As a keen chaser of lunar eclipses, it’s been a big disappointment that this year there’s been a real paucity of good events. So far during 2016, skywatchers in this part of the world have “enjoyed” only a couple of barely-visible lunar eclipses. The first on 23 March was just about visible to the naked eye. During the second, which took place last month on 18 August, the outer part of Earth’s shadow grazed the limb of the full moon to create an almost invisible darkening of the lunar surface.
This week, Otago stargazers have a chance to spot the third and final lunar darkening of this year’s triumvirate of what astronomers call penumbral eclipses.
As I’ve mentioned in previous columns, during a penumbral eclipse, Earth blocks sunlight from directly reaching the surface of the moon. As a result the outer part of Earth’s shadow, called its penumbra, falls upon the lunar surface. If an astronaut standing on the moon were to look back at Earth, in the middle of this they would see the sun partially covered by the Earth.
Friday morning’s eclipse begins at 4.53am, and over the next two hours more and more of the moon’s surface will slowly be covered by Earth’s penumbral shadow. With the moon setting at 6:11am and sunrise at 6:48am here in Dunedin, the best part of the eclipse will not be visible from these parts.
However, I will be fascinated to see how much the lunar surface will darken as it moves deeper into Earth’s shadow. This particular eclipse will be harder to see because the moon will be low in the sky, and because as the eclipse advances, the sky will be getting brighter and brighter. Whatever happens, the setting moon should be a very attractive sight just before sunrise on Friday morning.
Unfortunately the next total eclipse of the moon visible from New Zealand won’t take place until 31 January 2018, so we have a while to wait before we can enjoy a blood red moon from Otago.