© Veres Viktor / NASA
Every summer since the late 19th century, Earth's polar skies have lit up with eerie blue-white glowing clouds, slowly twisting and undulating in the twilight sky.
These mystifying clouds are referred to as "night-shining" clouds, or noctilucent clouds.
Such clouds form in an upper layer of the
Earth's atmosphere called the mesosphere during the summer and can be seen from the high latitudes on Earth.
Volcano drew attention
A series of massive eruptions from the
Krakatau volcano (also spelled Krakatoa) in late August 1883 may have serendipitously helped to draw attention to the phenomenon of noctilucent clouds.
Dust and ash injected high into the atmosphere from the Indonesian volcano
caused spectacular and colorful sunsets worldwide for several years.
On the evening of June 8, 1885, T. W. Backhouse was admiring one such beautiful sunset from Kissingen, Germany, when he noticed something rather strange: as darkness deepened and the ruddy glows faded, he noticed wispy bluish-white filaments seemingly glowing in the north and northwest sky. At that time, scientists dismissed this effect as some curious manifestation caused by the volcanic ash.
But after a few more years, the ash settled and the vivid sunsets induced by Krakatoa faded.
And yet the noctilucent clouds persisted.
Interestingly, there is some debate that Backhouse possibly was not the first to describe them, since in a report dated from 1854, Thomas Romney Robinson, situated at Armagh, Ireland, communicated his personal observation of the " . . . phosphorescent properties of ordinary clouds." So it might be that Robinson was making a reference to noctilucent clouds 31 years before Backhouse.
