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The Sky This Week, 2019 April 30 - May 7

The rosy star of spring.
Crescent Moon and Earthshine, 2018 January 20
Crescent Moon and Earthshine, 2018 January 20
HDR composite of 3 images made with an Antares Sentinel 80mm (3-inch) f/6 refractor
and a Canon EOS Rebel T2i DSLR from Alexandria, Virginia.

The Moon starts the week as a slender waning crescent in the pre-dawn sky and ends the week as a waxing crescent in the early evening.  New Moon occurs on the 4th at 6:45 pm Eastern Daylight Time.  Look for the Moon close to the bright star Aldebaran in the deepening twilight of the evening of the 6th.  On the following night Luna may be found three degrees south of ruddy Mars.

May 1st marks a special day in the annual cycle of the seasons.  It is one of the four “cross-quarter” days that occur each year marking the mid-point of each astronomical season.  Its origins go back to the Roman Republic, which celebrated the Floralia, a week-long festival celebrating the goddess Flora.  In medieval Europe we find two traditions that date to the 10th Century CE.  Germanic peoples celebrated Walpurgisnacht, the canonization of Saint Walpurga, while Celtic cultures observed Beltane, their traditional start to summer.  These observances were joyous occasions, featuring much food, drink, and general merrymaking.  Walpurgisnacht is still widely observed in Scandinavia and Germany, and the tradition of Beltane has evolved into the more familiar May Day throughout the Celtic world.  By the 14th Century the celebration became widely observed inn England with the crowning of May Queens and dancing around maypoles.  Early European settlers in America imported the festival as a part of their traditions, and many local celebrations of May Day still occur throughout the country.  Unlike the more somber cross-quarter days that have given us Halloween and Groundhog Day, the May Day tradition is a happy one, the unabashed celebration of the joy of warmer days, blooming flowers, and the promise of a new growing season.  

The May campaign for the Globe at Night program continues this week, focusing on the constellation of Leo, the Lion.  Leo crosses the meridian at the end of evening twilight, prominent in the southern sky.  You still have several nights to find the constellation and compare your view with the charts on the Globe at Night website.  Your observations will help scientists chart the effects of artificial light pollution which, unfortunately, is claiming more and more of the sky around urban areas.  Light pollution not only deprives us of a view of the night sky, it has serious consequences for birds and animals and has been shown to have detrimental effects on people as well.  Bright skies impede our circadian rhythms, and a growing body of evidence points to serious health effects from these disruptions.  Fortunately these trends can be reversed with public awareness, and solutions are quite easy to implement by using sensible lighting design.  I’m hoping that I will soon begin to see more than the handful of stars in Leo that are currently visible from my front yard. 

By 10:00 pm the last of winter’s bright stars form an arc over the western horizon.  In the east is a solitary bright star that careful scrutiny will show a pleasing rosy tint.  This is Arcturus, the fourth-brightest star in the sky and brightest luminary in the northern celestial hemisphere.  Arcturus is the brightest star in the constellation of Boötes, the Herdsman or Plowman, who follows the Big Dipper (known as “The Plough” in England and other parts of Europe) asterism around the sky.  Arcturus is an example of what the Sun may look like in a few billion years.  It has exhausted the supply of hydrogen in its core and is now fusing hydrogen into helium in a shell surrounding the core.  This has caused it to expand to some 25 times the diameter of the Sun and cooled its surface to one that is cooler and redder than that of Old Sol.  It shines with the luminosity of about 170 Suns and is located 37 light-years from the solar system.

The sole planet visible in the early evening continues to be Mars.  You’ll find his ruddy glow in the west as evening twilight fades.  This week he passes between the two stars that mark the ends of the “horns” of Taurus, the Bull.  The crescent Moon pays the red planet a visit on the night of the 7th.  Luna will pass just south of the star Zeta Tauri, which marks the Bull’s southern horn, as they settle toward the horizon before setting at 11:00 pm.

If you look toward the southeast as midnight approaches, you should see the bright glimmer of Jupiter climbing into the late-night sky.  Old Jove is firmly entrenched among the rising stars of summer’s signature constellations of Scorpius and Sagittarius.  He crosses the meridian at around 4:00 am, so your best time to view him in the telescope is still in the pre-dawn sky.  

Saturn follows Jupiter across the sky and crosses the meridian just before sunrise.  He should be high enough in the southeast to get a good view of as morning twilight begins to brighten the sky.  Saturn’s rings are tipped at their maximum toward the Earth, so you should have no trouble spotting them in any telescope.

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