2. An envelope of gas surrounding a planet, star, or other celestial body, where the gravitational field is strong enough to restrain the gases.
The actual pressure exerted by he atmosphere fluctuates around this value, which is assumed to be standard at sea level and zero degrees centigrade/32 degrees Fahrenheit, and is used when dealing with very high pressures.
On earth, atmospheric pressure decreases with altitude and in its lowest layer, earth's atmosphere consists of nitrogen (78%) and oxygen (21%), both in molecular form (two atoms bonded together) and 1% argon.
Small quantities of other gases are important to the chemistry and physics of the earth's atmosphere, including water and carbon dioxide.
The earth's atmosphere is divided into four regions of atmosphere classified by temperature and the thermal structure of the earth's atmosphere is the result of the complex interaction of the following:
- Electromagnetic radiation from the sun.
- Radiation reflected from the earth's surface.
- Molecules and atoms in the atmosphere.
The atmosphere consists of four distinct layers, whose boundaries are not precise:
- The troposphere (extending from sea level to about 5-10 miles [10 to 20 km] above the earth.
- The stratosphere (up to about 30 miles [50 km]).
- The mesosphere (up to about 60 miles [96 km]).
- The thermosphere (up to about 300 miles or more [480 km]).
The upper region of the troposphere is often regarded as a separate region known as the exosphere.2. The gas bound gravitationally to a planet or the pressure of the air on the earth at mean sea level; approximately 14.7 pounds per square inch or 760 millimeters high at 0 degrees Celsius under standard gravity: "Through the powerful telescope, the astronomers were able to study the atmosphere of the distant planets."
"Although some details about the atmospheres of other planets and satellites are known, only the earth's atmosphere has been well studied, the science of which is called meteorology."3. The outer layers of a star: "The atmosphere surrounding the star appears to cause the twinkle effect which romantic couples dream about."
4. A supposed outer envelope of effective influences surrounding various bodies: "The atmosphere of the capital city was one of individuals and corporations attempting to influence politicians."
5. Prevailing psychological climate; pervading tone or mood; characteristic mental or moral environment; fascinating or beguiling associations or effects: "The atmosphere in the office appeared to be edgy as if there were major staff changes anticipated but no one knew when that would happen."
6. Applied to the background sounds that evoke a particular mood, impression, setting, etc., in a broadcast program, etc.: "The atmosphere created by the music was dark and mysterious."
7. The air in any particular place; especially, as affected in its condition by heat, cold, purifying or contaminating influences, etc.: "The old wood stove was not well maintained and smoked, creating a smoky atmosphere in the cabin."
8. The predominant tone or mood of a work of art or the pervading quality, effect, or mood; especially, as associated with a particular place: "Henry lived in a dark old house with a depressing atmosphere."
9. A distinctively exotic or romantic quality or effect: "Willy and Gertrude went to an Italian restaurant where there was lots of atmosphere."
There are Layers in Space which Serve as Barriers to Gases and Radiations and so They Protect the Earth from the Many Dangers That Exist in Space
There is a mixture of gases in the atmosphere which is around the earth that is held in place by the earth's gravity.
The invisible mixture of nitrogen, oxygen, argon, carbon dioxide, and water vapor protects our planet from harmful radiation and makes life on earth feasible.
The atmosphere's density decreases with its height or distance from the earth; however, not at a uniform or consistent rate. Above approximately 90 kilometers, or 55 miles, the air is extremely rarefied, but it extends thousands of miles above the earth.
Different layers of atmosphere are distinguished by the levels of their temperatures:
- The troposphere extends 18 kilometers, or 11 miles, above the earth.
It is warmed by solar rays re-radiated from earth's surface.
This causes convection currents that bring changes in the weather.
Temperature in the troposphere decreases with height to -60°C, -76°F, but in the stratosphere it rises close to the freezing point.
- The stratosphere, which is just above the troposphere, extends to 50 kilometers, 30 miles.
It contains ozone, which absorbs ultraviolet rays from the sun.
- In the next layer above the stratosphere, is the mesosphere, which extends to 80 kilometers, 50 miles, above the earth and it is here that the temperature drops to -113°C, or -173°F.
- The previous three layers form the lower atmosphere.
- In the more rarefied upper atmosphere, temperature rises, reaching 227°C, 441°F, even at night where thermosphere and exosphere meet 450 kilometers, 280 miles, above the earth.
- The upper atmosphere absorbs much of the harmful radiation and as it does this, it produces electrically charged particles called ions.
- In this region, called the ionosphere, layers of greater ion concentration (the D, E, and F layers) exist, although they vary daily or seasonally.
- Humans use the the ions to bounce radio waves around the earth.
- Farther out in the ionosphere are two Van Allen Belts (Inner Van Allen belt and Outer Van Allen belt), which are zones of radiation concentration.