Flying back to UK at FL470 about this time 2 years ago, (from Zch, off maintenance, just because we could!) was most surprised to see a/c well above and contrailing..... with many a/c asking London ATC who/what it was. Well educated Qantas geezer explains that it was a comet whose name I have altzheimered, which passed within 90 miles of earth spewing a debris trail reckoned to be 800 miles long!
Great optical illusion....but I'm sure I could make out it's nav. lights...
