Readers of these pages may recall being asked to sit in a swivel chair and spin around with a pencil stuck through a Styrofoam ball in order to visualize the earth-sun-moon relationship.
Well, time to break out the astronomical HB one more time, because there’s a lunar eclipse coming in mid-May and it promises to be a doozy. The last time this area had such a great viewing opportunity for a total lunar eclipse was Jan 21, 2019, back when masks were for Halloween and hand sanitizer was for when the soap ran out. Good times!
But first things first. A total lunar eclipse occurs when the moon is on the side of the earth opposite the sun and enters the innermost cone of earth’s shadow, the umbra. In the Styrofoam visualization, you would be sitting with the sun-lamp on the kitchen counter behind you and the moon-ball in front of you at arm’s length. Your head is the earth. When the three bodies are aligned, the foam moon will be wholly covered by the umbra of your comparatively gigantic space-melon.
Interestingly, if you were standing on the moon during a lunar eclipse, you would see a solar eclipse of the earth, which no human eyes have witnessed. The temperature would drop by 100 degrees almost instantly and the moon’s jagged peaks would appear covered in blood. On the whole I prefer the drama from my back yard.
This particular eclipse will last for 84 minutes in its total phase and 318 minutes from beginning to end. During totality, the moon will appear orange to reddish brown depending on conditions. In contrast with a total solar eclipse, where the airless moon neatly blocks out the sun to leave a very dark disk, diffraction of sunlight by earth’s atmosphere during a lunar eclipse leads to a scattering of light in short wavelengths, as during sunsets when the sun slants through the thickest part of the troposphere. This scattering of the blue part of the visible spectrum allows longer red wavelengths to bend around the earth and gives the moon its characteristic watercolour blush.
To make the most of the event, plan for a pair of binoculars and maybe a blanket. The moon rises at a little after 8:00 PM on May 15 and the action begins around 10:00 PM. If you start early and bring binoculars or a telescope, you can watch darkness creep into the major craters, which can reveal details of the lunar surface not otherwise easily visible. Totality will occur around midnight, and the wee hours of May 16 will see the umbra appear to exit the moon’s right side. During totality, you may as well use the extra darkness to try and spot the elusive “Ghost” Globular Cluster (NGC 5897). This is a tricky target, but you might be able to see it with binoculars at about 4:00 o’clock to the moon and five moon-spans away. Then tell your friends you saw a ghost during an eclipse and see what they say.
Stargazer by Dennis Vanderspek