The Earth is able to support life as we know it here because the sun and the atmosphere come together to form the climates in which people are able to survive. Without the sun, the Earth would be a frozen mass and without the atmosphere there would be no water to freeze.
The circulation of the Earth creates wind, and when wind is combined with sun and water, climates are created. Air pressure is created when the air molecules on Earth become dense. The denser the molecules are, the higher the air pressure is. Air at sea level exerts approximately 14.5 pounds of pressure per square inch.
Air molecules are always moving. Their speed of movement is dependent on the temperature surrounding them. Higher temperatures cause more frequent motion; cooler temperatures make air molecules move much slower. Convection occurs when an air mass warms up, expands, rises, and causes the air mass to become lighter. Convection happens all of the time, but it happens in irregular patterns. As the warm air rises, it cools, as it cools, it goes back down again. This constant movement also changes the air pressure of an area.
Low pressure occurs where the air is on its way up. High pressure occurs when the air molecules are all coming together, heating up and sinking down onto the ground. The movement creates wind and the more movement there is, the stronger the force of the wind. The changes in weather formations are often determined by these movements.
The Earth moves around in a complete circle in 24 hours. It moves around the sun in this circular pattern in 8760 hours, or 365 days, and creates what we call a year. The elliptical shape of the orbit of the Earth around the sun brings the Earth closer to the sun at particular times during the orbit. The position of the Earth toward or away from the sun determines the heat and light directed at the Earth, leading to the changes that occur during the day and night. This position on the orbit, depending on the position of the location on the Earth determines the season. The tilt of the Earth on its axis of about 23.5 degrees is what determines what happens where and what weather types exist where.
During the month of December, the North Pole tilts away from the sun and the South Pole tilts closer. This makes the Northern Hemisphere colder and darker during this time. As the Earth moves along, it changes its poles' positions and in 6 months, the sun is closest to this same part of the Earth. During this time, the Northern Hemisphere is much warmer and the days are much longer. This explains the different weather styles that occur at the same time, such as is how it is summer in the United States when it is winter in Australia.
