Greetings, fellow SkyWatchers! Are you ready for the weekend? Then let’s spend it “stellar” as we take a look at a great series of open galactic star clusters. Gathering a few photons will enrich both the spirit and the mind! If you’re ready for some history, science and challenges, then follow me…
– This date celebrates the 1512 birth of Gerardus Mercator. Mercator was the cartographer who created the Mercator map projection, the series of parallels and meridians drawn as straight lines to allow an accurate ratio of latitude to longitude. Mercator also designed the first celestial globe in 1551.
Tonight let’s take in a galactic star cluster! Find the area easily by aiming binoculars about halfway between Alpha Orionis and Gamma Geminorum (RA 06 13 42 Dec +12 48 06). Look for a faint pair of stars known as K Orionis, but don’t confuse them with slightly brighter Xi and Nu. Concentrate on the northernmost of the K pair, and you’ll pick up a slight condensation of faint stars— NGC 2194. While this Herschel ‘‘400’’ target is sufficiently bright to see in small optics, its true beauty shines in larger telescopes. This rich, young concentration of stars is over 3, 700 light-years away and is less than 9, 000 years old. Photometric studies of this neophyte cluster show it to be metal-poor for its age, but NGC 2194 is definitely a very pleasing sprinkling of stars to enjoy on a winter’s night!
Are you ready for an open cluster that’s suited for all optics? Then let’s take on NGC2287. Located about two finger-widths south of Alpha Canis Majoris (RA 06 46 00 Dec +20 46 00), only an open cluster this bright could stand up against brilliant Sirius. From a dark-sky location, your unaided eye can even spot this magnitude 4.5 star vault as a hazy patch. Aristotle saw it as early as 325 BC! Officially discovered by Hodierna, we know it best by the designation Messier Object 41.
Even from 2, 300 light-years away, the cluster’s brightest star, an orange giant, stands out clearly from the stellar nest. With large aperture, you’ll notice other K-type stars, all very similar to Sol. Although small scopes and binoculars won’t reveal too much color, you might pick up on the blue signature of young, hot stars. NGC 2287 could be anywhere from 190 to 240 million years old, but its stars shine as brightly now as they did in Aristotle’s day!
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– If you see sunshine today, then celebrate the 1787 birth on this date of Joseph Fraunhofer—a trailblazer in modern astronomy. His field? Spectroscopy. Fraunhofer developed scientific instruments and specialized in the area of applied optics. While designing the achromatic objective lens for a telescope, he saw the spectrum of sunlight as it passed through a thin slit and the dark emission lines. Fraunhofer recognized that they could be used as wavelength standards, so he began measuring, labeling the most prominent with the letters still used today. His skill in optics, mathematics, and physics led Fraunhofer to design and build the very first diffraction grating. You’ve probably seen these little rainbows hundreds of times in your life without even realizing what they are. Would you like to create your own grating? Take a piece of ordinary clear cellophane (a bit of clean food wrapping is fine) and scratch it lightly a few times in one direction only with a piece of sandpaper. Hold it adjacent to a bright light source and tilt it until you see hundreds of hair-fine lines of color. Yes, it’s crude. . . but it works! Did Fraunhofer’s telescope designs also succeed? Of course! His achromatic objective lens is still used in modern telescopes.
Tonight journey south of Orion to Lepus and its brightest star—Alpha. Named Arneb, this double star resides about 900 light-years away. Its wide separation of 35.500 means it’s probably not a true physical pair, but the 11th magnitude disparate companion is a nice challenge. For binoculars and small scopes, hop due east of Alpha about a finger-width for brilliant multiple-star system and open cluster NGC2017. The gravitationally bound stars in this small open cluster are a well-studied source of radio and infrared emission. NGC2017 produces a dense wind from a thin HII region hidden within it, which may come from a loose distribution of gas and dust. Power up, and the primary colorful members begin to split into disparate pairs as the combination of aperture and magnification increases resolution. It’s a much underrated jewel box!
