Space Officially Begins at 100 Kilometres
Space is the expanse beyond Earth's atmosphere, and also an empty area. The boundary is a convention, not a physical line.
Space is the expanse beyond Earth's atmosphere, and also any empty area or interval. There is no physical edge to the atmosphere — it simply thins until nothing is left — so the boundary is agreed rather than found. The Kármán line at 100 kilometres is the usual convention, chosen because above it an aircraft would need to fly faster than orbital speed to generate lift. The United States often uses 80 kilometres instead. Latin *spatium* meant an interval or extent.
- Beyond the atmosphere. *Outer space.*
- An empty area. *Not enough space.*
- An interval. *A space of time.*
- Kármán line — the conventional boundary. *At 100 km.*
- Latin — *spatium*, an extent. *The source.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | space | Space. |
| Plural | spaces | Spaces. |
| Verb | space | Space them out. |
| Adjective | spacious | Spacious. |
| Adjective | spatial | Spatial. |
- The satellite reached space in minutes.Astronomy.
- There is no space left on the shelf.Room.
- The Kármán line is a convention.Definition.
Where the atmosphere ends
- Troposphere — weather happens here, up to about 12 km
- Stratosphere — holds the ozone layer, to about 50 km
- Mesosphere — where most meteors burn up, to about 85 km
- Thermosphere — extremely thin, includes the aurora
- Kármán line at 100 km — the agreed boundary, not a physical edge
Old French *espace*, from Latin *spatium*, an extent, room or interval of time.
Where does space begin?
By convention at the Kármán line, 100 kilometres up. The atmosphere has no physical edge, so the boundary is agreed rather than measured.
Why did Kármán choose that height?
Above it, an aircraft would need to travel faster than orbital velocity to generate enough lift, so aerodynamic flight stops being possible.