Can you link a Wikipedia article or similarly informative page where I can read more about this? Or give me a term I can Google? This is fascinating

Right, if it gets colder, that doesn't mean there's less water in the air. That makes sense, thank you.

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I think this is a common misconception. Cooler (denser) air molecules move more slowly than warmer air molecules, and that effect negates the 'packedness' that typically results in denser=faster sound. For ideal gases, denser=slower sound.

http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/souspe3.html

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No, you're thinking of absolute humidity.

Lower (higher) temperature for the same amount of water vapor results in higher (lower) relative humidity.

I would imagine yes but that’s because humid air is less dense. The more dense the air the faster waves can travel, so dry may equal farther distance sound can be heard.

Great- I would just add for additional nuance that the intended population is taken into account, as well. For example, if you’re developing a drug for a disorder in which many patients end up having feeding tubes, you may prefer to first test an oral solution even if you can make a tablet, because you can help more patients with that formulation.

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Isn't the RH already independent of the temperature? So 50% RH at 20 C would yield the same bext as 50% RH at -10 C. Do the lower temperatures also imply a lower RH?

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I agree with this, but there might be more to it. Hot air has a different refraction index due to the faster movement of particles in it. This is just something to add on.

I thought the twinkle was because stars have such a small solid angle, any fluctuation in their output is perceived as a huge difference visually. And since fluctuations always happen there’s always a change in what we see thus the twinkle.

Would cold, low humidity air also allow sound to travel more clearly (and more loudly)?

Nice. Just learned another something weird and cool about our universe!

In fact, they do. It's very useful for us, allowing us to get a lot more data from them.

https://www.newscientist.com/article/dn13792-cosmic-time-warp-revealed-in-slow-motion-supernovae/

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> The light comprising the CMB last scattered at the same time everywhere

Out of curiosity, what is "the same time"? Was this over the course of a few milliseconds? Years? Millenia?