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The Sky This Week, 2018 June 5 - 12

Hanging with Hercules
Globular cluster Messier 13 in Hercules
Imaged on 2016 August 23 from Fishers Island, New York
with a 10.2-cm (4-inch) f/6.5 AR102 refractor and a Canon EOS Rebel T2i DSLR.

The Moon greets early risers this week, waning through her crescent phases as she begins to climb northward on the ecliptic through the rising constellations of autumn.  New Moon occurs on June 13th at 3:43 pm Eastern Daylight Time.  Luna is a lonely traveler this week, passing near no bright objects during the course of her journey.

Despite their short duration, nights in June can often be quite pleasant for skywatching, and they can also be quite clear.  This offers us a chance to enjoy transparent nights that are generally free from the haze and humidity that will inevitably descend on us in July and August.  This clarity and the absence of the Moon make it a good week to make some observations for the Globe at Night citizen-science project.  The goals of this program are two-fold: on the one hand it’s an attempt to quantify the visibility of celestial objects from a variety of viewing locations while on the other it’s a chance to bring more people into the sphere of amateur astronomy.  This month the featured constellation is Hercules, which can be found in the area between the bright stars Arcturus and Vega.  Hercules has no stars brighter than second magnitude, so it can be a challenge to observe from densely lit urban areas.  It’s most prominent feature is a quadrilateral asterism that is popularly known as The Keystone which lies about a third of the distance from Vega to Arcturus.  I can just see this group from my urban back yard, but the further I move from the city the more stars that outline the rest of Hercules stand out.  It’s actually quite a large constellation when seen from a good rural location, and with a little imagination you might be able to trace out something that looks vaguely human, albeit he seems to be standing on his head!  Whether you see a classical Greek hero or not, the number of stars that you can see are what’s important to report to the Globe at Night project via their website.  

What Hercules lacks in bright stars is made up for by the presence of two superb “deep sky” objects, the globular star clusters Messier 13 and Messier 92.  These knotted balls of hundreds of thousands of stars can be seen as fuzzy blobs of light with binoculars under dark skies.  A modest telescope of 4-inches aperture will resolve them into countless pinpoints surrounding luminous cores, and larger telescopes reveal more and more details in these wonderful objects.  Messier 13 is the finest of its type in the northern sky, and Messier 92 would be a “showpiece” object if it weren’t located so close to M13 in the sky.  There are about 150 globular clusters in the Milky Way galactic system.  They are made up of very old stars and may be the cores of primordial “dwarf galaxies” that were consumed by our much larger galactic home.  They follow long looping orbits around the Milky Way’s center, which is why we see them predominantly in the summer sky.  Their cores are densely packed with stars which occasionally lead to stellar collisions.  Such events produce a very unusual type of star known as a “blue straggler”.

Closer to home we find the dazzling planet Venus dominating the western twilight and early evening sky.  Her eastward motion will take her past the Twin Stars of Gemini, Castor and Pollux, over the course of the week.  She forms a straight line with the stars on the evening of the 10th.  By the week’s end Venus begins to cross the faint constellation of Cancer, the Crab.

Jupiter appears high in the southeast as evening twilight fades and offers owners of small telescopes many hours of enjoyable viewing.  You don’t need a large telescope to get something out of looking at the giant planet since his four bright Galilean moons are visible with a simple spotting scope.  There will be an unusual configuration of the moons on the evening of the 7th.  Fromm 11:10 pm EDT until 12:20 am you’ll only see two of the moons.  Io will then emerge from the planet’s shadow at 12:20 am, and at 12:56 am Ganymede will pop out of the shadow well to the east of the planet.

Saturn joins the planet parade in the late evening hours, climbing into the southeastern sky after 10:00 pm.  His yellow hue may be found just above the top of the “Teapot” asterism of Sagittarius

Mars is still best seen in the morning twilight.  The red planet crosses the meridian in the south at around 5:00 am along with the faint stars of the constellation Capricornus.  Mars is steadily increasing in brightness, and his telescopic disc is now becoming easier to define inn modest telescopes.  Early morning skies tend to be very steady for planetary viewing, so if you’re up early give him a look with the telescope. 

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