On the evening of 7 July 2010 Xiaoshan airport at Hangzhou stopped work for almost an hour: controllers logged an unidentified object in the zone and eighteen flights were diverted. Passengers and residents photographed a bright trail in the sky. It is a rare instance of a report of an unidentified object shutting down a major airport. Days later the authorities said the phenomenon was connected with military activity and gave no details. The likeliest reading is a missile or aircraft trial; a contrail lit by a low sun produces exactly this picture, and the photographs are consistent with it.

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The Hessdalen Valley

A Norwegian valley where luminous objects have been observed since 1981, at times twenty times a week. Unlike most such places it has a permanent automated observation station, built in 1998 by Østfold University College, and the phenomenon has been under instruments for a quarter of a century. Hypotheses exist — dust ionisation, a piezoelectric effect in the rock — and none accounts for all of it.