# Understanding the Boundary Between Earth and Outer Space
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Chapter 1: Defining the Edge of Space
Where exactly does space start? While it might appear to be a straightforward inquiry, it carries significant ramifications. For ancient civilizations, this question was simpler; space was simply everything beyond their reach—an expansive sphere surrounding the Earth. However, in today’s world, space is not only reachable but also increasingly accessible. So, where does this boundary lie?
Is it determined by the point at which the atmosphere ceases? Or does it relate to the moment a spacecraft is no longer influenced by Earth's gravity? Unfortunately, neither of these criteria provides a clear distinction, as the Earth's exosphere extends far beyond what we can perceive, and its gravitational pull affects objects for countless miles around.
For most people, this question may seem trivial, but for the growing number of countries interested in space exploration, it is paramount.
Section 1.1: The Distinction Between Airspace and Outer Space
Current international law stipulates that a nation maintains authority over its airspace, which extends all the way to, well, outer space. This means that the air and the volume it occupies, from the ground up to space, falls under the jurisdiction of the nation below. A notable example of this was when Belarus compelled a commercial airline to land in Minsk while it was en route between two locations outside its jurisdiction, highlighting the complexities of airspace control.
While airspace is a familiar and easily comprehensible concept, the notion of "spacespace" is less clear. Do nations have dominion over the void above them? The unequivocal answer is no. Space is continuously changing concerning the Earth, with objects orbiting independently of airspace regulations. Thus, the question remains: where does airspace end and space begin?
Section 1.2: The Kármán Line
The challenge of defining this boundary was addressed by 20th-century physicist Theodore von Kármán. He asserted that a universally recognized point must exist where Earth’s atmosphere concludes, and space commences. In a world where intercontinental ballistic missiles (ICBMs), satellites, and space travel are prevalent, recognizing this boundary became critical.
Kármán proposed that this delineation occurs at an altitude of 100 kilometers (62 miles) above sea level. This height represents the threshold at which an aircraft would no longer be supported by aerodynamic lift but would instead rely entirely on orbital centrifugal forces. Though somewhat arbitrary, this measurement provides a clearer understanding of what constitutes space.
Kármán is credited with calculating the altitude at which an aircraft loses sufficient lift to remain airborne. This pivotal boundary is now named in his honor. In his autobiography, he remarked:
> "This is certainly a physical boundary, where aerodynamics stops and astronautics begins, and so I thought why should it not also be a jurisdictional boundary? Haley has kindly called it the Kármán Jurisdictional Line. Below this line, space belongs to each country. Above this level, there would be free space."
Today, the altitude of 100 kilometers is widely accepted as the point where Earth ends and space begins.
Chapter 2: The Importance of Defining Space
In summary, the quest to establish the boundary between Earth and space not only clarifies our understanding of the universe but also plays a crucial role in international law and space exploration.