Answer: The Transit method
Detecting extrasolar planets by direct observation (with a telescope) is a complicated task. This is because any planet constitutes an extremely dim light source compared to the star around which it orbits.
So, to detect this extremely dim source is quite difficult due to the glare of the star's light that dulls it.
In this sense, scientists and astronomers have made several methods to find these extrasolar planets, among which the most successful has been the transit method.
This method is based on astronomical transit, a phenomenon in which a body (a planet in this case) passes in front of a larger one (the star), blocking (eclipsing) its vision to some extent.
It should be noted that this is the method currently used in the search for extrasolar planets. Space agencies such as ESA (Europe) and NASA (USA) have put into orbit satellites with extremely sensitive photometric sensors to observe even the smallest variations of intensity of a star due to the passage of a planet.