Sentence:  Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely <WSD>speck</WSD> in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves. 
Meaning of the word marked with <WSD> tags:  A very small thing; a particle; a whit.