This excerpt is from a SETI blog. The explanation, so clear, so sweet, is about how those scientists go about looking for earth like planets, on the assumption that is a good place to start looking for extra-terrestrial life.
An Earth-size planet's radius is about 1/100 the size of a Sun-like star. We're looking for one part per 10,000 drop in brightness caused by this tiny planet blocking a small fraction of the light from the star. In order to confirm our findings, we need to observe at least three transits - three times when the star is blocked by the body of the planet crossing in front of it. This can take several years. The time interval between these transits tells us what the orbital period of the planet is, and the fractional drop in brightness tells us the size of the planet relative to its star.
And also, from the same blog, Life at the Seti Institute---
"Stars are like bells - they ring. They are big balls of fluid and gas so they tend to oscillate. When stars are singing songs as they oscillate and pulsate, they actually change their shape. This shape change causes an apparent change in brightness, which we can measure very well. As we study the brightness variations in time, we can essentially hear the songs of the stars. By then studying the tones, or the notes the stars are singing, we can learn about the star's interior structure and work from models to estimate the size and the age of the star."
An Earth-size planet's radius is about 1/100 the size of a Sun-like star. We're looking for one part per 10,000 drop in brightness caused by this tiny planet blocking a small fraction of the light from the star. In order to confirm our findings, we need to observe at least three transits - three times when the star is blocked by the body of the planet crossing in front of it. This can take several years. The time interval between these transits tells us what the orbital period of the planet is, and the fractional drop in brightness tells us the size of the planet relative to its star.
And also, from the same blog, Life at the Seti Institute---
"Stars are like bells - they ring. They are big balls of fluid and gas so they tend to oscillate. When stars are singing songs as they oscillate and pulsate, they actually change their shape. This shape change causes an apparent change in brightness, which we can measure very well. As we study the brightness variations in time, we can essentially hear the songs of the stars. By then studying the tones, or the notes the stars are singing, we can learn about the star's interior structure and work from models to estimate the size and the age of the star."
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