Follow the headline link for all the details, but here’s the short and sweet version. Fire up Siri and say:

Flights overhead

If you are in a relatively urban area, you might be amazed at how many planes are overhead at any given moment.

We did a small Twitter experiment this morning, and it seem like the Wolfram Alpha database that makes this work only has data for North America. If you see an exception to this, please let me know (@davemark).