Secrets in the shadows: What lunar eclipses teach us about Earth

Ready for a show? On the night of March 13 into the early hours of March 14, a total lunar eclipse will occur as the moon moves into the Earth's umbra, or shadow, turning the bright white lunar surface an eerie red. (It's no wonder this phenomenon is nicknamed the "blood moon.")

But eclipses aren't only an entertaining astronomical show — they have practical implications for science, too.

While eclipses might've inspired fear in many ancient civilizations, they also inspired scientific discovery. "In ancient Greece, philosophers realized that the Earth is round because the shape of the Earth's shadow on the moon is always curved during an eclipse," Christine Shupla, education manager at the Lunar Planetary Institute, told Space.com. "This is perhaps one of the best-known discoveries from lunar eclipses."

Today, lunar eclipses still teach us a lot about our planet, especially our atmosphere. The reddish color associated with total lunar eclipses occur because sunlight travels through our atmosphere and refracts towards the moon — the atmosphere scatters shorter-wavelength colors like blues and greens, allowing reds and oranges to reach the moon. It's the same reason why sunsets and sunrises feature those beautiful warm tones.

But the moon isn't always the same color during a total lunar eclipse. "How dark and what color the moon appears will tell us more about the changing composition of our own atmosphere," says Shupla. "For instance, sometimes the moon appears reddish, but other times it is much darker and brown-grey, for instance, after a large volcanic eruption has occurred."

We're also able to learn a bit about the moon during lunar eclipses, too, especially from lunar spacecraft. NASA's Lunar Reconnaissance Orbiter (LRO) "has made observations during prior eclipses, mainly focusing on how quickly the surface temperature changes once the moon is in the Earth's shadow," Noah Petro, LRO project scientist, told Space.com. "Some of the observations have shown that the surface doesn't cool down uniformly. That is, there are differences in surface properties around small craters that are only due to changes in the upper few centimeters of the surface, which is something we normally wouldn't detect."

LRO won't be taking active measurements during this eclipse, but it'll still be affected by it. The solar-powered spacecraft won't encounter direct sunlight during the eclipse, which lasts hours, affecting its power supply. "We put the spacecraft into an optimal orbit so that we fully charge our battery prior to the eclipse, turn off the instruments so we don't drain the battery, and then wait until the battery is recharged before turning the instruments back on," says Petro. "Think of it like putting your phone in low-power mode if you are away from a charger for an extended time."

As more spacecraft land on the moon and begin their scientific operations — and, perhaps, as humans return to the moon through NASA's Artemis program — we'll likely continue to learn more about lunar eclipses and their effect on the moon itself.

In the meantime, for us Earth-bound viewers, it's just time to enjoy the show! "Unlike a solar eclipse, which can only be observed by those people along the path that the moon's shadow makes on the Earth, a lunar eclipse can be seen by everyone who can see the moon at that time — everyone on the same side of the Earth," says Shupla. For this March 2025 lunar eclipse, more than a billion people will be able to see the moon turn red.

And keep a sharp eye out — you never know what you might see during the eclipse. "In 2019, observers saw the flash of light from an impact on the moon during an eclipse," says Shupla.

Catch up with the latest lunar eclipse news and events with our lunar eclipse live blog.