What is the radial velocity method used to detect planets orbiting other stars? Why is it difficult to use this method to detect planets like Earth?

Answer: The radial velocity method, also known as the Doppler spectroscopy method, is a technique used to indirectly detect exoplanets by observing the gravitational interaction between the planet and its host star, causing the star to "wobble." This wobble creates a Doppler effect observed as redshifts and blueshifts in the star's spectrum. Detecting Earth-like planets using this method is challenging because the wobble caused by small, less massive planets is harder to detect due to its small magnitude. Additionally, the longer orbital periods of Earth-like planets require extended observation periods, and factors like stellar activity or background noise may further complicate the detection process. Alternative methods, such as the transit method, have been developed to better detect smaller, Earth-sized planets.