 You know that the larger the diameter or aperture of a telescope, the more light it collects and that means you get a brighter image with more detail. How big are some of the telescopes NASA uses to study the universe? You'll be able to answer that question for your visitors with this activity. You'll need a large area depending on how many of the telescope apertures you'll be making, an auditorium or a parking lot or a playground. In the next scene, we're going to draw the apertures with chalk. Here are some other alternatives. If you have a crowd, you can let people just join hands or stand at intervals in circles for the larger telescopes. To make the apertures ahead of time, purchase a large plastic drop cloth from a painter's supply store. For contrasting colors, you could purchase plastic tablecloths from a party supply store. Cut out circles for the apertures from the drop cloth and or tablecloth. Lay the circles on the ground, putting the largest one down first. You may need to tape them down with masking tape or weight them down with rocks if it's a windy day. On a playground or parking lot, your visitors can simply use sidewalk chalk to mark the sizes, like we'll show next. Talk about what NASA uses these telescopes for as your visitors mark the apertures. NASA uses telescopes to study the universe. Telescopes need to collect a lot of light to detect very distant objects. Here we have a string that has markers marking the apertures of various telescopes NASA uses. The aperture is how big the telescope's light collecting area is. My telescope has a light collecting area eight inches across. That's about this big. How big are telescopes NASA uses? Who wants to be at the center of these telescope light collecting areas? I will. Great. You hold on to that. And why don't you hold on to the other end? Now who has heard of the Hubble Space Telescope? Great. Why don't you hold on to the string right there where the Hubble is? The Hubble is out in space going around the Earth. Now who wants to draw the Chandra X-ray telescope? Okay, stand right there where the Chandra is. That telescope has discovered black holes in the middle of galaxies. And why don't you draw the Keck Astronomical Mirror? Astronomers have discovered planets around other stars with that telescope. Now, let's hold the string on the ground. And as the end moves and the center stays still, we'll make marks every couple inches where our telescope is on the cement. Okay? So let's gradually just move the string this way in a circle. Compared to my telescope, can the Hubble collect more or less light? A lot more. This activity can generate a lot of discussion, including how much more light one telescope can collect than another. For example, if we used one teaspoon of grains representing photons to cover the 8-inch telescope mirror, how many teaspoons do you think it will take to cover the Hubble's mirror? It would be about 100 teaspoons or about 2 cups of grains. If doing this for a school group, you can have the kids calculate how much more surface area each telescope has using the formula pi times the radius squared. This is explained in the manual.