On a clear February night, even with the moon up, one can see what is called the Winter Hexagon in the southern sky. These seven stars might be called “beacon stars,” since they are very bright and most of them are very far away.
The band of the Milky Way runs through the center of the Hexagon, consisting of (listing clockwise) Aldebaran, Rigel, Sirius, Procyon, Castor and Pollux almost together, and Capella. Betelgeuse is at the center, while Praesepe, also known as the Beehive cluster and the Pleiades cluster lie outside.
It is entirely a winter spectacle. Within little more than a month the Hexagon will be gone as the sky gives way to spring.
But the Milky Way, that gigantic cloud of several hundred billion stars that form our galaxy, will never be gone from our nights. Perhaps it will become more visible than in the last decade. As more and more lights are switched off after midnight for environmental and economic reasons, it may reappear in all its glory.
It was once thought that the Milky Way constituted the entire universe. In the 1920s Edwin Hubble and others discovered that many of the fuzzy splotches in the sky astronomers had been viewing for hundreds of years were actually galaxies in their own right. In the visible cosmos we now know there are hundreds of billions of other galaxies.
Some of them are utterly unlike our spiral-shaped Milky Way, some uncannily resemble it. One in particular is almost indistinguishable. UGC 12158, 400 million light-years away in Pegasus is like an exact copy. Conveniently, it can be seen face on.
Prominent in the night sky this month is Hydra the Water Snake, the biggest of all constellations, named after the many-headed sea monster killed by Hercules as one of his 12 labors. It has only one bright star, Alphard, or Alpha Hydrae, known as the Solitary One because it is alone in that region of the sky. Tycho Brahe called it the Heart of the Snake, but it is truly a lonely heart.
North of Hydra is another seemingly boring constellation, Sextans the Sextant. But on closer examination it can be seen to contain thousands of faint stars. It has two particularly interesting galaxies: the Dwarf Spheroid galaxy, only discovered in 1990, is a small galaxy that orbits the Milky Way just as the Moon orbits the Earth. It is only 295,000 light years away which is very close for a galaxy. Much further, at 32 million light-years, is the giant Spindle Galaxy (NGC 3115) that is several times bigger than the Milky Way.
Saturn rises at about midnight in Virgo, its rings partly open. On the 21st it is just north of the Moon. Jupiter sets at about 8.30 pm. Jupiter cannot be missed in the southwestern sky. It is the brightest light in the night sky except for Venus which only appears at morning and evening