Typically, the Moon presents itself as pale gray or white. However, at times, our nocturnal luminary surprises us with vibrant orange, crimson, or even bluish hues. Let’s explore the reasons behind this phenomenon and ascertain the Moon’s true color.
Most frequently, the Moon exhibits these “colored” appearances when positioned low above the horizon—during its ascent or setting. At these moments, the light reflected from the Moon traverses an exceptionally thick stratum of Earth’s atmosphere. This operates under the same principle as a red sun at sunset.
The air scatters the shorter blue and violet light waves, permitting solely the longer red, orange, and yellow waves to reach human vision. The lower the Moon hangs, and the greater the atmospheric impurity in an urban setting, the redder it will appear.
The Moon also turns red during total lunar eclipses. During this event, the Earth intercepts direct sunlight, casting its shadow upon the satellite. Nevertheless, a small amount of sunlight grazes the Earth’s atmosphere, refracts, and reaches the Moon. Only the red spectrum successfully travels to the satellite, thereby imparting a sinister, coppery tint.
Conversely, a “Blue Moon” is a term that can be misleading. It usually refers to the second full moon occurring within a single calendar month, and this designation has nothing to do with actual color. Despite this, it is, in fact, possible—though exceedingly rare—to witness a genuinely blue Moon.
This occurs when the atmosphere contains a substantial quantity of particles of a specific size—slightly wider than the wavelength of red light. Such conditions arise following major volcanic eruptions or extensive wildfires. Ash and soot function as a filter, effectively blocking the red portion of the spectrum.
For instance, following the eruption of Krakatoa in 1883, observers worldwide perceived a greenish-blue Moon for several years. Therefore, should our Earth’s satellite display an anomalous coloration, the explanation resides solely in two primary variables: the celestial body’s spatial orientation and the composition of the surrounding air.
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