Full Green Corn Moon on August 22, 2021. | SkyNews
Full Green Corn Moon on August 22, 2021. (Chris Vaughan, Starry Night Education)

This Week’s Sky: August 16 to 22, 2021

Jupiter reaches opposition this week, and Mercury passes Mars. Also, look for Miine Giizis — or the full “Blueberry Moon” this week.

Wednesday, August 18 – Mercury just misses Mars (after sunset)

Mercury just misses Mars after sunset on August 18, 2021. | SkyNews
Mercury just misses Mars after sunset on August 18, 2021 (Chris Vaughan, Starry Night Education)

On Wednesday, August 18, the rapid eastward orbital motion of Mercury (red path) will carry it very closely past Mars, allowing both planets to share a blurry eyepiece view in a backyard telescope (red circle) — but use optics only after the Sun has completely set. Magnitude -0.46 Mercury will be eight times brighter than Mars. On Wednesday, Mercury will be located 9 arc-minutes to the lower right (southwest of) the red planet. The following evening, look for Mercury positioned 1 degree to Mars’ upper left. This conjunction will not be seen easily at mid-northerly latitudes; but observers in the southern United States and farther south can see the pair in a darker sky, sitting just above the western horizon before they set at 8:45 p.m. local time.

Friday, August 20 – Jupiter at opposition (all night)

Jupiter at opposition all night on August 20, 2021. | SkyNews
Jupiter at opposition all night on August 20, 2021. (Chris Vaughan, Starry Night Education)

On Friday, August 20, Jupiter will reach opposition among the stars of eastern Capricornus. Since Earth will be positioned between the Sun and the gas giant on that date, Jupiter will rise at sunset, remain visible all night long, and set at sunrise. At opposition, Jupiter will be 373.1 million miles, 600.4 million km, or 33.3 light-minutes from Earth, and it will shine at its maximum brightness of magnitude -2.88 for 2021. Because Jupiter is approaching perihelion in January, 2023, the planet will sport a generous, 49 arc-seconds-wide disk at this year’s opposition. Views of Jupiter in amateur telescopes (inset) will show its equatorial bands, and the Great Red Spot every second or third night. Around opposition, Jupiter and its four large Galilean satellites frequently eclipse and occult one another, and cast their round, black shadows on the planet singly and in pairs.

Friday, August 20 – Uranus pauses in Aries (overnight)

Uranus pauses in Aries on August 20, 2021. | SkyNews
Uranus pauses in Aries on August 20, 2021 (Chris Vaughan, Starry Night Education)

On Friday, August 20, Uranus will cease its motion across the stars of southern Aries and prepare to commence a westward retrograde loop that will last until January, 2022. Tonight the magnitude 5.7 planet will rise shortly before 11 p.m. local time and remain visible until the pre-dawn. Uranus will be surrounded by the 5th magnitude stars Sigma, Omicron, Pi and Rho Arietis, creating a distinctive asterism for anyone viewing Uranus in binoculars (red circle).

Friday, August 20 – Bright Moon below Saturn (all night)

Bright Moon below Saturn on August 20, 2021. | SkyNews
Bright Moon below Saturn on August 20, 2021 (Chris Vaughan, Starry Night Education)

After the sun sets on Friday evening, August 20, look towards the southeast for the bright waxing gibbous Moon shining several finger widths below (or 4.5 degrees to the celestial south of) yellowish Saturn, with much brighter Jupiter positioned off to their left (east). As they cross the sky during the night, the Moon and the ringed planet will (just barely) share the field of view of binoculars (red circle), and the diurnal rotation of the sky will lift the Moon to Saturn’s left. They’ll set together in the west-southwest before dawn.

Saturday, August 21 – Gibbous Moon joins Jupiter and Saturn (all night)

Gibbous Moon joins Jupiter and Saturn on August 21, 2021. | SkyNews
Gibbous Moon joins Jupiter and Saturn on August 21, 2021 (Chris Vaughan, Starry Night Education)

After 24 hours of motion, the gibbous Moon will hop east to sit below (south of) Jupiter and Saturn in the southeastern sky after dusk. The trio will make a lovely wide-field photo when composed with some interesting scenery. The Moon will be somewhat closer to brighter Jupiter than Saturn, and just close enough for them to fit together in binoculars (red circle) — but only until after midnight, because the Moon’s eastward orbital motion will draw it farther from the planet. By the time the Moon drops below the west-southwestern horizon as the Sun is rising (another photo opportunity), it will have shifted to Jupiter’s left.

Sunday, August 22 – Full Green Corn Moon (at 12:02 GMT)

Full Green Corn Moon on August 22, 2021. | SkyNews
Full Green Corn Moon on August 22, 2021. (Chris Vaughan, Starry Night Education)

The August full Moon will occur on Sunday, August 22 at 8:02 a.m. EDT or 12:02 GMT. This full Moon always shines among or near the stars of Aquarius or Capricornus, and is colloquially called the “Sturgeon Moon,” “Red Moon,” “Green Corn Moon” and “Grain Moon.” The Indigenous Anishinaabe people of the Great Lakes region call this Moon Manoominike-giizis, the “Wild Rice Moon,” or Miine Giizis, the “Blueberry Moon.” Cree peoples of the United States and Canada calls the August full Moon Ohpahowipîsim, the Flying Up Moon. The Haudenosaunee (Iroquois) of eastern North America call it Seskéha, the Freshness Moon. The Moon becomes fully illuminated because it is opposite the Sun in the sky, causing the Moon to rise at sunset and set at sunrise. Since the full phase will officially occur on Sunday morning in the Americas, the Moon will appear to be full on both Saturday night and Sunday night. But magnified views will reveal a thin strip of darkness along the Moon’s western and eastern limbs on Saturday and Sunday night, respectively.

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 AstroGeo.ca to tour the universe together.

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