一个从一艘沉船中挖掘出的史前器物可能是现在世上发现的最早用于导航的工具。海洋考古学家说这个物体是一个星座命盘，海员在航行中用它测量太阳的高度，以确定所在地方。这个星座命盘是在1503年在印度洋暴风雪期间沉没的一艘葡萄牙船舰中找到的。
The slim bronze disc was discovered during the excavation1 of the Esmeralda shipwreck2 a Portuguese3 vessel4 that was exploring the Indian Ocean when it sank in a storm in 1503.
The object is decorated with a royal coat of arms, but laser scanning also revealed faint etchings around its edges, each separated by five degrees. It confirms that this is an astrolabe - an instrument used by mariners5 to measure the height of the sun above the horizon, enabling them to navigate6 the seas.
only around one hundred of these items have been found, and this one most likely dates to the late fifteenth century, making it the earliest known example by several decades.