It’s the birthday of American astronomer A.E. Douglass (books by this author), born in Windsor, Vermont (1867). Douglass became interested in a correlation between solar radiation cycles and the growth rate of trees. Through his studies, he founded the field of dendrochronology — a method of dating wood by growth ring patterns.
The idea behind dendrochronology is as simple as it is clever. Each year, the trunk of a tree grows one ring wider. How much wider depends on how much water was available to the tree that year, so that rainier years are marked by wider rings. Scientists like Douglass learned to track climate patterns this way.
Dendrochronological techniques have shed new light on climate science, but they have also been hugely important in dating artifacts and artworks. For example, an oak panel portrait of Mary, Queen of Scots in London’s National Portrait Gallery was long thought to be a copy. But dendrochronology revealed that the painting was actually a much older 16th-century original.
Douglass died in 1962, but his legacy lives on today in the form of both lunar and Martian craters named in his honor. He also left behind the first Laboratory of Tree-Ring Research at the University of Arizona in Tucson.