Our season of conjunctions and comets ended when Venus and Jupiter passed each other on the morning of Feb. 11. Now, I plan to revisit a few constellations and discuss some of the interesting things to see in them. This month is Gemini.
The constellation Gemini is at its highest point in the sky this month at about 10 p.m. The twins of Gemini, Castor and Pollux, are within 5 degrees of each other. Castor, the northernmost of the pair is only slightly more than 5 degrees from the zenith point. Those two stars are so similar in apparent magnitude that ancient astronomers named them after the mythological twins.
When Gemini isn’t straight overhead, the easiest way to find it is to start with the more recognizable Orion. From Orion’s belt, you can look up toward the north, beyond the bright red Betelgeuse and slightly to the left. When looking up from Orion, left is toward the east.
The constellation Gemini is one of those originally labeled by Ptolemy and is one of the 12 in the zodiac. Gemini is an elongated rectangle, with Castor and Pollux as the heads at one end, and dimmer stars symmetrically filling in the rest, down to the feet at the other end.
The way I remember which is Castor and which is Pollux requires knowing two other bright stars of the winter hexagon, which I have written about in other columns. I just remember that Castor, with the “C,” is toward the star Capella, also with a “C,” and Pollux, with a “P” is toward Procyon, with the “P.”
Castor, at magnitude 1.58, is a visual binary star. That means that through a telescope you can easily see two stars of magnitude 1.93 and 2.97 respectively. Not readily apparent is a third, much dimmer star of magnitude 9.83 in the same system. But that’s not all! (This is where the description may sound like a television knife commercial.) Each of those three stars has also been found to be a spectroscopic binary, so there are a total of six stars in this one system.
Pollux, at magnitude 1.14, is slightly brighter than Castor. It is the closest giant star to the sun and has a confirmed exoplanet orbiting it.
The open cluster M35 is near the foot on the right. It is interesting for a couple of reasons. First, M35 shows a sharply higher star density compared with the surrounding star field. Second, NGC 2158 is another, much fainter cluster that is in the same field of view. In an 8-inch telescope, M35 shows up as a typical grouping, where you can easily see the individual stars. But in the more distant companion cluster, it is very challenging to make out individual stars. Instead, the combined light is more reminiscent of the faint, diffuse glow of a dim galaxy.
This monthVenus will be visible in the morning for a few more days, but then will be lost in the glare of the sun. Look for its return as the evening star in April. Saturn and Jupiter will continue to rise earlier and earlier, and will be visible again in the evening sky by late summer.
Between Orion and Gemini is the faint winter Milky Way. It crosses the sky going roughly north to south and contains many open clusters for your binocular viewing pleasure.
The full moon this month is on Feb. 27, so avoid that week to get the best view of the Milky Way. It will be darker before Feb. 20, after the first quarter moon has set, and a few days after the full moon before the moon rises.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. He can be reached at [email protected]