So, it snowed here (in Louisiana). Sure, it wasn’t a lot, but it was still a big deal. The following day, there was still some snow on the house roofs. I took some pictures. Here is a shot looking at the North side of a house.
And here is a view of the South side of the same roof.
What is so cool about that? All the houses were the same way. North side of roof = snow. South side = no snow. At first, I was going to use these pictures to talk about flux. Basically, since the Sun is lower in the South sky the southern side of the roof gets more solar energy flux. Then I realized my error. Not only does the southern side have a greater flux, it is also exposed to the Sun for a longer time (the northern side is in the shade from the south part of the roof for part of the time). What else depends on time and flux? The seasons. This roof is like a mini-Earth.
The South side of the roof gets more energy because it has sunlight for longer and a greater flux. First, let me show the longer time. Check out this diagram.
In the morning and evening, the sunlight doesn’t even hit the north side of the roof. But now let me talk about flux. Suppose the Sun is in a position to shine on both the south and north side of the roof. Here the lines represent light from the sun (which is far enough away that these lines would be parallel to each other)
How many lines hit the south side of the roof? I count 5 lines, with only 2 hitting the north side of the roof. If both sides of the roof are the same size, then the south side is going to get a lot more energy from the solar radiation. Also, think of it from the perspective of the Sun. If you were the Sun, looking at the roof, which side would look bigger?
In general, flux is the amount of “something” interacting with an area (in this case sun light). It depends on:
- The strength of the “something” (in this case light)
- The size of the area (roof in this case)
- The angle between the “something” and a line perpendicular to the surface.
This is the same flux that is seen in Gauss’ Law, but I am not sure it is the same as the flux in a flux capacitor. If the something is constant in direction and magnitude over the area, then the flux can be calculated as: (note the “something” has be a vector quantity)
Here, the vector S is the “something” and the vector A is a vector that has a magnitude equal to the area. The direction of vector A is perpendicular to the surface.
Back to the seasons and the roof. The time the sun hits each part combined with the flux is why one side has snow and the other doesn’t. Here is a graph I used when I previously talked about the seasons.
Let me end by just saying that the south side of the roof is clear and it is not closer to the sun than the north side.