Geolocation和navigator.geolocation是啥关系？

alert(navigator.geolocation);   //[object Geolocation]
alert(Geolocation);       //function Geolocation() { [native code] }

为啥Geolocation是函数，navigator.geolocation不是返回这个对象吗？它俩啥关系？

https://developer.mozilla.org/zh-CN/docs/Web/API/Navigator/geolocation
https://developer.mozilla.org/zh-CN/docs/Web/API/Geolocation