TOEFL Listening

🎧 Listening Transcript

Narrator: Listen to part of a lecture in an astronomy class. Professor: Today we're going to talk about the discovery of exoplanets, and specifically, the techniques astronomers use to find them. The first method, the radial velocity method, measures the wobble of a star caused by the gravitational pull of an orbiting planet. This technique is most effective for finding large planets that are close to their star, because they produce a stronger wobble. However, it has limitations. For example, it only gives us a minimum mass for the planet, because we don't know the tilt of the planet's orbit. If the orbit is highly inclined, we might miss the signal entirely. The second method, the transit method, involves observing a star's brightness over time. When a planet passes in front of the star, it blocks a tiny fraction of the star's light, causing a periodic dip in brightness. This method is great for detecting planets, and it also allows us to measure the planet's size and even study its atmosphere when it passes in front of the star. But transits only occur if the planet's orbit is aligned with our line of sight, so we only see a fraction of the planets out there. Both methods have their strengths, and astronomers often use them together to confirm a discovery and learn more about the planet.