See Mare Imbrium's golden handle on October 17, 2021 (Chris Vaughan, Starry Night Education)

This Week’s Sky: October 11 to 17, 2021

Watch as the Moon passes gas giant planets and Venus meets Antares in the night sky this week.

Monday, October 11 – Saturn stands still (evening)

Saturn stands still on October 11, 2021. | SkyNews
Saturn stands still on October 11, 2021 (Chris Vaughan, Starry Night Education)

On Monday, October 11, Earth’s faster orbit will cause Saturn to appear to stop moving with respect to the distant stars. The temporary pause in motion marks the end of a westward retrograde loop that began on May 23. After dusk, look for the yellowish, magnitude 0.5 planet in the lower part of the southern sky among the stars of western Capricornus — 15.5 degrees west of much brighter Jupiter.

Monday, October 11 – Ganymede’s shadow and Great Red Spot cross Jupiter (evening)

Ganymede's shadow and Great Red Spot cross Jupiter on October 11, 2021. | SkyNews
Ganymede’s shadow and Great Red Spot cross Jupiter on October 11, 2021 (Chris Vaughan, Starry Night Education)

Between 7 and 10:20 p.m. EDT on Monday, October 11, observers in the Americas with telescopes can watch the large, black shadow of Jupiter’s Moon Ganymede cross Jupiter’s disk, accompanied by the Great Red Spot. That start time corresponds to 8 p.m. CDT, 9 p.m. MDT, and 10 p.m. PDT. For observers in western continent, only the later stages of the event will be occurring in a dark sky.

Tuesday, October 12 – First quarter Moon (at 11:25 p.m. EDT)

First quarter Moon on October 12, 2021. | SkyNews
First quarter Moon on October 12, 2021 (Chris Vaughan, Starry Night Education)

When the Moon completes the first quarter of its journey around Earth on Tuesday, October 12 at 11:25 p.m. EDT (or 03:25 GMT on October 13), its 90-degree angle away from the Sun will cause us to see the Moon exactly half-illuminated on its eastern side. At first quarter, the Moon always rises around mid-day and sets around midnight, so it is also visible in the afternoon daytime sky. The evenings around first quarter are the best ones for seeing the lunar terrain, when it is dramatically lit by low-angled sunlight, especially along the terminator (the pole-to-pole boundary between its lit and dark hemispheres).

Wednesday, October 13 – Half Moon below Saturn (evening)

Half-moon below Saturn on October 13, 2021. | SkyNews
Half-moon below Saturn on October 13, 2021 (Chris Vaughan, Starry Night Education)

The Moon’s monthly visit with the bright gas giant planets Saturn and Jupiter will kick off after dusk on Wednesday, October 13. Before the sky has darkened, try using binoculars (red circle) to find the yellowish dot of Saturn positioned a generous palm’s width to the upper left (or 7 degrees to the celestial northeast) of the half-illuminated Moon. Or wait until Saturn is visible with your unaided eyes, after about 7 p.m. local time. Much brighter Jupiter will be shining off to their upper left all evening.

Thursday, October 14 – Moon between gas giant planets (evening)

Moon between gas giant planets on October 14, 2021. | SkyNews
Moon between gas giant planets on October 14, 2021 (Chris Vaughan, Starry Night Education)

After 24 hours of motion the waxing gibbous Moon will move east to sit below and between Jupiter and Saturn all evening on Thursday, October 14. The trio, with much brighter and whiter Jupiter to the left (celestial east) of 16 times fainter, yellow-hued Saturn, will make a nice widefield photo when composed with some interesting foreground scenery.

Friday, October 15 – Bright Moon below Jupiter (evening) 

Bright Moon below Jupiter on October 15, 2021. | SkyNews
Bright Moon below Jupiter on October 15, 2021 (Chris Vaughan, Starry Night Education)

After sunset on Friday, October 15, look low in the southeast for Jupiter shining a large palm’s width to the upper right (or 8 degrees to the celestial northwest) of the bright, waxing gibbous Moon. Somewhat fainter Saturn will become visible off to their right once the sky darkens more. The Moon will bid adieu to the bright planets after tonight, until November 10-12.  

Saturday, October 16 – Venus kisses Antares (evening)

Venus meets Antares on October 16, 2021. | SkyNews
Venus meets Antares on October 16, 2021 (Chris Vaughan, Starry Night Education)

In the southwestern sky on the evenings around Saturday, October 16, the orbital motion of the bright planet Venus (red path with labelled date:time) will carry it closely above the bright reddish star Antares, which marks the heart of Scorpius. The pair will be binoculars-close from October 11 to 20 (red circle), but at closest approach on Saturday, they’ll share the field of view in the eyepiece of a telescope at low magnification. If you have trouble seeing Antares beside 150 times brighter Venus, try hiding Venus just outside of your field of view.

Sunday, October 17 – Mare Imbrium’s golden handle (all night)

See Mare Imbrium's golden handle on October 17, 2021. | SkyNews
See Mare Imbrium’s golden handle on October 17, 2021 (Chris Vaughan, Starry Night Education)

On Sunday night, October 17, the terminator on the waxing gibbous Moon will fall west of Sinus Iridum, the Bay of Rainbows. The circular, 249-kilometre diameter feature is a large impact crater that was flooded by the same basalts that filled the much larger Mare Imbrium to its east, forming a rounded “handle” on the western edge of that mare. The “golden handle” effect is produced when sunlight strikes the prominent Montes Jura mountain range surrounding Sinus Iridum on the north and west. Sinus Iridum is almost craterless, but hosts a set of northeast-oriented wrinkle ridges that are revealed at this phase.

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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