| 单词 | twilight arc |
| 释义 | > as lemmastwilight arc twilight arc (also twilight arch), twilight curve, the outline of the earth's shadow, which rises in the east as the sun sets, forming an arch which divides the twilight or shaded portion of the sky from that which is lighted by the direct rays of the sun. twilight glow, a diffuse glow in the sky at twilight; spec. in Meteorology, that caused by spectroscopic emission in the upper atmosphere from atoms excited by solar radiation. twilight parallel, the small circle of the celestial sphere, parallel to and 18 degrees below the horizon, at the sun's crossing which evening twilight ceases or morning twilight begins (Webster, 1911). twilight vision, vision in which colours are hardly perceptible owing to the dimness of the light; scotopic vision.extracted from twilightn.< as lemmas |
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