Blood rain or red rain is a phenomenon in which blood is perceived to fall from the sky in the form of rain. Cases have been recorded since Homer's Iliad, composed approximately 8th century BC, and are widespread. Before the 17th century it was generally believed that the rain was actually blood. Literature mirrors cult practice, in which the appearance of blood rain was considered a bad omen. It was used as a tool foreshadowing events, but while some of these may be literary devices, some occurrences are historic. There is now a scientific consensus that the blood rain phenomenon is caused by aerial spores of green microalgae Trentepohlia annulata.
Woodcut by Hans Glaser depicting a blood rain that occurred near Dinkelsbühl on May 26, 1554
Photomicrograph of particles from a sample of red rain from Kerala
An omen is a phenomenon that is believed to foretell the future, often signifying the advent of change. It was commonly believed in ancient times, and still believed by some today, that omens bring divine messages from the gods.
Examples of omens from the Nuremberg Chronicle (1493): natural phenomena and unnatural births.
Manuscript of the mid-nineteenth century, possibly of Sgaw Karen origin, shows various appearances in the sun, the moon, clouds, etc., and indicates the primarily bad omens these appearances foretell. Explanations in English were added to this manuscript by a nineteenth-century American missionary.
Halley's Comet's appearance in 1066 was recorded on the Bayeux Tapestry. ISTI MIRANT STELLA literally means "These ones are looking in wonder at the star". National Geographic translated it in a 1966 article about the tapestry as "These men wonder at the star".
