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Analyzing Light Curves of Transiting Exoplanets

Periodic Changes

Astronomers look for regular patterns using the transit method. If the same amount of time passes between dips in brightness, and the dips last for similar lengths of time, the pattern is evidence that a planet may be orbiting the star.

Astronomers study the time between these dips to figure out how long it takes an exoplanet to make a full orbit around its star. They look for at least three identical dips to confirm that something is orbiting the star.

Earth takes 365 days to orbit the Sun. In everyday language, we call this amount of time a “year.” In astronomy, this is called the orbital period.

The dips in the light curves provide other information. Transit depth is the change in brightness during a transit. Larger planets block more light, so they have a greater transit depth. Transit duration is the time it takes the planet to cross from one edge of the star to the other. If the exoplanet takes a long time to transit, the dip will be wide; if the exoplanet moves quickly across the star, the dip will be narrow. 
A line graph showing relative brightness over a time period of seven days.

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In this graph, the y-axis is labeled “Relative Flux (brightness)” and marked from 0.992 to 1.002, from bottom to top, in increments of 0.002. The x-axis is labeled “Time (days)” and marked from 1 to 7, in increments of 1. A cluster of blue data points forms a rough line at about 1.000, with three dips occurring at about 1.2, 3.4, and 5.6 days. The dips include data points that drop to somewhere between 0.9930 and 0.9935. A red double-headed arrow labeled “Orbital Period/Length of year” indicates the span between the dips.

Can you spot a transit? Test your exoplanet detection skills in the Visualize It activity.

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