Saturday, March 13, 2021

Two worlds , One sun

The surface of the Earth is covered by more than 70% of water: it is therefore not surprising that it is called the Blue Planet.

Mars, on the other hand, is known as the Red Planet due to its typical color due to iron compounds that cover much of its surface.

However, at certain times of the day, the Earth and Mars exchange colors. The image on the left is in fact a terrestrial sunset of a beautiful  red photographed in Marseille, while on the right is shown a Martian sunset seen from inside the Gale Crater by the Curiosity rover.

The bluish tint seen during sunsets and sunrises on Mars is due to the composition of the Martian atmosphere. In fact, suspended in it there are many dust particles of a size comparable to the wavelengths of sunlight. When the Sun is very low on the horizon (therefore at sunset or sunrise) the light must pass through a denser layer of the atmosphere. Due to scattering phenomena, the dust particles block red light and let blue light through.

The inversion of colors is not the only difference found between the sunsets of the two planets. If you compare the size of the solar disk you will notice that it is slightly smaller seen from Mars than from the Earth, as it is obvious because of the different distance from the Sun of the two planets.

Credit: NASA, JPL-Caltech, MSSS, Damia Bouic. 

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