Light sphere – have radio waves reached any stars yet?
Yes, radio waves have long reached many stars near to the Earth. The visualization below shows a sampling of stars relative to the Earth and a selection of events on the Earth by number of light-years that radio waves would have travelled since the event happened. You can view the visualization here.
This visualization is a modified version of the very cool “The infographic book of space – Light Spheres” https://cosmos-book.github.io
For example, the first BBC radio broadcast was about 100 light-years ago and in that time those radio waves have travelled past many near Earth stars. If there were advanced radio receivers in these other star systems they theoretically could hear the radio broadcasts.
While the light spheres visualization above includes only a handful of selected stars around the Solar System in reality there are many more. The 3D representation of stars around the Solar System shows just how many stars are within 100 light-years.
However, while it may seem like radio waves from Earth have travelled long distances, the image below shows that it is actually a very, very small distance when compared to the entire Milky Way galaxy.
The image below, created by Adam Grossman, taken from the Planetary Society website, shows a tiny blue 200 light-years sphere around the Earth which represents the distance travelled by the very first radio transmission by the Marconi brothers about 200 years ago.
Many stars near Earth could have potentially heard our radio broadcasts but the rest of the universe has not!
