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The Sky This Week, 2017 May 30 - June 6

Come to Washington, see the stars!
Moon over Monument: Astronomy Festival on the National Mall
imaged 2014 June 6 at 15th Street & Constirution Ave., Washington, DC

The Moon waxes in the evening sky this week, passing through spring’s subdued constellations before moving into the summer’s sky offerings. First Quarter occurs on June 1st at 8:42 am Eastern Daylight Time. Luna brackets the bright star Regulus on the evenings of May 30th and 31st. You’ll find her very close to Jupiter on the night of the 3rd. On the following night she forms a photogenic triangle with Jupiter and the bright star Spica.

Come down to the National Mall on Friday evening, June 2nd, for the 8th annual Astronomy Festival in the shadow of the Washington Monument. Between 6:00 and 11:00 pm we’ll be offering safe views of the Sun, followed by views of the Moon, Jupiter, and many other celestial objects through telescopes of all sizes. In addition there will be a portable planetarium, talks by leading experts in astronomy and space exploration, as well as exhibits and demonstrations by representatives of leading government and private science and space organizations. Members of local astronomy clubs will be on hand with their telescopes to share the wonders of the night sky and to explain why astronomy can be such a rewarding amateur pursuit. Over two dozen telescopes will ensure that everybody gets a good view. If the weather is good we can expect a turnout of several thousand people. The event takes place on the northeast quadrant of the Washington Monument grounds near the intersection of 15th Street and Constitution Avenue. If it’s raining we’ll have a smaller-scale program at the School Without Walls High School, 2130 G Street, NW.

Among the objects we’ll be looking at on Friday night are double stars. Often overlooked, these star systems make up the vast majority of the stars we can see. To the naked eye almost all stars appear single, but if you use a big enough telescope, spectroscope, or interferometer their dual nature will be betrayed. Understanding the dynamics of double stars is vital to our understanding of stars in general, since the slow changes in their orbital geometry allows us to derive a number of the stars’ physical parameters. Once a double star’s orbit is observed we can use Kepler’s laws to derive the masses of the two stars, and by studying the composition of each star with a spectroscope we can begin to classify them by their colors and masses. We still use our 26-inch "Great Equatorial" refractor, the very same one Asaph Hall used to discover the moons of Mars in 1877, to make nightly observations of double stars. Several are within easy reach of amateur instruments, and some of my favorites are in the current night sky. The easiest to find is Mizar, which forms the "bend" in the "handle" of the Big Dipper. You might be able to discern a faint star near Mizar with your naked eye, but a small telescope reveals Mizar is itself made up of two components. The star Algeiba, which lies just north of the star Regulus in Leo, shows a closely-spaced pair of golden suns. For a challenge look at Izar, which lies 10 degrees northeast of Arcturus. Here you’ll find a closely-spaced pair consisting of a bright yellow and fainter blue companion.

Jupiter will be perfectly placed for the Astronomy Festival, shining down from the stars of Virgo throughout the dark hours of the event. All four of his bright Galilean moons should be visible that night. After the Moon, Old Jove will be the headliner for the evening. His motion against the stars is now almost at a standstill. He will begin to creep back toward the star Spica after June 10th.

We may get a view of Saturn by the end of the Festival evening. The ringed planet now rises before 9:30 pm, but he will remain mired in the haze near the southern horizon.

Look for Venus in the pre-dawn sky. You’ll have no trouble spotting her in the gathering morning twilight. She reaches her greatest elongation west of the Sun on the 3rd. She is currently at her greatest brilliancy for the year, so you can probably follow her into daylight for quite a while after sunrise.

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