Why does the sun/moon look larger when near the horizon?

General Questions
#21

While I obviously cannot provide a cite, I personally have noticed the full moonrise exhibit the distortion that everyone seems to have experienced with the sunset.

Perhaps it’s because that the “full” sun rises and sets everyday, yet the “full” moon only occurs once a month (except for the proverbial blue moon), so people have more experience with the sun’s distortion. scr4 mentions that it might also be because the moon isn’t as bright. This intuitively sounds like it might be the reason, but I’d be interested in any physicists’ perspective… does the relative brightness affect the prominence of the refraction?

#22

In my hometown there was an optical illusion with a bridge. One one street, you could look back and see the superstructure of the bridge completely framed by branches of two trees. As you drove away from the bridge, it appeared to get larger, and closer. A nice perspective condition, greatly magnified.

#23

OK, I admit it. This is bothering me. It doesn’t make sense that the intensity of the light would have any effect on the refraction of the setting moon vs the setting sun… but perhaps the wavelength of the light refracted through our atmosphere would explain it? The reflected light from the moon is gray-white, and the direct light from the sun is yellow… and as they’re setting they both of course get redder.

#24

The color of the moon is actually remarkably like that of the Sun, so much so that astronomers often take a spectrum of the Sun by pointing their scopes at the Moon or some other solar-system body. The refraction effects should be exactly the same for both. However, the brightness may have some effect on how the refraction effects are perceived by humans. For that, you’d need to ask a psychologist, not a physicist.

#25

Thanks Chronos, for your thoughts. I must confess that I am surprised that the moon and sun have essentially the same spectrum. I would’ve thought the moon’s surface would absorb some wavelengths.

Given that that doesn’t occur to any great extent, then I agree with your conclusion that we now need a psychologist to check in with their opinion on why the moon is generally not perceived to oblate as much as the sun does… though as I mentioned above, I’ve personally seen the refraction effect on the rising moon, so I know it happens.