May has always been a good time for skywatching, but this month has a few wonderful events that sweeten the pot.
Top of list is the first total lunar eclipse since Jan. 20-21, 2019. A total lunar eclipse occurs when the moon passes through the earth’s conical two-tiered shadow. The outer, pale shadow is called the penumbra, while the dark, inner shadow is called the umbra.
The eclipse technically starts at 2:46 a.m. May 26 when the moon enters the Earth’s outer shadow (penumbra). At this stage the phenomenon is unobservable. The drama only gets going when the moon crosses the line of the well-defined umbra at 3:45 a.m. during the partial eclipse.
This would be a good celestial event to catch even if you’re not normally an early riser. The total eclipse starts at 5:10 a.m., with the midpoint just nine minutes later. Since the moon will squeak beneath the line of the extreme northeast of the umbra, it’s only briefly immersed in darkness. Totality is a swift 18 minutes, 24 seconds long, and ends at 5:28 a.m. when the partial eclipse begins again on the eastern side of the umbra.
The moon sets at 5:44 a.m. for Colorado skywatchers when the moon is still partially eclipsed, but the episode continues for skywatchers further west until 7:51 a.m. (MDT) when the moon finally leaves the penumbra.
There will be a partial lunar eclipse Nov. 19, and the next total lunar eclipse will be May 16, 2022.
Another rare treat all month is Mercury’s exceptional apparition. If you’ve never seen it, either with the naked eye or with optical aid, now’s your chance.
Usually difficult to observe, the messenger god will climb higher in the sky during the next few weeks. About 45 minutes after sunset May 3, look to the west-northwest to find magnitude ˗0.9 Mercury low above the horizon. Over the next fortnight, Mercury loses brilliance but will compensate by reaching 11 degrees in altitude May 17 when it’s 22 degrees (greatest elongation) east of the sun.
In telescopes, trying to tease out Mercury’s surface features is a perpetual challenge. Because the so-called inferior planet is inside earth’s orbit, the little rock usually hugs the horizon. As one’s gaze drops from zenith to the horizon, the layers of atmosphere increase and light becomes increasingly perturbed by the atmosphere’s characteristic turbulence and dispersion. Naked eye observers have in this exception the rare advantage.
Again looking west-northwest May 3, find Mercury about 2 degrees from Alcyone, the kingfisher, in the Pleiades (Seven Sisters) open star cluster. About 30 minutes after nightfall May 13, witness the moon sidle up to the left of magnitude 0.0 Mercury, the two separated by about 3 degrees. In binoculars, both easily fit into the same field of view.
While you’re here, look for Venus just above the horizon, setting before the end of evening twilight all month long. As the month matures, watch how Mercury approaches the goddess of love until their conjunction May 28. Fading Mercury at magnitude +2.3 and brilliant magnitude ˗3.9 Venus will be separated by less than one-half degree. Note that Venus is about 300 times brighter than Mercury. In scopes, Mercury’s phase is just a sliver of a crescent while Venus appears almost full.
Venus meets the moon in a common but always beautiful encounter just after sunset May 12.
In the predawn hours, high in the south-southeast May 31, the waning gibbous moon is about 5½ degrees below and to the left of magnitude +0.6 Saturn. Magnitude ˗2.4 Jupiter is 18 degrees to the ringed planet’s left.
The moon is full at 5:13 a.m. May 26 and is called the Full Flower Moon to Algonquin speaking peoples, and the Full Moon of the Shedding Ponies to the Arapaho (Hinono’eiteen) nation.