You are here: Home USNO News, Tours & Events Sky This Week The Sky This Week, 2017 May 16 - 23

The Sky This Week, 2017 May 16 - 23

Support the Globe at Night!
Jupiter & its moon Io, imaged 2017 April 27
from Alexandria, Virginia

The Moon climbs northward along the ecliptic in the morning sky this week, passing through the dim constellations of the early autumn sky. Last Quarter occurs on the 18th at 8:33 pm Eastern Daylight Time

This week opens the May campaign for the Globe at Night citizen-science observing program. Initially launched during the 2009 International Year of Astronomy, the program has now compiled thousands of observations from participants in almost 100 countries. The goal of the program is twofold: to raise awareness of the night sky by familiarizing participants with the more prominent constellations, and to map the distribution of global light pollution. In the latter case it is important for people to realize that artificial night lighting has effects far beyond blocking our view of the night sky. More evidence is pointing to the correlation of bright nighttime light and health effects on many species, including our own. Light pollution interferes with circadian rhythms that affect such diverse activities in the animal kingdom as the mass migration of birds and the spawning and hatching of sea turtles. There is also mounting evidence that blue light has very detrimental effects on people, interrupting sleep patterns and possibly affecting our susceptibility to diseases. You can do your part to help science understand these effects by simply going out at night and looking at stars. This month we are featuring the constellation of Leo, the Lion. Leo may be found high in the southwest after the end of evening twilight at around 10:00 pm. Its brightest star, Regulus, forms the base of a "backwards question mark" asterism that is also often called "the Sickle". This grouping is followed by a right triangle of stars ending in the Lion’s second-brightest star Denebola. From a suburban location I can see the basic stars of the constellation on a good clear night. How many can you see? Go to the Globe at Night website and report your star count!

As evening twilight ends, look high in the east for the bright star Arcturus. This star is only outshone by Jupiter, and it’s easy to locate using the "handle" of the familiar "Big Dipper". Simply follow the "arc" generated by the curve in the dipper’s handle and "Arc to Arcturus". This star is the fourth-brightest star in the entire sky and the brightest north of the celestial equator. It is relatively nearby at a distance of just under 37 light-years. Its proximity and its luminosity, which is about 170 times that of the Sun, explain its prominence in our spring sky. It is an old star that is beginning to evolve into its "red giant" phase, and it belongs to a population of similar stars that orbit the center of our galaxy in an enormous halo. Light from Arcturus was used to illuminate a photocell to open the 1933 Chicago World’s Fair.

You can still catch the faint ruddy glow of Mars in the west during the late stages of evening twilight, but you’ll only have a limited window to do so. After keeping ahead of the advancing Sun for several months, the red planet now sets before the sky becomes fully dark.

Jupiter, however, is very hard to miss. The giant planet dominates the evening sky, appearing in the southeast shortly after sunset and crossing the meridian a bit after 10:00 pm. He is located in the constellation of Virgo, and if you’ve been watching him for the past several weeks you will have noticed the increasing gap between Old Jove and the constellation’s brightest star Spica. Binoculars or a small spotting scope will show the planet’s four bright Galilean moons, and larger instruments will begin to reveal details on his cloud-streaked surface. If you have a four-inch or larger aperture instrument try looking for the famous Great Red Spot, which should be prominent on the evenings of the 18th and 23rd.

Saturn will rise at around 10:00 pm by the end of the week, so late-night skywatchers should be able to see him low in the southeast by midnight. The ringed planet will grace the evening sky through the summer months, but right now your best bet to explore his rings and varied moons is by following the Cassini space probe’s mission as it swoops between the rings and the ball of the planet. By the time Saturn leaves us in the fall the probe will have completed its 13-year study, plunging into Saturn’s atmosphere in a grand finale.

Early risers are now being greeted by the bright glow of dazzling Venus. This planet will remain in the morning sky for the rest of the year, adding a bit of extra light to the cooler mornings that will come with autumn’s skies.

USNO Master Clock Time
Javascript must be Enabled