Saturn reaches opposition on August 2, 2021. | SkyNews
Saturn reaches opposition on August 2, 2021 (Chris Vaughan, Starry Night Education)

This Week’s Sky: August 2 to 8, 2021

Look for star clusters as the Moon reaches its new phase. Also, Saturn reaches opposition and Jupiter

Monday, August 2 – Saturn at opposition (all night)

Saturn reaches opposition on August 2, 2021. | SkyNews
Saturn reaches opposition on August 2, 2021 (Chris Vaughan, Starry Night Education)

During the wee hours of Monday, August 2 in the Americas, Saturn will reach opposition among the stars of central Capricornus. Objects at opposition are visible all night long — rising at sunset and setting at sunrise — because Earth is positioned between them and the sun. At opposition, Saturn will be at a distance of 830.6 million miles, 1.337 billion kilometres, or 74.3 light-minutes from Earth, and it will shine at magnitude of 0.18 — its brightest for 2021. While planets at opposition always look their brightest, Saturn’s peak magnitude 0.18 will be enhanced by the Seeliger effect, backscattered sunlight from its rings. In a telescope (inset) Saturn will show an apparent disk diameter of 18.6 arc-seconds, and its rings will subtend 43.3 arc-seconds. Saturn’s rings will be tilting more edge-on to us every year until the spring of 2025. This year they are already closed enough for Saturn’s southern polar region to extend beyond them. Opposition is also a fine time to view a handful of Saturn’s moons with a backyard telescope in a dark sky.

Wednesday, August 4 – Juno stands still (overnight)

Juno stands still on August 4, 2021. | SkyNews
Juno stands still on August 4, 2021 (Chris Vaughan, Starry Night Education)

On the night of Wednesday, August 4, the main belt asteroid designated (3) Juno will complete a westerly retrograde loop across the stars of central Ophiuchus. After standing still tonight, it will return to traveling prograde eastward. To see the magnitude 10.7 object, aim your telescope 2.3 degrees above and between the bright stars Saik and Yed Posterior, which outline the lower right (southwestern) corner of the Serpent-Bearer’s body.

Friday, August 6 – Milky Way star clusters (all night)

Milky Way star clusters during new Moon | SkyNews
Milky Way star clusters during new Moon (Chris Vaughan, Starry Night Education)

With the Moon approaching its new phase, this weekend’s darker evenings will be ideal to explore the countless knots and clumps of stars distributed along the Milky Way, many of which were included in Charles Messier’s list of the sky’s best deep sky objects. Scan with binoculars to spot the objects, and then follow up with a backyard telescope at low magnification. Particularly good clusters include Messier 39 and Messier 29 in Cygnus, Caldwell 16 in Lacerta, the Wild Duck cluster (Messier 11) and Messier 26 in Scutum, and the Sagittarius Star Cloud (Messier 24).

Sunday, August 8 – Double shadow transit on Jupiter (from 12:45 to 14:20 GMT)

Double shadow transit on Jupiter on August 8, 2021. | SkyNews
Double shadow transit on Jupiter on August 8, 2021 (Chris Vaughan, Starry Night Education)

In the wee hours of Sunday, August 8 observers with telescopes in the Pacific Ocean and Eastern Asia regions can see the round, black shadows of two of Jupiter’s moons drift across that planet together. At 12:45 a.m. Hawaiian Standard Time or 10:45 GMT, Ganymede’s shadow will begin to follow the Great Red Spot across Jupiter. At 2:45 a.m. HST or 12:45 GMT, Europa’s smaller shadow will begin to cross. Ganymede’s shadow will move off the planet at 4:20 a.m. HST (14:20 GMT). Europa’s shadow will complete its transit an hour later, just as the Ganymede itself clears Jupiter’s limb. Those on Canada’s very western edge may be able to catch the beginning of the double shadow transit around 5:45 a.m. PDT, just before the Sun rises.

Sunday, August 8 – New Moon (at 13:50 GMT)

New Moon on August 8, 2021 | SkyNews
New Moon on August 8, 2021 (Chris Vaughan, Starry Night Education)

The Moon will reach its new phase on Sunday, August 8 at 9:50 a.m. EDT or 13:50 GMT. While new, the Moon is travelling between Earth and the Sun. Since sunlight can only reach the far side of the Moon, and the Moon is in the same region of the sky as the Sun, the Moon becomes unobservable from anywhere on Earth for about a day (except during a solar eclipse). After the new Moon phase Earth’s planetary partner will return to shine in the western sky after sunset.

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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