The Transit Method—Changes in Brightness
Scientists cannot yet directly observe rocky Earthlike planets outside the solar system because rocky planets do not give off their own light. So how do we know that exoplanets are there?
Imagine that you are in a darkened room lit by one light bulb. Now imagine that a butterfly flies in front of the light bulb. Think about what happens to the brightness of the light that you can see at the moment the butterfly flies across, or transits, the light bulb.
Stop and Discuss: How would the brightness appear to change at the moment the butterfly crosses in front of it?
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Watch the animation to see how the light from a star is blocked as a planet transits, or crosses in front of it.
Astronomers measure a star’s brightness over time. If the brightness decreases (or dips) a little, this could be evidence of an exoplanet, comet, or asteroid passing across the star. This technique of finding exoplanets is called the transit method.
For you to see the butterfly transit, the butterfly must be directly between your eyes and the light bulb.
The same is true of finding exoplanets with the transit method. To observe a transiting exoplanet, the planet must pass directly between the telescope and the star. If everything lines up just right, the telescope will detect a small dip in the star’s brightness as the planet moves across the star.
Many exoplanets will not be visible from Earth because they do not pass between their star and Earth. Evaluate whether the exoplanet passing in front of its star would be visible through the telescope. Click Arrange It to begin.
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