Final answer:
Astronomers can derive information about a planet's atmosphere using photometry, which measures the star's brightness during a planet's transit, and direct imaging, where brightness at various wavelengths and spectral analysis reveal atmospheric constituents.
Step-by-step explanation:
To determine information about a planet's atmosphere, photometry and spectroscopy are key methods used by astronomers. Photometry involves measuring the slight dimming of a star when a planet transits in front of it. Through careful observation of the brightness and color of the star's light during these transits, astronomers can infer the size and composition of the planet's atmosphere. Direct imaging can also provide information by measuring the brightness of the planet at different wavelengths. Spectra obtained from the faint light can reveal the atmospheric constituents, such as the presence of hydrogen or methane.
While the Doppler method, which reveals a star's motion around a common center of mass with an orbiting planet by measuring its radial velocity, is effective for detecting planets, it does not provide direct information about the planet's atmosphere.
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