Mars meets Regulus on July 29, 2021. | SkyNews
Mars meets Regulus on July 29, 2021 (Chris Vaughan, Starry Night Education)

This Week’s Sky: July 26 to August 1, 2021

Look for Southern Delta-Aquariid meteors this week. Also, watch as Mars meets Regulus.

Thursday, July 29 – Southern Delta-Aquariids meteors peak (at 5:00 GMT)

Southern Delta-Aquariids meteors peak on July 29, 2021. | SkyNews
Southern Delta-Aquariids meteors peak on July 29, 2021 (Chris Vaughan, Starry Night Education)

The annual Southern Delta Aquariids meteor shower lasts from July 21 to August 23. It will peak before dawn on Thursday, July 29, but it is quite active for a week surrounding that date. This shower, produced by debris dropped from periodic Comet 96P/Machholz, commonly generates 15-20 meteors per hour at its peak. It is best enjoyed from the southern tropics, where the shower’s radiant, in southern Aquarius, climbs higher in the sky. Unfortunately, the bright gibbous Moon shining in the night-time sky on the peak date will severely reduce the number of meteors seen — so continue your meteor-watching on the following few nights, when the Moon will wane and rise later.

Thursday, July 29 – Mars meets Regulus (after Sunset)

Mars meets Regulus on July 29, 2021. | SkyNews
Mars meets Regulus on July 29, 2021 (Chris Vaughan, Starry Night Education)

On Thursday, July 29, Mars will follow in Venus’ footsteps and pass only 38 arc-minutes (less than a finger’s width) above Leo’s brightest star Regulus. They’ll be visible just above the west-northwestern horizon after sunset, with Venus shining brightly to their upper left (or celestial east). White-colored Regulus will shine slightly brighter than reddish Mars. The pair will be close enough to be seen together in a backyard telescope (red circle) for a night or two on either side of Thursday, too; but objects observed that low in the sky will be blurred by Earth’s atmosphere. Observers viewing from equatorial and Southern Hemisphere latitudes will see them higher, and in a darker sky.

Thursday, July 29 – Double shadow transit on Jupiter (from 20:05 to 20:41 GMT)

Double shadow transit on Jupiter on July 29, 2021. | SkyNews
Double shadow transit on Jupiter on July 29, 2021 (Chris Vaughan, Starry Night Education)

From time to time, the small round black shadows cast by Jupiter’s four Galilean moons become visible in amateur telescopes as they cross (or transit) the planet’s disk. On Thursday, July 29, observers with telescopes in Central Europe, the Middle East, and most of Asia can see two shadows crossing Jupiter at the same time. At 11:05 p.m. IDT (or 20:05 GMT) Io’s small shadow will join Callisto’s larger shadow already in transit. About 35 minutes later, at 11:41 p.m. IDT (or 20:41 GMT), Callisto’s shadow will move off the planet, leaving Io’s shadow to complete its crossing almost two hours later.

Saturday, July 31 – Third quarter Moon again (at 13:16 GMT)

Third quarter Moon again on July 31, 2021. | SkyNews
Third quarter Moon again on July 31, 2021 (Chris Vaughan, Starry Night Education)

When a lunar phase occurs in the first few days of a calendar month, it can repeat at month’s end. For the second time in July, the Moon will officially reach its third quarter phase at 9:16 a.m. EDT (or 13:16 GMT) on Saturday, July 31. The ensuing week of moonless evening skies will be ideal for observing deep sky targets.

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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