Why are the distant mountains changing in size?
March 18, 2022 12:00 PM   Subscribe

Every morning when stretching, I look out my bedroom window towards distant mountains. Some days, I can see the distant mountains clearly above the horizon, some days it's only the tips of the peaks, some days they aren't visible at all. Why?

I'm at around 1050m elevation; the main thing in front of the mountains is neighbourhood trees, as well as a 30m bluff about 2 km away. The mountains themselves have peaks in the 3000+m range, and are roughly 60-65 km away.

I feel sure it's atmospheric; even today, the peaks appear bigger now and are more visible at noon than they were in the morning. And this is a well known phenomenon; in small talk people around here sometimes say "the mountains look big today".

But I haven't been able to figure out what combination of weather leads to this. They can be different sizes at all times of day; in summer and winter. Obviously I can't see 60+ km if it's dark or raining or snowing or smoky, but otherwise, I have no leads.

I don't know what to search for - what atmospheric condition or phenomenon am I looking for?
posted by Superilla to Science & Nature (6 answers total) 6 users marked this as a favorite
 
Best answer: Atmospheric refraction.
posted by pipeski at 12:16 PM on March 18, 2022 [6 favorites]


Best answer: “Terrestrial Refraction” and “atmospheric refraction” seem to be the keywords you are looking for: Wikipedia link, though I can’t claim to fully understand the physics to explain it better!
posted by ecstaticcattle at 12:16 PM on March 18, 2022 [6 favorites]


Best answer: I believe that different air pressures -- and the greater density -- makes the air act more (rather than less) like a lens on some days...which is the refraction effect.
posted by wenestvedt at 1:56 PM on March 18, 2022 [2 favorites]


Best answer: Yes, basically there are layers of air of different densities, and these have the effect of bending the path of the light beams up or down in a curved path depending on the relative densities (which in turn are a factor of air pressure and temperature). So on some days you'll see light that comes from lower down the mountains - the rays are refracted so that they curve over things between you and the mountains. At other times there's less refraction (less bending of the light rays) and so the light doesn't quite bend enough to curve over the landscape and reach your eyes. So you see more or less of the bottom of the mountains, making them look bigger or smaller.
posted by pipeski at 2:40 PM on March 18, 2022 [3 favorites]


Best answer: When this same phenomenon happens over open water, it can result in a 'floating ship's illusion, which may lead you to some additional explanatory diagrams.
posted by Ausamor at 6:54 PM on March 18, 2022 [2 favorites]


Response by poster: Of course! I'm a little embarrassed; my grade 4 science fair project was on refraction; I may need to return the 'participation' ribbon I got.
posted by Superilla at 4:30 PM on March 21, 2022 [1 favorite]


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