1550s, "person who examines critically," agent noun from scan (v.). From 1927 as a type of mechanical device, at first often in television technology, by mid-20c. used of radar and radiation imaging devices; later of computer digital readers.
in physics, 1896, in Roentgen rays "X-rays," in recognition of German physicist Wilhem Conrad Röntgen (1845-1923), who discovered X-rays in 1895. As a unit of exposure to radiation, it is attested from 1922, proposed in French in 1921.
1896, "science or process of making images of objects on a sensitive plate by means of x-rays," from radiograph, the word for such an image-making device; from radio-, combining form of radiation, + -graph. Radiograph was used earlier as "device to measure and record the intensity of sunshine" (1880).
"highly magnetized, rotating compact star that emits beams of electromagnetic radiation," 1968, from pulse (n.1), the form on analogy of quasar. When discovered in 1967 via radio telescope, they were thought perhaps to be signals from alien civilizations and astronomers informally dubbed them LGM for "Little Green Men."
"water vapor deposited from the atmosphere by condensation, especially during the night," Middle English deaw, deu, from Old English deaw, from Proto-Germanic *dawwaz (source also of Old Saxon dau, Old Frisian daw, Middle Dutch dau, Old High German tau, German Tau, Old Norse dögg "dew"), perhaps from PIE root *dheu- "to flow" (source also of Sanskrit dhavate "flows, runs").
Used figuratively of something refreshing (late Old English), or suggestive of morning and youthful freshness (1530s). As a verb, "to wet with or as with dew," Old English deawian.
The formation of dew is explained by the loss of heat by bodies on the earth's surface through radiation at night, by which means they and the air immediately about them are cooled below the dew-point ....Dew is thus deposited chiefly on bodies which are good radiators and poor conductors of heat, like grass; hence also it appears chiefly on calm and clear nights--that is, when the conditions are most favorable for radiation. It never appears on nights both cloudy and windy. In winter dew becomes hoar frost. [Century Dictionary]
second letter of the Greek alphabet, c. 1300, from Greek, from Hebrew/Phoenician beth (see alphabet); used to designate the second of many things. Beta radiation is from 1899 (Rutherford). Beta particle is attested from 1904. Beta male, pejorative term for a risk-avoidant, non-confrontational man perceived as a follower or supporter rather than a leader, is by 2005, transferred from zoology (birds, primates), where it is attested by 1962 (compare alpha male under alpha).
"act of flowing or issuing from an origin; emission; radiation; what issues, flows, or is given out from any substance or body;" 1560s, from Late Latin emanationem (nominative emanatio), noun of action from past-participle stem of Latin emanare "flow out, spring out of," figuratively "arise, proceed from," from assimilated form of ex "out" (see ex-) + manare "to flow," from PIE root *ma- (3) "damp."
