| Last Sunday, I convinced two friends to stay up until midnight with me and stand in the bitter cold to watch as the full moon underwent a total eclipse. Over the course of several hours, the Earth's shadow crept across the lunar surface, engulfing it in an eerie red glow. The red color is a result of the way light from the sun gets filtered as it passes through Earth's atmosphere; the atmosphere scatters blue light (thus the robin's egg color of a cloudless sky) but redder wavelengths pass on through and get reflected back to us as they bounce off the moon's rocky surface. What we saw -- and you did too, if you watched it -- was the reflected red glow of every sunrise and every sunset on Earth, happening all at once. This phenomenon isn't just cool; it's scientifically valuable. The light that reaches the moon carries in it signatures of the molecules it encountered as it passed through the air around Earth. During the eclipse, astronomer Alison Youngblood, a postdoctoral fellow at NASA Goddard Space Flight Center, used the Hubble Space Telescope to split apart that light and parse it for clues about the chemical composition of Earth's atmosphere. You might ask: doesn't NASA already know what Earth's atmosphere is made of? And you'd be right. But Youngblood and her colleagues hope that this technique, called spectroscopy, might one day be applied to study the atmospheres of more alien worlds. As exoplanets pass in front of their stars, their atmospheres -- if they have them -- will filter a bit of sunlight. With new telescopes, Youngblood said, scientists might study that light to find signs of oxygen, water, and the other chemicals that life needs to live. Had my friends and I been watching the eclipse with a telescope, we could also have seen the tiny flash of light as a meteor struck the lunar surface. Observations first reported by eagle-eyed amateur observers, and supported by professional astronomers, suggest that a small space rock crashed into the western part of the moon. "This is something that people all around the world didn't know that they were going to sign up for," Noah Petro, a research scientist at NASA's Goddard Space Flight Center, told National Geographic. "I said going into the eclipse that this is really cool," he added. "This observation just reinforces how bloody cool it is. If you missed the eclipse -- or liked it so much you want to watch another one -- never fear! The next total lunar eclipse visible from North America will occur in May 2022. -- Sarah | 
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