Chapter 1: Defining the Start of Space

When we discuss space, we refer to the vast expanse above us, filled with stars and planets. But where exactly does space start after one departs from the Earth's surface?

Space is often defined as the region beyond the Earth's atmosphere. According to the Federation Aeronautique Internationale (FAI) and NASA, the boundary of space is set at 100 kilometers (62 miles) above sea level. This threshold is known as the Karman Line.

The concept of where space begins originated from the National Advisory Committee for Aeronautics, which later evolved into NASA. Initially, they defined the start of space as the altitude where atmospheric pressure drops below one pound per square foot. This altitude is approximately 50 miles (80 kilometers) above the Earth's surface.

This lower threshold was established because, at this height, aircraft could no longer generate lift, rendering them uncontrollable. Interestingly, this is also the boundary of space recognized by the United States Air Force, which awards astronaut status to pilots who cross this 50-mile mark. However, how did the definition shift to the higher distance of 62 miles?

The aerospace engineer Theodore von Karman determined that 100 kilometers was the appropriate starting point for space. He concluded that at this altitude, the atmosphere is so sparse that an aircraft would need to travel faster than orbital velocity to achieve lift, which is the speed required to maintain an orbit. This 62-mile threshold was later recognized by the FAI and became known as the Karman Line.

Section 1.1: The Extent of Earth's Atmosphere

Despite the Karman Line being often cited as the edge of space, it does not mark the end of the Earth's atmosphere. The Karman Line is located at the bottom of the thermosphere, which stretches up to 375 miles (600 kilometers) above the Earth. Above this layer lies the exosphere, which extends approximately 6,200 miles (10,000 kilometers) into space.

Thus, spacecraft and satellites must continually adjust their orbits due to the friction caused by gas molecules present in these outer atmospheric layers. There are various interpretations of where space begins, but reaching an altitude of 50 miles above the Earth seems to qualify one for the title of astronaut.

Want to delve deeper into fascinating facts? Explore "The Wonderful World of Completely Random Facts" series on Medium.

Chapter 2: Understanding Space Through Video Insights

In the video titled "Where Does Space Actually Start?", viewers are taken on a journey to explore the complexities surrounding the definition of space and its boundaries.

Another insightful video, "Where Does Space Begin? We Asked a NASA Expert," features expert opinions that further clarify the distinctions in defining the start of space.