Transcript: A clever way to detect extrasolar planets is to look for transits, the situation where the dark planet passes in front of the bright star. A giant planet in principle might cover about 1 percent of a star. However, in practice the situation is not this good because the giant planet has a diffuse atmosphere that doesn’t block out light very well, so really the drop in light intensity from the star would only be about a tenth of a percent or even less. So we’d be looking at a star varying in its brightness momentarily by less than a percent. In actual fact the situation is not even this good because we can only see the situations or geometries where the planet and the star were lined up so that the transit could occur. Geometry shows that only 1 in 500, or 0.2 percent, of all the situations will have this favorable orientation. Finally, the transit does not occur for very long. The time it would take a Jupiter to pass in front of a Sun as seen from afar is only 0.03 percent of its orbit, one day in a 12 year orbit.