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A showpiece globular

Map 8: North Equatorial 5
Boötes to Cygnus
m13_noao_250
Globular cluster M13 is located in the constellation Hercules.
N.A.Sharp, REU program/NOAO/AURA/NSF

The constellations Hercules the Hero and Lyra the Lyre are the two dominant star patterns on this map. Denser regions of the Milky Way congregate in our galaxy's arms, preventing us from seeing much of what lies beyond. Instead, nearby star clusters and nebulae abound.

Starting in Hercules, find Pi, Eta, Zeta, and Epsilon Herculis — the Keystone of Hercules. Two-thirds of the way from Zeta to Eta, you'll find M13, the eighth brightest globular cluster in the sky. At magnitude 5.8, this cluster can be glimpsed with the naked eye even from less-than-ideal locations. Any telescope pointed at M13 reveals a glorious swarm of stars. Through an 8-inch scope, you'll see more than 100. Increase the magnification beyond 150x, and try to spot the "propeller," the intersection of three dark lanes near the cluster's center.

Only slightly fainter than M13 is another globular cluster — magnitude 6.5 M92. This object lies on a nearly exact line between Iota and Eta Herculis. It's 5° from Iota and 7.6° from Eta.

Less than ½° northeast of M13 lies the magnitude 11.6 spiral galaxy NGC 6207. Insert an eyepiece that will give you a bit more than a half-degree field of view, and enjoy NGC 6207 and M13 at the same time.

Before you leave Hercules, check out NGC 6210, a small (25" by 15" in diameter) but bright (magnitude 8.8) planetary nebula. At magnifications under 100x, this object's color and uniform brightness are striking.

Midway between Alpha Aquilae and Beta Cygni lies Sagitta the Arrow. This star pattern ranks 86th out of the 88 constellations in size. It does contain a Messier object, however — M71. Glowing at 8th magnitude, M71 appears loosely arranged for a globular cluster. An 8-inch telescope resolves several dozen of the brightest stars set against a hazy background.

Because of its small size, parallelogram shape, and zero-magnitude star, Lyra the Harp is one of the easiest constellations to recognize. Two showpiece deep-sky objects reside there.

The Double Double (Epsilon Lyrae) is, as the name promises, a pair of double stars. Epsilon1 is the northern and wider pair. The stars shine at magnitudes 5.0 and 6.1, and their separation is 2.6". The components of Epsilon2 lie 2.3" from each other with each star glowing at magnitude 5.5. Even a small telescope at 100x will split both pairs.

The Ring Nebula (M57) is Lyra's other spectacle. A small scope reveals this object's doughnut shape. Move to a larger scope, and you'll notice the ring isn't exactly round but elongated roughly east-west. The darkened central area is easy to see, but the central star is a challenge object best left to telescopes 16 inches in aperture and larger.

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