2018 will feature two lunar eclipses: one in January, and one in July. Both will be total lunar eclipses, when the full moon passes through Earth's shadow.
Lunar eclipses are visible from anywhere on Earth where it is nighttime. However, the duration of the eclipse you see will depend on how close to moonrise or moonset the eclipse starts in your location. During total lunar eclipses, the moon turns a deep red color when it enters the depths of Earth's shadow. So why doesn't the moon just look like it's in darkness? The color change happens because Earth's atmosphere acts as both a lens and a scattering medium for the sun's light.
As light passes through any medium, it slows down a bit, and bends. So some sunlight gets bent toward the moon's surface as it passes through Earth's atmosphere during an eclipse. If you were standing on the moon, observing the Earth during a lunar eclipse, you'd see a ring of light around the Earth's edge as it passed in front of the sun. In addition to the bending, air scatters short-wavelength light more than longer-wavelength light. Colors such as green and blue have shorter wavelengths than red or orange, so they scatter more — and what's left is the redder end of the spectrum.
The January eclipse
On Jan. 31, the first lunar eclipse of the year will be visible from eastern Europe and eastern Africa, and from there eastward all the way to western South America. In Australia and eastern Asia, the eclipse will occur in late evening or near midnight local time, and this is where the moon will be highest in the sky.
The year's next eclipse will be on the night of July 27, or the wee hours of July 28 depending on the time zone, and the center of the eclipse visibility region is on the Indian Ocean. The eclipse will be fully or partly visible in South America, Africa, central Asia and India, and parts of Australia.
Viewers in New York City will have a chance to catch the January eclipse, but the July event will be below the horizon because it will be daytime in the U.S.
On Jan. 31, people on the U.S. East Coast will be able to see the moon enter Earth's penumbra — the lighter, outer part of the shadow — at 5:51 a.m. local time. The penumbra darkens the moon only a little; it is often hard to notice the difference in the moon's color. The moon will touch the umbra — the darker part of the shadow that produces the distinctive darkening and reddening of the moon during an eclipse — at 6:48 a.m. local time. The moon sets only 16 minutes later, so viewers on the Eastern Seaboard will see only the first part of the eclipse; they won't be able to see our lunar companion transform into a full "Blood Moon.".
As you travel west, the eclipse starts earlier, so more of it will be visible before moonset. Chicagoans, for example, will see the moon touch the penumbra at 4:51 a.m. local time and the umbra at 5:48 a.m., with the moon turning the characteristic red at 6:51 a.m. However, at that point, the moon will be only about three moon diameters above the western horizon, so observers should be sure to find a viewing spot with a clear view. That can make for some dramatic photos as the moon sets at 7:03 a.m.
People on the West Coast will be able to see the whole total phase of the eclipse, which starts at 3:48 a.m. local time. The moon will start to pass out of the umbra at 6:07 a.m. and will set at 6:54 a.m., before it fully emerges from the umbral shadow. (It will be mostly out, but not all the way.)
In Hawaii, the moon will start turning red at 1:48 a.m. local time and completely enter the Earth's umbra and 2:51 a.m. Maximum eclipse occurs at 3:29 a.m. and the moon exits the umbra by 5:11 a.m.
The July eclipse
July's eclipse will be partially visible from the east coast of South America as the moon rises. For example, observers in Rio de Janeiro will see the moon already deep in the umbral shadow of Earth as it comes up at 5:27 p.m. local time. About 45 minutes later, at 6:13 p.m., the moon will touch the edge of the umbra and begin coming out. It will emerge from the umbra at 7:19 p.m., and the penumbral phase will end at 8:28 p.m.
In Europe, observers will be in a similar situation. Londoners will see the moon rise at 8:51 p.m. local time, when the moon will already be in shadow, with the maximum eclipse occurring at 9:21 p.m. The moon will emerge from the umbra at 11:19 p.m.
In Athens, Greece, the penumbral phase of the eclipse will already be underway at moonrise (9:24 p.m. local time), and the umbral phase will start at 10:30 p.m. The maximal eclipse will happens at 11:21 p.m., and the moon will move into the penumbra at 1:19 a.m. By 2:28 a.m., it will have exited the penumbral shadow completely.
Skywatchers in New Delhi and other areas of central Asia will see the eclipse peak near midnight. In New Delhi, the penumbral eclipse will start at 10:44 p.m. local time, when the moon will be well above the horizon, and the umbral phase will begin at 11:54 p.m. The moon will appear to turn red soon after 1:00 a.m. on July 28. It will reach the edge of the umbra at 2:43 a.m. and will emerge from the umbra at 3:49 a.m.
In Cape Town, South Africa, the penumbral eclipse will start at 7:14 p.m. local time, with the umbral phase following at 8:24 p.m. Maximal eclipse occurs at 10:21 p.m.; by that point, the moon will have looked red for about 40 minutes. The umbral phase ends at 11:13 p.m.
In parts of Australia, the moon will be setting as the eclipse progresses. In Melbourne, for example, the moon will touch the umbral shadow at 4:24 a.m. and will become a Blood Moon at about 5:30 a.m. local time; the maximal eclipse will occur at 6:21 a.m. By the time the moon sets, at 7:28 a.m., the moon will be coming out of the umbra, but it won't emerge until the moon is below the horizon.