Johann Karl Friedrich Zöllner

Johann Karl Friedrich Zöllner (1834 – 1882) was a German astrophysicist who studied optical illusions. He invented the Zöllner illusion where lines that are parallel appear diagonal. The crater Zöllner on the Moon is named in his honor. For the first time he actually proved Christian Doppler's theory on the effect of motion of the color of stars, and the shift of absorption lines thereby (red-shift) (1869), by the invention of a very sesitive spectroscope which he named "Reversionspectroscope". He had shown also that the red-shift was in addition caused by variation in the stars' lights intensities with the help of his "Astrophotometer" (1865).