These great hollow globes of artificial super-metals, and artificial transparent adamant, ranged in size from the earliest and smallest structures, which were no bigger than a very small asteroid, to spheres considerably larger than the Earth. (Olaf Stapledon, STAR MAKER)
Thursday, September 28, 2017
Today's Astronomy Picture of the Day shows ripples in spacetime, courtesy of combined LIGO observations. When black holes collide, the universe rings.