Noctilucent Clouds and other Phenomena

Abstract

At those latitudes most favored for observations of aurorae, the summer night-time sky never becomes completely dark. In northern Scotland (59.N) at midsummer (21 June), for example, the Sun never sinks more than about 9. below the northern horizon. Under such circumstances, twilight persists all night, and only the brighter naked eye stars are readily visible: astronomical observations are difficult, and this might well be regarded as “goff-season” for aurorae, which will normally be swamped by the bright sky. There is, however, one high atmosphere phenomenon of which observations can usefully be made during the twilit summer nights at higher latitudes: noctilucent clouds.