Monday, October 27, 2008

A little bit less every day

Leer ésta entrada en español.

I would say that I have a problem with the sun, but it is not true. My problem is about the Earth, more precisely about the inclination of the planet or axial tilt. As you might know, the planets orbit around the sun in elliptical paths, more or less in the same plane. But the planets also spin (rotation movement), and the rotation axis is not perpendicular to the orbit plane.

The Earth has a an inclination of about 23.5 degrees, and that inclination is keep constant while the planet moves along it's orbit, more or less like a gyroscope (I would say a top, but is better to sound scientific). Because of that inclination, the northmen and southern hemispheres are not equally exposed to the sun light trough the year as depicted in this graphic:

The hemisphere having more sun becomes warmer, and the one having less sun becomes colder. The more you move to the poles, the more extreme the change becomes. If you stay in the pole you would find that the sun doesn't rise for half the year, and then doesn't sets for another half a year. If you stay at 66.5 degrees from the equator (23.5 from pole), there will be a day every year when the sun doesn't rise, and one day when the sun doesn't set. All this changes are what make seasons very distinct periods of the year. But they are actually caused by earth movement and inclination and not by the sun.

After this short introduction now we can go to the main point of this post: Yesterday I had to leave home at 6:30 AM, and it was dark as midnight, and there are two full months ahead before the shortest day in the year. I look forward to see how a day that short looks like, because I can't imagine.

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