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The Sky This Week, 2019 May 21 - 28

Late nights with spring's stars.
Ursa Major, imaged at Sky Meadoews State Park, Paris, Virginia, 2014 June 2
Ursa Major, 2014 June 2 05:15 UT
imaged with a Canon EOS Rebel T2i DSLR from Sky Meadows State Park, Paris, Virginia.

The Moon wanes as she glides through the southern reaches of the ecliptic this week, coursing her way through summer’s signature constellations.  Last Quarter occurs on the 26th at 12:34 pm Eastern Daylight Time.  She passes Saturn on the mornings of the 22nd and 23rd among the easternmost stars of the constellation of Sagittarius.  Luna spends the rest of the week passing through the dim star fields of the rising autumnal constellations.

Despite the absence of the Moon, we now have to wait until well after 10:00 pm for the end of evening astronomical twilight.  This puts many of us with daytime jobs at a disadvantage unless you can get by on minimal sleep.  By the time it does become fully dark, though, the springtime constellations are in prime view.  High in the northern sky you’ll find the seven stars of the familiar “Big Dipper” asterism.  None of these stars are brighter than second-magnitude, but their distinctive pattern is almost universally recognized by denizens of the Northern Hemisphere, and they have deep roots in the ancient sky lore of cultures throughout the boreal regions.  In addition to the familiar Dipper, the stars form a figure that represents a plow, a wagon, a team of oxen, and a meat cleaver in various Old World traditions.  Many Native American tribes identified the asterism as a bear (the Dipper’s “bowl”) being chased by three hunters.  The Dipper asterism covers about half the space in the sky as the entire constellation with which it is officially affiliated, Ursa Major, the Great Bear.  You’ll need a dark sky to see the fainter stars of the constellation, but careful scrutiny of the third- and fourth-magnitude stars will reveal a pretty acceptable outline of a large quadruped creature.  An interesting aspect of the Big Dipper is that five of its seven stars are moving together through space as a group, implying a common origin.  Among the constellation’s fainter stars, another nine share the same motion and are likely members of the moving group.  They are all located about 80 light-years from Earth.  Astronomers have also identified another 40 stars around the sky that seem to be part of the group.

The next campaign for the citizen-science Globe at Night program begins on the 25th.  This month the featured constellation is Boötes, the Herdsman.  The brightest star in this group is Arcturus, which is easy to spot high in the eastern sky during the late evening hours.  One way to find the star is to follow the “arc” of the Dipper’s “handle” to Arcturus; the rest of the constellation’s stars occupy the area of the sky to the left of the “arc”.  Most of the constellation’s stars are third- to fifth-magnitude and form a shape that reminds me of an ice-cream cone, with Arcturus marking the cone’s tip.  The group’s second-brightest star, Izar, is one of the most beautiful double stars in the sky.  Boötes sports a number of other fine double stars, all of which are treats for owners of small telescopes.  If you are located in a reasonably dark place, look to the left of Izar for a diminutive semi-circle of stars.  This group is called Corona Borealis, the Northern Crown, and represents a crown given by the Greek god Dionysus to Ariadne, a princess of Crete and the daughter of the infamous King Midas.  This constellation is known for several unusual variable stars and the Corona Borealis Supercluster of galaxies, a group of over 400 star systems located nearly a billion light-years away!

Much closer to home, the red planet Mars is still visible in the fading evening twilight.  You’ll find him low in the west, under the twin stars of Gemini, Castor and Pollux.  This week he drifts toward the third-magnitude star Mebsuta, which he will pass by next week.  Through the telescope he’s now just a tiny pink-hued dot.  

Jupiter offers a much larger disc for telescopic inspection.  The giant planet is making steady progress into the evening sky.  By the end of the week he rises at around 9:30 pm.  By midnight Old Jove should be high enough in the southeast to get a good telescopic view.

Saturn is still best seen in the hours before sunrise when he transits the southern sky.  He is located just east of the distinctive “teapot” asterism made up by the brightest stars in the constellation of Sagittarius.  You’ll find the waning Moon nearby on the mornings of the 22nd and 23rd.

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