An interesting and highly visual topic would be the Hubble Space Telescope and the fantastic photos we have obtained thru it. You could display some of the photos with a short explanation of the photos importance. It found areas of space that seem to have older dying stars. It also found nebulas with star "nurserys" light years in size where new stars are being born.
You could talk about HST initial focusing problem and correction but I would concentrate on the results.
You want to keep it highly visual as most people are visually oriented and good photos with a good story are memorable.
good photos plus interesting facts equal good grade
