If the night sky of site A is at 20 mag/arcsec2, the brightness of sky there is equivalent to a celestial object of 20 mag filling up a patch of sky of area 1 arcsec x 1 arcsec.是什么意思_If the night sky of site A is at 20 mag/arcsec2, the brightness of sky there is equivalent to a celestial object of 20 mag filling up a patch of sky of area 1 arcsec x 1 arcsec.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句