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The Sky This Week, 2015 May 26 - June 2

Waxing to the Honey Moon.
Jupiter & the Great Red Spot, 2015 may 26, 01:31.5 UT

The Moon brightens the evening sky this week, waxing to the Full phase, which occurs on June 2nd at 12:19 pm Eastern Daylight Time.  June’s Full Moon occurs along the southern reaches of the Ecliptic, so from our latitude she seems to hug the southern horizon.  Since her light must shine through more of the Earth’s atmosphere, her usually bright silvery glow is tinged by a slightly warmer tone.  This is why the popular names for this Full Moon have a warm “feel” to them, such as the Rose Moon, Strawberry Moon, Mead Moon, and Honey Moon.  Luna wends her way through the relatively star-poor regions of the springtime constellations.  She passes a few degrees northeast of the bright star Spica on the evening of the 29th.  On June 1st she shares the southeastern sky with the rising planet Saturn.

The Moon’s soft glow washes out most of the fainter stars in our late springtime sky.  Unlike winter, when we had a sky full of bright stars and constellations, the nights of spring offer only a few bright stars and few easily-traced constellations.  The brightest star in the springtime sky is Arcturus, which currently resides in the evening sky east of the meridian until it transits at around 11:00 pm.  Arcturus is the brightest star in the northern hemisphere of the sky and the fourth-brightest overall.  It is characterized by a rosy glow that stands out among the other stars of the season.  It is bright in our sky due to its relatively nearby distance and its intrinsic luminosity.  At 37 light-years’ distance it is one of the most luminous star in the Sun’s neighborhood, shining with 170 times the energy of the Sun.  Because it is so close and so bright, we have been able to make very high-resolution studies of the star’s spectrum, giving us great insight into its physical properties.  It is an old star that probably formed with the initial consolidation of the Milky Way Galaxy.  With a mass slightly greater than that of the Sun we can attribute its luminosity to the early phases of the star’s late-stage evolution in which it fuses hydrogen in an expanding shell around an inert helium core.  This has caused its diameter to expand to around 40 million kilometers versus the Sun’s 1.4 million.  The Sun itself will follow this path, but not for another couple of billion years!

Venus spends the week gaining ground on Jupiter as she begins to lose ground on the Sun.  This week she closes to within 20 degrees of the giant planet.  On the evening of June 1st she forms a straight line with the last of winter’s stars, Castor and Pollux the Gemini Twins.  If you point a telescope at Venus she will resemble a small first quarter Moon.  Over the next several weeks this will change to a slowly waning crescent as her disc becomes larger due to her closing the distance between her and the Earth.

Jupiter still shines brightly in the western sky as twilight fades to darkness.  A small telescope will still show considerable detail on his distant cloud tops even though his apparent disc is now over 10 arcseconds smaller than it was at opposition back in February.  On the evening of the 27th you’ll have a rare opportunity to see two of the planet’s moons drag their shadows across the planet’s face.  Ganymede’s shadow begins crossing the disc just before 9:00 pm EDT.  An hour later Io’s shadow begins its transit.  If you still have a good view at 11:48 pm, the two shadows will appear to merge as Io’s shadow catches up to Ganymede’s.  The Great Red Spot rotates across the disc on the evenings of May 30 and June 1.

Look for Saturn in the southeastern sky after sunset, rising with the stars that form the “head” of Scorpius, the Scorpion.  By the late evening hours the ringed planet should be high enough to train the telescope on.  Try to wait for moments of steady air to look for the Cassini Division in the planet’s generously tipped ring system.  During these calm moments you may also be able to see several of the planet’s small icy moons.


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