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 1895, Guglielmo Marconi transmitted the first radio signals. 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
Every radio broadcast, every television transmission, every radar pulse ever emitted by humanity is still out there, propagating through space at 300,000 kilometres per second. After 131 years the wavefront has reached a radius of about 131 light-years — roughly 40 parsecs.
That sphere, sometimes called the radio bubble, defines the volume of space in which an extraterrestrial civilisation could, in principle, have detected our presence. Every star inside the bubble has been washed over by our signals. Every star outside it has no electromagnetic evidence that we exist.
Scroll through the tour below to see the bubble from inside, from outside, and from the nearest star cluster just beyond its edge.
Sun orbit · inside the shell
Inside the bubble
From inside, there is nothing to see — the bubble is invisible. You are surrounded by stars, many of which have been bathed in our radio signals for decades. The faint blue shell marks the wavefront's current position at roughly 40 parsecs.
The stars inside this sphere are mostly nearby dwarfs — dim red and orange stars too faint to see with the naked eye. A few brighter ones stand out: Sirius at 2.6 parsecs, Vega at 7.7, Arcturus at 11. All of them have been receiving our broadcasts since the mid-twentieth century.
65 pc from the Sun · outside the shell
Seeing the shell
Pull back far enough and the bubble becomes visible — a faint sphere centred on the Sun, threading through the local stars. At 40 parsecs radius it contains roughly a thousand stellar systems. That sounds like a lot until you see how small it is against the backdrop of the galaxy.
The Milky Way is about 30,000 parsecs across. Our radio bubble is a millionth of that diameter. If the galaxy were the size of a football pitch, the radio bubble would be smaller than a grain of sand.
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.