Nancy Stevenson Graves
Fra Mauro Region of the Moon, 1972
lithograph on paper
57.15 x 76.2 cm
Collection of the Owens Art Gallery
© Estate of Nancy Graves / VAGA at Artists Rights Society (ARS), New York, SOCAN, Montreal (2021)
NACREOUS are rare and exceptional clouds that form far past the limits of the troposphere, more than 30 km above ground. They are also known as MOTHER OF PEARL clouds, because the ice crystals separate the setting sun’s light into a glittering iridescence, or as POLAR STRATOSPHERIC CLOUDS, since they are only visible at night, in the coldest, northerly latitudes.