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

This Week’s Sky: May 25 to 31

The highlights of this week include a double shadow transit on Jupiter, giving early risers in Canada a great show.

Wednesday, May 27 overnight – Juno stands still near Delta Virginis

Juno stands still near Delta Virginis (Chris Vaughan, Starry Night Education)

On Wednesday, May 27, the main belt asteroid Juno will cease a westward retrograde loop (red path) that began in February, and resume prograde motion in front of the distant stars. On that date, the magnitude 10.6 object will be located in northwestern Virgo, just under 6 degrees (red circle) to the west of the medium-bright star Delta Virginis.

Thursday, May 28 from 8:48 to 9:52 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 become visible in amateur telescopes as they cross (or transit) the planet’s disk. Starting at 8:48 GMT (4:48 a.m. EDT) on Thursday, May 28, observers in the Americas can see two of those shadows cross the northern hemisphere of Jupiter at the same time. At that time, Europa’s smaller shadow will join Ganymede’s larger shadow already in transit. 64 minutes later Ganymede’s shadow will move off the planet at 9:52 GMT (5:52 a.m. EDT), leaving Europa’s shadow to complete its crossing just before 11:33 GMT (7:33 EDT). The latter stages of the event favour observers in Canada’s west, where the sky will be darker.

Saturday, May 30 at 3:30 GMT – First quarter Moon

First quarter Moon (Chris Vaughan, Starry Night Education)

The Moon will reach its first quarter phase on Saturday, May 30 at 3:30 GMT. At that time, the relative positions of the Earth, Sun and Moon will cause us to see the moon half illuminated — on the western (right-hand) side. Sunlight striking the moon at a shallow angle produces spectacularly illuminated landscapes along the pole-to-pole terminator that separates the lit and dark hemispheres. First quarter moons rise at noon and set at midnight, so they are visible starting in the afternoon hours. The term “first quarter” refers not to the Moon’s appearance, but the fact that our natural satellite has now completed one quarter of its orbit around Earth, counting from the last new Moon.

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.