Mercury at greatest eastern elongation
Mercury at greatest eastern elongation (Chris Vaughan, Starry Night Education)
This Week’s Sky: June 1 to 7

Look for Mercury at greatest eastern elongation this week, and the waning Moon near Jupiter and Saturn.

Monday, June 1 pre-dawn – Jupiter and Saturn bracket a globular cluster

Jupiter and Saturn bracket a globular cluster (Chris Vaughan, Starry Night Education)

In the southern sky in the hours before dawn on the opening days of June, the globular star cluster Messier 75 will be positioned below and between the bright gas giant planets Jupiter and Saturn. In the dark, moonless sky before morning twilight begins, the magnitude 9.2 cluster should be visible in binoculars (red circle) and backyard telescopes as a small, fuzzy patch located approximately 1.5 finger widths below (or 1.5 degrees to the celestial south of) the two much brighter planets.

Wednesday, June 3 evening – Mercury at greatest eastern elongation

Mercury at greatest eastern elongation (Chris Vaughan, Starry Night Education)

In the western sky at 1 p.m. UT on Thursday, June 4, Mercury (orbit shown as red curve) will reach its widest separation, 24 degrees east of the Sun, for the current apparition. (Observers in eastern Asia and Australia will see Mercury’s greatest elongation after sunset there on Thursday, June 4.) With Mercury sitting above the evening ecliptic (green line), this appearance of the planet will offer good views for Northern Hemisphere observers and poor views for observers in the Southern Hemisphere. The optimal viewing times at mid-northern latitudes fall between 9:15 and 10 p.m. local time on Wednesday, June 3. Viewed in a telescope (inset) the planet will exhibit a waning half-illuminated phase.

Thursday, June 4 from 11:22 to 13:52 GMT – Double shadow transit on Jupiter

Double shadow transit on Jupiter (Chris Vaughan, Starry Night Education)

From time to time, the small, round, black shadows cast by Jupiter’s four Galilean moons can be seen in amateur telescopes as they cross (or transit) the planet’s disk for several hours. On Thursday, June 4, observers on the west coast of North America and across the Pacific Ocean region can see a double shadow transit event. At 11:21 GMT, Europa’s smaller shadow will join Ganymede’s larger shadow already in transit. Ganymede’s shadow will move off the planet at 13:52 GMT, leaving Europa’s shadow to complete its crossing just before 14:06 GMT. The Great Red Spot will be visible on Jupiter during the latter stages of the event.

Friday, June 5 at 19:12 GMT – Full Strawberry Moon and penumbral lunar eclipse

Full Strawberry Moon and penumbral lunar eclipse (Chris Vaughan, Starry Night Education)

The Moon will reach its full phase at 3:12 p.m. EDT (or 19:12 GMT) on Friday, June, 5. 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.

This Full Moon will be accompanied by a penumbral lunar eclipse between 17:46 and 21:04 GMT. At greatest eclipse at 19:25 GMT, the Moon will have only dipped about halfway into the Earth’s northern penumbral shadow, barely darkening the Moon’s southern limb. Sorry, Canada — the entire eclipse will be visible from most of Africa, the Middle East, central Asia, and most of Australia. Observers at the eastern edge of South America, where the Moon will rise as the eclipse is ending, will be the only ones in the Americas to see this one.

Saturday, June 6 evening – The Big Dipper as a star pointer

The Big Dipper as a star pointer (Chris Vaughan, Starry Night Education)

In early June the Big Dipper asterism, part of the larger constellation of Ursa Major, sits high in the northwestern sky after dusk. When viewed while facing northeast, the dipper’s bowl opens on the right, towards its Little Dipper counterpart. Its handle extends upward. A line extended from Merak through Dubhe, the stars which mark the bowl’s outer base and rim, respectively, will arrive at medium-bright Polaris, the North Star. Continue the arc of the dipper’s bent handle and “Arc to Arcturus”, the bright orange star in Böotes. Continuing that arc farther lets you “Spike to Spica”, the brightest star in Virgo. A line extended from Mizar at the bend of the handle and diagonally through the dipper’s bowl stars, will “Cast to Castor” in Gemini.

Monday, June 8 pre-dawn – Waning Moon near Jupiter and Saturn

Waning Moon near Jupiter and Saturn (Chris Vaughan, Starry Night Education)

The Moon’s monthly trip past the morning planets begins on Monday, June 8 in the southern sky during the hours before sunrise. The waning gibbous Moon will sit a palm’s width to the lower right (or 6.5 degrees to the celestial southwest) of very bright, white Jupiter and somewhat dimmer, yellowish Saturn. The trio will offer a lovely photo opportunity when composed with some interesting scenery.

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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