I don't know much about radio, so your question had me stumped for a second, and the other replies didn't help me much. Here's my explanation: Some celestial b

I don't know much about radio, so your question had me stumped for a second, and the other replies didn't help me much. Here's my explanation: Some celestial bodies like the moons of Jupiter, are too dim for us to see, because the amount of light that hits our pupils is too small for our retina to react to. But the light from the moons isn't pointed directly at our pupils, it goes in all directions. If the area of our pupils were twice as large as it is, we would be getting twice as much light from Jupiter's moons — and everything else (except a laser pointed at your eye, please don't point lasers at people's eyes). Telescopes work by being a HUGE pupil, collecting all the light from a wide area and pointing it all right at our pupils (that's not the only thing they do, but it's an important part). An antenna is like a pupil, and a satellite dish, or this piece of aluminum foil, are like a telescope. Some of the signal from your laptop in the bedroom goes and hits the antenna with a weak signal. A lot more of the signal misses the antenna and hits the foil, and then gets reflected where some more hits the antenna (since the foil was curved, more of the signal hits the antenna on the rebound than on the first pass).