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The Sky This Week, 2017 June 6 - 13

The Honey Moon brightens the night.
Jupiter, with Ganymede (left), Io (middle), Callisto (top)
and shadows of Io & Ganymede

imaged 2017 June 4, 03:48 UT in poor seeing from Alexandria, Virginia

The Moon dives southward along the ecliptic this week, waxing to the Full phase which will occur on the 9th at 9:10 am Eastern Daylight Time. June’s Full Moon has many popular names: Rose Moon, Strawberry Moon, Mead Moon, and Honey Moon. All of these names describe the somewhat warm tint that Luna takes on as she passes her most southerly declination at the time of the phase. Her light must shine through denser layers of air and atmospheric haze which preferentially scatters blue light, thus her disc appears less blue (or more red). Look for Saturn just south of the Honey Moon on the evening of the 9th.

The bright Moon effectively washes out much of the sky this week, limiting our view to only the brightest stars and constellations. The night gives us a chance to see the last of winter’s stars, Castor and Pollux in Gemini, setting over the western horizon in the fading evening twilight. By 10:00 pm, the brightest object after Jupiter is the rosy-hued star Arcturus, which is high in the south. This star is the brightest star in the northern hemisphere sky. Its prominence is due to its relative proximity to us, located at a distance of about 37 light-years, and its evolution into the red-giant phase of its life. It is a member of a class of stars that form a vast halo around the center of the Milky Way galaxy, and it is currently plunging almost vertically through the galaxy’s plane. It has the largest proper motion of any first-magnitude star visible from our latitude, moving about the apparent diameter of Jupiter over 10 years referenced to more distant background stars.

Almost as prominent as Arcturus are the seven stars that make up the asterism we call the "Big Dipper". The Dipper makes up about half of the stars that form Ursa Major, the Great Bear, and is one of the most recognized star patterns in the northern sky. Five of the stars are members of a group known as the Ursa Major Moving Group that share a common motion toward a point in the constellation of Sagittarius. Mizar, the star that forms the "bend" in the Dipper’s "Handle", is an attractive double star in the small telescope. Modern spectroscopy indicates that each component of Mizar is also a double, as is the nearby naked-eye star Alcor. Both Mizar and Alcor are part of the Moving Group and may be bound by gravity. If this is indeed the case, then they form a complex six star system!

By midnight you’ll see the rising stars of the Summer Triangle climbing in the eastern sky. Consisting of the stars Vega, Deneb, and Altair, they will become night-long companions as the warm summer nights take hold in another few weeks.

Jupiter can now be found near the meridian as evening twilight begins to gather. The giant planet should be easy to spot half an hour after sunset, and he provides a fine telescopic target for the next few hours. Old Jove is beginning to resume direct eastward motion against the stars, and over the next several weeks he’ll inch closer to the nearby bright star Spica.

Saturn will reach opposition next week, rising at sunset and setting at sunrise. He transits the meridian shortly after 1:00 am this week, and promises to offer great views of his wide-open rings throughout the summer months.

Venus is the prominent object that early risers see in the morning twilight hours. She will dominate the pre-dawn sky from now until the end of the year.

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