Echo 1 launched last week and you can see it with the naked eye.

It’s a 100-foot aluminized mylar balloon — inflated in orbit, reflecting sunlight, visible as a bright moving star from the ground. The first passive communication satellite: radio signals aimed at it from Earth bounce off its surface and can be received on the other side of the country.

The technology is elegantly simple. You don’t need active electronics aboard Echo 1; it’s just a mirror. Signal goes up, bounces off, comes down elsewhere. NASA and Bell Labs used it to transmit a recorded voice message from New Jersey to California — the first transcontinental communication via satellite.

The limitation is obvious: you can only use it when the satellite is above the horizon at both ends of the link, and a low-orbit satellite moves fast, so the window is short. And the signal degrades because most of the radio energy bounces away in directions nobody is listening. A passive reflector is inefficient.

But it proved the concept. Satellites can relay communications. The next step — active relay satellites with receivers, amplifiers, and transmitters aboard — is being developed. Telstar is coming in a couple of years, and it will do what Echo 1 does, but efficiently and reliably.

The thing that delights me about Echo 1 is the visibility. You can go outside on a clear night and watch a human-made object sail across the sky, and know that radio signals are bouncing off it. The technology is so tangible. No computer, no black box, no mystery — just a shiny balloon in orbit, doing physics.

My neighbor Harold looked at it last Tuesday evening and said, “That’s us?” — meaning that bright moving light is a human thing, not a star. I said yes. He watched it sail behind a tree and said, “Huh.”

Harold doesn’t make speeches. But that “huh” was a considered one.