Scientists using the Hubble Space Telescope have used the ageing space-based observatory to peer at the Earth during a total lunar eclipse.
It’s the first time a total lunar eclipse—often referred to as a “Blood Moon”—has been observed by a space telescope.
It’s also the first time a total lunar eclipse has been captured in in ultraviolet light that’s invisible to the human eye.
Published today in the Astronomical Journal, the study is an effort to study our own planet as if it was an “exoplanet”—a planet around a distant star.
It’s though that if astronomers practice on Earth they can create tools and techniques that will help them use an upcoming new fleet of powerful telescopes to help them tease-out the presence of life on other planets.
What was Hubble looking for during the total lunar eclipse?
In this case, astronomers were looking for ozone.
“Finding ozone in the spectrum of an exo-Earth would be significant because it is a photochemical byproduct of molecular oxygen, which is a byproduct of life,” said Allison Youngblood of the Laboratory for Atmospheric and Space Physics in Colorado, USA, lead researcher of Hubble’s observations.
Why did Hubble need a total lunar eclipse?
During a total lunar eclipse on January 20, 2019, the researchers used the Moon as a mirror. As it reflected sunlight that had first been filtered through Earth’s atmosphere—which is what happens during a total lunar eclipse—that light’s ultraviolet wavelengths were captured by Hubble.
Why ozone is so important in the hunt for life beyond Earth
Hubble was able to detect ozone in that light, which is seen as a prerequisite for the presence and evolution of life as we know it on Earth—essentially because of its role in photosynthesis. Ozone shields lifeforms from a star’s lethal ultraviolet radiation; without it, there would be no life on Earth.
However, finding ozone in an exoplanet’s atmosphere is no guarantee of life beyond Earth. “You would need other spectral signatures in addition to ozone to conclude that there was life on the planet, and these signatures cannot be seen in ultraviolet light,” said Youngblood.
What is a total lunar eclipse?
Earth is perfectly aligned with the Sun and Moon during a total lunar eclipse, a rare occasion that mimics the “transit” of an exoplanet across a star. One of the most popular ways of finding planets around distant star is to detect slight drops in a star’s light, which denotes that a planet has just “transited” across it.
“To fully characterize exoplanets, we will ideally use a variety of techniques and wavelengths,” said team member Antonio Garcia Munoz of the Technische Universität Berlin in Germany. “This investigation clearly highlights the benefits of the ultraviolet spectroscopy in the characterization of exoplanets.
“It also demonstrates the importance of testing innovative ideas and methodologies with the only habitable planet that we know of to date!”
When is the next total lunar eclipse in North America?
After a short drought there are a few total lunar eclipses coming to North America:
May 26, 2021: “Total Super Blood Flower Moon Eclipse”
The Moon’s lunar surface will turn a reddish color for 15 minutes, and during a “supermoon,” but only for those on the west coast.
May 16, 2022: “Total Blood Flower Moon Eclipse”
A much longer total lunar eclipse will result in the Moon being completely red for 84 minutes.
November 8, 2022: “Total Frosty Blood Moon Eclipse”
Another long “blood moon” for North America, this one will last for 85 minutes.
Wishing you clear skies and wide eyes.