International Ultraviolet Explorer was considered the most successful astronomical satellite ever. The human eye can perceive light with wavelengths between roughly 350 (violet) and 700 (red) nanometres. Ultraviolet light has wavelengths between roughly 10 nm and 350 nm. UV light can be harmful to human beings, and is strongly absorbed by the ozone layer. This makes it impossible to observe UV emission from astronomical objects from the ground. Many types of object emit copious quantities of UV radiation, though: the hottest and most massive stars in the universe can have surface temperatures high enough that the vast majority of their light is emitted
The empire on which the sun never sets the sun encircles.” Mesopotamian texts contemporary to Sargon of Akkad (c. 2334 – 2279 BC) proclaim that this king ruled “all the lands from sunrise to sunset.” In the early 16th century, the phrase, ""el imperio en el que nunca se pone el sol"" ("the empire on which the sun never sets") originated with a remark made by Fray Francisco de Ugalde to Charles I, who as king of Spain and as Holy Roman Emperor by the name of Charles V, had an empire, which included many territories in Europe, islands in the Mediterranean and Atlantic, cities in North Africa