The Sky This Week, 2017 April 18 - 25
|Messier 81 and 82, galaxies in Ursa Major, 2016 December 31
Imaged with a 102mm (4-inch) f/6.6 refractor and a Canon EOS Rebel T2i DSLR
from near Mollusk, Virginia
The Moon graces the pre-dawn sky this week, passing from summer’s constellations into the rising faint star patterns of the autumn sky. Last Quarter occurs on the 19th at 5:57 am Eastern Daylight Time. Look for Luna’s slender crescent near the bright glow of Venus before sunrise on the mornings of the 23rd and 24th.
The April campaign for the Globe at Night "citizen science" program runs throughout the course of the week and lasts until the 27th. Beginning on April 22, Earth Day, we will also observe Dark Sky Week in conjunction with the International Dark-Sky Association. Both of these events are designed to raise awareness of the effects of artificial outdoor lighting on not only our view of the nighttime sky but the various environmental and biological effects that bright night lighting has on the many nocturnal creatures that share the planet with us. Globe at Night is a chance for you to measure the brightness of your local sky and report your findings for scientific analysis. So far this year over 6200 people have reported on their skies worldwide. To participate in the current campaign, locate the constellation Leo, the Lion, which will be high in the south at 9:30 pm. The pattern’s brightest star, Regulus, will be on the meridian at this time. Above Regulus look for a "backwards question mark" asterism that forms the Lion’s head; just to the east is a right triangle of stars that marks the Lion’s hindquarters. Using the charts on the Globe at Night website, count the number of stars you can see and report your findings online. It’s as simple as that!
If you’re in a dark-sky location, this is the time of year to go galaxy hunting. The area bounded by Denebola, the star that marks the "tail" of Leo, the bright star Arcturus rising in the east, and the star Spica near Jupiter is the location of the center of the Coma-Virgo Galaxy Cluster, of which our Milky Way is an outlying member. Sweep a modest-size telescope over this area and you’ll see dozens of faint smudges of light, each of which betrays a distant galaxy made up of hundreds of billions of stars. They are so far away that the light from most of these objects started its journey toward us when the dinosaurs became extinct!
Closer to home, Mars is the nearest major object to us during the evening hours. At a distance of some 360 million kilometers (230 million miles) he glows in the western sky in the early hours after sunset. That said, there is a sizeable interloper that will pass the Earth at a much closer distance this week. A kilometer-wide asteroid known as 2014 JO25 will whiz by us at a distance of 4.6 times that of the Moon at around 8:00 am on the morning of the 19th. Mars continues to move eastward along the ecliptic, and this week he drifts between the Pleiades star cluster and the bright star Aldebaran in Taurus.
Jupiter blazes brightly in the southeast as sunset gives way to evening twilight. He is now the brightest object in the night sky in the absence of the Moon and Venus. Of all the planets he is the most satisfying to view in the small telescope, and this week you can watch the shadow of his largest moon Ganymede trace across the planet’s clouds tops on the evening of the 21st. As a bonus that evening you can see the Great Red Spot rotate onto the disc after 11:00 pm. The view of Old Jove constantly changes, and once you’ve had a few evenings with him he’s a hard habit to break.
Saturn is still best seen before the onset of morning twilight, where you’ll find him lingering among the stars of Sagittarius toward the southern horizon. Any telescope will show the planet’s famous rings, but you’ll need exceptionally steady air to make out their finer details.
The dazzling planet Venus has made her return to darker skies, rising as the first rays of morning twilight begin to brighten the eastern horizon. You’ll find her in the company of the waning crescent Moon on the mornings of the 23rd and 24th.