Thread by @fortiain

Wow! So much fun being a scientist and still learning cool stuff after all these years. What colour is milk? (see thread for some #homeschooling experiments about blue skies and red sunsets with a bottle/glass of milk) 1/9

I was doing some research for a new text book on #EarthObservation (via @SpeckledPress ) by reading my very old (25 years?) “Flying Circus of Physics” (an excellent book, by the way) and it had an experiment that showed Rayleigh scattering using milk. Milk!?...🤔
2/9

But milk is an optical/geometric scatterer. No wavelength (λ) dependence. That’s why it’s white — it scatters all incoming light equally, regardless of wavelength.
Surely everyone knows that!?
3/9

It’s an optical scatterer, like clouds! Milk has large droplets of fat suspended in water (1-2microns diameter). Clouds have large droplets of water, suspended in air. Both are much larger than wavelengths of visible light
=>optical scattering
=> white.

4/9

But I went ahead and did the experiment: a little bit of milk into a bottle.
Shine a white light from behind and ... orange glow!
Wow! 😮
How come? 🤔
5/9

And from the side - blueish glow!! 😮
Wow!
Milk.
Rayleigh scattering: shorter λ (blue) light is scattered (blue sky) and reds get through (sunsets).
But how is that?
Fat droplets too large for Rayleigh!
6/9

Turns out that fat droplets are not the only thing suspended. There are also casein droplets - this is where the protein is - much smaller - 100’s nm, so in the Rayleigh domain = shorter λ (blue) light is scattered and reds get through!!
7/9

So milk has both optical/geometric scatterers (like clouds) AND Rayleigh scattering (like the atmosphere)!
9/9 * (see footnote)
#ScienceFromHome #ScienceIsCool

(*Footnote: the pics have slightly different concentrations of milk. I chose the best pics so you can see the extremes. You need to experiment to find the optimum. Too much milk & the fat droplets dominate => optical scattering and no transmission.)

*add the milk to a bottle/glass of water. Sorry, forgot to mention the water! 🤦‍♂️😅