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What John Glenn Saw When He Became the First American to Orbit Earth
Five minutes and four seconds into the flight of the Friendship 7, as John Glenn prepared to become the first American to orbit Earth, he radioed to NASA, his capsule turned and brought the Earth into sight. “Oh, that view is tremendous,” he said.
[…]
After a trip across the Indian Ocean, mission control told Glenn that he’d be seeing the lights of Perth in western Australia. He confirmed that he did see them. “The lights show up very well and thank everybody for turning them on, will you?” Glenn joked.
“In the periscope, I can see the brilliant blue horizon coming up behind me; approaching sunrise. Over.” Mission Control replied, “You are very lucky.” Glenn said, “You’re right. Man, this is beautiful.”
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One of the many men I would love to have the honor to shake their hand.](http://25.media.tumblr.com/tumblr_lzqwscW4zl1qcokc4o1_500.jpg)
What John Glenn Saw When He Became the First American to Orbit Earth
Five minutes and four seconds into the flight of the Friendship 7, as John Glenn prepared to become the first American to orbit Earth, he radioed to NASA, his capsule turned and brought the Earth into sight. “Oh, that view is tremendous,” he said.
[…]
After a trip across the Indian Ocean, mission control told Glenn that he’d be seeing the lights of Perth in western Australia. He confirmed that he did see them. “The lights show up very well and thank everybody for turning them on, will you?” Glenn joked.
“In the periscope, I can see the brilliant blue horizon coming up behind me; approaching sunrise. Over.” Mission Control replied, “You are very lucky.” Glenn said, “You’re right. Man, this is beautiful.”
One of the many men I would love to have the honor to shake their hand.
Most people are familiar with the Doppler effect—in which the frequency of a wave changes depending on the motion of the observer relative to the wave source—from the shifting pitch of sirens as they pass. But the effect is important for pressure waves in addition to acoustic waves. When an object moves through air, its motion disturbs the surrounding air via pressure waves, which travel at the speed of sound. If an object moves slower than the speed of sound (top right), then those pressure waves extend in front of the object, carrying information about the object and allowing the air to shift and move smoothly around it.
If the object is moving at the speed of sound (bottom left), then it arrives at the same time as the pressure waves. In essence, the object is striking a stationary wall of air—this is what was meant by “breaking the sound barrier”. At Mach 1, the physics of the problem have fundamentally shifted. Now the only way for air to deflect to allow the object’s passing is by the sudden compression of a shock wave.
Moving even faster than the speed of sound (bottom right) the pressure and sound waves created by the object’s motion stretch in a cone behind it. The cone, known as a Mach cone, is the shock wave that deflects air around the moving object. The result is that the object will actually pass an observer before the observer will hear it. This is because no information can travel forward of the Mach cone’s leading edge. That’s why the area outside of the Mach cone is sometimes called the Zone of Silence. When the Mach cone passes an observer, the shock wave will register as a boom, like when the space shuttle passes overhead while landing. (via fyeahchemistry)
