出典:Wiktionary
出典:『Wiktionary』 (2007/07/21 23:44 UTC 版)
backstaff (複数形 backstaffs)
出典:Wikipedia
出典:『Wikipedia』 (2011/04/04 23:24 UTC 版)
The backstaff or back-quadrant, is a navigational instrument that was used to measure the altitude of a celestial body, in particular the sun or moon. When observing the sun, users kept the sun to their back (hence the name) and observed the shadow cast by the upper vane on a horizon vane.