As soon as I woke up this morning, I remembered Milutin Milanković (1879-1958), whose last name is often spelled the German way, as Milankovitch. A Serbian mathematician, astronomer, and geophysicist, he is famous for his explanation of earth’s climate variations caused by changes in its position relative to the sun. The so-called Milanković cycles have been debated for decades, but they are gaining in popularity in connection with rapid climate change. When I got up, I went to my Residua website and searched for his name. I found not a trace of it. I found quite a bit about him on the World Wide Web, though. All renditions of his cycles are predictably regular. The smooth curves going up and down seem to be coming straight from a textbook. But then I searched for glaciation cycles, and I found a bunch of charts showing average temperatures on earth over long stretches of time. One kind of chart goes back a bit less than three-billion years, and it shows five ice ages. By the way, we are currently in an ice age. Another kind of chart goes back a bit less than half a million years, and it shows four glacial and five interglacial periods. And we are currently in an interglacial period. Both charts are far from regular. In fact, they are all over the place with jigs and jags galore. Which is precisely why I have not paid greater attention to Milanković, of whose work I have been aware for at least a decade. All that is known with any certainty is that there are glaciation cycles. And that is about all we really know. Textbooks are for the birds, anyway.