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Headshot of Emily Lakdawalla

This is how far human radio broadcasts have reached into the galaxy

Posted By Emily Lakdawalla

24-02-2012 17:26 CST

Topics: fun, scale comparisons, stars and galaxies

The other day, I was playing around with stumbleupon and came across this photo, which -- well, it speaks for itself. Wow.

Extent of human radio broadcasts

Adam Grossman / Nick Risinger

Extent of human radio broadcasts
Humans have been broadcasting radio waves into deep space for about a hundred years now, since the days of Marconi. That, of course, means there is an ever-expanding bubble announcing Humanity's presence to anyone listening in the Milky Way. This bubble is astronomically large (literally), and currently spans approximately 200 light years. But how big is this, really, compared to the size of the Galaxy in which we live (which is, itself, just one of countless billions of galaxies in the observable universe)? To answer that question, Adam Grossman put together this diagram. It's not the black square; it's the little blue dot at the center of that zoomed-in square.

Gives you perspective, doesn't it? Actually, I'm a little surprised that the dot shows up on this image at all. Some people describe this as humbling, but for me, I see it as just the beginning. I'm very grateful to be a member of the very few generations of humanity that have ever lived who are (a) capable of creating radio broadcasts and (b) realizing how much more of the universe there is beyond what we've experienced.

I tweeted a link to it, and while I expected some retweets, I was surprised to see its spread -- I think it's probably the single most retweeted tweet I have ever written. There's probably several reasons for that. Links to photos are more likely to be retweeted than others. Very short but still substantial tweets are more likely to be retweeted, because it gives the repeater scope for their own commentary. And this is the sort of thing that can make just about anybody who is capable of operating a cell phone go "hmm," so it has wide appeal.

The one thing I feel bad about is that stumbleupon sent me directly to the photo on somebody else's website, and I didn't bother looking up its origin before I tweeted the link. So now I have, and I can tell you that the diagram was made by Adam Grossman on the jackadamblog, using an artist's concept of the Milky Way by Nick Risinger that he took from Wikipedia. They have a neato-looking iOS app, Dark Sky, that provides very short-term weather predictions. My apologies, Adam, for sending so much traffic directly to the photo rather than to your blog! Hopefully this post will correct that error.

A special note to the pedants: yes, I do realize that the signal from our radio and TV broadcasts is so attenuated by that 100-light-year boundary as to be undetectable except by some kind of magical alien technology. That's not the point. Don't be so literal!

One last thing: my apologies for no post yesterday and the likelihood of very few posts next week. I have a lot of other projects going right now that do not automatically produce blog posts, and not enough time.

See other posts from February 2012


Read more blog entries about: fun, scale comparisons, stars and galaxies


KennyC: 08/14/2013 06:23 CDT

Wonderful. I wrote a short piece on this as well. On my blog:

TXradioengineer: 02/12/2014 08:28 CST

The story has several facts wrong. AM and Longwave radio in the early years cannot escape the ionosphere. During day, one layer absorbs the signals as they travel night, there are other layers that bounce the signals back to earth (which is why you hear AM stations from far away at night)...Only when you get into the VHF range does signals get out of the atmosphere..VHF transmissions did not begin with decent power until the 1940s...Not even the TV signal in "Contact" would not have made it.

Bill: 08/20/2016 11:45 CDT

The inverse square law would apply to signals that escape from the earths atmosphere. How far away could we detect signals comparable to today's signals from another planet?

stevencohn: 03/10/2017 01:30 CST

I rather start with the simplest variables 1st - TIME. Just imagine it took 5 years for this post to get here (sic) How long will a civilization be able to send out messages compared to when we've been able to receive such? [Ships passing in the night]

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