Summer: hot summer days mean the milky way arching high at night.
The low southern sky holds one of the most attractive star patterns of summer: Sagittarius, the Archer. Traditionally, Sagittarius represents a centaur drawing his bow, but most skygazers find it easier to recognize the eye-catching Sagittarius Teapot. It's outlined on our all-sky charts for the summer months on pages 29-33, low in the south. Shown with it there are the deep-sky objects described here.
Our first treat is the magnificent globular cluster M22. Globular clusters typically contain hundreds of thousands of ancient stars in a dense ball. Whereas open clusters are confined to our galaxy's disk, globular clusters are distributed mostly in a huge zone around the galaxy's center, which is located in Sagittarius.
M22 is just 2 1/2[degrees] northeast of the star marking the Teapot's top; they easily fit together in the view of binoculars or a finderscope. The star shows a golden hue, while M22 is a misty little orb. Through a 4-inch scope at 50x it resembles a mound of sugar. Stars blend together in hazy confusion toward the core, and individuals stand out around the edges. At 90x more stars are visible down to the center. Seen from 10,000 light-years away the core looks dense to us--but in truth its stars are a good fraction of a light-year apart.
Now sweep westward to M8, the Lagoon Nebula, in the Milky Way cloud that rises like steam from the Teapot's spout. A low-power view through a 4-inch scope discloses a dash of stars held in the nebula's ghostly embrace. At 90x it blossoms into a complex cloud with the dark lane that gives the Lagoon its name. A few dozen stars are tangled just to one side in ashen billows. If light pollution brightens the sky, your view of the nebula will be improved with a nebula filter, one that blocks much of the skyglow while allowing most of a nebula's light through.
The Lagoon Nebula and the open cluster enmeshed in it are 4,300 light-years distant, considerably closer to us than M22. They're also much younger. The Lagoon's own stars were formed an astronomically recent 7 million years ago, while M22 is a staggering 12 billion years old--almost as ancient as the universe itself.
Let's climb up to the higher Milky Way. South of big Cygnus and north of the bright star Altair is Vulpecula, the Fox (mapped at left). The sly Fox is hard to see, with only two dim stars shown on our all-sky charts. The fainter one lies near the planetary nebula M27, also known as the Dumbbell Nebula. In a finderscope, the star marks the western peak of an M shaped by five stars, and the Dumbbell is just south of the M 's central star.
M27 takes magnification well and is a lovely sight through a 4-inch scope at 125x. The most prominent part of the nebula has an intriguing shape that looks like an apple whose sides have been munched away, as shown in the photograph above. Brighter rinds highlight the top and bottom of the apple core. A diagonal stripe connects them, and enhanced glows fill the interior. In a dark sky, faint extensions reaching out from the nibbled sides of the apple convert it into a football. A nebula filter makes all this easier to see.
A planetary nebula arises when an aging star with about the mass of our Sun sheds its outer layers into space. The core remains as a tiny, hot star at the nebula's heart. The Dumbbell's central star is quite faint even in a 10-inch scope. Because it's so hot, it appears pale blue in the photo at upper left.
Another vulpine treat is the delightful star pattern called the Coathanger. In a dark sky it's visible to the unaided eye as a fuzzy patch. Look for it about two-thirds of the way from Vega to Altair. You can just fit it in the same binocular or finderscope field with Vulpecula's brighter star on our all-sky map. In binoculars, the group looks very much like an old-fashioned coathanger suspended upside-down in the sky. Six stars form its bar, and four outline its hook.
The Coathanger is too large to fit well in a telescope's field at more than 25x. But the group is worth a closer look in any telescope, because it guards a well-kept secret off its eastern end: the small, faint open cluster NGC 6802. Easily overlooked at a casual glance, the cluster is a subtle, oblong mist in a 4-inch scope at 30x. Extremely faint stars dot the haze at 90x. In a 10-inch scope at 170x, NGC 6802 is a beautiful diamond-dust cluster rich in faint stars.
Although NGC 6802 is a true cluster of stars loosely bound together by their mutual gravity, the Coathanger is not. It's merely a chance alignment of stars lying at different distances from Earth. But as with every deep-sky wonder illuminating our summer sky tour, each has its own special charm.
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|Title Annotation:||Observing: Deep-Sky Delights|
|Date:||Jan 1, 2014|
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