I read somewhere that light is affected by gravity, so then why doesn't like us it move along with the earth?
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The geometry of the path that light follows definitely changes in the presence of massive objects, e.g. the Sun. Eddington's experiment indeed showed that for the Sun, concluding that the light bends $\sim 1$ arcseconds when it goes near. This in contrast with the earth that goes a full $360^\circ$ around the sun.
It is possible to make light go around a full revolution, but for that you would need to shrink the Sun to a radius of $R_s \sim 3$ km, and in this case, the light will move in an orbit of radius $3R_s/2\sim 5$ km. Compare this with the actual size of the Sun $\sim 7\times 10^{5}$ km, and the size of Earth's orbit $\sim 1.5\times 10^{8}$ km!
caverac
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The effect of the Earth's gravity on light is way too tiny to care for most purposes.
https://en.wikipedia.org/wiki/Gravitational_lens
Using a classical calculation to get the size of things without getting too fancy, the orbital speed (for a circular orbit) at the surface of the Earth is about $9 \frac{km}{s}$. The speed of light is about 33 thousand times faster than that.
The the relationship between the mass of the planet and the orbital speed goes like $M \sim v^2$. So in order for the orbital speed to be 33 thousand times as fast, the Earth would have to be about 1 billion times as massive.
David Elm
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