Observers of Wednesday morning’s total lunar eclipse might be able to catch sight of an extremely rare cosmic sight.
On Oct. 8, Interested skywatchers should attempt to see the total eclipse of the moon and the rising sun simultaneously. The little-used name for this effect is called a “selenelion,” a phenomenon that celestial geometry says cannot happen.
And indeed, during a lunar eclipse, the sun and moon are exactly 180 degrees apart in the sky. In a perfect alignment like this (called a “syzygy”), such an observation would seem impossible. But thanks to Earth’s atmosphere, the images of both the sun and moon are apparently lifted above the horizon by atmospheric refraction. This allows people on Earth to see the sun for several extra minutes before it actually has risen and the moon for several extra minutes after it has actually set. [How to See the Total Lunar Eclipse (Visibility Maps)]