“While we are certainly a part of the cosmos, we are unable to grasp its physical truths. To call a number astronomical is to say that it is extreme, but also, in some sense, unknowable. …However, there actually are properties of the cosmos that can be expressed at the scale of the everyday. Let’s begin at the human scale of time: It turns out that there is one supernova, a cataclysmic explosion of a star that marks the end of its life, about every 50 years in the Milky Way. …So throughout human history, each person has likely been around for one or two of these bursts that can briefly burn brighter than an entire galaxy.”