What happened during last week’s lunar eclipse?
Our recent lunar eclipse, visible in Madison at 5:25 a.m. Wednesday, resulted from the Earth being directly between the sun and the moon, thereby casting a shadow on the moon.
The degree of directness of the shadow determines the degree of completeness of the eclipse.
We were lucky enough to see a total lunar eclipse in this part of the country. In addition, we were fortunate that the sky was perfectly clear as it has been quite often during our recent beautiful autumn weather.
The timing of the eclipse, coupled with the perfectly clear skies, also delivered a rare selenelion – an event characterized by the simultaneous appearance of the sun and the lunar eclipse.
This was visible in Madison at 7:03 a.m. and was captured by the rooftop cameras on the Atmospheric, Oceanic and Space Sciences building on UW-Madison’s campus.
One might wonder how both the sun and the eclipse can be visible at the same time given that the eclipse is a result of the moon being directly in the shadow of the Earth. The answer is that the Earth’s atmosphere refracts, or bends, light that is traveling through outer space because the atmosphere is more dense than the vacuum of deep space.
This bending of light is the same type of phenomena that renders the illusion of a spoon being discontinuous at the fluid-air boundary in a clear glass of water.
The refraction in the selenelion case “lifted” the images of the sun and the eclipsed moon slightly above the horizons.
Had the sunrise been at a slightly different time, or had there been low clouds on either horizon at sunrise on Wednesday, we would not have been lucky enough to catch the rare selenelion in the act.
Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.