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In a month or two, on the night of July 27 to 28 the Grand Theater of Heaven will offer us a fascinating spectacle. In fact, we will have an eclipse of the Moon which, allowing the clouds, will be a particular and fascinating sight. In Italy, it will start around 19:30 and last until 2:00 the next day. the phase of totality, generally the most beautiful, will take place around 22h21. We immediately point out that the eclipses of the Moon are certainly not an exceptional event: this year, it has already had one on January 31, but the peculiarity is that it will be very long in terms of time: the phase of all will last about a year. hour and 43 minutes, 40 minutes more than average. It will also be the longest eclipse of 2100, a small record not to be missed.
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We remember that an eclipse of the Moon occurs when our Earth is in the middle between the Sun and the Moon itself, obscuring it. In fact, our satellite does not emit its own light, but rather reflects sunlight. To have an eclipse it is also necessary that the Sun, the Earth and the Moon are at the same level, which can happen only once or twice a year: the Moon has an orbit inclined around the Earth and around the Sun. an eclipse every month.
What will we see on July 27th, from 7:30 pm ? Lying on the beach or in the mountains or even, very simply, in our house – but not too bright – we will see the moon which, as it is darkened, penetrates into the dim light and slowly approaches the whole, towards 22h20, baduming a more or less reddish color. The output of the set is similar to the input, our satellite will resume its bright white color and the phenomenon will be completed.
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Why, one wonders, if the Earth is interposed between the Sun and the Moon, can we see our satellite even during the phase of totality? The appearance of weak reddish light during the apogee of the phenomenon is due to the fact that our planet completely covers the lunar disc, but also spreads the sunlight that reaches it in the space , thanks to the filter of our atmosphere. The color of this light varies from a milky white to a softer gray to a sometimes pale red, for a physical effect discovered by English physicists Raleigh and Jeans about 120 years ago. Indeed, the dust present in the atmosphere absorbs the sunlight and emits it again in the red frequencies.
The last thing we can understand is why the eclipse, this time, is so long . We must make a local mind about the fact that the Moon is circling the Earth, okay, but not in a circular orbit, but rather a little elliptical. For this reason, the Earth-Moon distance varies between 363.104 kilometers and 405.696: the first point is called the perigee – closer to the Earth, in ancient Greek – the other climax. On July 27, it will be at the apogee the farthest, and therefore, for the laws discovered by the great astronomer Giovanni Kepler in 1600, the Moon must travel its orbit a little more slowly In the sky So, here is the phenomenon will take us a good 40 minutes more than the average setting the record of the century.
There remains an important suggestion: let's look closely at the moon, as did the great Galilee in his day. This is true, although it may sound strange, but Galileo used for the first lunar observations a telescope, "cannon" called in the sense of big cane, that we would not hesitate to set poor quality , given the primitive technology of optical glbad construction in these days. However, the first used by him had only 3 enlargements, like a spotting scope that many of us have at home. Yet, the discovery of the true "face of the moon" that has changed the history of mankind.
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If then in the house there is a mountain or sea enthusiast who has a telescope with features like 7×50, then he will use something very similar to the second telescope used by Galilei, who with these two have managed to the winter 1609 understand, as he wrote himself in the "Sidereus Nuncius", the messenger of the stars, that "the surface of the moon is not at all smooth, uniform and very exact, as many philosophers believed, but on the contrary, irregular, rough, filled with cavities and protuberances, no other than the very face of the Earth … "
A piece of advice then: n & # 39; do not wait for the eclipse of July 27 to watch the moon, let's look at it every night in the next month for a moment, alone or in company, maybe children. Just a moment each night to see how it changes and how it is always mutually fascinating.
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