Mars at Opposition (Chris Vaughan, Starry Night Education)

This Week’s Sky: October 12 to 18, 2020

The biggest highlight is Mars’ opposition October 13, but look for other events like the crescent Moon near Venus and a double shadow transit on Jupiter later in the week.

Tuesday, October 13 all night – Mars at Opposition

Mars at Opposition (Chris Vaughan, Starry Night Education)

Mars will officially reach opposition on Tuesday evening, October 13. On that night, the bright red planet will rise among the stars of western Pisces at sunset, climb to its highest position, 51° above the southern horizon, at 1 am local time, and set at sunrise. At opposition, Mars will shine with a maximum visual magnitude of -2.62. Although it will be slightly farther from Earth (38.57 million miles; 62.07 million km ; 0.415 AU; 3.45 light-minutes) than it was a week prior, Mars will still be an impressive sight in backyard telescopes, showing an apparent disk diameter of 22.57 arc-seconds (Jupiter’s disk spans about 42 arc-seconds). Its Earth-facing hemisphere that night will display its bright southern polar cap, the dark Tyrrhena Terra, Cimmeria Terra, and Sirenum Terra regions, and the lighter toned Hellas Planitia region. Mars oppositions occur approximately every 25.5 months.

Wednesday, October 14 pre-dawn – Old Moon near Venus

Old Moon near Venus (Chris Vaughan, Starry Night Education)

In the eastern sky for several hours preceding sunrise on Wednesday, October 14, the delicate crescent of the old moon will make a pretty sight with the very bright planet Venus. Keep an eye out for Earthshine – sunlight reflected from Earth that is slightly brightening the moon’s darkened region. The moon and Venus will make a lovely photo opportunity, especially when composed with some interesting foreground scenery.

Thursday, October 15 pre-dawn – Morning zodiacal light for mid-northern observers

Morning zodiacal light (Chris Vaughan, Starry Night Education)

For about half an hour before dawn during moonless periods in September and October every year, the steep morning ecliptic favors the appearance of the zodiacal light in the eastern sky. Zodiacal Light is sunlight scattered from interplanetary particles concentrated in the plane of the solar system. From dark-sky sites during the two-week period from now until the October 31 full moon, look above the eastern horizon for a broad wedge of faint light centered on the ecliptic (marked by green line), which descends through the bright star Regulus in Leo and down past Venus. Don’t confuse the zodiacal light with the Milky Way, which is positioned further to the southeast.

For more on the zodiacal light, check out Elizabeth Howell’s piece about the phenomenon.

Friday, October 16 at 19:31 GMT – New Moon and large tides

New Moon and large tides (Chris Vaughan, Starry Night Education)

At its new phase, 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 will be completely hidden from view. This new moon, occurring only 4.5 hours after perigee (the moon’s closest approach to Earth), will trigger large tides around the world.

Saturday, October 17 dusk to 7:43 pm EDT – Rare double shadow transit with the Great Red Spot on Jupiter

From time to time, the Great Red Spot (GRS) and the little round, black shadows cast by Jupiter’s four Galilean moons are visible in backyard telescopes as they cross (or transit) the planet’s disk. On Saturday evening, October 17 observers in the Eastern Time Zone can witness the rare event of two shadows transiting with the Great Red Spot! As the sky darkens, the diffuse shadow of Callisto, the crisp, round shadow of closer-in Io, and the great Red Spot will all be completing a group transit event that began at 5:25 p.m. EDT. The three objects will rotate off of Jupiter’s limb at 7:25 p.m. EDT.

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.