ta152h0 wrote:I am guessing we wouldn't notice it but we might be in a molecular cloud ourselves . I often wondered where the sun gets all its hydrogen to maintain fusion for so many years..........
pass the beer
All the hydrogen the Sun burns is contained in a relatively small volume near the middle.
The hydrogen in the solar core is all it will ever have to "burn". All it will ever
have to convert into helium to warm our worlds. It is not an endless resource.
It will run out, someday.
The idea that Sol gets extra hydrogen from outer space, that it can pick up
fuel from the galactic clouds is erroneous. Sol projects a sort of force-field,
a bubble of relatively hot, fast-moving wind that pushes away the general
interstellar medium. This is the heliosphere. It is light-days across, and only a
couple of our robots have flown near to the edge of it, the heliopause. These
are the Voyagers and Pioneers.
http://en.wikipedia.org/wiki/Image:Heli ... rawing.gif
...and..
http://en.wikipedia.org/wiki/Heliosphere
Sol will, in about three or four gigayears, have used up enough of the
hydrogen in its core to cause the core to change state. It will start to use
helium to make things like carbon and oxygen. This will, for a time, produce
more heat than Sol does now. Sol will get hotter. It will expand. This will,
paradoxically, cause the outer surface to cool, to glow more red than yellow.
Sol will become a very hot Red Giant.
Sometime about then it would be very wise for Man to vacate the area.
Earth is not eternal.
When Sol heats up, it will pateurise the planet. Luckily, this will not happen
for another three thousand million years, at least. Most estimates give us five
or more gigayears before Red Giant Sol.
This does not mean we can sit here squabbling about who owns what land,
and which rules apply where until then. We are using up the treasure we need
to get us offworld at a great rate. We really should think of spreading out
right now. Of making this a Human Galaxy, a Human Cosmos.
[See "Life Cycle" at
http://en.wikipedia.org/wiki/Sun ]
Our children can always come home to watch Sol grow red.
But only if they live.
SDM.
I had no trouble recognizing the North American Nebula but the Pelican I haven't located yet! 
