The question about why the Moon sometimes appears larger than usual, and of a different color, is not simple because it has many ramifications. First let's go to the perception of color, which is real. Sometimes we see the Moon really orange, and sometimes even red. We see it orange when it is on the horizon and that is very easy to understand. It is for the same reason that we see the Sun more orange at sunrise and sunset. It is due to a phenomenon called Rayleigh scattering. The atmosphere is full of small molecules that scatter light differently depending on the color of that light. The bluer one that has a shorter wavelength is scattered in all directions. But red (or orange) light, which has a longer wavelength, is capable of traveling greater distances through these particles and reaching us. That is also the reason we see the sky blue.
When there is a lunar eclipse we can also observe this phenomenon even if it is high in the sky and not on the horizon. In this case, the light is passing through the Earth's atmosphere in the middle. In a lunar eclipse, the Earth gets in the way of the Sun's rays reflecting off the Moon's surface. The blue light that passes through the Earth's atmosphere is dispersed in all directions, so it does not reach the surface of the Moon, and the redder light does arrive because it is not dispersed as much and that is why we see the Moon in that color.
In short, there are two occasions in which we see the Moon of a different color, more reddish. One is when it is on the horizon and another is during a lunar eclipse. But the amount of suspended dust in the atmosphere can also cause us to see orange moons or suns, for example, in haze or if there are large fires.
In terms of size, large moons are always an optical illusion. On the same full Moon night, for example, the distance between our satellite and us does not change, we see it appear in the east and set in the west. And yet, we perceive that it is very large when it is on the horizon line and smaller when it is above our heads. What happens is that when it is on the horizon line, it is normal for us to have some point of reference: a tree, a mountain, a building… That is why it seems very big to us. However, when it is up it seems smaller to us because we have nothing to compare it to. But it is very easy to check that it is the same size. You can take a photograph with it zoom at both times or stretch your arm and compare it with your fingernail. If we measure it, the size is exactly the same. And this is because the distance between the Moon and the Earth does not change in one night. The size is exactly the same because the distance is the same. It is believed that this difference in appreciation is an effect of how our brain processes distances when it has a very distant object and has to look for a closer object as a reference.
That is, we know that its size is the same and we also know that when we look at it at those different moments it seems that it is not, but we still do not understand exactly why this happens.
Maybe you have ever heard of supermoons. Although it is a term that is not accepted by the International Astronomical Union, which is the organization that is responsible for naming and classifying celestial objects, is quite popular. The Moon's orbit is not circular, it is elliptical. That means that at some times it is closer to Earth than at others, and the difference in distance is very large. The shortest distance is 330,000 kilometers, it is called perigee, and the longest, the apogee, is about 407,000. The moment in which the Moon is closest to the Earth does not always coincide with the full Moon, but when it coincides it is what is called Super moon. Although it is important to remember that at that moment it does not look bigger, only if a professional telescope is used could the difference in size be measured, but with the naked eye it looks the same as always.
Eva Villaver Sobrino She has a doctorate in astrophysics, director of the Office of Space and Society of the Spanish Space Agency and Research Professor at the Astrophysical Institute of the Canary Islands.
Question sent via email by Luka Pérez Lazkoz (11 years).
Coordination and writing:Victoria Toro.
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