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Wolf and Centaur

Map 19: South Equatorial 4
Hydra to Scorpius
ngc_5139_noao_250
Globular cluster NGC 5139 is located in the constellation Centaurus.
Adam Block/NOAO/AURA/NSF

Two large, bright constellations — Lupus the Wolf and Centaurus the Centaur — dominate this star map. The majority of each constellation lies along the Milky Way's border, so a variety of deep-sky objects awaits your inspection.

Start in Lupus with NGC 5927, a magnitude 8 globular cluster that's 12' across. You may need a telescope as large as 16 inches to resolve this cluster's myriad faint stars.

Globular cluster NGC 5986 — at magnitude 7.5 — is a bit brighter than NGC 5927, and its stars resolve easier. A 6-inch scope shows a few stars. Move up to a 12-inch under a dark sky, crank the magnification up to 200x, and dozens more stars will pop into view. NGC 5986 makes a small triangle with a 6th- and 7th-magnitude star ¼° to the east.

Two planetary nebulae — IC 4406 and NGC 5882 — deserve some of your observing time. IC 4406 glows at magnitude 10.2 and is roughly 1.5' across. An 8-inch or larger telescope reveals a rectangular object much brighter at its center with fainter extensions stretching east and west. NGC 5882 shines at magnitude 9.4 and stretches 7' in diameter. It's circular and glows a vivid blue-green through an 8-inch or larger scope.

A visual survey of Centaurus reveals a fuzzy star — Omega — that happens to be the sky's brightest globular cluster, NGC 5139. Gleaming at magnitude 3.5, this object was misidentified by German stellar mapmaker Johannes Bayer. In his 1603 work, Uranometria — the first star maps to use Greek letters to identify the stars — Bayer assigned this globular the Greek letter Omega, a designation it has retained ever since.

Omega Centauri is a wonder to behold through binoculars or telescopes of any size. Omega appears slightly larger than the Full Moon, and, because it's rotating relatively quickly, its shape is slightly out-of-round. With an 8-inch telescope, you'll see 1,000 stars, each a faint pinprick of light. At high power, the stars appear nearly uniformly distributed across the field of view.

Move 4.5° north of NGC 5139 to find irregular galaxy Centaurus A (NGC 5128). Although this object shines at magnitude 6.7, you won't see it with unaided eyes even from the darkest site because its light is spread over an area that measures 31' by 23'. Through a 12-inch telescope, you'll see the central circular haze 8' across divided by a dark lane 1' wide. A 12th-magnitude star lies in front of the dust lane at the northwest end.

Only 17' from Iota Centauri sits spiral galaxy NGC 5102, which measures 10' by 4' and shines at magnitude 8.8. Most of NGC 5102's brightness comes from its core. Be sure Iota Cen lies outside the field of view when you observe this galaxy, or the glare will overwhelm the view.

For something a bit different, look 2° north of Phi Centauri. This object is the bright reflection nebula NGC 5367. Through a 12-inch telescope, you'll see an evenly illuminated haze roughly 2' across. To the northeast is a detached region that measures 2' by 1'.

Now, move to the eastern part of Hydra, which also lies on this star map. Hydra's brightest galaxy, and a showpiece of the "near-southern" sky, is M83 (NGC 5236). M83 is a barred spiral galaxy that appears nearly face-on. This fortuitous alignment lets us observe its spiral arms through telescopes as small as 6 inches in diameter. M83's bar is aligned northeast-to-southwest. The galaxy's core is brilliant and unresolvable. With a 12-inch or larger scope, look for dark lanes of dust and cold gas within the spiral arms. M83 shines at magnitude 7.5 and measures 15' long.

Another Messier object in southern Hydra is globular cluster M68 (NGC 4590). At magnitude 7.6, this object glows slightly fainter than M83. The star cluster looks brighter, however, because its light is spread over an area only 12' across. Although it's bright, M68 doesn't resolve well. Even through a 12-inch scope, you'll see fewer than 30 individual stars in front of the cluster's nucleus.

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