Noctilucent clouds Robert B Slobins Image taken: Jul. 14, 2009 Location: Prague, Czech Republic Details: This time, a clear sky at twilight. The noctilucent clouds started to be plainly visible 30 minutes after sunset. This display was much more widespread with clouds from west to north-northeast. ©2013, SpaceWeather.com -- This site is penned daily by Dr. Tony Phillips.