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The Sky This Week, 2014 July 1 - 8

Bright stars and fireworks highlight the 4th.
Saturn, imaged 2014 June 23, 01:48 UT

The Moon waxes in the evening sky this week as she dives toward the southern reaches of the ecliptic.  First Quarter occurs on the 5th at 7:59 am Eastern Daylight Time.  Luna has a busy week, sharing the sky with fireworks on the 4th, the red planet Mars on the 5th, and Saturn on the 7th.  The Moon will occult these bright planets for residents of the southern hemisphere.  She ends the week among the stars that form the head of Scorpius, the Scorpion.

Earth reaches aphelion, its farthest point from the Sun, on the 3rd at 4:13 pm EDT.  At this time we’ll be just over 94,550,000 miles (153,000, 000 kilometers) from the day-star.  Six months from now, in early January, we’ll find ourselves closest to the Sun by a mere 3 million miles or so.  Fortunately this annual excursion means that the planet’s orbit is nearly circular, so our climate remains relatively benign throughout the year.

While you’re out side waiting for the fireworks to begin (or waiting for the crowds to thin before heading home!) there are a number of bright objects in the sky that you can see despite the moonlight and the dazzle from the sparkling displays.  High overhead in the mid-evening hours you’ll find the bright star Arcturus, the brightest star in the northern sky.  This star sports a golden hue because it is a star that’s evolving toward old age.  Like some people, the star’s girth expands as it exhausts the hydrogen in its core, and as it expands its surface becomes a little cooler and redder.  Contrast this with Spica, the bright blue-tinted star that’s now just a few degrees from Mars in the southwest.  Moving toward the east, you’ll find Saturn hovering near a second-magnitude star called Zubenelgenubi, the brightest star in the otherwise nondescript constellation of Libra, the Scales.  This star is a fine example of a “binocular double” star whose components share the same proper motion and parallax and therefore must be gravitationally linked.  Continuing eastward past Saturn you’ll run into the distinctive figure of Scorpius, with the ruddy star Antares marking the celestial scorpion’s hear.  The star’s name means “rival of Mars”, and comparing the two objects reveals why that name is appropriate.  Now turn your gaze high to the eastern sky where a trio of bright blue stars awaits.  The brightest of these is Vega, lead star in the constellation of Lyra, the Harp.  This star is relatively close-by at about 27 light-years, but even closer to us is Altair, faintest and southernmost of the trio.  Altair is a mere 16 light-years away, making it one of the nearest bright stars in the sky.  The final star in the Summer Triangle is Deneb, which outwardly appears to be on par in brightness with Altair.  However, Deneb is nearly 100 times farther away from us, making it one of the most intrinsically luminous stars in the sky.  It shines with a luminosity some 65,000 times that of the Sun!

It’s time to bid Jupiter a fond farewell.  The giant planet now sets less than an hour after sunset, and you’ll be hard-pressed to see him in the glare and haze of evening twilight.  However, in a month of so he’ll be rising to greet early morning commuters and have a spectacular rendezvous with Venus.

Mars shares the early evening sky with Saturn and Spica, but you won’t have any trouble recognizing him thanks to his distinctive rosy glow.  The red planet is rapidly closing the gap with the star Spica, and in another week he’ll drift past the star as he heads eastward along the ecliptic.  Mars’ disc continues to shrink for telescopic observers, but you may still be able to make out a few details on nights with extremely steady air.

Saturn now straddles the meridian at around 9:30 pm.  After the Moon the ringed planet is the most telescopically rewarding sight foe telescope “newbies”.  Almost everyone lets out a gasp the first time they see this distant frozen world and his marvelous rings, and even us seasoned veterans at the eyepiece pause to take a good, long look.  It is hard to believe that 10 years ago the Cassini space probe dropped into orbit around Saturn and a year later parachuted the Huygens probe into the smoggy atmosphere of its largest moon Titan.  The images that the Cassini mission has gathered over that time are simply astonishing.  You can browse Cassini’s “greatest hits” at the mission’s website.

Bright Venus continues to dazzle early risers as morning twilight gathers.  Look for her in the north-northeast sky, rising about an hour before the Sun.

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