我们需要一些特殊的器械，比如一个类似三脚架的东西以便照相机可以跟踪天体。
We will need a special device, which somehow looks like tripod and makes the camera follow the sky objects.
这张数码照片是用架在能跟踪天体的望远镜上的照相机拍的，于美国弗吉尼亚一露营基地。
The digital photograph was made with a camera mounted on a telescope tracking the stars through dark skies above a camp ground in Virginia, USA.
这个查询是从一个上下文元素开始的，并遵照相反方向的跟踪关系从而发现更低抽象层的同一水平的元素。
This query starts at a context element and follows all trace relationships in the reverse direction to discover all elements in lower levels of abstraction.
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