Black Triangle Sighting in Henderson, Texas on July 10th 1975 – Three triangular shaped craft flying in formation

The event took place in the summer of 1975. It was late at night and I was laying in a hammock in my backyard when I observed three triangular shaped vehicles over head. They made no noise and the center of each craft was dark but the edges were light with a soft bluish light. As I observed the vehicles, the one on the right left the formation. It exited 90 degree to the direction that the others leaving in a streak of light. It instantly disappeared from view. I continued to watch the two remaining vehicles. About 10 to 15 seconds later, the vehicle that left returned. It returned in streaks of light and was suddenly in formation again. They flew in formation for a few more seconds before leaving to the East. They accelerated leaving streaks of light and were instantly gone from view.