Apollo 8 left Earth orbit traveling at 29,000 km (18,000 miles) per hour. Within the first 11 hours, the Earth’s gravity had slowed them to 9,000 km (5,600 miles) per hour. At 55 hours into the mission, the gravity exerted on the spacecraft from both the Earth and the moon was equal. They were 326,400 km (202,700 miles) from Earth and 63,000 km (39,100 miles) from the moon. Apollo 8 had slowed to 3,580 km (2,200 miles) per hour. The moon’s gravity now accelerated it for the next 14 hours until at Lunar Orbit Insertion, they were traveling at 9,200 km (5,700 miles) per hour. The engine firing slowed them to just under 6,000 km (3,700 miles) per hour, slow enough to be captured by the moon.