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The Sky This Week, 2010 July 20 - 27

Planets converge in the evening, Jupiter moves into the evening sky
Sunset, Morattico, Virginia, 2010 July 17

The Moon hugs the southern horizon this week, drifting through the stars of Scorpius and Sagittarius before venturing into the relatively empty regions of the autumnal constellations.  Full Moon occurs on the 25th at 9:37 pm Eastern Daylight Time.  July’s Full Moon is popularly known as the Hay Moon or Thunder Moon, and the latter name seems particularly appropriate this year.  Luna starts the week off hovering among the stars at the head of Scorpius, the Scorpion.  On the 21st she shines just east of the ruddy star Antares.  On the 23rd she sits just above the teapot-shaped asterism that forms the brightest part of Sagittarius, and by the week’s end she sets her sights on bright Jupiter, low in the east at the midnight hour.

The Moon’s southerly declination, coupled with high humidity and atmospheric haze, will render most of the starry sky very difficult to discern.  This is further compounded by the reflected glare of urban streetlights, which cast their green and orange-tinted palls over the entire sky.  There have been a number of evenings of late when I have found it almost impossible to sight the planets Mars and Saturn, even though they are both first magnitude objects, from my suburban home.  However, there are a few bright objects that can cut through the haze and glare other than the bright planets.  Most notable of these is the star Arcturus, which now hangs high in the western sky as twilight ends.  Arcturus is the brightest star in the northern hemisphere of the sky, and the third-brightest star in the heavens.  Its rosy glow is a fixture in the spring sky, but as summer progresses the star becomes overshadowed by other bright luminaries in the night.  At about the same altitude in the east is the fifth-brightest star in the sky, the blue-tinted luminary called Vega.  Both of these stars are bright because they are relatively close to us in space.  Arcturus lies at a distance of about 37 light-years, while Vega is practically around the corner at 25 light years.  Arcturus holds a singular place in the sky, but Vega has two bright companions that form a large distinct asterism known as the Summer Triangle.  Together with the stars Deneb and Altair, Vega and its companions point in a southerly direction where you might find the ruddy star Antares if it’s clear enough and the second magnitude stars that comprise the “Teapot” of Sagittarius if it’s clear enough.  It’s always good practice to identify these basic stars in a bright sky.  Once the Moon goes away and you head to that dark vacation spot you’ll now have some convenient guideposts to steer you toward more interesting sights!

The late twilight of the evening sky finds the beginnings of a planetary “traffic jam” in the southwest.  Venus will be the most obvious planet as the light of early evening fades, and she is steadily closing in on ruddy Mars and gold-hued Saturn.  I happened to view Venus shortly before she set last weekend from down on the Northern Neck of Virginia.  Thanks to a flat horizon, thin clouds, and haze, the normally dazzling white planet was glowing like a single orange-red coal in a dying campfire.  She spends the week in restless pursuit of Mars and Saturn, which are gearing up for their own conjunction next week.  

The late night sky now welcomes the bright glow of Jupiter, who is doggedly rising about four minutes earlier each night.  Old Jove reaches the first stationary point in the current apparition on the night of the 23rd, pausing for a few days in his eastward motion before seeming to back up toward the west over the course of the next four months.  Late night skywatchers are now enjoying the view of the giant planet in their telescopes.  Soon he’ll be delighting even those of us with early bedtimes.

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