The basis of Rutherford's planetary model is that negatively charged electrons orbit a positively charged nucleus. This was based off of his results of his Gold Foil Experiment where he aimed a narrow beam of alpha particles at the gold. The screen around the gold was made of a material that produced a flash of light when struck by a fast-moving alpha particle. By observing the flash, he could figure out the path of an alpha particle after it passed through the gold. Some of the locations of the flashes on the screen did not support Rutherford's prediction. More particles were deflected than he expected. This meant that the alpha particles whose paths were deflected must have come close to another charged object; the nucleus.