For the second time this year, the Moon will swim into the shadow of the planet you stand on, or sleep on. If you’re in America and especially if you forgot to do so at the total lunar eclipse of April 5, arise and go outside or at least to a Moon-facing window in the early dark hours of Wednesday October 8.
Totality begins at 10:24 Universal Time, which is 3:24 by Pacific Zone clocks, 6:24 in the eastern U.S. And totality lasts an hour and a minute. So those in the American west can see the whole course of it, and those farther west still, in Hawaii and eastern Asia, can see it more conveniently, in the early night. On the American east coast, the eclipsed Moon goes down, and the Sun comes up, before the spectacle is over. Europe has already rotated out of view of it into daylight.
There are awe-inspiring aspects to a lunar eclipse that get mentioned every time – the exciting moment when the dark hand of the shadow first touches the bright Moon’s edge, and the later one when the last bright point vanishes; the varying colors of the shadow, from black to dusky browns and golds, depending on Earthly clouds and smog through which light is being refracted onto the Moon; the great curve of the shadow’s edge, which made the Greeks realize that it is cast by a larger globe. I think it is useful to imagine being on the Moon, looking back, or rather looking up at the complementary eclipse of the Sun by the Earth.
This explains the sharp difference between the inner and outer shadow – for the shadow does have these two parts. Eclipse really begins more than two hours before that totality-beginning moment; it begins when the outer shadow or penumbra touches. We can’t see it happen, because that outer part of the outer shadow is too faint; but for your other self lying on your back in the middle of the Moon and looking up – or lying on your front with your chin propped on your hands in one of the craters near the Moon’s north pole, the craters that may have water ice in them, and gazing at the Sun and huge black Earth above your southern horizon – this is the moment when the Earth touches the Sun. Then the Earth slides over more of the Sun, and a sort of slight evening begins for you; the landscape around you slightly grays. The landscape is in the penumbra. But it’s only slightly darker, because the Sun is still blazing at you; you are still in full day, not night. You are watching the Sun set on that horizon which is the Earth. The Sun is so brilliant that, on Earth, day begins when the merest point of it appears over the horizon, and doesn’t end till the last drop of it expires at the horizon. Just so, for the viewer on the Moon, it is full day until the last point of the Sun disappears. All that landscape on the Moon that is in penumbral shadow is in daylight. This is why the contrast between penumbra and umbra – between partial and total eclipse – is so sharp.