2018 features two lunar eclipses, one in January and the other in July. On Jan. 31, there was a spectactular Super Blue Blood Moon eclipse. The July 27 Blood Moon will be the longest total lunar eclipse of the 21st century. 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 July 27 Blood Moon
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.