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Nights of the Hunter

Map 11: Equatorial Region 2
Eridanus to Hydra
m42_noao_as
The Orion Nebula is located in the constellation Orion.
Bill Schoening/NOAO/AURA/NSF

The heart of the winter sky fills this star map. Here, we encounter Orion the Hunter, the favorite constellation of many observers. Orion is just the start, however. Taurus, Gemini, Eridanus, Canis Minor, and Canis Major all contribute bright stars. And don't overlook Monoceros the Unicorn. Although it contains no bright stars, Monoceros is a treasure trove of deep-sky objects and double stars.

In Taurus, open cluster NGC 1817 glows at magnitude 7.7 and spans 16'. Simply put, look through bigger telescopes to see more stars. Through a 2.4-inch, you'll see only half a dozen stars. Between two and three dozen stars show up through a 6-inch, with most of them concentrated in a hazy cloud at the cluster's eastern edge; there's also a nice chain of stars to the west. At 100x through a 10-inch scope, you'll count 75 or more stars.

Because you're already in the area, try finding Hind's Variable Nebula (NGC 1554-5). At its brightest, this nebula has been seen through telescopes as small as 6 inches in diameter; at other times, it's invisible through a 16-inch scope. Also known as Struve's Lost Nebula, NGC 1554-5 is associated with the variable star T Tauri.

Lots of great observing awaits you in Monoceros. Messier listed one object here — M50 — but easily could have included three more open clusters, all of which are brighter than M50. That's not to say M50 is weak. Even through a 2.4-inch telescope, you'll see two dozen stars, and, on a steady night, you might glimpse this magnitude 5.9 cluster with your naked eyes. At 100x through a 10-inch telescope, 150 stars pop into view within an area slightly smaller than the Full Moon. Note the yellow star on the cluster's southern edge and the void near the group's center.

The three open clusters brighter than M50 lie in a 15°-long line that runs north-south. Starting at the southern end, NGC 2232 shines at magnitude 3.9 not quite 2.5° north of Beta Monocerotis. Only about a dozen stars belong to this cluster, the brightest being 5th-magnitude 10 Monocerotis, which lies on the northern edge.

Nearly 12° north of NGC 2232 is NGC 2244. This magnitude 4.8 open cluster measures 20' across. Through a 6-inch telescope, you'll see 20 stars forming an oval elongated northwest to southeast. As you use larger scopes, progressively more stars will appear. It's difficult to tell, however, which belong to the cluster and which are background Milky Way stars.

Surrounding NGC 2244, but slightly offset, is the Rosette Nebula (NGC 2237-9). You'll get your best views of this object through low-power eyepieces. The Rosette measures 1° across and, although faint, can be spotted through a 3-inch telescope. For a better view, however, use a 12-inch scope, wide-field eyepiece, and a nebula filter.

Now scan 5.5° north-northeast for the Christmas Tree Cluster (NGC 2264). Through a small telescope at 50x, a dozen or so stars extend to the east and west of 5th-magnitude 15 Monocerotis. This line forms the 0.5°-long base of the tree, whose top points southward. The southern stars of this asterism don't belong to the cluster. Larger telescopes will show a bright strip of nebulosity 5' long radiating westward from the brightest star. This is but one enhancement of the giant emission nebula Sharpless 2-273, which extends for 2° to the west. At the top of the Christmas Tree lies the Cone Nebula, an obscuring cloud of dust visible only in the biggest amateur telescopes.

Scan 1° south-southwest of the Christmas Tree Cluster, and you'll find the fascinating reflection nebula NGC 2261. Also known as Hubble's Variable Nebula, this object varies in brightness and structure over periods measured in days. NGC 2261 looks like no other object through a telescope. In a 10-inch scope, a bright wedge 2' on a side radiates to the north of the variable star R Monocerotis. The nebula's cometary form appears uniformly bright with a sharply defined edge.

In Orion, there's really only one place to start: the Orion Nebula (M42). Visible to the naked eye as the middle "star" in Orion's "sword," this spectacular object looks great through any size telescope and at any magnification. Through a 2.4-inch scope, you'll see the Trapezium, a group of 4 stars (Theta1 A, B, C, and D Orionis) that formed within the nebula's gas. If you increase your telescope aperture and magnification, you'll see up to five additional stars — Theta1 E, F, G, and H, the last of which is a double star. When you view this region at low power, note the Fish's Mouth, an area of dark material that protrudes into the brightest part of M42.

Just north of the Fish's Mouth lies M43, which is considered a separate object only for cataloging purposes. Look for the star NU Orionis in the center of this 15'-diameter object.

Move ½° north of the Orion Nebula to find the Running Man Nebula (NGC 1973-5-7). The two bright stars involved with the nebula are 42 Orionis (magnitude 4.6) and 45 Orionis (magnitude 5.2). Because the Running Man Nebula is a reflection nebula, observe it without a nebula filter. Its light is reflected starlight scattered throughout the gas and dust, not reddish light emitted by hydrogen (which a nebula filter transmits).

Point your telescope at Alnitak (Zeta Orionis). Move just 18' east-northeast to the Flame Nebula (NGC 2024). Normally, a large object like the Flame (30' across) would be easy to see, but the glare from magnitude 1.7 Alnitak interferes. Increase the magnification enough to capture the whole Flame and to place Alnitak out of the field of view to the west.

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