Fahrenheit 4,118

Space equavalency is said to begin at the Armstrong Line of the upper atmosphere located at 62,000 feet above sea level (11.8 miles). This imaginary line was first discovered by U.S. Air Force surgeon Harry George Armstrong. Pressure at the Armstrong Line is a mere 0.0618 atmospheres.

Today, some military and civilian jets travel to the edge of space-at or just above 70,000 feet in altitude. A few Russian MIGs, the Air Force's U-2, and NASA's ER-2 aircraft make occasional jaunts to this rarified place where the atmosphere isn't much to speak of. Here, the pilots are required to don fully pressurized spacesuits-just in case of cabin failure.

Exploration at the edge of space began in earnest during the 1950s and 1960s; research revealed some unusual aspects about temperature and heat in the near vacuum of the space-equivalent environment.

During his dangerous open-gondola balloon trip to 102,800 feet in Excelsior III in 1960, USAFCapt. Joe Kittinger uncovered an unusual phenomena. Outside his pressure suit, Kittinger noticed that the "air" temperature 21 miles up was minus 38 degrees Fahrenheit. Yet he observed that it was meaningless compared to how the rest of us define temperature back on Earth. At the edge of space, Kittinger experienced, there is a strong difference between temperature and heat-they are, in fact, very distinct from each other.

Temperature is a measure of motion-the motion of air molecules. When we stand at the beach, at sea level, air molecules are at their densest-the entire column of Earth's atmosphere pushes down on them (and us) from above. Without getting into the details of how, a researcher measured just how many molecules exist at sea level in a cubic inch of air. The answer is an incredible 400 quintillion molecules!

At sea level, air molecules are like ballroom dancers on a very crowded floor. They are elbow-to-elbow and don't have much room to demonstrate their Tango or Fox Trot moves-in fact, air molecules constantly collide at sea level being a mere four-millionths of an inch apart. The velocity of these air molecules bouncing off each other is slowed down thus lowering their temperature.

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