→ Widely unknown Exoplanet Astronomer

To be able to find the radius of an exoplanet, astronomers study the lighcurve. The lightcurve is made by plotting the flux form the host star as a function of time. Here is an example of a light curve:

The depth of the light curve will depend on a number of things such as the radius of the exoplanet and the distance of the exoplanet  from the host star. However, it is not only the properties of the exoplanet which matter. Imagine a star-planet system where we now double the radius of the host star whilst keeping the radius of the planet the same. In this case the exoplanet will block out the same amount of light, but the dip in the light curve will be smaller, since the host star has a greater flux.

Thus, from the transit method astronomers are only able to derive the radius of the exoplanet relative to the radius of the host star.  The unit used is the radius of the planet over the radius of the host star, Rp/R*.

The Kepler satellite was launched in March 2009 and has since June 2009 been sending data down to Earth. It has been pointing at only one portion of the sky the entire time looking for variations in the brightness of stars. The image below shows the field of view of Kepler.

Kepler Field of View. 42 CCDs each with 2200 × 1024 pixels are used in order to get a large field of view. Credit: NASA

When an exoplanet passes infront of a star a small portion of the light is blocked out. Studying how the light is being dimmed gives astronomers a wealth of information about exoplanet candidates. I say candidates as a dip in the light curve alone is not enough to confirm the existence of an exoplanet. Binary and variable stars are examples of what is known as false candidates.

To quickly learn more about the transit method the following video might be of interest: The Exoplanet Transit Method – The Method – Part 2