the cluster starts to resolve into dozens or hundreds of stars. M22 is sometimes called the “Arkenstone of the Stars”, after the description of J. R. R. Tolkien in The Hobbit of the jewel called the Arkenstone of Thrain, which “… was as if a globe had been filled with moonlight and hung before them in a net woven of the glint of frosty stars”.
Finally, look to the more modest globular cluster Messier 28. This cluster is not nearly as impressive as M22, but it is intrinsically just as spectacular and only appears fainter because it’s 18,300 light years away, nearly twice as far as M22. Once you find this cluster, if you have a telescope, use increasing degrees of magnification to resolve some of the outer halo stars. Some stargazers report seeing two curved “pincers” stretching out northward from the core.
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