![]() It is more difficult to disentangle these different measurements, but with sophisticated analyses, it is possible. This measurement encodes many observables, including the "impact parameter", or how close to the center of the star the planet transits, the size of the star (or more precisely, how dense the star is), and the eccentricity of the planet's orbit, or how close to a circle the planet's orbit is. The duration of the transit is the time it takes for the planet to cross over the face of the star. The grey points and purple points are averages over 1 minute and 15 minute intervals, respectively: The average secondary eclipse of HAT-P-7 b using the entire Kepler data is shown below. It is barely discernible by eye in the previous plot, but if you observe many of these eclipses and average the data, the secondary eclipse is quite apparent. This decrease in brightness is called the "secondary eclipse", and for planets is usually quite small. When the planet goes behind the star, any light from the planet, either starlight reflected off the planet's surface, or light being emitted by the planet because it is glowing hot, is blocked. The amount of time between two successive transits is the "orbital period" of the planet, which is the length of that planet's year: Using the formula for the planetary radius:Īnd plugging in values for depth = 0.6% = 0.006, R * = 2 solar radii, we find a planetary radius R p of about 1.5 Jupiter radii. Here, the transits decrease the flux from 1.0 to about 0.994 - a decrease of about 0.6%. The depth of these transits encodes the size of the planet. The Kepler light curve of HAT-P-7 shows three very convincing transits - the large dips highlighted with red arrows below. The entire span of the graph is within 1% of the total brightness of the star! Searching for transiting planets requires highly precise brightness measurements. This planet is a hot Jupiter - one of the easiest types of planets to detect.įirst of all, notice the scale of the plot above. The figure below shows a Kepler light curve of an exoplanet called HAT-P-7 b. The best part is that all of the data ever collected by Kepler are freely available to the public and can be downloaded from the internet by anyone. When it was operating, it was the most powerful planet-hunting observatory ever built. ![]() Launched in 2009, Kepler searched for transiting exoplanets for nearly a decade, before the end of its mission in 2018. In this section, we will show a light curve from the Kepler mission and determine planet parameters. ![]()
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