Of course I’m referring to Castor and Pollux, who, according to Greek mythology, were twin brothers. Their mother was the Spartan Queen, Leda; Castor was the son of Tyndareus, the king of Sparta, and Pollux the divine son of Zeus. I’ll let you do the research yourself to discover how that came about. Castor and Pollux have also been associated with St. Elmo’s fire. Here they played the role of protectors of sailors. It’s to my understanding that Castor was a mortal (like the rest of us) and when he died, Pollux begged his father Zeus to give Castor immortality, which he did, by uniting them together in the heavens. Therefore giving us mortals here on Earth the constellation known as Gemini, which in Latin means “the twins”.
The constellation Gemini rides along the Ecliptic and is nearly centered on the local Meridian at 02:20 UT for mid-northern latitudes. This is a perfect time to view Gemini’s deep sky targets with a small telescope. Gemini is home to open clusters, double stars and planetary nebula of which a few are visible to telescopes of 60mm and larger.
Our first target is the double star Castor which, although it carries the Bayer designation “Alpha”, is the second brightest star in Gemini. This showpiece double is one of the finest double stars visible in the northern hemisphere. In the 90mm f/10 refractor, Castor is easily split at 101x. Both stars appear white with a separation of about 4.2” in PA 62°. An interesting note about Castor is that it is really a sextuple star. Larger telescopes may show a 9.8 magnitude companion about 71” from the main pair and each of these stars is a spectroscopic binary. Let’s take a look at the other twin, Pollux. There are a few references to Pollux being a double star however, according to Robert Burnham, Jr. (1931-1993); none of the faint visual companions to Pollux listed in the Aitkin’s Double Star (ADS) Catalogue are gravitationally bound. Nevertheless, Pollux is an interesting star indeed. Pollux is an orange giant star with the classification of K0III. This luminary shines at magnitude 1.15 and is about 33 light-years distant. This star boasts twice the Sun’s mass and almost ten times the solar radius. But, Pollux real claim to fame is its extrasolar planet with a mass almost 2.5 times that of Jupiter. The planet, Pollux b, has an orbital period of 590 days.
M35 can be found with the naked eye under dark skies but it will take a little star hopping to locate it in light polluted areas. Referring to a star atlas, locate the star Eta Gem (Propus, Tejat Prior) in your finder scope and move your scope about 2° north-west and you should see M35 enter the field-of-view. Center M35 and looking through your main telescope, use a low power eyepiece for the best view. In the 90mm refractor at 33x, the cluster covers an area just about the size of the full Moon. The cluster appears somewhat like a fan shape with several chains of stars spreading out in a north-east direction. Larger telescopes may show the fainter NGC2158 about 15’ southwest of M35. Interesting note here is that NGC2158 was once thought to be a globular cluster.
Going back to your finder scope and keeping M35 centered, look a little toward the southwest and there should be a magnitude 4.15 star there. That’s 1 Geminorum. Place that star in the center of your finder and just over a half a degree more is the 6.7 magnitude open cluster NGC2129. It may be too faint to see in your finder but in your main scope at low power you should be able to see the cluster’s two bright B-type stars. These two stars share the same proper motion and it is likely they are a binary system. The cluster itself isn’t very impressive. In the 90mm refractor at 33x I count just 13 stars.
Going back to your star atlas, locate the 3.5 magnitude star Wasat (Delta Gem) and center it in your finder. Move your telescope just about 2° south-east and center on the 5.1 magnitude star 63 Geminorum. Now, nudge your telescope ½ degrees south. In your low power eyepiece you should see a faint, out-of-focus star. That’s NGC2392 the Eskimo Nebula or, as some call it, the Clown Nebula. At low power it doesn’t look like much but using a 10mm eyepiece with the 90mm refractor (151x) the planetary nebula starts to reveal itself as a blue disk. It does require a larger telescope at high power to see the facial features this planetary has to offer but all the same, it’s a quite a sight in small telescopes. Planetary nebulas typically stand up to high powers due to their high surface brightness. Few however, reveal their central star to small telescopes.
February nights are typically cold here along the mid-northern latitudes so bundle up and don’t forget hot chocolate or coffee and a snack to keep your energy levels up. Gemini offers more deep sky objects then I mentioned here. This is just a sample for those of us using telescopes of 60mm and up to 150mm in aperture. Plan your observing time well and your time at the eyepiece will be more enjoyable. Dont forget to get your Sky Map for February here. After you’re done observing, why not stop back here and tell us what you saw in your eyepiece. We love to here from our readers!