Early astronomers spent much of their time mapping and cataloging celestial objects and looking for patterns. They hoped that these patterns would help them understand the forces at work throughout the universe. One pattern they noticed was the changing number and distribution of sunspots over time. They created detailed records of the number of sunspots and their latitudes—how far north or south of the sun's equator they appeared.

The graphs below show two ways of plotting sunspot data to look for patterns. The top graph shows the latitudes where sunspots occurred each year, and the bottom graph shows the number of sunspots measured each year. (The top graph is called a "butterfly" graph—can you see why?)

The number of sunspots goes up and down in a regular pattern. In the bottom graph, a peak is called a "solar maximum", and a valley is called a "solar minimum." The length of a solar cycle is the amount of time from one solar minimum to the next. To find the average length of a solar cycle, calculate the number of years from the first solar minimum on the graph to the last solar minimum. Divide the number of years by the number of full solar cycles that occur over that time.

7. What is the average time interval between solar maxima?

8.Predict the year in which you think the next solar maximum will occur.