In descriptions of the newly discovered exoplanet, named Proxima Cen b, orbiting Proxima Centuri, it is mentioned that a determination of its size could be established by observing the planet’s transit in front of Proxima centuri, which would reveal the exoplanet’s diameter. It is my understanding that, to date, such projects have failed. I have also read that such projects are “expected” to fail, since geometrically speaking, there is only a 1.5% chance that Proxima Cen b passes across the face of Proxima. Why is is? And how is 1.5% calculated.