An annual ring is one of the circular bands visible when you cut through a tree trunk. Each ring represents one year of the tree's growth. If you count the rings from the center outward to the bark, you can determine how old the tree was when it was cut down.

Trees grow differently depending on the seasons. During spring and summer, when water and sunlight are abundant, trees grow quickly and produce light-colored wood. In fall and winter, growth slows down and creates darker, denser wood. This pattern of light and dark wood forms one complete ring per year.

The rings tell stories about the tree's life. Wide rings indicate years when the tree grew vigorously, probably because of plenty of rain and good weather. Narrow rings reveal difficult years, perhaps because of drought or unusually cold temperatures. Scientists called dendrochronologists study these rings to learn about climate patterns from hundreds or even thousands of years ago.

You can see annual rings most clearly on a tree stump after a tree has been cut down. The rings aren't always perfectly circular because trees don't grow evenly in all directions. A tree growing on a hillside might have thicker rings on one side, or rings might be distorted where a branch once grew.