- published: 08 Jul 2015
- views: 150023
Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 450–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal mixture of red and green light. On a colour wheel based on traditional colour theory (RYB) where blue was considered a primary colour, its complementary colour is considered to be orange (based on the Munsell colour wheel).
In Modern English, "blue" is one of the basic colour terms, and one of the seven spectral colours, intermediate between violet (purple) and cyan. It comprises a considerable number of identifiable subcategories that can be identified with descriptive terms like navy blue (a dark blue), cyan blue (or "blue-green", on the boundary to the green range), or sky blue (azure).
The word itself was loaned into Middle English from the Old French word bleu, blo "pale, pallid, discoloured; blue, blue-grey", itself from an Old Frankish *blao.
Dreams are successions of images, ideas, emotions, and sensations that occur involuntarily in the mind during certain stages of sleep. The content and purpose of dreams are not definitively understood, though they have been a topic of scientific speculation, as well as a subject of philosophical and religious interest, throughout recorded history. The scientific study of dreams is called oneirology.
Dreams mainly occur in the rapid-eye movement (REM) stage of sleep—when brain activity is high and resembles that of being awake. REM sleep is revealed by continuous movements of the eyes during sleep. At times, dreams may occur during other stages of sleep. However, these dreams tend to be much less vivid or memorable.
Dreams can last for a few seconds, or as long as twenty minutes. People are more likely to remember the dream if they are awakened during the REM phase. The average person has about 3 to 5 dreams per night, but some may have up to 7 dreams in one night. The dreams tend to last longer as the night progresses. During a full 8-hour night sleep, two hours of it is spent dreaming.