Eight of the 25 brightest stars are gathered together in the southern sky this month. If you haven’t made their acquaintance they are Sirius, Capella, Rigel, Procyon, Aldebaran, Pollux, Castor and Betelgeuse, in order of brightness. Betelgeuse normally fits between Procyon and Aldebaran, but it’s currently experiencing a deep fade though still shining at a respectable magnitude 1.6.
According to astronomer Edward Guinan of Villanova University, who recently reevaluated the star’s behavior, Betelgeuse should bottom out around Feb. 21 and then slowly begin to brighten. Keep an eye on it. To watch for changes compare it to Aldebaran (magnitude 0.9) and Bellatrix (magnitude 1.6), the star to the right or west of Betelgeuse.
No other region of the sky is replete with so many bright stars so close together as this section of the winter sky. If you draw imaginary lines to connect all these luminaries (leaving Betelgeuse out) they form a gigantic six-sided figure called the Winter Hexagon measuring 65° from top to bottom (6.5 outstretched fists) and 45° side to side. Betelgeuse is trapped inside the hexagon like a butterfly in a net. If you include it, the geometric figure becomes the letter “G.”
No matter how light or moon-polluted your sky the hexagon holds forth every clear winter night. Sirius, the brightest star, defines the southernmost apex while Capella, located near the zenith, shines from its pinnacle. All the stars are first magnitude or brighter. If you can find the Winter Hexagon you can use the map provided to star-hop from each of the bright stars to the fainter ones that define the constellations they’re part of. In this way you’ll recognize Auriga (Capella), Orion (Betelgeuse and Rigel), Taurus (Aldebaran), Canis Major (Sirius), Canis Minor (Procyon) and Gemini (Pollux and Castor.)
The moon now rises well after sunset, allowing these stars and constellations to twinkle in all their glory. Did you see the full moonrise last night? My sky was cloudless for a change, and the moon literally burst on the scene as a small light at the eastern horizon with no forewarning from haze or clouds. It quickly grew into a skinny bean and eventually rounded itself into a disk as it ascended from the horizon. The transformation took my breath away.
An inferior mirage — a reflection-like second moon — appeared below the real moon at moonrise and stayed for many minutes. As the rose and brightened it laid down one of the prettiest glitter paths I’ve ever seen. Meanwhile, on the opposite side of the sky, Venus and Mercury dominated the fading dusk.
Venus was obvious of course, and Mercury nearly so, located well below and to the right of Venus about a fist above the horizon. The coming week will be the best time to hunt for the solar system’s innermost planet.