Orion is perhaps the most famous of the 88 constellations in the night sky, and it’s likely the easiest to find for stargazers all over the world. And unlike most constellations, Orion looks like its legendary namesake: a mighty hunter with a shield, a raised arm, and a sword hanging from his star-jeweled belt. The constellation harbors some dazzling sights including what may be the most beautiful object in the night sky for a small telescope, the famous Orion Nebula, a bright blister in the nearest star-forming region to our solar system. In this little tour, we’ll have a look at some lesser-known sights in the constellation Orion north of the three bright stars of Orion’s Belt.
NOTE: This tour has been adapted from the course ‘What to See in a Small Telescope (January-March’) at CosmicPursuits.com.
NGC 2175 and NGC 2174
The first stop on the tour is the nebula NGC 2175 at the top of the upraised “club” of Orion. It’s about 1.5o east-northeast of χ2 (chi-2) Orionis. At 7th magnitude, the nebula is bright enough to discern without a filter in reasonably dark sky. But a narrow-band nebula filter helps with contrast, especially if you endure some light pollution. The nebula appears circular with a diameter of about 30’ (half a degree). There’s an 8th-magnitude star near the center and another 10-12 stars superimposed on the nebula. At 75-100x, you may see some mottling and dark patches among the brighter regions. If you have a 10-inch or larger telescope, try to see a separate knot of nebulosity on the northern edge of the cluster. This is NGC 2174.
In images, the shape and mottling of NGC 2175 inspire the informal name of “Monkey Head Nebula” for this little emission region (see image at the top of the page).
NGC 2169 and NGC 2194
Now look about 5o north-northeast of the bright orange star Betelgeuse in Orion’s eastern shoulder. Find the 5th-magnitude star μ (mu) Orionis, then move to the pair ξ (xi) and ν (nu) Orionis. The 6th-magnitude open star cluster NGC 2169 sits just one degree west-southwest of xi (the easternmost star).
At moderate magnification, you’ll see in NGC 2169 about 15-20 stars of 7th magnitude or fainter arranged in two groups about 0.1° across. One group contains 6-7 stars and the other perhaps 10-12 stars. This cluster is sometimes called the “37 Cluster”, because the larger group forms the number “3” and the smaller group forms the number “7”. Depending on your optics, the numbers might be flipped left-to-right or upside down, so use your imagination to unscramble the apparent numbers. NGC 2169 is about 3,400 light years from Earth and is just 8 million years old.
Much further away, about 12,000 light years, lies the faint open cluster NGC 2194. Find it about 1.6o south-southeast of NGC 2169. In a 4 to 6-inch scope, it appears as a faint icy glow, with few of its brightest stars resolved even at 150x. In an 8-inch or larger scope, the cluster reveals a few more stars on an unresolved silver background.
Collinder 69 and the Head of Orion
A pleasant group of stars marks the somewhat undersized head of Orion. The small cluster called Collinder 69 gathers around the 3rd-magnitude star λ (lambda) Orionis, also called Meissa. The cluster spreads across a full degree and reveals 40-50 stars in a 4-inch scope at moderate magnification. Only six stars are particularly bright, and the rest blend into the background star field. Lambda Orionis is a double star with blue-white components of magnitude 3.5 and 5.5 separated by about 5”; 75-80x should split them nicely.
Rho Orionis and 32 Orionis
Between the shield and the torso of Orion lies a pretty double star ρ (rho) Orionis. Orion’s Belt points the way… follow the line from the belt to the northwest about a distance equal to 2.5x the Belt’s length. The primary is a golden-yellow star of magnitude 4.6; the secondary is magnitude 8.5 and lies about 7” to the northeast. The star splits well in a 3 to 4-inch scope at 75-100x.
If you want more of a challenge, look for the star 32 Orionis, just east of γ (gamma) Orionis (Bellatrix) in the constellation’s western shoulder. The star has components of magnitude 4.4 and 5.8, but they are separated by only 1.3”. Use 150x or more to split the pair. The air needs to be steady to split this pair, no matter how large your telescope.