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The Sky This Week, 2013 August 20 - 27

A Blue Moon and two "new" stars!
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 Nova Delphini 2013, imaged 2013 August 15, 03:30 UT


"The Sky This Week" is back from its summer hiatus. While we were gone we experienced a great display of the Perseid meteor shower, some wonderful nights under dark skies, and the discoveries of a bright supernova in a nearby external galaxy and a "naked eye" nova much closer to home. More on these in a few moments.

The Moon starts the week off as a bright Full Moon, then wanes in the morning sky as she climbs through the dim stars of the rising autumnal constellations. Full Moon occurs on the 20th at 9:45 pm Eastern daylight Time. August’s Full Moon is popularly known as the Sturgeon Moon, Corn Moon, or Grain Moon, but this year it also represents a phenomenon known as the "Blue Moon". Most people think of a "Blue Moon" as the second Full Moon to occur in a calendar month, but the traditional definition is that of the third Full Moon to occur in an astronomical season in which four Full Moons fall. While somewhat more cryptic than the "second-of-the-month" variety, this scheme helped farmers and other people who used traditional Full Moon names to keep the proper names in synch with the occasional "extra" Full Moon that occurs about every 2.6 years. The "controversy" over the proper definition of the "Blue Moon" dates back to an erroneous discussion of the phenomenon that was originally published in 1946 and subsequently re-discovered in 1999. Personally I prefer the twice-in-a-month approach, but I guess this issue, as with many of our tumultuous times, will never be fully settled. Luna won’t pass any particularly bright objects this week until the morning of the 27th, when she will be closing in on the rising Pleiades star cluster.

If you’re looking for the brighter planets, you’ll need to be out in either the early evening or early morning hours. Shortly after sunset you should be able to see the bright glow of Venus hovering in the southwestern sky. The dazzling planet is only easily seen during the twilight hours, but she is very hard to miss unless there’s lots of haze near the horizon. Venus will continue to hug the horizon for the next several weeks before gradually creeping into darker skies in the late fall.

Saturn is also located in the southwestern sky and can still be glimpsed in a telescope for a few minutes before settling into the murk of the horizon. You should be able to locate the ringed planet by about an hour after sunset, and you should have half an hour or so to see his rings in the telescope before atmospheric distortion washes them out.

Saturn sets at around 10:00 pm, and you’ll have to wait until 2:00 am for Jupiter to rise. After another hour or so Old Jove should be high enough to train the telescope his way, but the best time to observe him is just before morning twilight when he’ll be much higher and the atmosphere will be steadiest. You should have no difficulty seeing his four bright Galilean moons, and with good steady conditions his cloud belts and bright zones should be easy to spot in modest instruments.

Mars starts the week off as a third "companion" to the Twin Stars of Gemini, Castor and Pollux. Look for him and the rising stars of the Great Winter Circle at around 5:00 am. Don’t expect to see much of the red planet in the telescope right now except a tiny pink-hued disc. He won’t reach opposition until the spring of 2014, so save your efforts to observe him until then.

As I mentioned earlier, there were two unusual discoveries made over the past three weeks. The first was a bright supernova in a galaxy known as Messier 74. This galaxy is a well-known face-on spiral in the constellation of Pisces, located some 30 million light-years from Earth. It is visible as a small fuzzy patch of light in telescopes as small as 3 inches. The supernova, first spotted on July 25, is bright enough to be visible in similar-sized instruments, making this one of the rare supernovae visible to amateur astronomers. A supernova is the result of the cataclysmic collapse of a supergiant star in the host galaxy, and the resulting explosion brightens the star until its light outshines the rest of the galaxy’s stars combined! This one is currently about 12th magnitude and shines with a luminosity of several billion suns.

The second unusual event was a somewhat more subdued stellar explosion known as a nova. This star appeared in the constellation Delphinus the Dolphin on August 14th and quickly brightened to its current 4th magnitude glow. Novae are caused by the nuclear detonation of material accreted onto a "white dwarf" stellar remnant from a nearby orbital companion star. This explosion increases the star’s luminosity by a factor of some 100,000 times that of the Sun. Nova Delphini 2013 is currently visible to the naked eye from dark-sky sites and is an easy target for binoculars. It may be found along the southeastern periphery of the Summer Triangle asterism, a few degrees northwest of the small constellation Delphinus. You can read more about this "guest star" and download a finder chart for it here.