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The Sky This Week, 2014 June 3 - 10

Come see the sky on the National Mall!
Lunar surface features at low sun angle, 2014 May 7

The Moon waxes in the evening sky this week, wending her way through the springtime constellations.  First Quarter occurs on the 5th at 4:39 pm Eastern Daylight Time.  Look for Luna just two degrees south of ruddy Mars on the evening of the 7th.  On the 8th she glides past the bright star Spica in the constellation of Virgo.  The Moon then parks herself just east of Saturn on the evening of the 10th.

This is another good week to acquaint yourself with the varied landscapes of our closest neighbor in space.  As the terminator reveals more of the Moon’s disc each night, new features come into view while those that were prominent the night before take on a different aspect under the higher Sun angle.  It is always fascinating to see how individual landmarks appear to evolve as the local lighting changes.  Fine details on small craters, rilles, and other surface features stand out shortly after the terminator reveals them, but a day later they are washed out under the Sun’s relentless glare.

You’ll have a great opportunity to look at the Moon as well as the planets Jupiter, Mars, and Saturn and other celestial sights if you come down to the Washington Monument grounds on the evening of June 6th.  We will be participating in the fifth annual Astronomy Festival on the National Mall that evening between 6:00 pm and 11:00 pm EDT, weather permitting.  The program, sponsored by Hofstra University, will feature a number of telescopes provided by local astronomers as well as demonstrations and talks by amateur and professionals in the field.  Last year we hosted some 1500 people and about two dozen telescopes.  We’re hoping for a repeat this year.  Details and directions to the event may be found here.

We may still be able to get a telescopic peek at the shy planet Mercury at the festival, but your chances of spotting this elusive planet with the naked eye are now getting pretty slim.  Mercury is now racing toward conjunction with the Sun on June 19th, so he’s dropping from the evening sky like a stone.  I managed to get a peek at him through the telescope last weekend at Sky Meadows State Park on the Virginia Blue Ridge, but I only had about 10 minutes to view him before he dropped below the ridgeline.

Jupiter should still be an easy target shortly after sunset.  The giant planet can still be found in the western sky, but he’s only about 20 degrees high at 9:00 pm when the sky will be dark enough to show his Galilean moons.  Looking at Old Jove under these conditions id a bit like looking at him at the bottom of a swimming pool; atmospheric turbulence and refraction blur out almost all of the fine detail, but under decent conditions you should still be able to see his prominent equatorial cloud belts. 

Mars will be on the meridian at 9:00 pm for the festival, and we’ll try our best to provide good views of the red planet’s dusty disc.  His apparent diameter will only be about one-third that of Jupiter, but his position higher in the sky should be less subject to atmospheric effects.  Fortunately the planet will be showing a side that has some of the most prominent dark albedo features, and two bright white areas should be visible near the planet’s limbs.  The larger of the two is a huge depression on Mars’ surface known as Hellas.  Similar to the large “seas” on the Moon, this basin is the result of a huge impact that occurred very early in Mars’ history.  It tends to fill with clouds and fog, so it is often mistaken for a polar ice cap.  The true north polar ice cap is smaller but stands out as a tiny bright spot on the opposite limb.

Saturn should be the star of the festival, and during the course of the evening I’m sure just about every telescope will point toward the ringed planet.  In steady air Saturn presents one of the most captivating sights in the sky as the sphere of the planet seems to magically balance in the center of the rings.  The rings themselves look almost razor sharp, and indeed in reality they are the flattest and thinnest structures known in the universe.  The distance across the outer rings as about three quarters the distance from the earth to the Moon, yet they are only about 100 meters thick!  They are kept in place by the gravity of the planet and its innermost moons, and it is these small icy worlds that cause the gaps that one can see in the rings through modest telescopes.

You won’t see Venus at the festival, though.  She doesn’t rise until shortly before the Sun, but if you’re up early on any morning you’ll find her blazing away in the gathering twilight, low in the eastern sky.  She is resolutely marching in the wake of the Sun, and in another few weeks you’ll see her in the company of some of the stars of early winter!

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