空はなぜ青い？ : Why the skies are blue?

I am studying for my geography exam, and today... Oh, already yesterday, I studied about Atmosphere, Radiation and Earth-Sun Geometry. Then I found this question. "Why the skies are blue?" I think I learnt the answer for this quesion before, but I forgot it already. Ok, let's figure out again. The sky blue color is affected by "scattering of light" according to what I learnt yesterday. In our lecture note, there is an explanation about the scattering like following.

Rayleigh scattering:
- Scattering particles are much smaller than the wavelength of the radiation
- Performed by individual gas molecules
- Scattering is both forward and backward
- Biased towards shorter wavelengths (in particular VIS light, in particular blue) which results in blue skies and red sunrises and sunsets (because of longer transmission pass through atmosphere blue wavelengths are filtered out and only the longer VIS wavelengths remain)

Hum... I can easily understand why we can see red sunrises and sunsets, but I cannot understand why the skies are blue in the day time from this explanation. What is the meaning of "Biased towards shorter wavelengths"?? Why it biased??

1. Why it looks "blue"
When light (radiation wave) reach the surface of object, the light is absorbed, reflected, scattered or transmitted. If all the light is absorbed, the objest looks BLACK, and in the case of transmittion, it looks WHITE. But if the object reflect or scatter any wavelengths of light (radiation), the object looks coloered. So if the object reflect or scatter wavelength of blu light, the object looks "blue"

2. Blue light and Red light
What is the differentces between blue light and red light? This is easy to answer. Blue light is shorter in wavelength and red light is longer in wavelength. And shorter wavelengh radiation of blue light has more energy than longer wavelength radiation of red light.

3. Selective scattering

Selective scattering (or Rayleigh scattering) occurs when certain particles are more effective at scattering a particular wavelength of light. Air molecules, like oxygen and nitrogen for example, are small in size and thus more effective at scattering shorter wavelengths of light (blue and violet). The selective scattering by air molecules is responsible for producing our blue skies
Source: Scattering of Light

Here is better explanation about Rayleigh scattering, but still, this doesnt show why small size air molecules are more effective at scattering shorter wavelengths of light... This is because blue light has shorter wavelength so it is more easier to hit air molecures than longer wavelength of red light. (Shorter wavelength radiation vibrate more than longer wavelength radiation to move same in distance... Am I correct?) So, blue light is easily scattered by atmosphere, thus skies looks blue.

Ok, this is enough. Actually, for final exam, I dun have to write this long. Just need to write, "Blue skies are produced as shorter wavelengths of the incoming visible light (violet and blue) are selectively scattered by small molecules of oxygen and nitrogen" as it written in the link here. That is enough, I think...
BTW, why it is said "skiES" in English? I can see only one sky above me though.