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The Sky This Week, 2020 October 13 - 20

Mars in the spotlight.
Mars, imaged 2020 OCT 9 from Alexandria, Virginia.
Mars, imaged 2020 OCT 9, 03:40 UT from Alexandria, Virginia
with a Celestron 23.5-cm (9.25-inch) f/10 Schmidt-Cassegrain telescope,
Orion 2X 3-element "Shorty Plus" Barlow lens, and a ZWO ASI224MC color imager.

The Moon’s thin waning crescent opens the week sharing the pre-dawn sky with dazzling Venus.  New Moon occurs on the 16th at 3:31 pm Eastern Daylight Time.  Luna returns to the evening sky by the week’s end, skirting the southern horizon as she moves through the departing summer constellations.

Luna’s absence from the evening sky gives us a chance to participate in the citizen-science Globe at Night observing campaign, which runs through the evening of the 17th this month.  The featured constellation is Cygnus, the Swan, which may be found directly overhead at around 8:00 pm local time.  Deneb, the constellation’s brightest star, is the easternmost apex of the Summer Triangle asterism, so it’s very hard to miss.  The rest of the constellation resembles a cross that extends into the center of the Triangle.  The major stars of Cygnus are second- and third-magnitude luminaries, so the basic outline of the group should be easy to fund under suburban skies.  From dark locations many more stars become visible, and the summer Milky Way resembles a cloud behind the Swan’s flying figure.  The Swan’s head is marked by the third-magnitude star Albireo, which is located close to the center of the Triangle asterism.  Albireo is a treat for owners of small telescopes as it easily splits into a pair of strongly colored stars.  Their blue and gold colors are quite bold in small instruments, but these hues become washed out in larger apertures.  To participate in the Globe at Night program, simply go to their web app and compare your view of Cygnus to the star provided star charts.  These will help determine your limiting magnitude and the relative darkness of your observing location.  Your data will enable scientists to map the encroachment of artificial night lighting throughout the planet and hopefully lead to a plan to bring the night sky back.

As I am typing this Mars is closing in on opposition, which occurs on the 13th at 7:26 pm EDT.  At this moment the red planet will be on the opposite side of the Earth as seen from the Sun, rising at sunset and setting at sunrise.  Beaming down like a hot coal set in the sparse star fields of the autumnal constellations, this is “prime-time” for examining the planet with a telescope.  Gleaning detail from the planet’s bright pink-hued disc takes patience and steady air, but a good four-inch telescope should begin to reveal some of Mars’ larger surface features.  Larger apertures will show more detail, and in moments of steady “seeing” the surface takes on a mottled appearance that baffled astronomers of the “golden age” of visual observation.  The feature known as Syrtis Major, visible this week at around 2:00 am EDT, was the first surface feature to be glimpsed on the surface of another planet when it was drawn by the Dutch astronomer Christiaan Huygens in 1659.  

Despite the fact that we have now mapped Mars from orbit to a resolution measured in meters, the fascination with gleaning detail through telescopes remains high among today’s amateur astronomers.  The features we see are indicative of topography, and changes in the large-scale appearance of these change from one apparition to the next.  These changes reflect global events such as dust storms in the martian atmosphere and still contribute valuable understanding of this tantalizing planet.  Many of the best astronomers of the 19th Century honed their observing skills by spending countless hours sketching Mars through the great telescopes of the era.  Thanks to the digital imaging revolution today’s astronomers can capture details only hinted at by these pioneer observers using very modest instruments.  I am continually amazed at what I can now capture with my modest telescope from my yard, especially when I compare these images with sketches that I have made in the past with much larger instruments.  Like the Moon, the surface of Mars continually beckons, and even though we have virtually “been there”, in both cases there is always some new detail to see.

Mars is now stealing the show from Jupiter and Saturn, but both of these planets are still visible in the early evening.  You will find Jupiter low in the southern sky as evening twilight fades, and Saturn pops into view just east of Old Jove about 20 minutes later.  Unlike Mars, whose apparent disc varies widely in size depending on the distance we see him from Earth, these giant planets generally appear the same through the typical telescope throughout their apparitions.  In addition, they are surrounded by bevies of moons.  The four bright Galilean moons of Jupiter can be seen with any telescope, while an 8-inch instrument will reveal five or six moons circling Saturn.  While Mars has two moons, they are tiny chunks of rock that are almost impossible to see in the typical backyard telescope.

The evening’s planetary parade ends with the rising of Venus about three hours before the Sun.  Your best time to look for her is during morning twilight as she climbs into the eastern sky.  Look for the thin waning crescent Moon nearby on the morning of the 14th.