A diagram of the full Strawberry Moon on June 24, 2021. | SkyNews
Full Strawberry Moon (Chris Vaughan, Starry Night Education)

This Week’s Sky: June 21 to 27, 2021

As the Moon reaches its full phase this week, look for its meetups with Saturn and Jupiter during the wee morning hours.

Monday, June 21 – Jupiter reverses direction (wee hours)

A diagram of Jupiter reversing direction (wee hours) on June 21, 2021. | SkyNews
Jupiter reverses direction, wee hours (Chris Vaughan, Starry Night Education)

On Monday, June 21, Jupiter will pause in its regular eastward motion in front of the distant stars of western Aquarius and then begin a retrograde loop (red curve with dates) that will last until mid-October. The apparent reversal in Jupiter’s motion is an effect of parallax produced when Earth, on a faster orbit, begins to pass Jupiter on the “inside track.” Starting this week, Jupiter will rise before midnight local time, and its 19-degree angular separation from Saturn will slowly decrease.

Wednesday, June 23 – Mars invades the Beehive (after sunset)

A diagram of Mars invading the Beehive on June 23, 2021. | SkyNews
Mars invades the Beehive (Chris Vaughan, Starry Night Education)

In the west-northwestern sky after dusk on Wednesday, June 23, the orbital motion of Mars will carry it directly through the large open star cluster known as the Beehive or Messier 44 in Cancer. The passage will be a terrific sight in a backyard telescope (red circle), although binoculars will show the cluster’s stars, too. Mars will be telescope-close to the “bees” on the surrounding evenings. The event will be better for observers at southerly latitudes where the cluster will be higher as the sky darkens.

Thursday, June 24 – Full Strawberry Moon (at 18:39 GMT)

A diagram of the full Strawberry Moon on June 24, 2021. | SkyNews
Full Strawberry Moon (Chris Vaughan, Starry Night Education)

The Moon will officially reach its full phase at 2:39 p.m. EDT (or 18:39 GMT) on Thursday, June 24. The June full Moon, colloquially known as the Strawberry Moon, Mead Moon, Rose Moon, or Hot Moon, always shines in or near the stars of southern Ophiuchus, the Serpent-Bearer. The Ojibwe people of the Great Lakes region call this Moon Ode’miin Giizis, the Strawberry Moon. For the Cree Nation, it’s Opiniyawiwipisim, the Egg Laying Moon (referring to the activities of wild water-fowl). The Mohawks call it Ohiarí:Ha, the Fruits are Small Moon. The Cherokee call it Tihaluhiyi, the “the Green Corn Moon,” when crops are growing. Because the Moon is full when it is opposite the Sun in the sky, full moons always rise in the east as the Sun is setting, and set in the west at sunrise. Since sunlight is hitting the Moon vertically at that time, no shadows are cast; all of the variations in brightness you see arise from differences in the reflectivity, or albedo, of the lunar surface rocks.

Saturday, June 26 – Io’s shadow passes Callisto’s on Jupiter (from 05:04 to 07:22 GMT)

A diagram of Io’s shadow passing Callisto’s on Jupiter on June 26, 2021. | SkyNews
Io’s shadow passes Callisto’s on Jupiter (Chris Vaughan, Starry Night Education)

The last spectacular Jupiter shadow transit event of June will occur during the wee hours of Saturday, June 26. For more than two hours, observers in the eastern half of North America and all of Central and South America can use amateur telescopes to watch two of the small, round, black shadows cast by Jupiter’s four Galilean moons cross (or transit) the planet’s disk together. At 1:04 a.m. EDT (or 5:04 GMT), Io’s smaller, faster-moving shadow will join Callisto’s larger shadow already in transit. Io’s shadow will catch up and pass a short distance north of Callisto’s shadow at 2:25 a.m. EDT (or 6:25 GMT) – and then it will lead the way across Jupiter until 3:22 a.m. EDT (or 7:22 GMT). Callisto’s slower shadow will complete its crossing at 4:21 a.m. EDT.

Saturday, June 26 – Neptune stands still (wee hours)

A diagram of Neptune standing still on June 26, 2021. | SkyNews
Neptune stands still (Chris Vaughan, Starry Night Education)

On Saturday, June 26, the distant blue planet Neptune will pause in its regular eastward motion in front of the stars of eastern Aquarius and begin a retrograde loop (red curve with dates) that will last until early December. The apparent reversal in Neptune’s motion is an effect of parallax produced when Earth, on a faster orbit, begins to pass the planet on the “inside track.” Neptune will be visible in the southeastern sky only during the wee hours of the morning.

Sunday, June 27 – Gibbous Moon and Saturn (wee hours until dawn)

An image of the Gibbous Moon and Saturn on June 27, 2021. | SkyNews
Gibbous Moon and Saturn (Chris Vaughan, Starry Night Education)

Between midnight and dawn on Sunday morning, June 27, look for the yellowish dot of Saturn shining a palm’s width above (or five degrees to the celestial north of) the bright, waning gibbous Moon. When the Moon and Saturn rise over the southeastern horizon at about 11:30 p.m. local time, Saturn will be positioned to the Moon’s upper left. By sunrise, the diurnal rotation of the sky will shift Saturn directly above the Moon. The pair will fit into the field of view of binoculars (red circle), with bright Jupiter positioned well off to their upper left (or celestial east).

Monday, June 28 – Bright Moon between Jupiter and Saturn (post-midnight)

A diagram of the bright Moon between Jupiter and Saturn on June 28, 2021.  | SkyNews
Bright Moon between Jupiter and Saturn (Chris Vaughan, Starry Night Education)

The Moon’s monthly visit with the gas giant planets will continue in the southeastern sky between midnight and dawn on Monday, June 28. After 24 hours the waning gibbous Moon will hop to a position below and between Jupiter on the left (or celestial east) and Saturn on the right (or celestial west). The trio will make a lovely photo opportunity when composed with some interesting landscape.

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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