Look west 30 to 60 minutes after sunset when the Sun has dipped 6 to 16 degrees below the horizon. If you see luminous blue-white tendrils spreading across the sky, you’ve probably spotted a noctilucent cloud. Although noctilucent clouds appear most often at high latitudes–e.g. places like Scandinavia and Canada–they have been sighted as far south as Colorado, Utah and Virginia.