This artist's conception depicts the Kepler-10 star system, where Kepler has discovered two planets. Kepler-10b (the dark spot in front of the yellow star) is one of the smallest planets outside our solar system. Kepler-10c, the larger planet to the left is much bigger. Both planets would be blistering hot worlds. (Credit: NASA/Ames/JPL-Caltech)

Many explorers of "new worlds" set out seeking knowledge. The Discovery Expedition to Antarctica was organized to carry out scientific research and geographical exploration. Lewis and Clark's expedition to the Pacific Ocean was to learn more about the American West; they returned with careful records, maps and samples of the plants and animals they encountered. Captain James Cook's expedition on the Endeavour to Tahiti was sent both to explore the South Pacific, but also to observe the 1769 transit of Venus across the sun in order to calculate the distance to Venus, and set the scale of the solar system.

Venus transited in front of the sun on June 5, 2012; the next Venus transit won't be until 2117!

Many modern explorers are using telescopes to discover new worlds. These telescopes can search the skies, finding and studying planets that orbit other stars in our galaxy. The NASA mission Kepler has a spacecraft which trails the Earth as it orbits the sun, observing stars and looking for planets that may cross in front of the star (transiting) and blocking some of that star's light. It is sensitive enough to detect Earth-sized planets -- including some that may have life!

This topic investigates planet transits; learn more about how distant worlds are being discovered through the Kepler and other missions! Check out transit activities in the Classrooms and Organizations and Clubs sections, and find a variety of powerpoints, articles, videos, interactives, and more under Educational Resources..