Some notes from the slides
The Earth from space: note that clouds play an important role in the Earth's atmosphere.
Solar system: the inner and outer planets are distinctly different in size. Most planets revolve around the sun along a general plane. Pluto is the biggest exception.
Aurora borealis: also called the northern lights (and the aurora australis is the southern lights), they are best seen at high latitudes. They are caused by the interactions of charged particles from the sun with Earth's magnetic field, which "comes out" of the North Pole and "goes into" the South Pole.
Sunspots: unusually light and dark spots on the sun are places of unusual magnetic activity. Their cause is not certain. They occur in a quasi-cyclic pattern; high sunspot activity happens about every 11 years and can interfere with electromagnetic fields on Earth.
Sunspots have been postulated to affect Earth's climate as well. For instance, the 1600's was a period of low sunspot activity. Coincidentally, the period from about 1650-1900 was called the "little ice age" due to lower temperatures on Earth. One hypothesis is that the little ice age was somehow related to the low sunspot activity, because low sunspot activity might indicate that the sun is putting out less energy than normal.
The sun's energy
The sun's energy is mostly visible light. The energy intercepted by the Earth is called insolation.
Why do we have seasons?
Because the Earth's axis is tilted, not straight up and down. If there were no tilt, there would be no variation in the amount of incoming light from day to day, and there would be no seasons.
The tilt of the axis means that for part of the year, the northern hemisphere is tilted toward the sun and gets more light than the southern hemisphere. This period is summer for the northern hemisphere. During this time, the days in the northern hemisphere are long and the days in the southern hemisphere are short. The longest day of the year in the northern hemisphere occurs during this period and is called the summer solstice.
When the northern hemisphere is tilted away from the sun, the southern hemisphere gets more light and so it is winter in the northern hemisphere. During this time, the days in the northern hemisphere are short and the days in the southern hemisphere are long. The shortest day of the year in the northern hemisphere occurs during this period and is called the winter solstice.
In between these two seasons are of course spring and fall. These seasons are transitions between the extremes of summer and winter, and therefore are also transitions between extremes of daylength. Thus, there are two times when every point on the Earth has 12 hours of daylight: the spring and fall equinoxes. So the seasons affect the length of day, which changes the amount of insolation.
Latitude also affects the amount of insolation received. Higher latitudes receive more diffuse sunshine because the same amount of energy is "smeared" over a larger surface area (see figure 5.7 in the text). Not only is the energy more "smeared," but it also has more atmosphere to penetrate through before it hits the ground. Remember that even when the North and South Poles have 24 hours of daylight, it is still very cold because the energy they receive is so diffuse.
Summary of factors influencing insolation
1. distance from sun
2. variation in solar output
3. latitude, or angle of sun above horizon-"smearing" effect and amount of atmosphere to penetrate through is greater at higher latitudes
4. weather changes which change amount of atmosphere to penetrate through (cloudy day vs. clear day)
5. length of day, influenced by seasons
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