“What’s wrong with the moon?!”
That was the question I overheard as I walked back to my dorm on Sunday night.
This past Sunday night and Monday morning there was a complete lunar eclipse of the moon. Many of you probably knew that, too, as I was in good company watching the celestial show from the lawn behind Maple Street Station. An eclipse is caused by the Earth moving between the moon and sun casting a shadow over the moon. Since the moon does not produce its own light and merely reflects sunlight, it appears completely non-existent in the sky. What you may not know was that this was the final of four lunar eclipses that have all happened within a year and a half. It is also worth mentioning that these eclipses have all happened on the Jewish feasts of Passover (The Feast of Unleavened Bread) and Sukkot (The Feast of Tabernacles).
This tetrad of lunar eclipses has happened before, with the most recent happening in 2003-2004 and many times prior. In total there will be eight lunar tetrads this century, the most there can be in century. The last time this happened was during the 9th century!
The red tinge to the moon you may have saw, giving this type of moon its name “blood moon”, is actually caused by Rayleigh scattering. This is the same mechanism that gives the sky a blue color and sunsets their reds and oranges. Rayleigh scattering is simply the atmosphere and all those little water droplets that make up the vast majority of it, filtering out the blues and greens in light and bending the red light from the sun on to the moon, which then in turn reflects off the moon and into your eye. And hey, presto, the moon appears red.
On top of being a blood moon, this was also a super moon! A super moon is caused by the orbit of the moon around the sun. While we like to think of this orbit as round with Earth perfectly in the center, it really isn’t. It is more elliptical, or egg shaped. This means that at certain times the moon is closer to earth then at other times. Meaning it appears bigger and brighter in the sky.
While it was a lot of fun watching super-blood-lunar-eclipse, we have to wait until 2033 until the next super-blood-lunar-eclipse. Perhaps maybe some of us will have children watching it with us who will ask us “what’s wrong with the moon?!”