Earlier today, Virgin Galactic sent its SpaceShipTwo commercial aircraft into space, a historic first for the private company. But at a maximum altitude of 51.4 miles (82.68 kilometers), the spaceplane fell 10.6 miles (17.32 kilometers) short of the Karman line—the internationally recognized boundary separating the atmosphere from space. Prompting the inevitable question: What the hell is space, anyway?

Before we nitpick Virgin Galactic’s achievement, let’s give credit where it’s due.