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The Sky This Week, 2017 April 4 - 11

A very popular Moon.
The Moon at 10 days, imaged 2017 March 9 at 03:00 UT
with a 102mm (4-inch) f/6.6 refractor, 1.6X Barlow lens,
and a Canon EOS Rebel T2i DSLR

The Moon waxes in the evening sky this week, reaching the Full phase on the 11th at 2:08 am Eastern Daylight Time. The popular names for April’s Full Moon all reflect the signs we see around us in nature. It is variously called the Seed Moon, Flower Moon, Sprouting Grass Moon, Egg Moon, or Fish Moon. This year it is also the Paschal Moon, the first Full Moon following the vernal equinox. This Full Moon begins the Jewish observance of Passover and defines the date of Easter for Christians. Luna passes close to the bright star Regulus in the constellation of Leo, the Lion on the evening of the 6th. She forms an attractive grouping with the bright planet Jupiter and the bright star Spica late in the evening of the 10th.

With the Moon brightening the evening sky all but the night’s brightest stars are washed out by her increasing glare. However, Luna also presents herself as the best target for observation through the telescope as she waxes toward Full. During the week the terminator line slowly reveals ever-changing details exposed to the slowly rising Sun. As the week starts the terminator lies across rugged cratered terrain, where shoulder-to-shoulder craters bear mute testimony to the violent origins of the solar system. Over the course of the next several evenings the large, relatively smooth lava plains of Luna’s largest named feature, Oceanus Procellarum, come into view. These large dark features date to a more recent time, erupting from deep fissures caused by the impacts of large asteroids that collided with the young Moon between 35. To 4 billion years ago. Here we find more isolated impact craters and interesting features caused by subtle changes in the surface composition. As the sun angle increases, take particular note of the bright "rays" that appear to radiate from some of the Moon’s more prominent craters. The most prominent of these ray systems is associated with the prominent crater Tycho, located in the battered southern lunar highlands. As we approach Full Moon this ray pattern begins to resemble a longitude grid centered on the bright crater itself. There rays are now known to be secondary impacts of material flung out from the violent collisions of small asteroids in more geologically more recent times. The impactor that created Tycho did so about 108 million years ago and may be related to the one that created the Chixlub impact that ended the Cretaceous Period and caused the extinction of the dinosaurs!

You might still have a chance to glimpse the elusive planet Mercury in the early evening sky. The fleet planet hovers about 10 degrees above the western horizon half an hour after sunset. You’ll probably want to use binoculars to locate him, especially by the end of the week. He fades by a full magnitude as the week progresses, then he dives toward the encroaching Sun.

Mars is still visible in the early evening sky. He’s about 15 degrees up at 9:00 pm, shining with his characteristic pinkish hue. He is doggedly pressing eastward toward the stars of Taurus, and you can watch his daily progress toward the constellation’s brightest star, Aldebaran.

Jupiter reaches opposition on the 7th. On this date Earth passes between the Sun and the giant planet, so he rises at sunset and sets at the following morning’s sunrise. This is the time when Jupiter is at his best and brightest as well as at his closest distance to us. As bright as he is, he’s still an awfully long way from us, over 680 million kilometers (423 million miles) distant at his closest approach. You can watch his outermost Galilean moon, Callisto, glide north of the planet’s disc on the evening of the 6th. On the following night the planet’s famous Great Red Spot will rotate across the view.

Saturn may be found close to the meridian as morning twilight brightens the sky. You can spot him low in the south among the stars of Sagittarius.

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