 What power is your telescope? When the public asks this question it's most likely that they're thinking of magnifying power. This set of activities helps your visitors understand that the much more important power of a telescope is its ability to create a bright image with more detail. Brightness and detail are primarily based on a telescope's aperture, the diameter of the primary mirror lens, not the magnification you're using. The power that observers are concerned with is primarily the telescope's ability to collect a lot of light. In the What Power Is Your Telescope Activity Bag you'll find cutouts of an eye, one with the hole already punched for the pupil, eight-inch paper plate, a container of vermiculite to represent photons of light, sidewalk chalk, a roll of string, labels with the diameters of various telescopes, a small flashlight, a tape dispenser, and a concave mirror. You should already have assembled the foam strips and sticks from the Ready to Observe bag and added it to this activity bag as shown in the previous section. You'll need to provide a tape measure. Let's see how we put all this together. Tape one eye to the center of the plate. Use the tape measure to assemble the string and labels. This is used to mark the apertures for various telescopes that NASA uses to study the universe. We'll demonstrate a few alternate ways to mark the apertures in just a minute, but first let's put the aperture string together. Here's what you do. Tie a loop in one end of the string. This will be the center of all your telescope apertures. Each label is marked with both the aperture and radius for each particular telescope. The radius is the distance you should place the label from the loop. For instance, this one is for the Chandra X-ray telescope. It has an aperture of four feet, so mark the string at half that, or 24 inches, and place the label there. You might want to put a single knot on either side of the label to keep it from slipping. To make the label stronger and more moisture resistant, place tape over the label. When you're all done, it should look like this. You may want to wrap the string around a paper tube or other object to prevent it from tangling. This string is long enough to go the size of the 10-meter Keck telescope mirror. Aerocebo is a thousand feet in diameter. Go find a few football fields for that one. Let's see how you might use all these materials.