Question
Hi Mr. Hyland,
  My partner and I are 11th graders and we are workin together on a science fair project on "How does sunspots affect local climate?" by looking at tree rings. A professor from NH University provided us with about 80 core samples of Norway Sprunes from the Czech Republic that were collected in 1998 and 2002. The tree cores from 1998 were above 50 years old and the samples from 2002 were younger than 50 years old. We determined the age of each tree by using a simple equation we found online.
1.After measuring the DBH and obtaining a core sample Divide the DBH by 2 to find the radius of the tree.
2.Measure the length of the core sample (cm).
3.Divide the length by the number of rings to determine the annual growth rate of the tree.
4.Divide the radius (cm) by the annual growth rate to calculate the age of the tree.

I was wondering if you know how we can determine a specific period of time by looking at the tree rings. For example, sunspots activity were above 90 per year ten years ago, and supposedly we can tell that by looking at the rings. When the rings are narrowly packed together, they tend to tell us that in those years, the conditions were dry and hot because sunspots appear more regularly, which affected the climate by increasing the temperature therefore the trees didn't get the amount of water needed. The tree rings that were a bit wider showed us that the sunspots didn't appear as often during those years, which allow the trees to receive enough water needed resulting in wider rings.

Therefore, we would appreciate it if you can show us how to determine a specific period of time on the tree and if you have any additional information that we could use, please include.

         Thank you very much
              Bieu

Answer
The best method of back dating a increment borer sample is determine the end that is where the bark (outside edge) is and count the rings back to the year that you are interested in. Each ring is one year so if you are using the 1998 core count back 8 years to 1990. Actually all the calculations you did to find the age is not necessary all you do is count the rings and add about 5 years since the core is taken at 4.5 feet about the ground ( this 5 years allows time for the tree to reach 4.5 feet tall).
Here a couple of web links that may help:
http://www.sonic.net/bristlecone/dendro.html
http://web.utk.edu/~grissino/
http://www.library.arizona.edu/library/teams/set/earthsci/treering.html