The labels are for the Northern Hemisphere, and this is not even close to drawn to scale, of course. So, while it's true that the Northern Hemisphere is pointed towards the Sun in northern summer and away from it in northern winter, the axis itself hasn't (really) moved. Solstices are a result of our position in our orbit, not because of any wobble of the Earth's axis. we will be in the exact position of the winter solstice at precisely 11:35 A.M. MST (18:35 UT).
The seasons result from the fact that during winter the rays of energy from the Sun strike the surface of the Earth at a steep angle. Because of this, the same amount of energy is spread over a much larger area, so the energy per square foot shining on the Earth is much less. Seasons have nothing (much) to do with the length of the day. After all, at the poles, we have six months of continuous daylight, yet they are still the coldest places on Earth! Here's a diagram which shows what's happening:
The area on the ground at B is much larger than the area on the ground at A, but each area is receiving the same amount of sunlight. As a result, it is colder at B than at A. This is also why it's colder in Boston than in Florida!
Now don't you feel smart?
*It does wobble, but very, very slowly. This is called precession, and is the same thing that makes a top wobble as it spins. Precession will make our axis point towards Vega instead of Polaris when I'm a great grandfather -- in about 23,000 years or so. The effect over the course of a year is too small to be noticed. The great pyramids are aligned to the North Star, but it was not Polaris.
1 comment:
Thanks for the explanation! I actually researched the whole seasons thing when you challenge it back several blogs ago. I have always been fascinated with astronomy and the workings of the earth as a planet, but I have also always struggled with assimilating the information. Diagrams help. Models help more. ;-)
It is fascinating to experience the lengthening and shortening of the days firsthand. I moved from Texas to Oregon several years back, and I never noticed the change in the length of day much in Texas. But in Oregon, it is unavoidable. In summer, we have sunlight as late as nine at night. And in winter, it's dark by 4:30. I always learned that I wake much better to sunlight. I woke to it almost every morning in Texas. I have the hardest time getting up in the winter months in the northwest. I got a sunlight similating alarm clock to help (and it really does).
Thanks again!
Ris
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