sun's angle?

Question

Sunlight reaches my hip while reading at a window. Last year it reaches only my knee. This year (2006) it reaches my face. I sit in the same chair, same place. Does the sun's angle change each year ?

Answer 1

The sun doesn't change its angle, but due to the movement of the Earth around the sun and due to the tilt of Earth about 23.5 degrees from its axis of rotation around itself, the sun appears to rise from a different location at the east every day. If you can visualize this movement of the sun rise from the east, you can understand why we have 4 seasons in the year. Let me explain it for you: Let me start from the spring season. On this day the sun is perpendicular to the equator. We call this event as the vernal equinox, which happens twice a year; Once on March 21, and once on September 21. On these dates the sun rises exactly at the location where the equator crosses the horizon when you look towards the East. Now from here on the sun starts to rise north of the equator gradually every day and with a different daily rate. This is true because the motion of the earth around the sun is not constant. When the sun rises above the equator or north of the equator 23.5 degrees, it becomes perpendicular to the tropic of Cancer, during which time the northern hemisphere enjoys more than 20 hours of sun light during the summer especially at the areas near the North Pole. In fact any body lives with the North Pole Arctic circle enjoys 6 months of sun shine which never sets except on September 21 when it goes below the horizon only to return on March 21 of the following year.

Now when the sun is perpendicular to the tropic of cancer, it begins to go downward as at this time it has reached the maximum rise above the equator. On September 21, the sun again is above the equator and returns to the same point it was during the beginning of spring. The suns continues to go down below the equator until it reaches the tropic of Capricorn, at which time the sun rises from a location about 23.5 south of the equator. During this time the sun shines only 5 to 6 hours to countries that are far above or north of the equator. This whole movement of the sun occurs due to the tilt of the Earth axis around which it rotates on daily basis, and due to Earth rotation around the sun. Earth makes one revolution around the sun once every approximately 365.6 days. I hope that makes sense to you.


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Answer 2

One explanation which comes in my mind is:
the earth axis performs two motions.
First: The earth is rotating around it the way you know.
Second: There is a slight motion of the axis itself called chandler-wobble. This motion (i don't know how large it is) makes the axis not directly pointing to the polar star in the northern hemisphere. instead the axis is following a circle near the polar star.

Another fact is that the earth's surface is lifted by the moons gravity a little (i heard about 50cm)

I don't know if this fits your observations, but it's what i would think. Along with the knowledge that even most advanced computers cannot calculate trajectories of 3 bodies in space with all there movements (Sun, Earth, Moon) to maximum precision.

Answer 3

No, it does not. It is cyclic so each year at the same time of year, it should be the same. Of course, though, if it was not measured at the same time on the same day of each year, you would not get accurate results. Yes, the azimuth and declination of the sun changes each day, and the declination changes each day of the year (declination being the altitude, azimuth being the distance along the horizon).