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The Sky This Week, 2019 April 23 - 30

Looking at lions and bears...oh, my!
The Big Dipper rising, imaged with a 24mm lens at f/4.5 2019 February 16
The Big Dipper rising, imaged with a 24mm lens at f/4.5
and a Canon EOS Rebel SL2 DSLR, 2019 February 16 from Mollusk, Virginia.

The Moon wanes in the morning sky this week, greeting pre-dawn dog walkers, joggers, and the cacophony of morning bird calls.  Last Quarter occurs on the 26th at 6:18 pm Eastern Daylight Time.  Luna starts the week over the teapot-shaped asterism of Sagittarius on the morning of the 24th.  The next morning you’ll find her just over two degrees southwest of golden Saturn.  As the week progresses the Moon moves into the rising stars of the autumnal sky.

The next citizen-science observing campaign for the Globe at Night program begins on the evening of the 25th and runs through May 4th.  This program, now in its tenth year, is designed to engage the public in learning about the night sky and the conditions that threaten it.  In addition to learning to identify constellations, the program uses data collected by observers to map the presence of light pollution as well as dark places where the sky can be appreciated in its full glory.  This week we’re featuring the constellation of Leo, the Lion, one of the more prominent star patterns in the springtime sky.  Leo is relatively easy to find.  He’s well up in the southern part of the sky, crossing the meridian between 9:00 and 10:00 pm.  Leo’s brightest star is Regulus, whose name means “Little King”, an appropriate moniker for the heart of the King of Beasts.  Regulus is a first-magnitude star and is the 21st brightest star in the sky.  It is located just over 79 light-years from the solar system and shines with a luminosity that’s nearly 300 times that of the Sun.  Just north of Regulus is a semi-circle of fainter stars that delineate the Lion’s head.  The brightest star in this group is called Algieba, a second-magnitude star with a yellowish tint.  Algieba is a treat for owners of small telescopes, resolving into a close pair of gold-tinted stars.  The asterism is popularly known as “The Sickle” and consists of Algieba and four other fainter stars.  While the Sickle and Regulus mark the Lion’s head, his hindquarters are marked by a right triangle of stars just over 15 degrees to the east.  The brightest star in this group is Denebola, which marks the tuft at the end of the Lion’s tail.  Once you’ve identified Leo, follow the instructions on the Globe at Night website to report your observations.  Try your hand at observing from different locations on different nights to help the program boost the number of responses.

Another signature star pattern of spring may be found by turning toward the north.  By 10:00 pm the seven stars of the Big Dipper asterism are beginning to cross the meridian.  Even though it lacks a true first-magnitude star, these seven stars form one of the most distinctive patterns in the sky.  The dipper should be easy to find even from urban locations, but it takes a much darker sky to spot the fainter stars that flesh out the entire constellation of Ursa Major, the Great Bear.  The middle star in the Dipper’s “handle” is another treat for neophyte astronomers.  Known as Mizar, it is interesting for both naked-eye and telescopic observation.  Keen-eyed skywatchers should be able to pick out the 4th-magnitude star Alcor nestled close to Mizar.  The ability to see this star was once a test of visual acuity.  Point a telescope at the pair and you will see that the brighter Mizar is itself a double star.  In fact, it was the first double star I observed through my very first telescope.  We now know that Mizar and Alcor are physically related, and each of the three components are spectroscopic binary stars, thus forming a six-star system some 83 light-years away.  If there are any planets in this system, their nights must be pretty spectacular!

You will still find ruddy Mars in the western sky as evening twilight ends.  The red planet is wending his way through the stars of Taurus, the Bull, and in another week he’ll pass between the two stars that mark the ends of the Bull’s horns.

Jupiter has finally made it to the evening sky, albeit barely.  He rises between 11:30 and midnight, so he’s still best placed for viewing as the first glimmers of morning twilight appear.  This week he begins the slow westward drift of his retrograde loop, set between the summer constellations of Scorpius and Sagittarius.

Saturn receives a visit from the Moon on the morning of the 25th.  The ringed planet is parked just east of the “Teapot” of Sagittarius, where he will remain throughout the coming summer months.

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