Full Green Corn Moon (Chris Vaughan, Starry Night Education)

This Week’s Sky: August 3 to 9, 2020

In this week’s sky, a Full Moon that wanes and meets Mars, and Comet NEOWISE passes close to Messier 53.

Monday, August 3 at 15:59 GMT – Full Green Corn Moon

Full Green Corn Moon (Chris Vaughan, Starry Night Education)

On Monday at 11:59 am Eastern Time (or 15:59 Greenwich Mean Time), the moon will officially reach its full moon phase. The August full moon, colloquially called the “Sturgeon Moon”, “Black Cherries Moon”, and “Green Corn Moon”, always shines among or near the stars of Aquarius or Capricornus. The indigenous Anishinaabe people of the Great Lakes region call this moon Manoominike-giizis, the Wild Rice Moon, or Miine Giizis, the Blueberry Moon. The Cree Nation of central Canada calls the August full moon Ohpahowipîsim, the Flying Up Moon. The Haudenosaunee (Iroquois) of Eastern North America call it Seskéha, the Freshness Moon.

Full moons are always opposite the sun in the sky, causing them to rise at sunset and set at sunrise. Since the full phase will officially occur around mid-day Monday in the Americas, the moon will appear to be full on Sunday night, too. But magnified views will reveal a thin strip of darkness along the moon’s western and eastern limbs on Sunday and Monday night, respectively. Only observers living at Middle Eastern longitudes will see the moon rising while it’s precisely full.

At this time of year, the moon’s orbit makes a shallow angle with the eastern horizon in evening. From one evening to the next, the moon’s orbital motion carries it more right-to left than up-to-down, causing the moon to rise at almost the same time. The effect is most pronounced when the moon is full close to the September Equinox. We call that one the Harvest Moon.

Tuesday, August 4 all night – Reiner Gamma Lunar Swirl

Reiner Gamma Lunar Swirl (Chris Vaughan, Starry Night Education)

Oceanus Procellarum is the large, dark mare region near the western (left-hand) limb of the moon. The Reiner Gamma Lunar Swirl is a small, high-albedo area located just inside the western edge of Procellarum, due north of the dark crater Grimaldi and due west of the bright, rayed crater Kepler. It is best seen a night or two after the moon’s full phase. The 18 mile or 30 km diameter crater Reiner is located east-southeast of Reiner Gamma. The swirl is composed of ancient lunar basalt that has not been darkened by weathering, likely due to protection from cosmic rays by a strong localized magnetic field – the swirl has one of the strongest magnetic anomalies on the moon! At high magnification, its complex, swirling shape can be discerned.

Tuesday-Wednesday, August 4 and 5 overnight – Ceres passes 88 Aquarii

Ceres passes 88 Aquarii (Chris Vaughan, Starry Night Education)

On the nights surrounding Wednesday, August 5, the dwarf planet (formerly asteroid) Ceres will pass by the medium-bright star c2 Aquarii or 88 Aquarii, which marks the western foot of Aquarius (the Water-Bearer). The star and magnitude 8 Ceres will fit into the field of view of a backyard telescope at medium magnification (red circle) from now until next Saturday – with Ceres moving steadily to the right (or towards celestial southwest) compared to that star (red path with labelled dates:times). At closest approach on Tuesday and Wednesday, Ceres will sit just 10 arc-minutes (or one-third of the moon’s diameter) below 88 Aquarii. Remember that your telescope will likely flip the view around (inset). 

Thursday, August 6 evening – Comet NEOWISE close to Messier 53

Comet NEOWISE close to Messier 53 (Chris Vaughan, Starry Night Education)

In the western sky after dusk on Thursday, August 6, the path of fading Comet C/2020 F3 (NEOWISE) will carry it closely past the globular star clusters Messier 53 and NGC 5053. Find the trio a finger’s width above (or 1 degree to the celestial northeast of) the medium-bright star Diadem, also known as Alpha Comae Berenices. The comet, the star, and the two clusters will all appear together within the field of view of a telescope at low magnification (red circle), offering a nice photo opportunity. The comet will not be as bright as depicted here.

Saturday, August 8 overnight – Waning Moon meets Mars

Waning Moon meets Mars (Chris Vaughan, Starry Night Education)

When the waning gibbous moon rises in the east shortly before midnight on Saturday, August 8, it will be positioned only two finger widths to the lower right (or 2.3 degrees to the celestial southwest of) bright, reddish Mars. The pair, which will fit nicely together in the field of binoculars (red circle), will cross the night sky together. During that period, the moon’s eastward orbital motion will carry it closer to Mars, and the diurnal rotation of the sky will shift Mars to the moon’s upper right. They will not set in the west until mid-morning on Sunday – offering a chance to see Mars in the morning daytime sky using binoculars and backyard telescopes, by using the moon as a reference. Observers in most of western Antarctica, southeastern South America, and the Ascension Islands will see the moon occult Mars around 08:00 GMT on August 9.

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.