Observational Techniques The direct detection of extrasolar planets is very difficult because the star's light is usually at least one billion times stronger than that of the planet. The problem has been likened with that of a lighthouse: if the lighthouse keeper would stand next to the powerful light source and point a pocket lamp towards us, its feeble point of light would "drown" in the stronger light and be completely invisble to us. In fact, in order to see the faint light of a planet near another star, we must use a telescope that has two important properties: it must be large in order to collect sufficient light to be able to see the faint object and it must also have extremely good optics that produce very sharp images so that we can "block" the light from the central star. No planets seen directly so far When the exoplanet is located too near its central star, we cannot see it. However, in some cases, faint objects have been seen near stars and hopes were raised that they might be bona-fide planets. For instance, in the case of the nearby star Gliese 229 it was possible to see a faint companion. However, it was found that that object, Gliese 229 B was not a planet, but a Brown Dwarf, an object that is 10 times lighter than the Sun, and which is created like a star but which cannot burn its hydrogen as the Sun does. Indirect methods Fortunately, there are indirect methods to discover planets. Those that have been most successful are based on gravitational effects caused by the planet and detectable by observation of the light from the central star. They include: Astrometric perturbations - this means that the central star is seen to move a little back and forth ("rocking") in the sky, as the planet pulls it in different direction during its orbital motion around the star. Very accurate positional measurements are need for this method to work. Velocity variations - this method is based on the star's motion along the line-of-sight and it is the way all of the known exoplanets have been found so far. The measurements are carried out with a spectrograph and the velocities are determined by the Doppler effect that causes the absorption lines from the star to change wavelength as the velocity changes. Another indirect method consists of observing the minute dimming of the light from the star, whenever the planet happens to pass in front of the stellar disk, as seen from the Earth. Only one such observation has been successful so far. Yet another possibility, at least in theory, is to search for signatures in the star's spectrum that may originate in the planet, but this may be extremely difficult and we may have to await much better instruments than now available. However, the search is on! Direct observations When it has become possible to obtain a direct image of an exoplanet, an observational feat that may actually happen soon, the next step will be to observe its spectrum. A careful analysis may then reveal particular spectral lines that can tell us about the physical conditions on the planet, for instance whether or not it possesses an atmosphere. Spectral observations of Earth-like planets will hardly be possible with today's astronomical instruments, but the next generation of extremely large ground-based telescopes or specialized space observatories may be be able to achieve this very difficult feat. Only then will we know whether any of these exoplanets are "hospitable" to Life.