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taking advantage of the total lunar

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eclipse of january 2019 astronomers

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using nasa's hubble space telescope have

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detected ozone in earth's atmosphere

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in this observation hubble did not look

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at earth directly instead astronomers

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use the moon as a mirror to reflect

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sunlight that passed through earth's

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atmosphere

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this method serves as a proxy for how

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they will observe planets around other

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stars in search for worlds similar to

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our own

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though numerous ground-based

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observations of this kind have been done

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previously this is the first time

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ultraviolet light passing through

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earth's atmosphere was observed from

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space

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the measurements from this experiment

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detected the strong spectral fingerprint

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of ozone

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on earth photosynthesis over billions of

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years is responsible for our planet's

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high oxygen levels and thick ozone layer

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that's one reason why scientists think

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ozone or oxygen could be a sign of life

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on another planet

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but finding ozone on distant worlds

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isn't an easy task

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ultraviolet observations like this can

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best be conducted from space telescopes

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above the limiting effects of looking

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through earth's skies because ozone

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blocks most ultraviolet light from

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beyond the atmosphere

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one of nasa's major goals is to identify

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habitable and inhabited planets but how

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would we know whether a distant planet

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has ozone or not

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the atmospheres of some extrasolar

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planets can be probed if that distant

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world passes across the face of its

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parent star called a transit

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during a transit starlight filters

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through the backlit exoplanet's

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atmosphere

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tell-tale signature by filtering out

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certain colors of starlight astronomers

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have used hubble to observe the

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atmospheres of several gas giant planets

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that transit their stars but terrestrial

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planets are much smaller objects and

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their atmosphere thinner like the skin

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on an apple

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therefore teasing out these signatures

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is much more difficult

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to prepare for future studies with

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larger telescopes astronomers used

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hubble to conduct experiments on a much

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closer and only known inhabited

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terrestrial planet earth

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our planet's perfect alignment with the

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sun and moon during a total lunar

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eclipse mimics the geometry of a

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transiting terrestrial planet with its

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star

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but the observations were also

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challenging because the moon is very

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bright and its surface is not a perfect

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reflector because it is modeled with

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bright and dark areas

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the moon is also so close to earth that

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it appears to move very quickly in the

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sky making it harder for hubble to stay

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pointed at the same location however in

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spite of the challenges the experiment

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was an incredible success and hubble is

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supporting the ongoing quest to find

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planets that are similar to our own and