Every Day Is Special: July 5 – Happy Birthday, Andrew Douglass

July 5 – Happy Birthday, Andrew Douglass

Posted on July 5, 2014

Have you ever seen a tree stump with clear, countable tree rings?

Well, today's birthday boy (born on this date in 1867) is the fellow who didn't just look at tree rings – he figured out that they could be used to date events and learn about long-ago weather!

In other words, Andrew Douglass invented dendrochronology!

Would it surprise you to learn that Douglass studied tree rings while working as an astronomer? You may wonder how the study of space and the study of tree rings relate...

...and the answer is “the sunspot cycle.”

The sunspot cycle is the change in the Sun's activity and appearance over time. Each cycle lasts an average of 11 years, and the cycle (or its effects) have been observed for years. For example, there are a lot more auroras when the Sun is “active” - that is, when it is busy having flares and ejecting material into space. Sunspots are temporary dark spots caused by intense magnetic activity. I find it interesting to note that sunspots look black on the sun's surface because they are cooler than their surroundings, but they would appear brighter than the moon if they could be seen separated from the rest of the Sun. Sunspots occur when and where solar flares and ejections occur.

The sunspot cycles is more and more important to us humans. Not so much so we can plan our viewing of auroras (although I'd love to see one in real life), but because solar activity can cause disruptions in our power grid and radio and satellite transmissions, and it can even damage the electronics in our satellites. We're talking cell phones and satellite TV and GPS, folks!

Okay, so the Sun has cycles, and it's important that we understand the cycles because they affect us here on Earth. What does any of that have to do with tree rings?

Well, sunspots and solar activity affect Earth's weather, too, because the disturbance to Earth's magnetosphere allows much more UV radiation to penetrate our atmosphere. Our weather systems are so complex, we're not certain exactly how the extra UV light affects weather—so we need a lot of data to crunch so that we can better see patterns.

It turns out that tree rings are affected by weather. The inner portion of a tree's growth ring forms early in the spring growing season, when growth is rapid and therefore the wood is less dense. In the late summer and early fall, the wood that is produced is denser. That's why each tree ring – which is basically a band of less and then more dense wood – represents one year of growth. When there was a lot of sunlight and water in a year, the ring is relatively wide. When conditions were bad in a year, the ring is quite narrow. Since some trees live hundreds or even thousands of years, and since we have access to old wood that was used in buildings, tree rings provide information about local weather conditions dating back several thousand years – up to 11,000 years ago in some cases!

Today we give a shout-out to A. E. Douglass and his dendrochronology. His work helps us better understand astronomy (the study of the Sun and other space stuff), botany (the study of trees and other plants), meteorology (the study of climate and weather), physics (the study of radiation, magnetism, and all the other physical forces in the universe), and even archeology (the study of bones, tools, monuments, and other remnants of ancient peoples) as scientists began to use tree ring dating as they studied ancient civilizations.

Because all things are interrelated. Even if you study just one topic, you're bound to wander through lots of fields. Discoveries made in one area of science are bound to impact other areas as well. I love that about the universe!

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