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The Sky This Week, 2017 August 30 - September 5

Not quite a harvest Moon.
Total Solar Eclipse of 21 August, 2017, 15:32 UT,
imaged from Smith's Ferry, Idaho by Geoff Chester
with an 80mm f/6 Antares Sentinel refractor and a
Canon EOS Rebel T2i DSLR. Note the star Regulus at lower left.
Composite of 1/2000, 1/250, & 1/4 sec exposures @ ISO 200

The Moon waxes through her gibbous phases as she skirts the southern horizon this week. Starting from a perch near Saturn she drifts eastward through the stars of Sagittarius before entering the barren star fields of the autumn sky. Full Moon occurs on the 6th at 3:03 am Eastern daylight Time.

We normally associate September’s Full Moon with the name "Harvest Moon", but this year it occurs well before the autumnal equinox. The harvest Moon is defined as the one that occurs closest to the equinox, so we’ll have to wait until October 5th to see it and the interesting phenomenon that gives it the name. So what do we call this Full Moon? The most popular name for it is the Corn Moon, which seems entirely appropriate to me as this is the best time of year to get New England sweet corn, one of my favorite delicacies of summer.

Many of us are still buzzing about the first total solar eclipse to cross the U.S. from coast to coast since 1918. Those of us on the Observatory staff who ventured to the path of totality shared our experience with perhaps the largest gathering of people to ever witness such an event. It has been estimated that well over 20 million people witnessed the eclipse, and for the most part had a glimpse of this most amazing of sky phenomena. For most of these people the few minutes of totality provided a once-in-a-lifetime sight. For many others it will ignite a desire to see another one. I can attest to the desire to see more of them, as this was the fifth time I have basked in the Moon’s umbral shadow. Each time I have seen one I have noticed more and more fine details, and each one leaves a more lasting impression than the previous one.

The evening sky is dominated by the waxing Moon, so only the brightest of summer’s stars pierce the scattered lunar glare. Directly overhead at midnight is the brightest star of the Summer Triangle asterism, the blue-tinted Vega, brightest star in the diminutive constellation of Lyra, the Harp. Lyra itself is easy to see in binoculars as a small parallelogram extending southeast of Vega. The star at the lower right of the parallelogram is Beta Lyrae, one of the most unusual binary stars in the sky. The two components of the system are very close, orbiting each other with a period of just under 13 days. The brighter, "primary" companion is transferring material to the fainter one, losing about one solar mass to the secondary every 50,000 years. This forms a dark accretion disc around the secondary that eclipses the primary star every 12.94 days. You can see this eclipse, dropping the combined magnitudes of the stars from 3.2 to 4.4 during

Jupiter lingers in evening twilight and sets just after twilight ends. You can still get a few decent peeks at him shortly after sunset, but he quickly settles into the turbulence and haze above the western horizon.

Saturn remains quite bright in the southwestern sky as twilight fades. Despite his southerly declination, you still have a couple of hours in the evening to admire his signature ring system. The best way to observe him, though, is through the electronic "eyes" of the Cassini orbiter, which will make its final trips around the planet before a fiery plunge into the planet on September 15 that will end its 13-year mission to the ringed planet.

Look for dazzling Venus in the gathering glow of morning twilight. She is traversing the faint stars of the constellation of Cancer, the Crab this week. On the mornings of the 1st and 2nd look at her with binoculars as she passes a degree south of the Beehive star cluster.

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