Transits

By looking at the amount of observable light from a star, we can find out whether or not there are any orbiting exoplanets. To do so, we first observe a star's light using photometers, devices that can measure electromagnetic radiation. Next, we compile this data into a graph that measures the amount of light, or relative brightness of a star. This graph is called a light curve. If nothing moves in front of the star, then the relative brightness will be constant. However, if the star has an orbiting exoplanet, the relative brightness will be lower (and a dip in the graph will be obvious) when the planet is perfectly in front of the star. This is because the planets will block some of the stars light, similar to our solar eclipses. 

Finally, through these dips in the graph, scientists are able to determine many factors including the size of the planet and its orbit. Bigger planets show deeper dips in the light curve and the longer it lasts, the further away the planet is from its star. We are able to find how large the orbit is and also how fast the orbit goes circling back to Kepler's Second Law explaining how planets move over equal areas of space over equal areas of time. To learn more about the specifics of Kepler's Laws, click here.