Headlines like the one shown below have been in the news for years. Scientists have been talking about a hole in the ozone layer, saying that they can actually measure its size on a regular basis.

The so-called "ozone hole" is not really a hole. Rather, it's a region where the concentration of ozone gas in the upper atmosphere is much lower than normal.

In this investigation, you'll analyze the same images that scientists use to measure global changes in the ozone layer.