# Where exactly does "Outer Space" begin **URL:** \ **Category:** Factual Questions\ **Created:** [May 14, 2004, 5:39pm UTC](https://boards.straightdope.com/t/where-exactly-does-outer-space-begin/245142 "2004-05-14T17:39:21Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Starguard](https://avatars.discourse-cdn.com/v4/letter/s/8dc957/32.png) [@Starguard](https://boards.straightdope.com/u/Starguard)\ **Post date:** [May 14, 2004, 5:39pm UTC](https://boards.straightdope.com/t/where-exactly-does-outer-space-begin/245142/1 "2004-05-14T17:39:21Z")
If I am correct, I do believe that there are four basic layers in our atmosphere Tropisphere Stratosphere Ionisphere Exodosphere (If i spelled those correctly) And there are several smaller layers that lay between each one If I am correct, I do believe that the top layers of the exodosphere is the exact point where the earths atmosphere ceases and the vacuum of space begins. There are others who argue that this info is incorrect for various reasons. Do you agree/disagree with this? If so…why? why not? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 14, 2004, 5:48pm UTC](https://boards.straightdope.com/t/where-exactly-does-outer-space-begin/245142/2 "2004-05-14T17:48:49Z")
There isn’t any “exact point” at which we can say Earth’s atmosphere ends and space begins. > [@](#): > > So, how do we define where space begins? Many different definitions exist. The United States awards astronaut status to anyone who flies above 50 miles in altitude. Many flight engineers, dealing with the effects of friction and heating of spacecraft due to atmospheric particles, define the boundary to be at 400,000 feet (75.76 miles). They call this the “entry interface,” the point at which heating on reentry becomes observable. From [NASA](http://liftoff.msfc.nasa.gov/academy/space/boundary.html). ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [May 14, 2004, 9:42pm UTC](https://boards.straightdope.com/t/where-exactly-does-outer-space-begin/245142/3 "2004-05-14T21:42:39Z")
That might be a workable definition of _space_, but what are the differences between near space, outer space and deep space? ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [May 14, 2004, 11:16pm UTC](https://boards.straightdope.com/t/where-exactly-does-outer-space-begin/245142/4 "2004-05-14T23:16:17Z")
The X-prize people set the edge of space at 100km. A privately built ship made it to an altitude of [64km just this week](http://news.bbc.co.uk/2/hi/science/nature/3713119.stm). Defining the edge of the atmosphere is tricky as it [expands and contracts with the phases of the solar cycle](http://science.nasa.gov/headlines/y2000/ast30may_1m.htm) > [@](#): > > Increased solar heating makes the thermosphere (~100 - 500 km) puff out as denser layers from lower altitudes expand upward. The density of the thermosphere can soar by a factor of 50 during solar maximum, with a commensurate increase in atmospheric drag on satellites. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 14, 2004, 11:30pm UTC](https://boards.straightdope.com/t/where-exactly-does-outer-space-begin/245142/5 "2004-05-14T23:30:08Z")
> [@](#): > > That might be a workable definition of space, but what are the differences between near space, outer space and deep space? “Outer space” is synonymous with the colloquial usage of “space”, i.e., above the atmosphere. Technically, any point with a position is in “space”, hence the distinction. I’m not familiar with the term “near space”, but I would presume that it’s synonymous with low Earth orbit, that is, an orbit about as low as you can make it without crashing. And the meaning of “deep space” varies with context. As far as NASA is concerned, it seems to mean “beyond the Moon” or “beyond where the Earth’s gravity is significant”. It can also mean “far enough away from any mass that gravity is negligible”. Of course, “significant” and “negligible” depend on your context, too.