Turner originally planned to begin the rebellion on July 4, Independence Day, 1831, but he had fallen ill and used the delay for additional planning with his co-conspirators. An atmospheric disturbance on August 13 made the sun appear bluish-green, possibly the result of lingering atmospheric debris from an eruption of Mount St. Helens in present-day Washington state; he took it as the final signal and began the rebellion a week later, on August 21. He started with several trusted fellow slaves, and ultimately gathered more than 70 enslaved and free blacks, some of whom were on horseback. The rebels traveled from house to house, freeing slaves and killing all the white people whom they encountered.