Since the earliest humans walked the earth, the vast mysteries and wonders of the night sky have fascinated and beguiled us, as we’ve struggled to understand our place in the cosmos. Even after the last century, which saw important and startling discoveries about our own planet, our solar system and the stars and galaxies beyond, there remain more questions than answers. But those questions—What is dark matter? Are we alone in the universe? Is time travel possible?—provide a fascinating insight into the vastness and infinite possibilities of space that we’re yet to determine.