 Chuck Yeager was the first to break the sound barrier in the X-1. In October 1947, he reached 1,100 km per hour. We used Mach numbers to signify the multiple of the speed of sound a vehicle travels. This was Mach 1.06. The Lockheed SR-71A Blackbird set the current world's record for jet aircraft at 3,530 km per hour in 1976. That's Mach 3.3. The fastest rocket-powered manned aircraft was the X-15. It set the record at 7,258 km per hour in 1967. That's Mach 6.7. To graph the speeds these cars and aircraft have achieved, we'll need to adjust the units on the X-axis again. This time, we'll make each interval on the X-axis equal to the distance sound travels in air in one second. That's 341 meters. The line at 45 degrees that divides the area in half is the line that represents the speed of sound in air. We're now getting close to as fast as humans and machines can move. The last three we'll cover are all spacecraft. Apollo 10 reached 39,896 km per hour in 1969 as it paved the way for man's first landing on the Moon. I remember watching this launch. The New Horizons spacecraft was launched in 2006, headed for Pluto. It is traveling at 58,536 km per hour. The record for unmanned spaceflight as measured relative to the Earth. It started sending back never-before-seen pictures of Pluto in July 2015. Helios A and Helios B are a pair of probes launched into orbit around the Sun in order to study solar processes. Launched on December 10, 1974 and January 15, 1976, the probes were notable for having set a maximum speed record for spacecraft at 252,792 km per hour. But this speed is measured relative to the Sun, not the Earth. At these speeds, we have to increase the distance intervals again. We'll set them at 10,000 meters per mark. Helios is moving 204 times faster than the speed of sound in air and 17.5 million times faster than the snail in my backyard.