In the words of Carl Sagan, "The Earth is a very small stage in
a vast cosmic arena." But to us, it's everything. The place
where we live, love, work and play. The place where we are born
and where we die. From space, Earth is big, blue and beautiful;
fragile and inspiring. It's the only planet we've ever been to.
In honor of Earth Day, take a moment to enjoy some spectacular
images of our home, available for download, in our gallery
below. And take a moment to appreciate the only home we've ever
known. LATEST IMAGE: Nocturnal wonders These night-shining
clouds were spotted over Billund, Denmark on July 15, 2010.
These rare clouds are technically called "noctilucent" or "polar
mesospheric" clouds, and form at high altitudes, 80 to 85
kilometers (50 to 53 miles) high, where the mesosphere is
located. The clouds' high position in the atmosphere allows them
to reflect sunlight long after the sun has dropped below the
horizon. They only form when the temperature drops below –130
degrees Celsius (-200 degrees Fahr