Tuesday, June 1 — Half moon below Jupiter (predawn)
For several hours preceding sunrise on Tuesday, June 1 the waning, half-illuminated moon will shine a slim palm's width to the lower right (or 5 degrees to the celestial south) of the very bright planet Jupiter. The pair will just squeeze into the field of view of binoculars (red circle). Somewhat fainter Saturn will be positioned to the right (celestial west) of them. The trio will make a lovely wide field photograph when composed with some interesting landscape.
Wednesday, June 2 — Third quarter moon (0724 GMT)
The moon will officially reach its third quarter phase at 3:24 a.m. EDT (0724 GMT) on Wednesday, June 2. The name for this phase refers not to the moon's appearance — but to the fact that it has completed three quarters of its orbit around Earth, measuring from the previous new moon. At third quarter our natural satellite always appears half-illuminated, on its western side — toward the predawn sun. It rises in the middle of the night and remains visible in the southern sky all morning. The ensuing week of moonless evening skies will be ideal for observing deep sky targets.
Saturday, June 5 — Transiting shadows merge on Jupiter (2322–0139 GMT)
On Saturday, June 5, lucky observers across most of Europe and Africa will be treated to a rare treat in the eastern predawn sky! From time to time, the small round black shadows cast by Jupiter's four Galilean moons become visible in amateur telescopes as they cross (or transit) the planet's disk. Starting at 2:22 a.m. EEST Io's smaller shadow will join Ganymede's larger shadow already making its way across Jupiter's equatorial region. Because Io orbits closer into Jupiter, its shadow crosses Jupiter faster — allowing it to catch up to, and then temporarily merge with, Ganymede's shadow for a few minutes surrounding 3:34 a.m. EEST (0034 GMT). Io's shadow will then lead Ganymede's shadow across the rest of Jupiter's disk until 04:40 a.m. EEST (0140 GMT). Ganymede's shadow will complete its own passage 40 minutes later.
Sunday, June 6 — Juno at opposition near Messier 10 (all night)
On Sunday, June 6, the major main belt asteroid designated (3) Juno will reach opposition. At that time, Earth will be passing between Juno and the sun, minimizing our distance from Juno and causing it to appear at its brightest and largest for this year. The magnitude 10.1 asteroid will be visible in backyard telescopes all night long. On opposition night, Juno will be traversing the stars of Ophiuchus, and positioned just two finger widths to the left (or 2.5 degrees to the celestial east) of the bright globular star cluster Messier 10. On June 17-18 Juno's westward motion (red path with labeled date:time) will carry it through that cluster, allowing both objects to appear together in telescopes for several nights.
Monday, June 7 — Old moon near Uranus (before sunrise)
Look low in the east-northeastern sky before dawn on Monday, June 7 to see the old crescent moon shining three finger widths below (or 3 degrees to the celestial southeast) of the magnitude 5.9 planet Uranus — close enough for them to fit together in the field of view of binoculars (red circle). Observers viewing the duo from more southerly latitudes will see them more easily since they'll be higher and in a darker sky.
Thursday, June 10 — New moon and annular solar eclipse (1052 GMT)
The first solar eclipse of 2021 occurs ten days before the June solstice and 2.3 days past lunar apogee, resulting in an annular eclipse. The moon's shadow will first touch Earth along the northern shore of Lake Superior at 5:55 a.m. EDT (0955 GMT), and then it will sweep across northwest Greenland and the North Pole. The eclipse will end when the moon's shadow lifts off the Earth in northern Siberia at 7:29 a.m. EDT (1129 GMT). The partial eclipse will be visible in eastern North America, the North Atlantic, and most of Europe and Asia. When the sun rises at about 5:30 a.m. EDT in the Great Lakes region, it will already be at mid-eclipse and will be approximately 75% obscured by the moon. The partial phase will persist until the moon completely moves off the sun at approximately 6:30 a.m. EDT. (Use Starry Night to look up your local circumstances.) Proper solar filters will be required to view any portion of this eclipse in person; however, it will be widely available to watch online.
Friday, June 11 — Young moon meets Venus (after sunset)
Look low in the west-northwestern sky after sunset on Friday, June 11 where the very young crescent moon will be positioned several finger widths to the lower right (or 3 degrees to the celestial west) of the very bright planet Venus — allowing both objects to appear together in binoculars (red circle). Watch for Earthshine illuminating the darkened portion of the moon. The scene will make a lovely wide field photograph when composed with some interesting landscape.
Saturday, June 12 — Double shadow transit on Jupiter (02:41–03:33 GMT)
The next significant Jupiter shadow transit event of June will occur in the predawn sky on Saturday, June 12, when observers with telescopes in the Atlantic Ocean region, Western Europe, and Western Africa can see two shadows on Jupiter. At 3:43 a.m. BST (0241 GMT), Ganymede's large shadow will join Io's smaller shadow already in transit. Io's shadow will move off the planet at 4:34 a.m. BST (0334 GMT), leaving Ganymede's shadow to complete its crossing hours later.
Sunday, June 13 — Crescent moon above Mars (early evening)
After sunset on Sunday, June 13, look low in the west-northwestern sky for a young crescent moon shining prettily just a few finger widths above (or 3 degrees to the celestial northeast of) the reddish dot of Mars. The moon and planet can be viewed together in binoculars (red circle) before Mars sets at about 11:30 p.m. in your local time zone.
Thursday, June 17 — First quarter moon (0354 GMT)
When the moon completes the first quarter of its orbit around Earth at 11:54 p.m. EDT on Thursday, June 17 (0354 June 18 GMT) its 90-degree angle away from the sun will cause us to see it half-illuminated — on its eastern side. At first quarter, the moon always rises around noon and sets around midnight, so it is also visible in the afternoon daytime sky. The evenings surrounding first quarter are the best ones for seeing the lunar terrain when it is dramatically lit by low-angle sunlight.
Sunday, June 20 — June solstice (0332 GMT on June 21)
On Sunday, June 20 at 11:32 p.m. EDT (0332 GMT on Monday, June 21), the sun will reach its northernmost declination for the year, resulting in the longest daylight hours of the year for the Northern Hemisphere and the shortest daylight hours of the year for the Southern Hemisphere. The solstice marks the beginning of the summer season in the Northern Hemisphere, and winter in the Southern Hemisphere.
Monday, June 21 — Jupiter reverses direction (wee hours)
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)
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 (1839 GMT)
The moon will officially reach its full phase on Thursday, June 24 at 2:39 p.m. EDT (1839 GMT). 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 indigenous 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 (05:04–0722 GMT)
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 (0504 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 (0722 GMT). Callisto's slower shadow will complete its crossing at 4:21 a.m. EDT (0821 GMT).
Saturday, June 26 — Neptune stands still (wee hours)
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)
Between midnight and dawn on Sunday morning, June 27, look for the yellowish dot of Saturn shining a palm's width above (or 5 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)
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.