Bringing the Universe to America's Classrooms
Analyzing Light Curves of Transiting Exoplanets

Plotting Brightness Data

Changes in a star’s brightness can be plotted on a graph called a light curve. The light curve on this page shows observations of one star over a period of three days. The x-axis is time, and the y-axis is the star’s brightness. Most of the dots show a measured brightness of 1.000. This is called the baseline brightness. Each dot represents one measurement of brightness.
A line graph showing relative brightness over a time period of three days.

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In this graph, the y-axis is labeled “Relative 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 3, in increments of 1. A cluster of blue data points forms a rough line at about 1.000, with a dip at about 1.2 days. The dip includes data points that drop to somewhere between 0.9930 and 0.9935.

Did you notice the brightness changes only a tiny amount from the baseline? Most orbiting exoplanets cause only a very small dip in the observed brightness of their much-larger stars.

Take Notes

If we extended the light curve to a longer time interval, what additional information could it provide? Explain why.

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