Plenty on the web about last night's display which was seen right across Northern Europe and further south than usual. You need to be looking at a clear northern horizon at least an hour after sunset. They are visible only in midsummer. Thankfully the moon isn't interfering at the moment. Once you've seen them you can't mistake them for cirrus clouds. They are silvery-blue streaks with waves and ripples with a ghostly luminosity. I'll be out there again tonight! Rare!