August-15-at-1245-am-Rare-Double-Shadow-Transit-with-GRS-on-Jupiter
Rare double shadow transit with Great Red Spot on Jupiter (Chris Vaughan, Starry Night Education)
This Week’s Sky: August 10 to 16, 2020

After the Perseids peak August 11-12, a double shadow transit on Jupiter and the crescent Moon passing close to Venus bring excitement to the weekend.

Tuesday, August 11 at 16:45 GMT – Last quarter Moon

Last quarter Moon (Chris Vaughan, Starry Night Education)

At its last quarter phase, the Moon rises around midnight and remains visible in the southern sky all morning. At this phase, the Moon is illuminated on its western side, towards the pre-dawn Sun. Last quarter moons are positioned ahead of the Earth in our trip around the Sun. About 3.5 hours later, Earth will occupy that same location in space. During the following week, the waning Moon will complete the last quarter of its orbit around the Earth, on the way to new Moon. The moonless evening skies between last quarter and new Moon are ideal for observing deep sky targets.

Tuesday, August 11-12 overnight – Perseid Meteor Shower peak

Perseid Meteor Shower peak (Chris Vaughan, Starry Night Education)

The spectacular Perseid meteor shower, which runs annually between July 17 and August 26, will peak before dawn on Wednesday, August 12. The best time for seeing Perseid meteors starts after midnight, when the shower’s radiant is higher in the northeastern sky. Derived from debris dropped by Comet Swift-Tuttle, this is the most popular shower of the year, delivering up to 100 meteors per hour at the peak. Many Perseids are extremely bright, and leave persistent trails. This year, the last quarter moon will be close to the radiant on the peak morning. That will reduce the number of meteors seen before dawn, but should not adversely affect evening meteor-watching.

For more on the Perseid Meteor Shower, read “Getting ready for the Perseid Meteor Shower” by Elizabeth Howell.

Thursday, August 13 pre-dawn – Venus at greatest angle west of the Sun

Venus at greatest angle west of the Sun (Chris Vaughan, Starry Night Education)

On Thursday, August 13, Venus will reach its greatest separation, 46 degrees west of the Sun, for its current morning appearance. The very bright, magnitude -4.43 planet will be shining in the eastern sky between 2:45 a.m. local time and dawn. Viewed through a telescope, Venus will show a half-illuminated disk (inset).

Friday, August 14 from 10:30 p.m. EDT – Ganymede’s shadow and the Great Red Spot cross Jupiter

Ganymede’s shadow and the Great Red Spot cross Jupiter (Chris Vaughan, Starry Night Education)

From time to time, the Great Red Spot (GRS) and the little round, black shadows cast by Jupiter’s four Galilean moons become visible in backyard telescopes as they cross (or transit) the planet’s disk. Commencing at 10:30 p.m. EDT on Friday evening, August 14 (or 02:30 GMT on Saturday, August 15), observers in the Central Time zone and east of it can watch both Ganymede’s large shadow and the Great Red Spot travel across Jupiter’s northern and southern hemispheres, respectively. The show gets even better after midnight when…

Saturday, August 15 at 4:08 GMT – Rare double shadow transit with Great Red Spot on Jupiter

Rare double shadow transit with Great Red Spot on Jupiter (Chris Vaughan, Starry Night Education)

Commencing a few minutes after midnight EDT on Friday, and continuing during the wee hours of Saturday, August 15, observers in the Americas can witness the rare event of a double shadow transit — accompanied by the Great Red Spot! At 12:06 a.m. EDT (or 04:06 GMT) Io’s small shadow will join Ganymede’s larger shadow and the Great Red Spot already progressing across Jupiter’s northern and southern hemispheres, respectively. The trio will remain visible until Ganymede’s shadow and the Great Red Spot move off Jupiter at about 1:53 a.m. EDT (or 05:53 GMT). Io’s shadow will complete its transit at approximately 2:25 a.m. EDT (or 06:25 GMT).

Saturday, August 15 all day – Crescent Moon close to Venus

Crescent Moon close to Venus (Chris Vaughan, Starry Night Education)

In the eastern sky for several hours before dawn on Saturday, August 15, the waning crescent Moon will be visible just to the upper left (or 3.5 degrees to the celestial north) of the bright planet Venus. The pair, both sitting among the stars forming the feet of Gemini, will fit within the field of view of binoculars (red circle), and will make a nice wide field photograph when composed with interesting landscape. The moon and Venus will not set until 6 p.m. local time on Saturday. Venus is bright enough to see in the daytime, even with unaided eyes. Taking extreme care to avoid the sun, aim your binoculars at the moon and look for Venus’ bright point of light below it. Then try seeing Venus without them. 

Saturday, August 15 overnight – Uranus stands still

Uranus stands still (Chris Vaughan, Starry Night Education)

On Saturday, August 15, the distant blue-green planet Uranus will cease its eastward motion through the distant stars of southern Aries and commence a retrograde loop that will last until January (red path with labeled dates:times). The magnitude +5.75 planet is visible in binoculars in a dark sky. To help you find it, Uranus will be sitting 11 degrees, or 1.5 binoculars fields, to the south of medium–bright Hamal, Aries’ brightest star.

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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