In case you haven’t heard, there’s a total lunar eclipse coming up this Saturday, April 4, 2015. North Americans will see the eclipse Saturday morning. Australians and Asians will see it Saturday evening. Read more about the April 4 eclipse here.
If you’re in just the right spot on Earth, you might observe the eclipsed moon setting while the sun rises – or the eclipsed moon rising while the sun sets. This is called a selenelion. Celestial geometry says this should not happen. After all, in order for an eclipse to take place, the sun and moon must be exactly 180 degrees apart in the sky, in a perfect alignment known as a syzygy. Such perfection – needed for an eclipse to take place – would seem to make it impossible to view the sun and eclipsed moon above your horizon simultaneously.
But – thanks to atmospheric refraction, the same effect that causes a spoon in a glass of water to appear broken in two – you might actually see images of the sun and totally eclipsed moon, both above your horizon at once, lifted up by the effect of refraction.
You need to be positioned in just the right spot on Earth’s surface to see a selenelion. The chart below shows you who has a shot at it for Saturday’s eclipse:
The eclipse map above is courtesy of the NASA eclipse site. It shows your best chance of witnessing selenelion – a totally eclipsed moon and sun both above the horizon simultaneously – along the very narrow band labeled U3 on the worldwide map above.
In North America, it’s along this narrow U3 path where the totally eclipsed moon is setting in the west as the sun is coming up in the east at sunrise April 4 (Louisiana, Arkansas, Missouri, Iowa, Minnesota; and in Canada: Manitoba and the Northwest Territories).
In Asia, the U3 path marks where the totally eclipsed moon is coming up in the east as the sun is sinking in the west at sunset April 4.
However, you still might be able to see a selenelion of a partially eclipsed moon and the sun both above the horizon from a wider swath of the world. Given clear skies and an unobstructed horizon, anyplace on the worldwide map between U1 (beginning of partial umbral eclipse, before totality) and U4 (end of partial umbral eclipse, after totality) might have some chance of seeing a partially eclipsed moon and the sun in the same sky. Click here for a larger view of the worldwide map.
Click on this handy sunrise/sunset calendar to find out your sunrise/sunset times and moonset/moomrise times. Be sure to to check the moonrise and moonset box.
Even if you’re along the U3 path, or near it, you’ll want to have your binoculars handy because the eclipsed moon will be contending with the light of day.
Moreover, the short duration of the very shallow total lunar eclipse on April 4 (less than five minutes long! shortest eclipse of this century) might make this selenelion of the totally eclipsed moon and the sun all the harder to observe this time around.
Bottom line: Who will see a selenelion – the eclipsed moon and sun in the sky simultaneously – for the April 4, 2015 total eclipse of the moon? Charts and info here.
Deborah Byrd created the EarthSky radio series in 1991 and EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.