During the night of March 13, most of North and South America will be treated to a total lunar eclipse, an event popularly referred to as a Blood Moon. The event is aptly named — the Moon is cast in a dark red, brown, or orange color during totality, giving it an eerie appearance in the night sky.
A lunar eclipse occurs when the Moon lies directly behind Earth from the Sun, an arrangement that occurs two or three times per year. Any given location on Earth is graced with a total lunar eclipse every 2.5 years on average. One might think that this should occur every month at Full Moon, but the Moon’s orbital plane is not exactly in line with the Earth’s plane around the Sun, so alignments occur less frequently. When the Moon only passes through the edges of the shadow cast by the Earth, we experience a penumbral eclipse, in which the Moon will darken almost imperceptibly.
The Moon’s red color is due to how different colors of light scatter in Earth’s atmosphere — bluer wavelengths scatter more than redder wavelengths, so more red light is refracted onto the lunar surface. How red and dark the Moon appears depends on the amount of dust and aerosols in Earth’s atmosphere at the time. Lunar eclipses in the months and years following major volcanic eruptions are often dark due to the volcanic ash lofted into the atmosphere.
Unlike solar eclipses, where totality only lasts a few minutes, the darkest phase of lunar eclipses can last for more than an hour. For this month’s eclipse, we will enjoy 1 hour 5 minutes of totality. This gives skywatchers plenty of time to observe and take photos. During the partial phase, bites are taken out of the Moon as it slips into Earth’s shadow, going through all its phases in only an hour. During totality, the Moon appears as though a colored velvet blanket was laid on it, a beautiful and haunting sight against the black night sky. Binoculars or a telescope of any size can make the experience even more special.
For the shutterbugs among us, a DSLR on a tripod with a cable release will achieve the best images, although you can try with a smartphone as well. Depending on how dark the Moon is during totality, exposures of several seconds may be required. I often use a 70-300mm zoom lens atop a sky-tracking device such as a Vixen Polarie or Sky-Watcher Star Adventurer, but you can also adjust the camera’s position on a tripod manually as the Moon moves across the sky and keep the exposure times short enough to avoid streaking.
Make sure you have a clear view of the Moon ahead of time using the PhotoPills app or a planetarium app such as SkySafari. You will have plenty of time during the eclipse to find the right ISO, f-stop, and exposure settings, so take a variety of test shots to make sure you get the ones you want. You don’t need an f/1.4 lens to take great lunar eclipse photos; in fact, you may want to stop down your lens a bit to improve the appearance of background stars and keep from over-saturating during the partial phase. Taking photos throughout the eclipse and composing a final image that showcases all the phases is a fun way to share it with your friends who are clouded out. I recommend shooting in RAW so you can more easily modify the images later. Use “Live View” if your camera has it to bring the Moon into focus, and then tape down the focuser and zoom so they don’t move during the eclipse.
Lunar eclipses are absolutely worth staying up late for — they may not have the awe and drama of a solar eclipse, but the velvety red button in the sky is hard to tear your eyes from. Take plenty of photos with your DSLR or smartphone, or just sit back and enjoy the spectacle with binoculars or just your eyes.
