where does space begin

Space does not have a single sharp “starting line,” but most organizations treat space as beginning somewhere around 80–100 km (50–62 miles) above Earth, near what is called the Kármán line. The exact height depends on whether the boundary is defined legally, physically, or for awards like astronaut wings.

The big idea

• Earth’s atmosphere thins gradually; it does not suddenly end at a crisp edge.

• Different scientific and regulatory communities have therefore adopted slightly different “space begins here” altitudes as rules of thumb.

The Kármán line

• The Kármán line is a commonly used boundary where aerodynamic flight stops being practical and orbital-style motion takes over.

• Many international and sporting bodies place this line at about 100 km above sea level, while some analyses argue a more physical boundary is closer to 80–84 km.

Other definitions in use

• Some U.S. standards, such as historic Air Force astronaut wings, have used roughly 80 km (50 miles) as the threshold for being in space.

• NASA scientists sometimes emphasize that if the question is “where does the atmosphere end,” you can trace very thin atmospheric gases hundreds of kilometers up, around 400 miles (about 640 km) and beyond.

Why there’s no single answer

• Gas molecules high above Earth are sparse and unevenly distributed, so drawing a strict physical cutoff is more a matter of convention than of a sudden physical change.

• As a result, experts propose ranges from a few tens of kilometers to much higher, but in practice 80–100 km is the widely used “boundary of space” for conversations, records, and regulations.

Information gathered from public forums or data available on the internet and portrayed here.