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The Sky This Week, 2019 July 16 - 23

Apollo's anniversary, and summertime favorites.
Jupiter, Saturn, Scorpius, and the Milky Way, imaged 2019 July 5 from Mollusk, Virginia.
Jupiter, Saturn, Scorpius, and the Milky Way, imaged 2019 July 5
with a Canon EOS Rebel SL2 DSLR from Mollusk, Virginia.

The Moon wanes as she wends her way into the barren star-scapes of the autumnal constellations.  She also moves into the morning sky, allowing skywatchers to enjoy the bright stars and diaphanous glow of the summertime Milky Way.  Last Quarter occurs on the 24th at 9:18 pm Eastern Daylight Time.  As Luna transits the sparsely populated autumnal constellations, the only relatively bright objects she will encounter are the third-magnitude stars Delta and Gamma Capricorni, which she will pass by in the early morning hours of the 19th.

This is the week when we take time to look back on an amazing milestone, the 50th anniversary of the flight of Apollo 11.  Unfortunately, the Moon herself won’t be around in the evening sky to remind us of the destination of that pioneering voyage, but there will be a number of commemorations of the flight throughout the nation.  Here in Washington there will be multiple events sponsored by the National Air and Space Museum throughout the week, culminating on the 19th and 20th with a celebration on the National Mall.  The showpiece will be a full-scale reproduction of the Saturn V rocket projected onto the east face of the Washington Monument.  At 363 feet tall, this was (and still is) the world’s largest space launch system and the first one designed specifically to put humans into space.  

As mentioned earlier, we won’t have the Moon around to celebrate the moment of Neil Armstrong’s first step fifty years ago.  Luna won’t rise in Washington until 11:00 pm, and her phase will be a waning gibbous rather than the waxing crescent that hung in the sky on July 20, 1969.  If you’d like to celebrate the anniversary with the same phase that the Apollo 11 crew witnessed, you’ll have to wait until July 20, 2026.  By the time that anniversary rolls around we may once again see humans working on the Moon’s “magnificent desolation”.

By late in the week the Moon will be far enough along in her circuit of the sky to give us a few hours of darkness to enjoy the stellar sights of the summer sky.  At the end of evening astronomical twilight you’ll find the distinctive constellation of Scorpius crossing the meridian above the southern horizon.  The brighter stars of this constellation actually give a fair resemblance to their namesake, and we find that they have been associated with the desert arthropod in very ancient times.  One of the earliest depictions of the constellation was found on a stone mace head from pre-dynastic Egypt and is dated to around 3200 BCE.  Scorpius’ brightest star is Antares, whose name means “rival of Mars”.  It is a red supergiant star of colossal size that has reached the end of its evolution and will soon (in cosmic terms) become a supernova.  It is similar to the star Betelgeuse in Orion, but you’ll never see the two stars in the sky together.  In mythology Orion was killed by the sting of a scorpion, so the two figures occupy opposite parts of the sky, never to meet in darkness.  Scorpius lies just west of the center of the Milky Way, and from a dark location the central bulge of our home Galaxy stands out in splendor.  Binoculars and small telescopes will begin to resolve these luminous clouds into countless distant stars, punctuated here and there by bright knots of glowing gas clouds and bright star clusters.  Follow the Milky Way up to the eastern sky where it pierces the heart of the Summer Triangle stars, Vega, Deneb, and Altair.  Continue your sweep to the northeast and you will find the rising stars of Cassiopeia, a group of five stars that form a distinctive “W” pattern.  

Jupiter continues to be the main attraction in the summer sky. The giant planet is spending the season against a background of the edge of the Milky Way’s central bulge. If you happen to stumble across Old Jove when sweeping with your binoculars, look carefully for the planet’s four Galilean moons. Their configuration changes from night to night; on the evening of the 18th you should have a good view of the outermost of these moons, Ganymede and Callisto.

Saturn doesn’t command your attention the way Jupiter does, but he is easy to find as he trails Old Jove across the sky.  He is the brightest object after Jupiter in the southern sky, and you’ll find him perched just to the east of the “Teapot” asterism of Sagittarius.  Binoculars will reveal the odd elliptical shape of the planet’s rings, and a small telescope will begin to show the planet as it appears in almost all astronomical books.  The view through telescopes of six inches or larger aperture is truly stunning, especially when you consider that 1.35 billion kilometers (842 million miles) separate us from this distant, mysterious world.

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