h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

This has been making me curious. Where exactly does the earth's atmosphere end and space begin? How many feet above sea level is it? And how did scientists find this out, if anyone knows...

Try http://liftoff.msfc.nasa.gov/academy/space/atmosphere.html

I suspect it's too much of a gradual thing to be exactly verified.

The exosphere is the upper part of the Earth's atmosphere and consists of mostly hydrogen molecules, which decrease in density as you go further away. However, you could define that as space. The Americans, when they flew their X-15 tests, called it sub-space.

B

Pedantry alert!

The earth is a constituent of the space-time continuum, and is thus, space, as is everything in and on it. You can't be outside of space, you are it! You are awash with the stuff of stars, a bubble of energy burped from your antecedents and, for a limited time, blessed with the opportunity to experience and determine your path in the continuum and relate with other burps. To say you are outside of space is to forget your place.

Excuse me now I have to go to work.

And in next-week's Spot The Geek competition...

B

Well that link is quite good, thanks for that. As for being a burp, that makes me think of lunch...

I guess for arguments sake we are technically IN space as a planet, I was just wondering how NASA knew how far they had to make shuttle blast off to before it escapes the earth's atmosphere

I remember someone asking me "How far do you think you'd have to travel to 'officially' be in space?", and being surprised when he told me it was about the distance from London to Northampton, or 60 miles.

I've no idea whose 'official' measurement that is

The Ordanance Survey?

B

Between some people's ears.

Incog.

We are stardust

I think it is the point where your orbit won't decay due to atmospheric drag. as this changes with space weather, it varies a bit, but around 60 miles sounds about right.

According to posting 4 (which I agree with, but it made me think - yes scary I know) does that make space God?

There's no clear definition in international law defining where space starts (or rather where a nation's sovereign airspace ends), but all parties to discussions seem to agree that it should be set at somewhere between 100km and 110km.

And from http://www.inesap.org/bulletin20/bul20art08.htm#t13 there's this:

"The US Air Force (USAF), for example, uses 80 km as the altitude required for the award of 'Astronaut Rating'. Soviet delegates to the United Nations repeatedly called for a figure of '110 km or less'. During ascent to orbit, NASA's space shuttles complete their main engine burn at an altitude of about 84 km, and NASA uses 400,000 ft (122 km) to define 'entry interface' when returning shuttles first begin to encounter aerodynamic forces."

Yeah, I thought there would have to be a certain point where shuttles would have to make sure their heat sheilds were working, and they were at the right speed and angle etc. as we well know from the recent crash of Columbia.

But why do the US and the Russians have different "measurements" of where this point is?
Is it just an old Cold War thingy?

Or is it an imperial versus metric problem?

That was how NASA lost that Mars Orbiter (I forget which just now).

Metric - NASA
Imperial - MacDonald Douglas

At least I think it was that way round...?

*wanders off, mumbling to self about bl**dy foreign measurements and the Cubit*

http://www.sover.net/~rc/deep_secrets/index.html
turvy

I think that was how the first Boeing 737 almost crashed, coz they had just converted from using pounds of fuel to kilograms and they didnt do the conversion right and ran out of fuel!

Heres something fun - tell an American or Canadian how much you weigh in stone, they usually get really baffled about that

yes, that's what happened.

and when they ran all the other pilots through the simulation, they all crashed.

it was made into a film for tv called "Freefall: Flight 174"