Via FlightRadar24.com, a real-time view of the airliners in the skies over Europe right now. If you have seen one of these in normal circumstances, you know that it's basically all airplanes. Today you can see traffic headed in and out of Istanbul, and Milan, and Rome, and... that's it. No Heathrow, no Charles de Gaulle, no Frankfurt, no Schiphol.
For comparison, from a Dutch site, a thumbnail view of normal circumstances below. This is becoming quite an amazingly profound effect, at least in the short term.
