This month the western part of the country gets to see an eclipse of the Moon—and next month the northeast will glimpse an eclipse of the Sun. (see the June Sky Talk). This will largely be a “horizon-hugging” event, with the most dramatic views being along the coast.
Lunar eclipses occur when the Earth passes between the Moon and Sun, casting its long back shadow into space and onto our satellite. Our planet actually has two shadows—the dark inner one called the “umbra” and a very faint outer one called the “penumbra.” It’s the umbra that’s seen during a lunar eclipse. This month’s event occurs on the early morning of Wednesday May 26th with the Moon just inside the edge of the umbra, resulting in a very short duration eclipse.
Since this eclipse occurs with the Moon about to set in the west, we list the event times for several cities along the coast. A clear unobstructed view of the horizon will be needed to fully enjoy this spectacle in each case. In San Diego partial eclipse begins at 2:44 a.m. PDT with the Moon 28 degrees above the horizon. Total eclipse occurs at 4:11 with our satellite 16 degrees high and ends at 4:25 at 14 degrees up. The Moon will have set at 5:52 before the partial phase ends. In San Francisco the times for partial eclipse, and the beginning and end of totality, and elevations are all the same as for San Diego— but the end of totality will be visible at 5:52 with the Moon just a degree above the horizon!
Moving north along the coast, for Portland and Seattle the times for each phase also remain the essentially the same—but the altitudes are 19, 11, and 9 degrees and 17, 9, and 8 degrees, respectively. In both cases the Moon will set at 5:38 before the eclipse ends. As you move away from the coast, the eclipse will still be visible at approximately the same times but the altitudes above the horizon compared to the coast get lower the further east you go. In Las Vegas, for example, it will be 25, 13, and 11 degrees with the Moon setting before the eclipse ends.
Lunar eclipses are famous for their vivid copper or blood-red color due to refraction of sunlight in the Earth’s atmosphere shining onto the Moon. The actual color seen depends on the amount of cloud cover around the Earth, and also any volcanic dust or smoke from forest fires aloft. Since this is essentially a low-altitude event, our satellite will likely appear extra ruddy due to atmospheric obscuration near the horizon. And something to keep in mind as you watch this spectacle. We’ve spoken here of the Moon setting—but actually it’s the horizon rising, as our Spaceship Earth spins eastward!
— James Mullaney
Former assistant editor at Sky & Telescope magazine & author of nine books on stargazing. His latest, Celebrating the Universe!, is available from HayHouse.com.