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The Sky This Week, 2018 July 17 - 24

Remembering a great adventure.
Crescent Moon and outcrop, Desolation Canyon, Utah, 2018 June 20

The Moon waxes in the evening sky this week, diving down to the southern reaches of the ecliptic to join the signature constellations of the summer sky.  First Quarter occurs on the 19th at 3:52 pm Eastern daylight Time.  Luna will be just north of bright Jupiter on the evening of the 20th.  She sidles up to yellow-hued Saturn on the evening of the 24th.  

Forty-nine years ago this week one of the most incredible voyages of exploration and discovery played out to a world-wide audience as Apollo 11 crossed the 238,000-mile gulf between the Earth and the Moon.  On July 20, 1969 two humans, Neil Armstrong and Edwin “Buzz” Aldrin, became the first emissaries from Earth to set foot upon another celestial body.  Their feat was witnessed in real time by a significant portion of the world’s population on television.  Some of us (myself included) had telescopes trained on Luna at the time when Armstrong took his first historic step.  While no terrestrial telescope could resolve the landing site, there was something magical about realizing that there were three people who were actually there at that moment.  Since that time 10 other astronauts have trod the Moon’s dusty surface, and another 13 have seen it from lunar orbit.  Sadly, these spectacular journeys are now becoming a footnote in history, and only a few of the participants are left to share their stories.  There are few things that I remember from 50 years ago, but the Moon voyages of Apollo will always be fresh in my mind every time I look at the Moon’s “magnificent desolation”.

As the Moon moves to the southern part of the sky her increasing brightness gradually hides the summer Milky Way.  Although your view of the home galaxy is curtailed, there are several bright stars along its path that betray its presence.  Looking south at the end of evening twilight will reveal the ruddy star Antares, brightest star in the constellation of Scorpius.  If you have a good view of the southern horizon and are away from city lights you should have no trouble tracing out the Scorpion’s shape.  To the east of Scorpius look for the teapot-shaped asterism that is made up by the brightest stars of the constellation of Sagittarius, the Archer.  If you’re stuck in the city there are three bright stars that should be easy to spot even if you’re standing under a streetlight.  Vega, Deneb, and Altair form an asterism known as the Summer Triangle.  Each star belongs to a separate constellation, and the farther you are from the city the more of the fainter background stars of these sky patterns you’ll see.  Vega, the brightest of the three, is the fifth-brightest star in the sky, thanks in part to its relatively nearby distance of 25 light-years.  Altair, southernmost of the Triangle’s stars, is even closer, a mere 16.7 light-years distant.  Deneb, the faintest of the trio, turns out to be one of the most intrinsically bright stars in the sky.  Located some 100 times farther from us than Altair, it shines with a luminosity well over 150,000 times that of our Sun!  

Venus spends the week drifting below the stars of the constellation of Leo, the Lion.  If you’ve been following her progress over the past few months you’ve probably noticed that she is moving southward with respect to the western horizon, and she is also gradually beginning to slip lower in the sky each successive evening.  That said, she is also gradually growing brighter as she begins to approach Earth on her faster, inner solar orbit.

Jupiter gets a visit from the Moon on the 19th, but you won’t need Luna to help to find him.  The giant planet appears just west of the meridian shortly after sunset and dominates the southwestern sky during the late evening.  If you train the telescope on him when he first appears you’ll have several hours to enjoy the view of his four bright moons and the famous Great Red Spot, which should be visible to east coast observers on the evenings of the 19th and 21st.  Speaking of jovian moons, a group of astronomers have recently reported their discovery of another 12.  Most of these are very small and are likely captured asteroids, but they bring the total number of Jupiter’s known moons up to 79.  Time to update the almanacs again!

Saturn may be found low in the south during the late evening hours, hovering just above the “top” of the teapot asterism in Sagittarius.  The ringed planet isn’t as bright as Jupiter, but you should still be able to identify him without much trouble.  A peek through the telescope will verify your hunch; the planet’s rings are visible in virtually any telescope.

Mars is just over a week away from opposition and his closest approach to the Earth.  The red planet rises shortly after 9:00 pm and by 11:00 pm should be prominent in the southeastern sky.  For the next several weeks he will outshine Jupiter, and his distinctive ruddy tint should easily identify him.  His telescopic disc is now approaching its greatest apparent diameter for the current opposition.  At the moment the planet’s surface is obscured by a planet-wide dust storm.  Hopefully this will abate before the best opposition viewing opportunities end.

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