The moon is utterly familiar. We see it all the time, in the blue sky during the day, among the stars and planets at night. Every child knows the outlines of the moon's lava seas: they trace the Man in the Moon or, sometimes, a Rabbit.
This familiarity goes beyond appearances. The moon is actually made of Earth. According to modern theories, the moon was born some 4.5 billion years ago when an oversized asteroid struck our planet. Material from Earth itself spun out into space and coalesced into our giant satellite.
Yet when Apollo astronauts stepped out onto this familiar piece of home, they discovered that it only seems familiar. From the electrically-charged dust at their feet to the inky-black skies above, the moon they explored was utterly alien.
Thirty years ago their strange experiences were as well-known to the public as the Man in the Moon. Not anymore. Many of the best tales of Apollo have faded with the passage of time. Even NASA personnel have forgotten some of them.
Now, with NASA going back to the moon in search of new tales and treasures, we revisit some of the old ones, with a series of Science@NASA stories called "Apollo Chronicles." This one, the first, explores the simple matter of shadows.
Dark Shadows
On the next sunny day, step outdoors and look inside your shadow. It's not very dark, is it? Grass, sidewalk, toes--whatever's in there, you can see quite well.
Your shadow's inner light comes from the sky. Molecules in Earth's atmosphere scatter sunlight (blue more than red) in all directions, and some of that light lands in your sha
dow. Look at your shadowed footprints on fresh sunlit snow: they are blue!
Without the blue sky, your shadow would be eerily dark, like a piece of night following you around. Weird. Yet that's exactly how it is on the Moon.
To visualize the experience of Apollo astronauts, imagine the sky turning completely and utterly black while the sun continues to glare. Your silhouette darkens, telling you "you're not on Earth anymore."
Shadows were one of the first things Apollo 11 astronaut Neil Armstrong mentioned when he stepped onto the surface of the moon. "It's quite dark here in the shadow [of the lunar module] and a little hard for me to see that I have good footing," he radioed to Earth.
The Eagle had touched down on the Sea of Tranquility with its external equipment locker, a stowage compartment called "MESA," in the shadow of the spacecraft. Although the sun was blazing down around them, Armstrong and Buzz Aldrin had to work in the dark to deploy their TV camera and various geology tools.
This familiarity goes beyond appearances. The moon is actually made of Earth. According to modern theories, the moon was born some 4.5 billion years ago when an oversized asteroid struck our planet. Material from Earth itself spun out into space and coalesced into our giant satellite.
Yet when Apollo astronauts stepped out onto this familiar piece of home, they discovered that it only seems familiar. From the electrically-charged dust at their feet to the inky-black skies above, the moon they explored was utterly alien.
Thirty years ago their strange experiences were as well-known to the public as the Man in the Moon. Not anymore. Many of the best tales of Apollo have faded with the passage of time. Even NASA personnel have forgotten some of them.
Now, with NASA going back to the moon in search of new tales and treasures, we revisit some of the old ones, with a series of Science@NASA stories called "Apollo Chronicles." This one, the first, explores the simple matter of shadows.
Dark Shadows
On the next sunny day, step outdoors and look inside your shadow. It's not very dark, is it? Grass, sidewalk, toes--whatever's in there, you can see quite well.
Your shadow's inner light comes from the sky. Molecules in Earth's atmosphere scatter sunlight (blue more than red) in all directions, and some of that light lands in your sha
dow. Look at your shadowed footprints on fresh sunlit snow: they are blue!Without the blue sky, your shadow would be eerily dark, like a piece of night following you around. Weird. Yet that's exactly how it is on the Moon.
To visualize the experience of Apollo astronauts, imagine the sky turning completely and utterly black while the sun continues to glare. Your silhouette darkens, telling you "you're not on Earth anymore."
Shadows were one of the first things Apollo 11 astronaut Neil Armstrong mentioned when he stepped onto the surface of the moon. "It's quite dark here in the shadow [of the lunar module] and a little hard for me to see that I have good footing," he radioed to Earth.
The Eagle had touched down on the Sea of Tranquility with its external equipment locker, a stowage compartment called "MESA," in the shadow of the spacecraft. Although the sun was blazing down around them, Armstrong and Buzz Aldrin had to work in the dark to deploy their TV camera and various geology tools.
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