This week's episode of FOX's "Cosmos," hosted by Neil DeGrasse Tyson, focuses on astronomer William Herschel's observations on the effects of light on time and gravity. In a nutshell, what we see up in the night sky may actually no longer exist due to the extreme amount of time it takes light to travel such great distances. In essence, some of our night sky is actually composed of "ghost stars." 

To explain this phenomenon, Patrick Stewart voices William Herschel - who in addition to his observations on the stars, also coined the word "asteroid." You can check out a preview of the voice cameo below. 

Related on MNN: