Place your coins on a sheet of paper and draw a circle around them-the smallest possible circle that will fit all the coins. Then divide the circle into three parts as shown in Figure 15.26. This circle represents a star with a changing temperature. The coins represent H- ions. Removing a coin from the circle means that the H- ion has turned into a neutral hydrogen atom. Placing a coin in the circle means that the neutral hydrogen atom has become an H- ion.
Place all the coins back on the circle.
How many "H- ions" are now in the star?