Photometry
The technique involving photometry uses the change in brightness of the star that occurs when the extrasolar planet transits its star, resulting in a dimming effect. The time periods involved as well as the variability of the star during a transit enables planets of about half Earth size to be detected at about 1 AU orbiting a 1Mo star in four years. Planets with a longer orbital period than two years would take longer to observe, as the odds of a transit become smaller. The larger planets may be detectable from their reflected light which will vary as the planet orbits, such that the further towards Earth it gets the dimmer the light received from the system. If the planet does transit the star, then the data can be combined with Doppler data to determine the density of the planet. In these cases accuracy in the mass is better as the orbital plane must be close to ninety degrees in order to cause transits, thus a lower uncertainty.