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South of the Dog Star

Map 17: South Equatorial 2
Fornax to Pyxis
m79_noao_250
Globular cluster M79 is located in the constellation Lepus.
NOAO/AURA/NSF

The night sky's two brightest stars — Sirius (Alpha Canis Majoris) and Canopus (Alpha Carinae) frame the northern and southern boundaries of this star map. Between these two stars lie many superb deep-sky objects, especially galaxies and globulars.

Most beginning observers know how to locate Sirius — draw a line down from Orion's belt. If you continue that line for an equal distance past Sirius, you'll find yourself amid the stars of Puppis the Stern, most of which lies on this map.

Start 4° south of Sirius at M41, an open cluster you'll locate easily with unaided eyes. A 6-inch telescope reveals more than 50 stars across the ½° diameter of this magnitude 4.5 cluster.

An even brighter open cluster lies 8½° southeast of M41 — the Tau Canis Majoris Cluster (NGC 2362). Indeed, most of this cluster's brightness comes from the star Tau Canis Majoris, which shines 3 magnitudes brighter than the group's next brightest member. And when you look closely at Tau, you'll see a group of 10th-magnitude stars in a 6'-wide region surrounding it.

The brightest star cluster in Puppis isn't a star cluster at all. Through a telescope, NGC 2451 appears as an impressive array of roughly a dozen bright stars around a reddish 4th-magnitude luminary. But because these stars are moving independently, and not as a group with a common center of gravity, NGC 2451 is just a chance alignment.

You'll find a true star cluster 1½° southeast of NGC 2451. At magnitude 5.8, open cluster NGC 2477 is visible without optical aid to most observers from a dark site. So many stars of similar brightness are packed into an area ¼° across that NGC 2477 looks a bit like a loose globular cluster. Through a 6-inch scope, the central 5'-wide area resolves into 100 stars. Double your telescope's aperture to 12 inches, and you'll double the number of stars you can count. The 4th-magnitude star just south of NGC 2477 lies in the foreground.

At the upper left of Map 17 is the bright planetary nebula NGC 2440. This magnitude 9.4 object looks slightly oval through a small telescope. A 12-inch scope shows the faint lobes at the northeast and southwest edges, as well as a faint haze surrounding the bright disk. Lepus the Hare is a small constellation west of Canis Major that boasts a single Messier object — globular cluster M79. Although it glows at magnitude 7.7, this cluster is difficult to resolve in telescopes smaller than 8 inches. A larger scope will reveal many stars in M79's outer regions, as well as a large, densely packed core.

Look on Lepus' border with Canis Major to find NGC 2196. This galaxy is easy to find, even at magnitude 11.1, because it's small and, therefore, has a high surface brightness — well, at least the nucleus does. NGC 2196's spiral arms are faint and difficult to see because they wind closely around the nucleus.

When you're ready to observe in Columba the Dove, don't miss three standout deep-sky objects in its southwest corner: NGC 1792, NGC 1808, and NGC 1851. The first two objects are galaxies that have interacted in the recent past. You'll need at least a 12-inch telescope just to see faint signs of the interaction.

NGC 1792's shape is not quite an oval. It's twice as long as wide with tightly wrapped spiral arms you'll need a big telescope to see. Notice how uniformly the magnitude 9.9 brightness is spread over NGC 1792's area. Lying 40' to the northeast, NGC 1808 is a near twin of NGC 1792.

NGC 1808 also shines at magnitude 9.9, and its dimensions are the same. Insert a low-power eyepiece, and you'll see both galaxies at once. The third bright deep-sky object in this area is globular cluster NGC 1851. At magnitude 7.2, it's on the brink of naked-eye visibility. This cluster's outer stars resolve easily, but even at high magnification, the core remains too densely packed with stars to separate.

In the southwest (lower right) corner of this map, you can find two galaxies in the northern section of Horologium the Clock. NGC 1512 makes an isosceles triangle with Alpha and Delta Horologii, lying roughly 2° from each. This magnitude 10.2 barred spiral galaxy has most of its brightness concentrated in its bar. A 16-inch scope reveals traces of the spiral arms, which extend from each end of the bar.

NGC 1527 lies 4½° south of NGC 1512. This magnitude 10.7 galaxy is twice as long (3') as wide. Look for two nearby stars: One shines at magnitude 12 and lies just north of the galaxy; the other glows at magnitude 13 and appears superimposed on NGC 1527's western region.

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