Final answer:
The altitude at which 'space' begins is commonly considered to be 100 kilometers (62 miles) above sea level, known as the Kármán line. At this altitude, the atmosphere is very thin, making it difficult for aircraft to generate lift. The Kármán line is a widely accepted practical definition for the start of space.
Step-by-step explanation:
The altitude at which 'space' begins is commonly considered to be 100 kilometers (62 miles) above sea level. This region is known as the Kármán line, named after the Hungarian aerospace engineer Theodore von Kármán.
At this altitude, the atmosphere is so thin that the air density becomes very low, making it difficult for traditional aircraft to generate lift. Additionally, objects in this region experience the effects of microgravity, which is why astronauts on the International Space Station appear weightless.
It's important to note that there isn't a clear boundary when it comes to defining space, as the atmosphere gradually transitions into the vacuum of outer space. However, the Kármán line is widely accepted as a practical definition for the beginning of space.