Atmosphere On The Moon

"Ever wonder why people on the moon appear as they are flying or can jump for a far distance. The reality is that those people can't really fly or jump for miles. They aren't people like superman who have the capability to fly. It is because the moon has a very low gravitational pull. Unlike Earth's where objects stay on the ground due to the gravity. The moon's gravity is so much less then Earths that objects float or can jump high in the air. Thus because the Moon has low gravity it is to weak to hold an atmosphere. So for those who believe that once you are on the moon you have the capability to fly, it's not true. Its the realivily low gravity and the low escape velocity."


Atmosphere On The Moon
Why There Is no Atmosphere on the Moon
Weak Gravity Allows Gas Atoms to Escape so no Air on Small Planets
Buzz Aldrin saw such "magnificent desolation" when he stood on the Moon in July 1969 in part because it lacks an atmosphere. With no air or liquid water to erode the lunar geology, surface features retain their initial ruggedness. This lack of breathing air forced astronauts to wear special sealed spacesuits contributing to the desolation.
To understand why Earth's Moon and other small moons and planets have no atmosphere, it is first necessary to understand a little about gravity and escape velocity.
Gravity on the Moon
Some people think the Moon has no air because there is no gravity on the Moon. This is incorrect. Because the Moon is less massive than Earth the gravitational force on the Moon's surface is weaker than Earth's. There is still gravity on the Moon, but it is too weak to hold a significant atmosphere. Why?
Escape Velocity
When NASA launches a rocket into space, the rocket must reach a minimum speed to break the bonds of Earth's gravity. Rockets not reaching this minimum speed, called the escape velocity, fall back to Earth. Anything traveling at the escape velocity, or faster, can escape into space. Gravity pulls back anything traveling more slowly.
Earth's escape velocity is 11 kilometers/second. With less surface gravity, the Moon's escape velocity is 2.4 kilometers/second. Hence it is much easier to escape into space from the Moon than from Earth.
Heat and Molecular Motions
Gas atoms and molecules don't rest quietly. They move around fairly rapidly in random directions. As the gas temperature increases the average speed of the gas atoms increases. If the speed of a gas atom exceeds the escape velocity, that gas atom can escape into space.
Earth's average temperature is approximately 300 Kelvins. At this temperature the average (technically root mean square) speed of a nitrogen molecule is about 0.5 kilometers/second. Because this speed is much less than Earth's escape velocity Earth holds on to its nitrogen very tightly.
This speed is also less than the escape velocity from the Moon, but it is closer. So gas atoms and molecules can more easily escape from the Moon. To understand why, think about this analogy.
The average height for adult males is somewhere between five and six feet. However there are plenty of men that are either taller or shorter than this range. For example NBA basketball players are often over seven feet tall. However they don't have players over ten feet tall because that is too far above the average.
Escape Velocity and Atmosphere
As a rule of thumb, if the escape velocity is more than ten times the average speed of a particular type of molecule, that type of gas will remain in the atmosphere. Otherwise the molecules will escape over time. On Earth the escape velocity is high enough to hold its atmosphere. Molecules would have to be like the ten foot tall players to escape. On the Moon however the escape speed is low enough that the faster moving atoms can escape. Molecules would have to be like the almost seven foot tall NBA players to escape. So these gas atoms and molecules fly off into space. The Sun heats the remaining gas enough that those atoms and molecules eventually speed up and escape.
Hence less massive moons and planets including the Moon and Mercury have no significant atmospheres. Mars is a little more massive so it has a thin atmosphere. More massive Earth and Venus have significant atmospheres and the very massive gas giant outer planets retain very thick atmospheres.
This article was found from the website (http://physics.suite101.com/article.cfm/why_there_is_no_atmosphere_on_the_moon)