"We could look for beacons." "It could be that there are alien civilizations that have simply created something a little bit like a lighthouse that sweeps the plane of the galaxy, goes bleep, and it's there to attract attention, or it's a monument, or an aesthetic symbol or even a religious symbol.

VOA: standard.2010.04.16

So, let me get a little bit more specific about what we mean by nodal plane and where the idea of nodal plane comes from, and nodal planes arise from any place you have angular nodes.

关于节面的意义,或者节面概念的起源，让我们讲的更具体一点，节面起源于角向节点。

麻省理工公开课 - 化学原理课程节选