So the researchers used a common technique among astronomers, observing the light's Doppler shift. Because it is so large and close to tau Bootis, the planet observed by Cameron and his colleagues moves swiftly. The wavelength of its light changes when the planet is moving rapidly toward us in its orbit compared to when it is moving just as rapidly away from us. Capitalizing on this Doppler shift, the researchers picked the planet's light signal out, separating it from the light emitted directly from the star. The pair note that previous observations by other researchers did not come to similar conclusions.
Time increases from bottom to top.
The signature is strongest when the planet is on the far side of the star with its illuminated face turned towards us, halfway up the diagram. In the right-hand panel, a synthetic planet signature has been injected into the data, and the resulting dark streak is clearly seen crossing from right to left halfway up the diagram. The slope of the streak tells us that the orbit is inclined at 60 degrees to the line of sight. The left-hand panel shows the actual data without the injected planet signature. In this case the dotted line shows the path of the planet as inferred from the signal analysis.