n. 弧秒（量度平面角的单位，是弧分的六十分之一）
1°中包含了60角分（arcminute），写作60'。1角分中含有60角秒（arcsecond），写作60"。一台好的望远镜在良好的天气条件下可以分辨出天球上小至1"的细节。
... arcminute——弧分 arcsecond——弧秒 asteroid——小行星 ...
NASA's Jet Propulsion Laboratory, it will be possible to measure stellar positions to within 20 millionths of an arcsecond by 2005.
Viewed from a distance of ten light-years, the sun's side-to-side wobble due to Jupiter causes its position to change by 1.6 thousandths of an arcsecond.
It will have two telescopes mounted at opposite ends of a ten-metre boom, and will be able to measure astrometric wobbles as small as a millionth of an arcsecond.