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The Sky This Week, 2020 July 14 - 21

A comet and a plethora of planets
Comet C/2020 F3 NEOWISE, imaged 2020 July 12, 09:58 UT from Alexandria, Virginia.
Comet C/2020 F3 NEOWISE, imaged 2020 July 12, 09:58 UT from Alexandria, Virginia
with a Canon EOS Rebel SL2 DSLR, 55mm @ f/5.6, HDR composite of 4 exposures at ISO 1600.

The Moon wanes through her crescent phases in the pre-dawn sky this week, with New Moon falling on the 20th at 1:33 pm Eastern Standard Time.  Luna forms an attractive grouping with Venus and the bright star Aldebaran before dawn on the mornings of the 16th and 17th.  Look for her slender crescent low in the west as evening twilight falls on the 21st.

If you didn’t get up before dawn last week to look for Comet C/2020 F3 NEOWISE, your procrastination has been rewarded.  The comet moves into the evening sky this week, gradually climbing higher in the northwestern sky with each passing night.  It has been putting on a very good show for early risers over the past couple of weeks, visible with the unaided eye before dawn even from urban locations.  I had a very nice view early on the morning of the 12th from the ball field behind my neighborhood school in the Washington suburbs, and folks who have seen it from dark skies say that it’s the brightest comet we’ve had since Comet Hale-Bopp back in 1997.  From my suburban site it displayed a bright nucleus with a distinct tail several degrees long.  During the course of this week it will move toward the “bowl” of the Big Dipper, and by the week’s end it will be located about one-third of the way from the Dipper’s “pointer” stars and the “head” of Leo, the Lion.  Currently it seems to be running about 1.5 magnitudes brighter than predicted, so it should be an easy object to spot from a dark location.  It has passed perihelion, its closest point to the Sun, so we expect it to fade over the course of the next few weeks, but it should remain bright enough to see in binoculars well into August.  However, comets are notoriously finnicky beasts, so don’t be surprised if it remains bright or fades rapidly; that’s what comets do!  A finder chart for the comet may be found here.

If you follow the arc of the Big Dipper’s “handle” you will spot the brightest star in the northern sky, Arcturus.  A simple way to remember this is “arc to Arcturus”.  This is the brightest star in the constellation of Boötes, the Herdsman, which is the target constellation for this month’s Globe at Night campaign.  The constellation itself reminds some people of a kite with Arcturus marking the bottom point.  This time of year, though, I prefer the idea of a great cosmic ice cream cone.  Either way, the fainter stars in the group can be a challenge from urban locations, but try to see how many you can spot and report your results to the Globe at Night web app.  If you have a modest-aperture telescope, look at the constellation’s second-brightest star, Izar, which lies about ten degrees northwest of Arcturus.  You will see a very close pair of stars that have a beautiful color contrast that I see as blue and yellow.

As Arcturus and its companions slide westward with the passing hours, the Summer Triangle climbs higher in the east.  The brightest and highest star in the asterism is Vega, which leads the diminutive constellation of Lyra, the Harp.  Here you will find another interesting star system for the small telescope.  Look just northeast of Vega with a pair of binoculars for a pair of equally bright stars.  Now point the telescope at the pair; a three-inch aperture telescope should resolve each component of the binocular pair into a pair of close double stars.  Well-known to amateur astronomers as Epsilon Lyrae or the “Double-double”, the system is a true quadruple star system.  Recent observations indicate the presence of a fifth component as well, but more observations are required to tie it to the other four.  

Jupiter is now at opposition, the time when it lies directly opposite the Sun in the sky.  The giant planet now rises at sunset, crosses the meridian at around 1:00 am, and sets at sunrise.  Your best times to observe him are between about 10:30 pm and 3:30 am, when he is above the “3 airmass limit”, a measure of the density of Earth’s atmosphere.  This is also the time when he is closest to us, some 619 million kilometers (385 million miles) away.  Despite this vast distance, he shows the largest apparent disc of any planet, making him an easy target for owners of small telescopes.

Saturn reaches opposition on the 20th, and like Jupiter remains in the sky all night long.  The ringed planet comes up shortly after Old Jove, and the pair will remain close together in the sky for the remainder of the current evening apparition.  Saturn is almost twice as distant as Jupiter from us, so his disc is less than half the size of Jupiter’s, but his rings are the sight to see in the telescope.  Look for the rings to brighten on the days surrounding opposition.  Known as the Seeliger Effect, it makes the rings appear about twice as bright as their normal appearance.

Mars continues his lonely trek through the autumnal constellations.  I had a nice view of him with the Moon while I was looking at the comet, and I could easily spot his ruddy hue as morning twilight brightened the sky.

Dazzling Venus has vaulted into the morning sky and is currently gliding through the stars of Taurus, the Bull.  Look for her with the crescent Moon and the star Aldebaran on the mornings of the 167th and 17th.