Bright Moon near Uranus again on August 27, 2021. | SkyNews
Bright Moon near Uranus again on August 27, 2021. (Chris Vaughan, Starry Night Education)

This Week’s Sky: August 23 to 29, 2021

Check out some bright summer constellations this week as the gibbous Moon wanes.

Wednesday, August 25 – Double stars in Lyra’s parallelogram (all night)

Double stars in Lyra’s parallelogram on August 25, 2021 (all night). | SkyNews
Double stars in Lyra’s parallelogram on August 25, 2021 (Chris Vaughan, Starry Night Education)

Each corner of Lyra’s parallelogram is marked by a double star. Zeta Lyrae (ζ Lyr), the corner closest to bright Vega, can be split with binoculars. Both components are white, one star slightly brighter than the other. Each of these stars also has a partner that is too close together to split visually. Moving clockwise, the southwest corner star is Sheliak, the brightest of a tight little grouping of stars visible in a telescope. Sheliak itself has a close-in, dim companion in an eclipsing binary system with a 13-day period. The hot, blue giant star Sulafat sits at the farthest corner from Vega. 620 light-years-distant Sulafat is much larger than Vega, an old star on its way to becoming an orange giant many years from now. Add the slightly dimmer stars Lambda Lyrae and HD 176051 to its south and west, respectively to form a naked-eye triple. Delta Lyrae (δ Lyr) marks the northeast corner of the parallelogram. Sharp eyes and binoculars will easily split the double into one blue and one red star. The blue star is one hundred light-years farther away than the red one; they just happen to appear close together along the same line of sight.

Friday, August 27 – The Teapot tilts west (evening)

The Teapot tilts west on August 27, 2021. | SkyNews
The Teapot tilts west on August 27, 2021. (Chris Vaughan, Starry Night Education)

Moonless August evenings are ideal for viewing the deep sky objects near one of the best asterisms in the sky, the Teapot in Sagittarius. This informal star pattern features a flat bottom formed by the stars Ascella on the left (east) and Kaus Australis on the right (west), a pointed spout on the right (west) marked by the star Alnasl, and a pointed lid marked by the star Kaus Borealis. The stars Nunki and Tau Sagittarii form a handle on the left-hand (eastern) side. The bent line of three stars named Kaus — Borealis (north), Meridianalis (centre), and Australis (south) — refer to the archer’s bow. The asterism reaches maximum height above the southern horizon before 10 p.m. local time, when it will look as if it’s serving its hot beverage, with the Milky Way representing rising steam.

Friday, August 27 – Bright Moon near Uranus again (overnight)

Bright Moon near Uranus again on August 27, 2021. | SkyNews
Bright Moon near Uranus again on August 27, 2021. (Chris Vaughan, Starry Night Education)

For the second time this month, the bright, waning gibbous Moon will pass close to Uranus. After the Moon has climbed high enough to become visible above the treetops late on Friday evening, August 27, look for the magnitude 5.8 planet sitting several finger widths to its upper left (or 3.5 degrees to the celestial northeast) — close enough for them to share the view in binoculars (red circle). While the blue-green dot of Uranus can be seen in binoculars, it’s a good idea to note its location between the stars of Aries and Cetus and hunt for it on a night when the bright Moon has moved away.

Monday, August 30 – A second third quarter Moon (at 07:13 GMT)

When a lunar phase occurs in the first few days of a calendar month, it can re-occur at month’s end. For the second time in August, the Moon will reach its third quarter phase at 3:13 a.m. EDT or 07:13 GMT on Monday, August 30. 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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