There are no stars near the earth or the moon because they reflect too much light and blot out the stars. The stars are so far away that they're dim
enough to be blotted out by not much light from another source.
Originally posted by backtoreality
Why do you think they mention the cabin is "pressurized"?
Pressurized air for the cabin comes from the compressor stages in the aircraft's jet engines. Moving through the compressor, the outside air gets very hot as it becomes pressurized. The portion drawn off for the passenger cabin is first cooled by heat exchangers in the engine struts and then, after flowing through ducting in the wing, is further cooled by the main air conditioning units under the floor of the cabin.
The cooled air then flows to a chamber where it is mixed with an approximately equal amount of highly filtered air from the passenger cabin. The combined outside and filtered air is ducted to the cabin and distributed through overhead outlets.
Inside the cabin, the air flows in a circular pattern and exits through floor grilles on either side of the cabin or, on some airplanes, through overhead intakes. The exiting air goes below the cabin floor into the lower lobe of the fuselage. The airflow is continuous and quickly dilutes odors while also maintaining a comfortable cabin temperature.
About half of the air exiting the cabin is immediately exhausted from the airplane through an outflow valve in the lower lobe, which also controls the cabin pressure. The other half is drawn by fans through special filters under the cabin floor, and then is mixed with the outside air coming in from the engine compressors.
These high efficiency filters are similar to those used to keep the air clean in hospitals. Such filters are very effective at trapping microscopic particles as small as bacteria and viruses. It is estimated that between 94 and 99.9 percent of the airborne microbes reaching these filters are captured.
Originally posted by cmdrkeenkid
Cabin Pressurization
Get educated!
If you think about it, it should be obvious that the lower you are in the atmosphere, the more air you have above you, and therefore the higher the air pressure. Indeed, the change in pressure with height is so regular that meteorologists use pressure as a vertical coordinate instead of height. So instead of seeing weather maps at, say, 1.5 km, you would see a map at 850 mb, which is approximately 1.5 km above sea level.
To convert from pressure to height, just remember two rules:
Sea level pressure is about 1000 mb;
For every 5.5 km increase in height, the air pressure decreases by a factor of two.
Air pressure decreases with height because as you move up through the
atmosphere, there is less and less air above you pushing down. Because
pressure decreases with height, air expands as it rises. When the air
expands, it uses up energy by pushing the surrounding air outward. The
molecules in the air lose energy and slow down. So air cools as it rises and
warms as it sinks. Rising air cools at a rate of 5.5 degrees F for every 1000
feet.