This expansive region of the sky is home to plenty of bright stars and deep-sky wonders.
With the February dark of the Moon upon us, we have a fine opportunity to enjoy some winter sights. Perhaps most appealing for naked-eye observers is an impressive collection of stellar luminaries. Face south at nightfall, and no fewer than seven stars of first magnitude or brighter can be taken in with a single view. Most are included in the Winter Hexagon, as shown in the chart above.
The Winter Hexagon's Bright Lights
Let’s take a quick tour, beginning at the bottom of the Hexagon with Sirius. At magnitude –1.4, Sirius dominates Canis Major and is the brightest star in the night sky. It’s also one of the nearest. At a distance of only 8.7 light-years, Sirius is the closest star we can see from mid-northern latitudes without optical aid.
Proceeding clockwise, we reach Procyon (magnitude 0.4) in Canis Minor, then Pollux (magnitude 1.2). Pollux and nearby Castor are the so-called Gemini Twins, though the two are not exactly twins when it comes to brightness. Castor is just a bit too dim to qualify for membership in the first-magnitude club.
Next in the Hexagon, high overhead, is Auriga’s leading light, Capella. At magnitude 0.1, Capella is second only to Sirius among brilliant winter stars. Turning south, we come to Aldebaran (magnitude 0.9) in Taurus. Can you detect its golden hue? Aldebaran is not as red as Betelgeuse, in Orion, but its color should be quite apparent.
The last stop on our tour is Rigel, also in Orion. There’s a nice symmetry to concluding with Rigel. We began with the closest star in the Hexagon, Sirius, and we end with the most distant. Rigel is roughly 100 times farther away than Sirius and yet, at magnitude 0.2, only a little fainter.
A star’s brightness, of course, depends both on its distance and its intrinsic luminosity. Rigel is a blue supergiant shining with more than 100,000 times the intensity of our Sun. Indeed, if all the stars in the Winter Hexagon were at the same distance from Earth, Rigel would best Sirius as the sky’s brightest star by a huge margin.
Within the expansive confines of the Hexagon are some of the season’s finest deep-sky treasures, including the Orion Nebula, which I wrote about here. And of course, near the center of the figure is Betelgeuse, the much talked about variable star that has recently hit a new low and is, for the moment, slightly too faint to count as first magnitude.
Telescope users will also be familiar with M36, M37, and M38 — the lovely trio of Messier open clusters nestled within Auriga’s pentagon — as well as M41, parked just south of blazing beacon Sirius.
But among the many deep-sky treasures available in the Hexagon, I’d like to plead the case for a personal favorite: Gemini's fine (but often overlooked) open cluster, M35. The 5.1-magnitude object is easy to find, as it’s located just above the westernmost foot of the Twins, marked by 2.9-magnitude Mu (μ) and 3.3-magnitude Eta (n) Geminorum.
Tripod-mounted 10×50 binoculars are powerful enough to show a few individual cluster members in M35, but this rich specimen really comes into its own in a telescope, which has the ability to resolve many more stars.
If you’re up for a moderate challenge, see if you can spot M35’s celestial neighbor, the 8.6-magnitude cluster NGC 2158. It’s a tough catch in binoculars, but even a small scope has no trouble pulling in little NGC 2158 if you have a reasonably dark sky. The two clusters are physically similar but look quite different to us because one is much nearer the Earth than the other. M35 is the closer object—at roughly 2,800 light-years, it’s only one-fifth the distance of NGC 2158.