DX Cancri, Part Two

Observing DX Cancri

     As I’ve already mentioned, we’re starting out with what might be the worst possible star on our list to observe through the eyepiece or to locate by star hopping. This is not only due to the intrinsic dimness of our target star, but also to its being situated in a particularly nondescript region of the sky. There are no bright, splashy landmarks (?skymarks?) by which to steer. The nearest naked eye stars (the widely separated optical binary Phi Cancri 1 and 2), at magnitudes 5.58 and 5.55 respectively, scarcely deserve the label (at least when observed from Howard County, Maryland). The closest really bright star is Pollux way over in neighboring Gemini.

     I personally always like to get my bearings in the sky prior to zeroing in on a specific object. In this case, a good idea is to take in the Big Picture: Gemini off to one side, and Leo to the other. Sandwiched between these two gorgeous constellations is what has got to be the dullest of the signs of the zodiac (at least to the naked eye), Cancer. Its brightest star, Beta Cancri, which shines at a measly 3.53 magnitude, is about as far away from DX Cancri as one can get and still be within the constellation’s boundaries. Closer to our target, Delta Cancri (Asellus Australis) is a 3.94 magnitude star nestled up against the spectacular Beehive cluster (M44). (Off topic, but fun to know: Delta Cancri also goes by the utterly ridiculous name of Arkushanangarushashutu, a Babylonian word meaning “Southeast Star of the Crab”.) Iota Cancri is the closest relatively bright star to where we want to end up. It boasts a magnitude of 4.02, with a fainter 6.57 magnitude companion. (By the way, take the time to check out Iota Cancri before going on from there. It is a breathtakingly beautiful, easily splittable double star often referred to as the “Albireo of Spring”, having a bright yellow primary accompanied by a deep blue companion.)  DX Cancri lies within a right triangle formed by Pollux, Delta Cancri, and Iota Cancri.

     So far, we could have gotten to this point by naked eye alone on a reasonably dark night. Using my 8X56 Celestron binoculars, I can easily see Phi Cancri 1 and 2, our next signpost. They are found  just below a line from Iota Cancri and Pollux,  a little more than a third of the distance between them from Iota Cancri.  Centering our view on these two stars, we see a 6th magnitude star about a full moon’s distance to the southwest of Phi Cancri 2, which serves to guide us to the next level. If we make an imaginary right triangle extending to the north and west, with the line between Phi Cancri 2 and this star being the hypotenuse, our target now lies just south of where the two legs would meet.  Switching to telescope view (and remembering that, if you are using a diagonal, from here on in everything is mirror-imaged), with my 5-inch refractor I can just make out three closely-spaced 12th magnitude stars to the immediate left of where DX Cancri should be. They form an approximately north-south line, with the more northerly pair being separated from each other by about half again as much as the other two. Our star lies right where the third point of an equilateral triangle would be, with this line of stars being the triangle’s base.

     But here, alas, is where I must admit defeat. With my largest telescope, using my best eyepiece at highest magnification, on a clear, steady, moonless night and with infinite patience, at the point in question, I see… nothing. DX Cancri is simply too faint for my largest telescope.

But trust me. We began with the worst. After this one, all else seems easy!

(I saw DX Cancri with my own eyes only one time, ever. On May 11th, 2012, Govind Rao and I searched for it using his 16-inch Schmidt-Cassegrain. We managed to finally see it after about a half-hour’s difficult search. Even through his huge light bucket, it still required averted vision to observe this star through the suburban light pollution of Howard County’s Alpha Ridge Park. And even then, it took some while before we were satisfied we were actually looking at the correct star! After seeing how unbelievably faint this object was in even such a large instrument, I realized that my earlier search for it with a 5-inch telescope had been doomed from the very start.)