The seemingly impossible to happen on Saturday's eclipse

Saturday's Lunar Eclipse Will Include 'Impossible' Sight

For most places in the United States and Canada, there will be a chance to observe an unusual effect, one that celestial geometry seems to dictate can't happen. The little-used name for this effect is a "selenelion" (or "selenehelion") and occurs when both the sun and the eclipsed moon can be seen at the same time.


A selenelion or selenehelion occurs when both the Sun and the eclipsed Moon can be observed at the same time. This can only happen just before sunset or just after sunrise, and both bodies will appear just above the horizon at nearly opposite points in the sky. This arrangement has led to the phenomenon being referred to as a horizontal eclipse. It happens during every lunar eclipse at all those places on the Earth where it is sunrise or sunset at the time. Indeed, the reddened light that reaches the Moon comes from all the simultaneous sunrises and sunsets on the Earth. Although the Moon is in the Earth’s geometrical shadow, the Sun and the eclipsed Moon can appear in the sky at the same time because the refraction of light through the Earth’s atmosphere causes objects near the horizon to appear higher in the sky than their true geometric position