I thought we were talking stars, but we can discuss planets too. In the case of planets the answer is unequivocally no - we do not rely entirely on visual data for our knowledge about them. As for stars, unless you interpret âvisual dataâ widely to mean all electromagnetic wavelengths, from radio waves, through microwave, infrared, visible (which is the only part of the EM spectrum to which the term âvisualâ is normally applied), ultraviolet, X-rays and gamma rays, which interpretation would be rather eccentric, then, again, the answer is no. Certainly we donât know everything that we know about stars simply by looking at them with or without telescopes.