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The Summer Milky Way Returns

by Geoff Chester, USNO Public Affairs | 11 July 2023

by Geoff Chester, USNO Public Affairs | 11 July 2023

The southern summer Milky Way, imaged 2022 August 22 from Thoroughfare Mountain Overlook, Skyline Drive, Mile 39
with a Canon EOS Rebel SL2 DSLR and a mechanical Omegon MiniTrack LX-2 star tracker.

The Moon is a waning crescent in the pre-dawn sky this week, making her way into the first rising stars of the winter sky.  She begins the week to the east of bright Jupiter on the morning of the 12th, then passes two degrees south of the Pleiades star cluster on the following morning.  New Moon occurs on the 17th at 4:32 pm Eastern Daylight Time.

The July campaign for the Globe at Night citizen-science program continues this week, and you should have ample time to make some observations of your local sky.  The target constellation is Hercules, which occupies the region of the sky between the bright stars Arcturus and Vega.  Hercules doesn’t have many bright stars within its sprawling boundary, but it boasts a distinctive asterism known as the “Keystone”.  This trapezoid figure, which lies about 20 degrees west of Vega, consists of second- and third-magnitude stars and should be relatively easy to spot from suburban locations.  The rest of Hercules is formed by chains of moderately faint stars that radiate from the central Keystone.  Once you have found Hercules, compare your view with the star charts on the Globe at Night web app and record your observation.  You will be helping scientists who track the spread of light pollution that is rapidly eroding our views of the night sky.

If you look at illustrations of Hercules in classical star atlases you will see that he is depicted upside-down, with his “head” close to the “head” of Ophiuchus, the Serpent Bearer.  The two “heads” are marked by the stars Ras Alhague (“Head of the Serpent Bearer”) and Ras Algethi (“Head of the Kneeler”).  Ras Algethi, the fainter of the two stars, is one of the most colorful double stars in the sky.  It can be easily split with a three-inch telescope, and in my 4-inch refractor the two components glow with pleasing red and green hues.

As midnight approaches, the summer Milky Way spreads its ghostly glow from the northeast to the south.  The brightest of the Galaxy’s star clouds hover over the southern horizon above the distinctive outline of Scorpius, the Scorpion.  When we look in this direction we are gazing toward the center of the Galaxy, which is located some 30,000 light-years from the solar system.  We can’t actually see the galactic center, though, due to the billions of stars and huge opaque clouds of gas and dust that attenuate the view.    However, this is a wonderful part of the sky to explore with a good pair of binoculars.  The first thing you will notice will be the vast number of stars that constitute the Milky Way’s bright patches.  You will also notice a number of concentrated patches of light that betray the presence of star clusters and softly glowing gaseous “nebulae”, the signatures of stellar nurseries that are liberally sprinkled along the galactic plane.  Under rural dark skies, another thing to look for along the Milky Way are places where there is an absence of light.  The most obvious of these is the so-called “Great Rift” that seems to bisect the Milky Way from the heart of the Summer Triangle to the southern horizon.  This rift is a vast cloud of cold gas that blocks the light of the more distant stars behind it.  Your binoculars will also show smaller dark patches and meandering dark tendrils that seem to carve channels among the star clouds.  If you have a small telescope, use your lowest power eyepiece to further explore these fascinating structures.
Venus is now plunging toward the western horizon, setting some four minutes earlier each night.  The dazzling planet now sets before the end of evening astronomical twilight, and by the end of the week she will set before 10:00 pm.  However, she is at her peak brightness for the current evening apparition, so you should have no trouble spotting her shortly after sunset.  A small telescope will show her disc, which resembles a waning crescent Moon. 

Mars is now pulling away from Venus and the bright star Regulus as he continues his eastward trek across the constellation of Leo, the Lion.  The red planet is also losing in his race with the advancing Sun, but he will linger in evening twilight for a few weeks after Venus disappears.

Saturn continues to gradually climb into the evening sky.  You should be able to spot his warm-hued yellow glow in the southeast by midnight.  If you’re up during the wee hours you should be able to get a good view of him in the telescope, but your best view this week will still be during the onset of morning twilight.

Jupiter is well up in the east at 5:00 am local time.  You will find him in the company of the waning crescent Moon on the morning of the 12th.  If you’re an early riser, this is a good time to get a “sneak peek” at Old Jove through the telescope if you can’t wait to see him in the evening sky this fall.


Commander, Naval Meteorology and Oceanography Command | 1100 Balch Blvd. | Stennis Space Center, Mississippi 39529

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