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The Sky This Week, 2013 April 2 - 9

Another round for "Globe At Night", and what's behind the stars?
LeoTriplet_130330_04small.jpg

The "Leo Triplet" of Galaxies: M66 (left), M65 (right),
and NGC 3628 (top)

Imaged from Vaucluse Spring near Stephens City, VA
with an 80mm (3.1-inch) f/6 Antares Sentinel refractor
and a Canon EOS T2i DSLR camera,
aggregate exposure time 3m 30s @ ISO 3200.


The Moon wanes in the pre-dawn sky this week, scudding low in the southeastern sky as morning twilight gathers. She sets a lonely course through the dim autumnal constellations with no bright objects to call upon along the way. New Moon occurs on the 10th at 5:35 am Eastern Daylight Time.

The absence of the Moon from the evening sky means that it’s time for the fourth "Globe At Night" observing campaign for 2013. This world-wide "citizen science" program seeks to record some 15,000 observations of the night sky from all over the world to help scientists map the distribution of dark skies and light pollution. The past three campaigns have netted over 9500 observations so far, so the program is on track for its target goal. For the past several months we’ve been using Orion as the target constellation for determining the "limiting magnitude" at a given observing site, but with the coming of spring we’ll shift to a different constellation. Leo the Lion is now high in the southeast and approaches the meridian by around 10:00 pm EDT. You should have no trouble locating it between the stars Castor and Pollux in Gemini high in the west and the bright rosy glow of Arcturus rising in the east. Leo’s brightest star is first-magnitude Regulus, which shows a pale blue tint. Regulus sits at the Lion’s "heart", just below a small arc of second- and third-magnitude stars that resemble the blade of a sickle. The brightest of these stars is gold-hued Algieba, which is one of the prettiest double stars for small telescope examination. To the east of Regulus is a right triangle of stars with second-magnitude Denebola representing the Lion’s "tail". Once you’ve located Leo, download the observer’s guide from the Globe At Night website, make your observations, and report them. A few minutes of your time will go a long way toward helping astronomers monitor the long-term changes in the nighttime environment.

When Leo approaches the meridian it kicks off one of my favorite times of the year. Sports fans revel in the opening of baseball season, but to me it’s now open season on galaxies. The sky behind the stars of Leo, the Big Dipper, the vast constellation of Virgo, and the bright star Arcturus surrounds the north pole of the Milky Way galaxy, so peering in this direction takes our gaze far beyond the nearby stars of home and into the vast depths of space. You can almost randomly point an 8-inch telescope at any part of the sky in this vicinity from a dark-sky site and spot a fuzzy blob of light wafting through the field of view. Each of these blobs is a distant galaxy like our own Milky Way, and there are hundreds of them sprinkled around this part of the sky. Many of the brighter ones, designated with an "M-number" on a star chart, are visible in binoculars. Most of these galaxies are members of the "Coma-Virgo Galaxy Cluster" centered around three vast elliptical systems, M84, M86, and M87, which boast nearly a trillion stars each. Our Milky Way is an outlying member of this cluster, some 55 million light years from the center.

If you have good horizons and a fairly dark sky you can see a much closer galaxy, M31, about an hour after sunset in the northwest or an hour before sunrise in the northeast. Known as the Great Andromeda Galaxy, when it is at its best in the fall you can see it with the naked eye, but for now you’ll want to use binoculars. At these twilight times it will only be about 10 degrees up, but unlike most other times of the year it will have a companion for most of the week in the form of Comet Pan-STARRS, which slides within a couple of degrees of M31 over the next several evenings. Both objects are about fourth magnitude, so you’ll need to find a dark place to view them from, but it should be well worth the effort. Alignments like this don’t happen very often!

Jupiter appears shortly after sunset in the western sky, then drifts down to settle into the horizon haze by midnight. There’s still time to enjoy the view of Old Jove in the telescope, but as he gets lower in the sky we are forced to sight him through more of our turbulent atmosphere. While detail on his surface might be lacking, his four bright moons should be easy targets for investigation.

If you’re up at around midnight you can now get a decent look at Saturn in the southeastern sky. The ringed planet is just over 15 degrees east (to the left) of the bright blue star Spica, and the two objects offer a nice contrast in colors. Point the telescope at Saturn and you will instantly recognize it. There is nothing else in all of nature that quite compares to that view!

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