Europa shadow transit with Great Red Spot (Chris Vaughan, Starry Night Education)

This Week’s Sky: July 20 to 26, 2020

Comet NEOWISE climbs higher in evening sky, Saturn reaches opposition and Mercury reaches greatest western elongation.

All week – Comet NEOWISE climbs higher in evening sky

The path of Comet C/2020 F3 (NEOWISE) during the week of July 19 to 26, 2020, shown here at 10 pm local time. For reference, the Big Dipper sits at top centre. (Chris Vaughan, Starry Night Education)

Comet C/2020 F3 NEOWISE will continue to be visible after sunset this week. It’s beginning to diminish in brightness, but you can still see it with your unaided eyes against a dark sky. All you will need are clear skies to the northwest and a view that is free of obstructing trees and buildings. If you live in an apartment with western or north-facing windows or a balcony, you’re in luck.

The easy way to find the comet in evening is to look for the bright stars Dubhe and Merak high in the northwestern sky. They mark the bottom edge of the Big Dipper’s bowl. The comet will be directly below them Monday evening. If your view to the north is unobstructed, you should be able to watch the comet until at least midnight.

Each night this week, the comet will shift left with respect to the Big Dipper’s stars. On Wednesday, the night when the comet is closest approach to Earth, the path of Comet NEOWISE will carry it just a couple of finger widths above a pair of medium-bright stars named Tania Australis and Tania Borealis. They form the bear’s rear paws. On the coming weekend, the comet will sit about 1.5 fist diameters to the lower left of the Big Dipper’s bowl star Phecda.

For more on the comet this week, click here.

Monday, July 20 at 17:33 GMT – New Moon

New Moon (Chris Vaughan, Starry Night Education)

At its new phase on Monday, July 20 at 1:33 p.m. EDT, or 17:33 GMT, the Moon will be travelling between the Earth and the Sun. Since sunlight is only shining on the side of the Moon aimed away from us, and the Moon is in the same region of the sky as the Sun, the Moon will be hidden from view everywhere on Earth for about a day.

Monday, July 20 all night – Saturn at opposition

Saturn at opposition (Chris Vaughan, Starry Night Education)

On Monday, July 20, Saturn will reach opposition among the stars of eastern Sagittarius — rising at sunset, and remaining visible all night long. At opposition, Saturn will be located 836.6 million miles, 1.346 billion kilometres, or 74.9 light-minutes from Earth, and it will shine at its maximum brightness of magnitude 0.13 for 2020. In telescopes (inset) Saturn will show its greatest apparent disk diameter of 18.5 arc-seconds — and its rings, which will be narrowing every year until the spring of 2025, will span 43 arc-seconds. A handful of Saturn’s moons are readily observable with backyard telescopes in a dark sky. This year, Saturn will share the sky with brighter Jupiter.

Wednesday, July 22 pre-dawn – Mercury at greatest western elongation

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

On Wednesday, July 22, the planet Mercury will reach a maximum angle of 20 degrees from the Sun, and peak visibility for this morning apparition. Look for the swiftly-moving planet sitting very low in the east-northeastern sky between about 5 and 5:30 a.m. in your local time zone. In a telescope (inset) Mercury will show a 37-per-cent illuminated, waxing crescent phase. Mercury’s position below the morning ecliptic (green line) will make this apparition less than ideal for Northern Hemisphere observers, but a good showing for those located near the Equator, and farther south.

Friday, July 24 from 05:20 to 08:00 GMT – Europa shadow transit with Great Red Spot

Europa shadow transit with Great Red Spot (Chris Vaughan, Starry Night Education)

For the second time this month, observers in the Americas can watch Europa’s shadow and the Great Red Spot transit Jupiter together in their telescopes. Europa’s shadow will join the red spot, already at mid-transit, at 1:20 a.m. EDT, or 05:20 GMT. The spot will vanish around Jupiter’s edge at about 3:40 a.m. EDT, or 7:40 GMT, leaving Europa’s shadow to complete its passage about 20 minutes later.

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.