Stars twinkle, planets don't

Sirius, Jupiter and Betelgeuse

It's easy to think that all the small dots in the night sky are stars. They aren't of course. There are at least 5 planets that you can easily see with the naked eye. Mercury can be seen with the naked eye, but being so close to the Sun it's usually at dawn or dusk and not at night you can see it. The others are Venus, Earth (duh...), Mars, Jupiter and Saturn. So how can you tell the difference between a star and a planet if you just happen to look up at the night sky? Stars twinkle. Yes the nursery rhyme is true. Twinkle, twinkle little star. Although they aren't exactly small they appear small to us.
The photo above illustrates the difference between stars and planets. Left to right it's Sirius, Jupiter and Betelgeuse. Why I chose to have two stars is because they are different colours so they appear to twinkle differently. Jupiter as you can see does not twinkle at all. So why is that? From what I can guess, and what seems logical to me, is that stars shine light in all wavelengths and Earth's atmosphere lets the different wavelengths through at different speeds so that it appears to twinkle. That would also explain why they twinkle more near the horizon. Planets on the other hand reflects just a few wavelengths of light from our Sun so they always appear to be a solid dot.
Even if I got this right I'm sure there are people out there that can explain it better.
The photos are 10-second exposures taken handheld with my Canon EOS 550D (Rebel T2i), Canon EF 70-200mm f/4L. At least the stars make really nice artworks that way.