A diagram of the Full Milk Blood Supermoon on May 26, 2021. | SkyNews
Full Supermoon (Chris Vaughan, Starry Night Education)

This Week’s Sky: May 24 to 30, 2021

Look for the full blood “supermoon” this week, as a total lunar eclipse is visible from Canada’s west.

Wednesday, May 26 – Full supermoon (at 11:14 GMT)

A diagram of the Full Milk Blood Supermoon on May 26, 2021. | SkyNews
Full Supermoon (Chris Vaughan, Starry Night Education)

The Moon will reach its full phase at 7:14 a.m. EDT (or 11:14 GMT) on Wednesday, May 26. May’s full Moon always shines in or near the stars of Libra or Scorpius. Every culture around the world has developed its own stories about the full Moon, and has assigned special names to each full Moon. The Indigenous Ojibwe groups of the Great Lakes region call the May full Moon Zaagibagaa-giizis “Budding Moon” or Namebine-giizis, the “Sucker Moon;” it signifies a time when Mother Earth again provides healing medicines. The Cree of North America call it Athikipisim, the “the Frog Moon,” the time when frogs become active in ponds and swamps. The Cherokee call it Ahnisguti, the “the Planting Moon,” when the fields are plowed and sown. In European cultures, the Moon is commonly called the full Milk Moon, full Flower Moon, or full Corn Planting Moon. When fully illuminated, the Moon’s geology is enhanced, especially the contrast between the bright, ancient, cratered highlands and the darker, younger, smoother maria. This full Moon will occur nine hours after perigee, the point in the Moon’s orbit when it is closest to Earth, making this the largest supermoon of 2021.

Wednesday, May 26 – Total lunar eclipse (11:11 to 11:26 GMT)

A diagram of the total lunar eclipse May 26, 2021. | SkyNews
Total lunar eclipse (Chris Vaughan, Starry Night Education)

The full Moon of Wednesday, May 26 will also generate a total lunar eclipse. Due to the enlarged “supermoon” effect, this eclipse will barely qualify as a total one. When at maximum eclipse, the northern limb of the Moon will be a scant 0.3 arc-minutes from the northern edge of the umbra, limiting the length of totality to just 14.5 minutes.

Observers should expect the southern half of the Moon, which will extend much deeper into the umbra, to look noticeably darker than the northern half. The Moon will first contact the umbra at 9:44:57 GMT (or 2:45 a.m. PDT) and will last touch the umbra three hours later at 12:52:22 GMT (or 7:52 a.m. CDT).

Western Canada will have a good view of the total lunar eclipse, seeing the Moon set before the eclipse ends. The entire eclipse will be visible across the Pacific Ocean, and from New Zealand and eastern Australia. Except for the northeastern states and provinces, observers in the Americas will see at least the initial stages of this eclipse. Lunar eclipses are completely safe to observe unfiltered with your unaided eyes, binoculars, and telescopes.

Friday, May 28 – Double shadow transit on Jupiter (21:29 to 22:18 GMT)

May 28, 2021, will see a double shadow transit on Jupiter. | SkyNews
Double shadow transit on Jupiter (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. Before dawn on May 28, observers located in Central Asia — unfortunately, not visible from Canada — can see two of those shadows on Jupiter at the same time. At 21:29 GMT, Io’s small shadow will join Ganymede’s large shadow already in transit. The two shadows will cross Jupiter together for 45 minutes until Ganymede’s moves off the planet at 22:18 GMT. Io’s shadow will continue to transit Jupiter until 23:46 GMT.

Friday, May 28 – Mercury passes Venus (after sunset)

Mercury passes Venus on May 28, 2021. (Chris Vaughan, Starry Night Education) | SkyNews
Mercury passes Venus (Chris Vaughan, Starry Night Education)

On the evenings surrounding Friday, May 28, speedy Mercury’s descent sunward (red curve) will bring it very close to much brighter Venus. At their closest approach on Friday, the two planets will be separated by only 25 arc-minutes – close enough to appear together in the eyepiece of a backyard telescope (red circle). (Don’t point optical aids in that area of sky until after the Sun has completely set.) Start looking for magnitude -3.85 Venus above the west-northwestern horizon after about 8:30 p.m. local time. Once the sky darkens sufficiently, magnitude 2.26 Mercury, 280 times dimmer than Venus, will appear to Venus’ left (or celestial south).

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.