Northern winter on Mars begins (Chris Vaughan, Starry Night Education)

This Week’s Sky: August 31 to September 6, 2020

This week, the Moon meets with Mars. The Red Planet will also experience a solstice and the start of its northern winter.

Tuesday, September 1 from 9:55 to 11:13 p.m. EDT – Moon occults star Tau Aquarii

Moon occults star Tau Aquarii (Chris Vaughan, Starry Night Education)

In the eastern evening sky on Tuesday, September 1, observers using binoculars and backyard telescopes (red circle) in the eastern half of North America can see the almost-full Moon occult the medium-bright (magnitude 4.05) star designated Tau Aquarii or 71 Aquarii. That star marks the western knee of Aquarius, the Water-Bearer. In the Great Lakes region, the left-hand edge of the Moon will cover the star at approximately 9:55 p.m. EDT (or 01:55 GMT on Sep 2). The star will re-appear from behind the opposite limb of the Moon at about 11:13 p.m. EDT. Ingress and egress vary based on your latitude, so start watching a few minutes before the times quoted above — or use Starry Night or another planetarium app to look up the exact times for your town. 

Wednesday, September 2 at 5:22 GMT – Full Corn Moon

Full Corn Moon (Chris Vaughan, Starry Night Education)

The September full Moon will occur on Wednesday morning at 1:22 am EDT, or 5:22 Greenwich Mean Time. Traditionally known as the “Corn Moon” and “Barley Moon,” this one always shines in or near the stars of Aquarius and Pisces. The Indigenous Anishinaabe people of the Great Lakes region call this Moon Waatebagaa-giizis or Waabaagbagaa-giizis, the Leaves Turning or Leaves Falling Moon. The Cree Nation of central Canada calls the September full moon Nimitahamowipisim, the “Rutting Moon” — when the bull moose scrapes the velvet from his antlers as a sign that mating shall begin. The Haudenosaunee (Iroquois) of Eastern North America call it Seskehko-wa, the Time of Much Freshness Moon.

In most years, the September full Moon is also the Harvest Moon. But October’s full Moon will be the one happening closest to the equinox in 2020 — so it will have that honour. Since the full phase will officially occur in the wee hours of Wednesday in the Americas, the Moon will already look full when it rises there a few hours earlier, on Tuesday evening. Only in the central Pacific Ocean region will the Moon be precisely full when it rises at sunset. 

Wednesday, September 2 evening – Asteroid Pallas changes direction

Asteroid Pallas changes direction (Chris Vaughan, Starry Night Education)

On Wednesday, September 2, the main belt asteroid designated (2) Pallas will complete a retrograde loop that began in May, causing it to temporarily stop moving through the background stars. On this night, the magnitude 10 asteroid will be located halfway up the southwestern evening sky – about a palm’s width to the right (or 6.25 degrees to the celestial west of the medium-bright star Zeta Aquilae, which marks the western wingtip of Aquila, the Eagle. After tonight, it will return to a regular eastward motion through the stars.

Thursday, September 3 – Northern winter begins on Mars

Northern winter on Mars begins (Chris Vaughan, Starry Night Education)

On Thursday, September 3, the southern polar axis of Mars will reach its maximum tilt of 24 degrees towards the Sun, triggering the solstice, and the beginning of winter in Mars’ Northern Hemisphere. Mars’ longer year means that its seasons are longer, too — slightly more than five months. Viewed in amateur telescopes from our vantage point on Earth, Mars’ southern polar cap will shine as a bright, white spot on the red planet (although your telescope’s optics may flip Mars upside-down).

Saturday, September 5 overnight – Bright Moon dances with Mars

Bright Moon dances with Mars (Chris Vaughan, Starry Night Education)

When the bright, waning gibbous Moon rises in the east at about 9:45 p.m. local time on Saturday, September 5, it will be positioned only a finger’s width to the right (or 1 degree to the celestial southwest) of Mars. That’s close enough to appear together in binoculars and telescope at low magnification (red circle). As the duo crosses the sky together during the night, the diurnal rotation of the sky, and the Moon’s eastward orbital motion, will combine to shift the Moon clockwise around Mars — placing it above the planet by sunrise on Sunday morning. Since the pair will not set in the west until mid-morning on September 6, skywatchers have a chance to see Mars in the morning daytime sky using binoculars and backyard telescopes by using the Moon as a reference. (Observers in central and northeastern South America, Cape Verde Islands, northern Africa, and southern Europe will see the Moon occult Mars around 05:00 GMT on Sunday.)

Sunday, September 6 overnight – Gibbous Moon and Uranus

Gibbous Moon and Uranus (Chris Vaughan, Starry Night Education)

When the bright, waning gibbous Moon rises in the east at about 10 p.m. local time on Sunday, September 6, it will be positioned several finger widths to the lower right (or 4 degrees to the celestial south) of blue-green Uranus. That magnitude 5.71 planet is visible in binoculars (red circle) and backyard telescopes – if you know where to find it. This bright Moon will be too bright for dim-planet hunting. Note the positions of the brighter stars in Cetus (below the Moon) and Aries (above Uranus), and use them to find Uranus on a night when the Moon isn’t nearby.

Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through to tour the universe together.