The last time scientists got a good look at half the Earth in far ultraviolet light came in 1972, when astronaut John Young snapped some photos with a special camera during a spare moment of the Apollo 16 mission to the Moon. Since then, heliophysicists and other scientists interested in the complicated interplay between Earth’s upper atmosphere and outer space have suffered from a paucity of data.

That should finally change later this year, after two NASA-sponsored satellites begin to collect data about the composition and temperature of the ionosphere, ranging from an altitude of about 60km above Earth to more than 1,000km. Scientists used to think the Sun’s radiation dominated the Earth’s extremely tenuous atmosphere at this altitude, but in the last decade they have begun to understand that weather at the planet’s surface also can change conditions far above.

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