How Astronomers Know — Evidence Lab
Finding an Exoplanet with a Transit Light Curve
- Estimated time
- ~20 min
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Learning goals
- When a planet passes in front of its star, the star's brightness dips a little. That tiny, repeating dip is a signature of a transiting planet.
- MS-ESS1-2 — Students relate orbital motion to gravity and distance.
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Question 1 of 3
Look at the star-brightness table over 10 hours. During which hour did a planet most likely transit (block a small amount of the star's light)?
A 'light curve' shows a star's brightness over time. When a planet passes in front, the brightness drops by a small percent, then returns.
| Hour | Relative brightness |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 0.999 |
| 4 | 1 |
| 5 | 0.988 |
| 6 | 0.988 |
| 7 | 1 |
| 8 | 1.001 |
| 9 | 1 |
| 10 | 1 |
Table of relative brightness by hour: 1.000, 1.000, 0.999, 1.000, 0.988, 0.988, 1.000, 1.001, 1.000, 1.000.
Sources
- The Transit Method — NASA Exoplanet Exploration — NASA · NASA Exoplanet Exploration · Accessed 2026-09-01