You are here: Home USNO News, Tours & Events Sky This Week The Sky This Week, 2013 May 14 - 21
The USNO websites,,,,,, and are undergoing modernization efforts. The expected completion of the work and the estimated return of service is Fall 2020, subject to change due to potential impacts of COVID-19.

The Sky This Week, 2013 May 14 - 21

Looking over the Moon again, and a planetary palaver in the west.

The Moon, 2013 April 16 

The Moon waxes in the evening sky this week, passing through the springtime constellations as she sets her sights on Saturn, now rising in the southeast. First Quarter occurs on the 18th at 12:35 am Eastern Daylight Time. Look for Luna between the last of winter’s stars on the evenings of the 14th and 15th, when she’ll be positioned between the Twin Stars of Gemini, Castor and Pollux, and the bright star Procyon. By the end of the week she cozies up to the bright star Spica in the constellation Virgo, on the evening of the 21st.

This is another good week to get to know our nearest neighbor in space as she waxes through the phases around First Quarter. I enjoy observing the Moon in the early evening during twilight since the contrast between her dazzling surface and dark shadows is tempered by the glow of fading dusk. Luna’s bright presentation in the telescope eyepiece belies the true nature of her surface, though. Overall the Moon only reflects about 7% of the sunlight that strikes her, which means that a typical patch of lunar regolith is about as dark as a charcoal briquette! However, lack of an atmosphere means that the Sun’s rays strike the surface full-force. Under these circumstances even a charcoal briquette would look very bright compared to the blackness of space. The landforms that reveal themselves as the terminator line creeps eastward each evening is another testament to Luna’s lack of atmosphere. Countless impacts have left scars of all shapes and sizes scattered across the Moon’s face, preserving an era of intense bombardment by "planetessimals" during the formative years of the solar system. Here on Earth many of these objects never made it through our atmosphere, and the remnants of those that did have been ground out of existence by erosion and plate tectonics. Think of this the next time you look at the Moon in a telescope. The features that you see are older than any that you’ll see on our home planet, and many of them look almost as fresh as the day they were made!

Much of the action in the sky over the next couple of weeks will take place in the early evening. Jupiter, which has been doggedly hanging tough in the western twilight sky, will get some reinforcements as the week passes by. By the weekend you’ll want to keep your eyes peeled along the west-northwest horizon at around 9:00 pm and look for the bright glow of Venus about five degrees above the skyline. Venus will gain about a degree each evening as she sets her sights on Jupiter. By early next week you should also see the fleet planet Mercury just below and to the right of Venus. These three planets will be playing a game of cosmic "tag" over the course of the next several weeks, with the closest grouping occurring right around Memorial Day. This will be one of your best chances to glimpse the elusive Mercury, which never strays very far from the Sun’s glare, and it should provide a number of very nice photo opportunities for sunset and twilight shutterbugs.

Saturn now pops into view in the southeastern sky as the last glow of twilight fades about an hour after sunset. By 10:00 pm the ringed planet is reasonably high in the sky for detailed telescopic viewing. Unfortunately his southerly declination means that clear views of his subtly banded disc and icy rings are subject to the whims of our atmosphere. Motion of air currents tends to blur the normally razor-sharp edges of the rings, and the denser air acts as a prism, causing a small amount of spectral dispersion that tinge the planet with blue and red fringes. However, in moments of very steady air the view is always rewarding as the rings snap into sharp view and tiny moons pop out of the surrounding blackness. It’s well worth the wait for these magical moments of good "seeing"!

USNO Master Clock Time
Javascript must be Enabled