I learned something yesterday from Neil deGrasse Tyson’s “Death by Black Hole“, (an otherwise so-so book). The mysterious “Canals on Mars” that many people actually thought for a time were real were initially “discovered” by Percival Lowell – one of the preeminent astronomers of the late 19th and early 20th centuries. Lowell was the founder of the Lowell Observatory, which at the time boasted the best telescope in the world. Other astronomers of the time could not duplicate Lowell’s observations, but they all simply assumed it was because they did not have access to the equipment Lowell did. However as telescopes got better, Lowell’s observations were still not duplicated, and after Lowell died in 1916 the source of the canals remained a mystery. Until recently that is. A retired Optometrist from Minnesota noticed that Lowell’s setup was similar to what is commonly used when examining patients for cataracts. Combine this with the fact that Lowell was known to have high blood pressure, and Lowell was actually seeing the blood vessels in his eye! (The blood vessels cast a shadow directly on his retina). A comparison of the maps Lowell drew with the arrangement of blood vessels in the eye yield a remarkable correlation.