Notice
The bubble is tiny
From outside, the radio bubble is barely visible against the stellar background. Fly further out and it disappears entirely. Our electromagnetic footprint is vanishingly small on a galactic scale.
Learn
The radio bubble
In summer 1895, Guglielmo Marconi took wireless telegraphy outdoors at Villa Griffone near Bologna. Those electromagnetic waves have been expanding outward at the speed of light ever since — a growing sphere centred on Earth. It sounds impressive. It is not.
A sphere of signal
The tour models a simple version of humanity's radio footprint: an outward-moving shell centred on Earth and travelling at 300,000 kilometres per second. Using 1 July 1895 as an approximate marker for Marconi's outdoor tests, the wavefront has reached a radius of about 131 light-years — roughly 40 parsecs.
That sphere, sometimes called the radio bubble, shows where the earliest signals could have arrived by now. It is a model, not a guarantee of detectability: signal strength, direction, receiver sensitivity, and background noise all matter.
Scroll through the tour below to see the bubble begin, grow, and reach toward the nearest star cluster just beyond its edge.
Earth orbit · before radio
Before the bubble
Before wireless telegraphy, there is no radio bubble. From Earth, the stars look exactly as they always did: distant, quiet, and unaware of us. At this scale, Earth and the Sun share the same point — the solar origin.
No modelled interstellar signal front has crossed the gap yet. The story begins with a signal too local to matter to the stars — until time gives it distance.
Summer 1895 · Villa Griffone
Marconi starts the clock
Summer 1895 — Marconi’s outdoor wireless telegraphy experiments, Villa Griffone, Pontecchio, Italy. The historical record does not give us a precise day, so the tour uses 1 July 1895 as an approximate calculation marker.
As the chapter begins, the shell grows from Earth at light speed. The camera rides just outside the wavefront, turning a century of radio history into a few seconds of motion. By the time it settles, the radio bubble has reached its present radius.
175 pc from the Sun · outside the shell
Seeing the shell
Pull much farther back and the bubble becomes visible as a small, faint sphere centred on the Sun, threaded through the local stars. At about 40 parsecs radius, it contains roughly a thousand stellar systems. That sounds like a lot until you compare it with the Milky Way.
The galaxy is about 30,000 parsecs across. An 80-parsec-wide radio bubble is large enough to matter locally, but tiny on a galactic scale. From this distance, it starts to feel less like a frontier and more like a small neighbourhood around one ordinary star.
And the signals themselves are weakening. Broadcast-strength radio waves follow the inverse-square law: double the distance, quarter the power. At 40 parsecs, an ordinary television broadcast is billions of times too faint to detect with any technology we currently possess. Only a civilisation with an extraordinarily sensitive receiver — or one specifically pointed at us — would notice.
~48 pc from the Sun · just outside the bubble
The Hyades: almost in reach
The Hyades — the nearest open star cluster to the Sun — sit at about 48 parsecs. That puts them just outside the radio bubble. Our earliest signals are roughly 8 parsecs short. At the speed of light, they will arrive in about 25 years.
Could anything be listening? The Hyades are about 680 million years old — old enough for planets to have formed, settled into stable orbits, and cooled. On Earth, life appeared within the first billion years. Microbial life at Hyades-age is not impossible, though it would be speculative. Complex multicellular life, by Earth's timeline, took over three billion years longer.
Several Hyades stars have confirmed exoplanets, though the ones found so far are hot Jupiters — gas giants in close orbits, unlikely to be habitable. The cluster's age means its most massive stars have already died; what remains are Sun-like stars and cooler dwarfs. Whether any of them host rocky planets in temperate orbits is still unknown.
The honest answer: we do not know if anything in the Hyades could hear us. But the fact that our signals will reach a real star cluster within a human lifetime makes the radio bubble feel less abstract and more like a question with a deadline.
Return · 0 pc
Back inside
The journey back from the Hyades is short — only 48 parsecs. Watch the bubble's shell pass over you as you re-enter the volume of space that knows we are here.
From inside, the bubble is invisible again. That is perhaps the most sobering part: we cannot see our own signal, and neither can most of the galaxy.
Things to try
Try this
Count the stars inside
From outside the bubble, look at how many stars the shell contains. There are roughly a thousand stellar systems inside — a tiny fraction of the Milky Way's hundreds of billions.
Think about
Signal vs. detectability
The bubble shows where our signals have reached, not where they could be detected. Broadcast-power radio fades with the square of distance. Even inside the bubble, most signals are far too faint for any plausible receiver.
Key idea
Light-speed is the hard limit
The bubble expands at exactly one light-year per year. Nothing we do can make it grow faster. This is not an engineering problem — it is a law of physics.
Next lesson
Explore the clusters themselves
The Hyades are just one of many star clusters within a few hundred parsecs. The star clusters lesson flies between five clusters — from stellar nurseries to ancient globulars — to see how age, gravity, and the galaxy shape stellar families.