Transcript: The most obvious way to detect an extrasolar planet is direct by imaging. However, some very simple numbers show that this is a very difficult experiment. As seen from afar Jupiter reflects some of the Sun’s light, but it’s very little, only two-billionths. You can work this out from the inverse square law and the size of Jupiter relative to its distance from the Sun. It’s actually worse than that because we only see half of the reflected light, think of the phases of Venus, and Jupiter is not a perfect mirror, reflecting only 30 percent of the photons that fall on it. So the total fraction of light reflected by Jupiter from the Sun is 3 times 10-10, a very small fraction. What about a smaller planet? For the Earth the situation is actually worse. Although Earth is five times closer to the Sun than Jupiter and intercepts twenty-five times more light, from the inverse square law, it’s ten times smaller, and so its cross-sectional area is a hundred times less. The product of those two means a four times more difficult experiment. Also, as seen from afar, the distance of a nearby star, the angular separation of the Sun and Jupiter is only a couple of arcseconds, and the angular separation of the Sun and the Earth would be less than an arcsecond. Thus, it’s like trying to see a candle flame in close proximity to a football stadium arc light, an extremely difficult experiment that has not yet succeeded.