People wait in line during one of McDonald Observatory's many public star-gazing events. With its 6,800 foot altitude, Ft. Davis, Texas is one of the darkest spots in the continental United States. The glow on the horizon between the two domes is known as the zodiacal light. The zodiacal light is a result of small particles orbiting the sun, which scatter its light. It is visible from dark locations on winter evenings and fall mornings in the northern hemisphere.