Books by Philip S. Harrington

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Astronomy For All Ages

Cosmic Challenge

The Deep Sky: An Introduction

Eclipse!

The Illustrated Timeline of the Universe

The Space Shuttle

Star Ware, 4th edition

Star Watch

Touring the Universe Through Binoculars
 

Phil's Binocular Pick for July/August:

M4 and M80

Globular Clusters in Scorpius

With its long, winding body deeply immersed in the plane of our galaxy, Scorpius the Scorpion is a veritable playground for the binocularist.  Within its borders is a bountiful selection of beautiful deep sky objects strewn across some of the finest heavenly star fields.  One of my favorite ways to spend a warm, clear summer evening is to simply sit back and casually scan the Scorpion's crooked body from head to toe.  Along the way are many elegant asterisms, clusters and nebulae which provide hours of fascinating sky watching.

M4 (NGC 6121) is an exciting globular cluster to view through just about all optical instruments.  Some sharp-eyed observers have reported seeing this 6th-magnitude object without any optical aid, while binoculars make it plainly visible as a large, amorphous globe only 1-1/2 degrees west of Antares.  Visual observers typically note M4 as only about half as large as its 26 arc-minute photographic extent.

The brightest stars in this distant horde just crack the 11th-magnitude barrier. Their brightness, combined with the cluster's fairly loose structure, makes partial resolution possible in 15x glasses under ideal sky conditions.  Perhaps even easier to see is a bright "bar" of light slicing across the cluster's center.  This unusual feature is unmistakable in giant glasses and even susceptible in steadily-held 7x50's.  At nearly 7000 light years away, M4 is considered by some authorities to be the closest globular cluster to earth (others believe NGC 6397 in Ara is slightly closer).

M80 (NGC 6093) is a bright globular cluster found about halfway between brilliant Antares (Alpha Scorpii) and Graffias (Beta Scorpii).  History is not clear as to who discovered M80, for its first sighting was made almost simultaneously by Messier and Méchain in January, 1781.

Binoculars willingly detect the 7th-magnitude disk of M80 spanning 9' of arc. Set in a striking star field, it presents itself as a softly glowing, round blur highlighted by a more intense center.  Resolution of the stars in M80 requires at least an 8- to 10-inch telescope, as the brightest stellar elements are 14th magnitude.

M80 has the distinction of being one of the few globular clusters to ever spawn a nova.  The event was seen in May, 1860, when an anonymous star suddenly flared to 7th magnitude.  Now known as T Scorpii, the star slowly faded back into obscurity in about three months.

Stats:
 

Object
Type
RA
Dec
Mag
Size
M80
Globular Cluster
16 17.0
-22 59
7.2
9'
M4
Globular Cluster
16 23.6
-26 32
6.0
26'
 

Finder Chart:

Note: The circle marks a 7-degree field of view, typical for 7x binoculars.

Text copyright 1990 by John Wiley & Sons
Chart copyright 1999-2010 by Philip S. Harrington and G. Dean Williams