Astronomy

One of the most important things that we need to learn about the planet that we live on is how we can acctually survive on it and breathe all of the air we can breathe without dying. Many people are not quite sure how earth can sustain oxygen when other planets are unable to do this. Or how the sun can shine down without burning us to a crisp. The thing that protects this planet and keep us alive is the atmosphere that surrounds us.

The atmosphere is made up od 79% nitrogen, 20% oxygen, and 1% other gases. There are three very important layers that make up this layer of gases that surrounds the earth and protects us from harmful uv rays. The first layer is called the troposphere. In this layer we can see all the weather that occurs. It is the region of the rising and falling packets of air, which usually causes the weather to be rainy or sunny. The air pressure at the top of the troposphere is only 10% of that at sea level. There is a thin buffer zone between the troposphere and the next layer. This buffer zone is called the tropopause.

The next layer above the troposphere in the atmosphere is called the stratosphere. In this layer the air flow is predominatly horizontal. The thin ozone layer in the upper stratosphere has a high concentration of ozone, which is a particularly reactive form of oxygen. This layer is primarily responsible for absorbing the ultraviolet radiation from the Sun. The formation of this layer is a delicate matter, since only when oxygen is produced in the atmosphere can an ozone layer form and prevent an intense flux of ultraviolet radiation from reaching the surface, where it is quite hazardous to life.

Above the stratosphere is the mesosphere and above that is the ionosphere (or thermosphere), where many atoms are ionized (have gained or lost electrons so they have a net electrical charge). The ionosphere is very thin, but it is where aurora take place, and is also responsible for absorbing the most energetic photons from the Sun, and for reflecting radio waves, thereby making long-distance radio communication possible.

The structure of the ionosphere is strongly influenced by the charged particle wind from the Sun, which is in turn governed by the level of Solar activity. One measure of the structure of the ionosphere is the free electron density, which is an indicator of the degree of ionization.