On Friday, July 27, there will be a total lunar eclipse the longest of all the 21st century. With a duration of 1 hour and 43 minutes during the total phase, it is one of the most anticipated events of the year in the world of astronomy . The phenomenon will be visible from Spain and the best place to contemplate the eclipse of the Moon will be Balearic Islands .

The event will begin at 20:25 (time peninsular) and will end at 00:19, almost four hours later. The total phase of the eclipse at 9.30 pm, will coincide with the departure time of Luna in Madrid. The satellite will remain at a fairly low altitude, which will make observation difficult. In fact, when it leaves the East, it will already be partially or totally eclipsed in the peninsula, according to Observatory of Real Madrid .

At 22:21 it will be the maximum of the eclipse, a phenomenon that occurs when the Moon enters the Earth's cone of shadow . The three bodies are aligned in the same plane, so that our planet is interposed between the Sun and the satellite. This object will then be dyed red, a shade that earned him the nickname Blood Moon without having any kind of relationship with any prophecy. The color change has an explanation known by science for years.

The satellite acquires a red color due to the refraction of the sun's rays due to the Earth's atmosphere. During an eclipse, the moon ceases to receive direct sunlight because it is located in the shadow zone that our planet is projecting. The rays continue to reach the atmospheric layers of the Earth, which act like a kind of prism: they refract them, that is, they deflect them with different angles for each color. . The red tone continues to reach the surface of the satellite, so explains why the moon turns red during an eclipse .

The incarnated color that colors the satellite can however vary. According to the greater or lesser transparency of the Earth's atmosphere, the Moon can become more or less red during the eclipse. For example, the particle concentration of suspended dust may change its hue, as was the case in 1991. At that time the eruption of the Philippine volcano Pinatubo threw a large amount of particles in the atmosphere, which caused the satellite to have intense reddish colors. The appearance of the Moon during an eclipse is studied by the scale of Danjon designed by the French astronomer André-Louis Danjon .