Map 23: South Polar 2
Vela to Telescopium
August 24, 2007
Map 23 contains plenty to observe, including all of Crux the Southern Cross, the smallest of the sky's 88 constellations. You can see something interesting just looking at Crux without optical aid. Near its brightest star, Alpha Crucis, is a dark, 4°-wide swath of sky called the Coalsack. Only one 5th-magnitude star intrudes here.
On the eastern edge of Crux, the Jewel Box Cluster (NGC 4755) also is visible to the naked eye. This well-defined clump of colorful stars contains at least 25 members brighter than 12th magnitude and looks great in any size telescope. Three bright stars — one yellow, one blue, and one orange — form a line across the cluster's center. The rest of the stars are white and form a sparkly background to the three luminaries.
Planetary nebula NGC 4071 lies 2° east-southeast of Lambda Muscae. Long-exposure images show it is an ellipse flanked by bright ends and containing a bar that crosses the nebula's minor axis. In a 12-inch or larger telescope, NGC 4071 appears like a ghostly, oval bubble about 1' across with a diffuse edge. A 13th-magnitude star appears near the center, but this is not the planetary's true central star, which is 19th magnitude. An OIII filter is a must if you want to see any of this object's details.
Less than a degree south of Gamma Muscae lies NGC 4372, one of the least-concentrated globular clusters. At a distance of 15,000 light-years, its brightest stars glow at 12th magnitude and are visible easily in small telescopes. An 8-inch scope shows NGC 4372 as a loose collection of 13th- and 14th-magnitude stars spread over an area 19' across.
This cluster shows almost no concentration toward its center; at 150x, it looks like a circular open cluster. In a 14-inch or larger scope, you can resolve NGC 4372 to the core, and it becomes a magnificent collection of mostly equal-magnitude stars with no background glow.
A more typical globular cluster is nearby NGC 4833, a nice contrast to NGC 4372. This is a moderately concentrated ball of stars that resolves well in 6-inch scopes. Use a 10-inch telescope, and you'll see dozens of 13th-magnitude cluster stars. Unlike NGC 4372, the broadly concentrated core displays a haze of unresolved stars.
The central region of NGC 4833 appears like an oval stretched both east and west. This globular shines at magnitude 7, measures 13.5' across, and lies 25,000 light-years away.
Don't miss 10th-magnitude NGC 5189 some 5¾° northeast of NGC 4833. This planetary nebula is a real oddball. At 5,000 light-years away, NGC 5189 is 2' across. Sometimes called the Barred Spiral Nebula because of its resemblance to a barred spiral galaxy when viewed through small telescopes, this planetary displays an S shape that's hard to miss.
Be sure to explore the small constellation Chamaeleon because it contains one of the highlights of the south polar region: planetary nebula NGC 3195. Although it glows at a paltry magnitude 11.6, this object's high surface brightness allows you to use high magnification to study it.
If your sky permits, use at least 200x on the 40" disk to reveal a slight north-south elongation and subtle brightness differences along NGC 3195's minor axis. The central star — listed at magnitude 15.3 — is a test only for the largest amateur telescopes because of the nebula's brightness.
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