Today I saw a tweet from @airlivenet that a Virgin Boeing 747 was "circling at 5,000ft with serious gear issues", and the embedded URL brought me to emergency.airlive.net. I didn't know this but you can track the position of any air plane in the air anywhere in the world. Sure enough the Virgin jet was circling south of London Gatwick Airport, and later flew out over the channel - presumably to dump some fuel before an emergency landing - here's a screen grab from emergency.airlive.net of its flight path (in both shades of green) while circling (the pile of planes near the top is Gatwick airport):
Thankfully the plane later landed safely after circling for four hours. This site got me thinking about how many planes there are in the sky at any one time - above you can see three planes approaching Gatwick from the east in their landing paths. According to Science on a Sphere, at any given moment, "roughly 5,000 planes are in the skies above the United States". Here's what a screen shot of the world looks like today - screen grab taken from www.flightradar24.com:
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This is a fun site (www.flightradar24.com) to look at as you can zoom in and out over any location in the world for more detail. Some of the things you will notice is the low number of flights over Africa as well as being able to see flights avoiding Ukraine.