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Star Watch

Eagle, dolphin, and arrow fly through October nights

Face south after a crisp, clear October twilight turns to night, look fairly high, and one bright star greets you: Altair, the glittering eye of the constellation Aquila the Eagle, looking down at you.

Like a lot of constellation patterns, the Eagle requires a bit of imagination and an eye for the abstract. The connect-the-stars pattern here, by which modern stargazers know Aquila, looks more like a roosting bat than an eagle. Or maybe it’s a pterodactyl. But at least it’s something that flies and watches. Whether this is how the ­ancients connected the dots we don’t know, but the idea that there’s an eagle here is extremely old. It dates back at least to the Sumerians, who marked the dawn of written history about 5,000 years ago. And, for all we know, it could be older still.

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From inside the city, bright Altair may be all you can see. But from as close in as Milton or Newton or Medford you can make out more stars of Aquila’s pattern. Recognize it once, and you’ll know it forever.

In particular, look for the star at the top of the Eagle’s head just upper-right of Altair. It’s the second brightest, separated from Altair by about a finger’s width at arm’s length. It’s named Tarazed. Can you see its slight reddish-orange tint?

These two seeming companions, forever traversing the night and the seasons together, are a fine example of things that look related in the sky but ­aren’t. Altair is one of our near-neighbor stars, 17 light-years away. The sparkling light of it that you see tonight has been traveling toward us only since 1995. Tarazed is 400 light-years distant; its light tonight predates the Pilgrims’ landing. And although it looks dim ­because of its great distance, it’s actually a huge, red giant emitting 220 times as much light as Altair does.

Keep looking. More faint stars glimmer into view the longer you pay attention. Take two star-steps down Aquila’s midline to the tail at the bottom. This star is a little fainter than Tarazed. It’s separated from Tarazed and Altair by about twice the width of your fist held at arm’s length.

This particular star is well-traveled by amateur astronomers, and with a good pair of binoculars you can see why. It’s the first in a little curly row of three (spanning about half a binocular’s field of view) pointing to a rich, deep star swarm known as M11, the Wild Duck Cluster.

Recognize Aquila once, and you’ll know it forever.

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From the suburbs and viewed with binoculars, the cluster is an odd little patch of faint gray glow looking very different from the pinpoint stars all around. In a good amateur telescope, it’s a breathtaking swarm of tiny fireflies on a frosty background. The frost is an even greater number of suns just a little too faint to resolve individually. It gained its Wild Duck nickname in 1844 from one astronomer’s comment that some of its brighter stars seem to form V patterns, like an autumn flight of ducks in ­migration.

Those binoculars you’re holding? They’ll stand you in good stead as a stargazer in many other ways. Above Aquila fly two delicate, much smaller constellations: Sagitta the ­Arrow and Delphinus the ­Dolphin. They’re lovely sights in a dark natural sky, but few people live under that kind of sky anymore. Binoculars, however, can more than make up the difference.

Look for Sagitta one fist-width above Altair. It’s about as wide as the field of view in typical binoculars. It’s supposed to have been shot by Sagittarius, the Archer, who’s currently far down near the horizon.

Look a slightly greater distance to Altair’s upper left. Here’s distinctive little Delphinus, the leaping Dolphin, which may be a little easier to pick up with the naked eye. It’s my wife’s favorite; we have no trouble seeing it from Bedford just outside Route 128. Like Sagitta, it more or less spans a binocular’s field of view.

Why don’t more people know these lifelong delights floating over their roofs? ­Astronomy has a reputation as a tough hobby to learn, and there’s a reason why. Too many sky maps for beginners are badly designed and poorly ­explained. I hope my efforts here work better, and a lot of newbies have told me they do. In fact my wife, when we first met, told me how she’d been using these charts (they’ve been running here since 1986) and liked the simplicity of measuring sky things in fist widths. This definitely boosted my opinion of her.

What do you think? Tear or print this out, take it outdoors right after dark (with a flashlight just bright enough to read the chart), look south, and give it a try. I’d like to hear how you do. Any suggestions? Write me at macrobert@SkyandTelescope.com.

Whole-sky maps

Easy-to-use maps of stars and constellations across the entire evening sky are available at SkyandTelescope.com/
gettingstarted.

Alan M. MacRobert is a senior editor of Sky & Telescope magazine in Cambridge (Skyand­Telescope.com). His Star Watch column appears the first Saturday of every month.
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