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Eco-photos of the week: June 19-25

One side of Mercury descends into darkness and the planet's terminator, the line between night and day, is in full view.

Photo: NASA/Johns Hopkins University Applied Physics Laboratory

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Mercury's terminator

In this color photo taken by the Messenger spacecraft and released by NASA on June 21, one side of Mercury descends into darkness and the planet's terminator — the line between night and day — is in full view.

Mercury spins around its axis three times for every two orbits around the Sun, meaning that three days is equivalent to two years on Earth.