Even through a telescope, a star appears to be a single star but through the spectroscope it shows a pattern of two absorption lines for each of the lines in the spectrum of a star like our sun. For each member of the pattern, one line, which is somewhat stronger than the other, is at a shorter wavelength. The weaker is at a somewhat longer wavelength. Over the 5 days the two lines merge into one then separate during the next 5 days back to the former maximum difference. However, now the stronger line is at a longer wavelength. From this evidence, there are actually stars which orbit one another once every days.