Why does the moon look orange/red?

Sometimes, you may notice that the moon appears to have a bright orange or red color, especially when the moon is closer to the horizon.

This happens for a couple of reasons. First, it's due to Earth's atmosphere. Second, it has to do with the angle at which you are viewing the moon.

The Earth's atmosphere is like a blanket surrounding the planet. The light that is reflected off the moon has to travel through the atmosphere to reach us. When you are viewing the moon closer to the horizon, there is a greater distance for the light to travel vs. when you are viewing the moon overhead. This is part of the reason why the bright orange/red moon is typically seen closer to the horizon.

The atmosphere contains many particles and what happens is the light that's traveling through gets absorbed and scattered. Well, the atmospheric particles tend to scatter shorter wavelengths of light (such as blue) more often. The longer wavelengths (such as red) are therefore able to pass through the atmosphere and reach us... which is why we see the orange/reddish hue! When the moon is being viewed closer to the horizon, that longer distance paired with the scattering of light can lead to this phenomenon. There is just more atmosphere at that angle for the light to get through in order to reach our eyes.

Looking at the diagram above, pretend you're where the X is. As you can see, when the moon is overhead (position A), the distance (green line) is shorter than the distance (orange line) when the moon is near the horizon (position B). The light has more atmosphere to travel through from that angle in order to reach us, hence more shortwave light gets scattered and we end up seeing orange/red.

Sometimes you see this happen when the moon is a bit higher in the sky. This tends to be more due to extra pollutants, dust or smoke in the air which scatters light the same way.

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