Some two billion years ago, the first photosynthetic algae evolved the ability to respond to light—the brilliant Sun by day, the spectral Moon by night. Around 700 million years ago, primitive eye-pits appeared; then, during the Cambrian era, arthropod-like creatures gazed at the sky through true eyes, sensing the lunar rising and setting with their arthropod-like comprehension. So it continued, into the succeeding chapters of life featuring mammals, primates, hominins, and Homo sapiens, the