This Little Light of Mine

Ok. Now we'll get to that question that you had a while ago, which is: but what if I'm designing my own solar system and can adjust the eccentricity of the orbit and the tilt of the planet however I want? Well, then we can get a bit more funky. There are essentially two parameters we can change here: the relative sizes of the two effects and the offset between them. First, let's line up the two effects as they currently exist to instead of partly cancelling each other out, they build on each other. It's not very impressive, and life would remain basically the same for us; we get a little more sun in the summer, and a little less in the winter.

Next, we'll leave them out of phase as they are for us, but make them about the same size. Specifically, I've made it so when we're far from the sun, we get only half the sunlight we would at the near point. Instead of the max and min distance differing by only 3%, now they differ by 41%. This one makes life pretty weird. The folks in Fairbanks never get much sun now, and nobody gets much in the middle of summer when we're far from the sun. People in Utah or Michigan type zones get the most consistant light through the year, while the equator now has 4 seasons. (In this situation we might need to crank up the temperature knob on the sun to keep us all from freezing, but that might be difficult. In the real life system the 5 locations recieve 340, 311, 269, 244, and 142 artibrary units of sunlight over the course of a year. Now they get 263, 234, 199, 178 and 96. If we turn up the sun to get St George back up to where it was, those points shift to 356, 316, 240 and 130. We've kept St. George reasonable (well, as reasonable as it ever was), but made the equator 5% more sunny, while Fairbanks is still 8% less sunny than before. Essentially, this world is more sunlight-diverse.)

Next, we'll make them roughly the same magnitude, but with a 90° phase shift (one curve peaks 3 months before the other). Specifically, we hit the near point of our highly elliptical orbit about April 1st, with the tilt unchanged. This gets a little crazier. The total sunlight is not as low as the last model (263, 241, 209, 190, 111, which "St. George Adjusts" to 338, 310, 269, 244 and 143.) So, if we crank up the sun about 30%, we get the same total sunlight through the year. Unfortunately, it's going to be packed into a few really bright (hot) months. The equator has more seasonal variation than before, but is dominated by the position in the orbit, not the direction of the tilt. Also, everyone now has seasons!

Finally, what if we leave the orbit how it is, but tilt the earth over more . . . 45° sounds good. Well, Fairbanks now doesn't get sunlight for 100 days a year. Michigan gets the sun directly overhead in the summer now, but the sun barely makes it over the horizon in the winter. (Insert joke about how "it barely makes it over the horizon in the winter as it is" here.) The most interesting thing though, is that we've nearly introduced seasons to the equator. The total variation is something similar to what a place like Hawaii has on our earth (I know, doesn't really qualify as seasons) but the interesting thing is that they get 2 complete sets each year. More sun in March and September, with less in December and June. Really, that's how it is now (go back and look at the graph) but this would make the effect about 3.5 times bigger, so it would probably be noticable. If we roll the earth over further and push the angle to about 55°, then the equator gets double St. George like seasons, but gives even St. George 33 days without sunlight each year (and 67 for Michigan) so I'm voting against that one.

So, in the end, the earth is neat.

(It is a worthwhile reminder that there are still other things that are important to sunlight that I haven't considered. The most important is the dispersion through the atmosphere. As the sunlight moves closer to the horizon, it has to go through more of the atmosphere to reach the surface, and more light is scattered out. Then there are things like clouds to consider. Also, while this sunlight is the cause of our seasons, there are many other things that effect temperatures, such as residual ground heat, ocean and air currents and butterflies flapping their wings in China.)