 Like waves in the ocean, sound makes waves in the air. Air jostles back and forth as the sound energy waves pass.
If
you put something like paper in the path of the sound wave, it will
also vibrate quite a lot. If you give this paper surface the right
shape, the sound waves will be funneled to a point. So your super sound
cone is a sound funnel! The same sort of idea makes NASA's giant dish
antennas work. These antennas listen for signals from the planetary
spacecraft now exploring space far from Earth. |
The
antenna dish in this picture is 34 meters (about 110 feet) across. This
antenna is in Australia. See how tiny the sheep look as they graze
peacefully beneath its attentive ear.
|
We
can't just build a spacecraft, tell it to phone home once in a while,
then launch it to Mars or Jupiter! We must have a way to hear its tiny
voice and talk to it when it is very far away. |
| Of course, no
spacecraft actually communicates by sound. Messages wouldn't get very
far, since sound waves can't travel in the vacuum of space! But the
spacecraft do send out radio waves, which can travel practically
forever. The trouble is, the radio waves spread out and get weaker and
weaker the farther they travel. So NASA's radio wave "ears" must be very big indeed!
Some of the Deep Space Network antennas are twice as big as the one watching over the sheep above!
These
dish antennas don't look much like your sound cone, do they? But the
path the radio signals take once they hit the dish is like a folded up
cone. Once the signal hits the focus (like the small end of your cone),
electronic instruments take over to turn up the volume even more.
Then we can begin to decode the message and figure out what the spacecraft has to show and tell us!
|
, Dr. Marc?
