Eli5 Why is water see through?

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My 4 year old asked me and I think it’s a rather good question that I would like to answer so she understands. Thanks 🙏🏻

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Anonymous 0 Comments

For a less inside-out answer (although still good to know / keep in mind), see link. Basically, water doesn’t have any mechanisms that strongly absorb photos in the visible spectrum. A lot of materials (like pure gas out in space) “require” photons of specific energy to change state in some way, so have very specific absorption lines. The more complex the molecule, generally the broader and more complex the absorption bands.
“The absorption of electromagnetic radiation by water spans a wide range of physical phenomena, characteristic of the general interaction of radiation with matter. It absorbs strongly in the microwave region by excitation of molecular rotations. In the infrared it exhibits strong absorptions from vibrations of the water molecule. As you go above the visible through the UV toward x-rays, it successively absorbs by photoelectric effect, Compton scattering and finally pair production.”
(Additional info via hyperlinks in original.)
http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.html

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