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The Sky This Week, 2014 July 23 - August 19

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Messier 8, the "Lagoon Nebula" in Sagittarius
Imaged from near Morattico, Virginia, 2014 July 5
with an 80mm (3.1-inch) f/6 Antares Sentinel refractor and a Canon EOS Rebel T2i DSLR

“The Sky This Week” will be taking a few weeks’ vacation away from the hustle and bustle of Washington, DC.  Here are a few things to note during our absence.

The Moon will be new on July 26th at 6:42 pm Eastern Daylight Time.  First Quarter falls on August 6th at 8:50 pm.  The Full Sturgeon Moon occurs on the 10th at 2:09 pm EDT, within hours of the closest lunar perigee for the year.  Yes, at this time Luna will be about 12% bigger and 30% brighter than it was in January, when Full Moon occurred near lunar apogee, but you’d be hard-pressed to notice much of a difference between now and then.  This is being touted as yet another “Super-Moon” by popular and social media for reasons that I still can’t fathom, but for the most part it is a “non-event” that is almost purely hype.  Last Quarter will occur on the 17th at 8:26 am EDT.  Look for nice groupings of the Moon, Mars, and Saturn on the evenings of August 2nd, 3rd, and 4th.

The usual highlight of August is the annual Perseids Meteor shower, which are active throughout the month but peak on the night of August 12/13.  This is one of the year’s most reliable displays, with hourly rates of from 50 – 75 per hour for a single observer at a dark site.  Unfortunately this year’s shower coincides with a nearly-full Moon which will wipe out all but the brightest shower members.  Fortunately the Perseids are known for having numerous bright “fireballs”, so you may still be able to catch a few in the hours after midnight.  Look toward the northeastern sky for your best chance at spotting one.

In the early evening sky ruddy Mars moves over 15 degrees during the time we’re away.  By August 19th he’s cozying up to Saturn and the third-magnitude star Zubenelgenubi.  In the meantime Saturn plods just half a degree eastward as he resumes direct motion against the stars.

For me the summer highlight is the magnificent summertime Milky Way, which is now ideally placed for late-night enjoyment.  I’ll have a few good nights to view it from a dark-sky site before the waxing Moon washes out its delicate structure, and I’ll have a few days with a waning Moon to view it before I return home.  On those nights when I can enjoy it I hope to spend many quiet hours exploring its many interesting features, and hopefully many of you will be able to do the same.  Despite its subtle, gauzy glow it is one of the most amazing sights for exploration with a small telescope.

Early risers can watch the rising of the bright winter constellations in the gathering morning twilight over the course of the next several weeks.  If you have a good ocean horizon that faces to the east you can repeat an observation that was one of the first absolute time markers for the ancients, the “heliacal rising” of the star Sirius.  This phenomenon, which now occurs for our latitude during the second week of August, occurs when the brightest star in the night sky can be seen cresting the horizon just before sunrise.  To the ancient Egyptians this event marked the beginning of their secular year and was the harbinger of the annual flooding of the Nile.  Due to the precession of the Earth’s rotational axis this event occurred for them about a month earlier than it does today.  The Romans adopted this yearly marker when they conquered Egypt.  Since Sirius was the brightest star in the constellation of Canis Major, the Large Dog, they called the days subsequent to the heliacal rising the “Dies Canicularum” or “Dog Days”, a tradition that seems especially true in Washington at this time of the year!

We hope that your next few weeks are peaceful and enjoyable and that you have ample chances to go out and enjoy the splendors of the nighttime sky.  We’ll be back in a few weeks, but if we see something interesting while we’re away we’ll share it on the USNO’s Facebook page.