Here in the United States, we spend most of our time in an always-on world—a place where internet connections are as constant and reliable as the lights or running water. But this sort of always-on internet is very much a first-world luxury, and it appears to be confined to countries that were early users of the net, snatching up super-sized quantities of internet addresses. In much of the world, the internet regularly goes to sleep.

What this means is that for web surfers in Asia and and Africa and South America, their internet connections get switched off at night. Internet cafes shut down, and so do home routers. "One of the strongest correlations we found is the poorer your country is, the more likely your network is to turn off at night," says John Heidemann, a professor at the University of Southern California.

Heidemann and other researchers at USC recently mapped out the diurnal rhythm of the global internet. Over the course of about two weeks, Heidemann tracked these patterns by pinging every available IP (internet protocol) address they could find every 11 minutes. Of the 4 billion available addresses in the eternally-being-phased-out IPv4 address system, less than 800 million are being used, he estimates.

He and his team at USC are masters of surveying the internet. They created the their first Internet Census in 2006. It turns out that it's a pretty tricky task to map out a sprawling, decentralized network like this, but Heidemann says that this latest work is going to help them get a clearer picture of what's going on. Using this data, for example, they'll create more accurate maps of internet outages, because they'll know how many computers should be offline because of the daily shut-off.