Entertainment had to be, and show was. On 27 July 2018 there was the total Moon eclipse, visible throughout Italy and Europe.
An eclipse of the Moon occurs when the Earth stands between the Sun and the Moon. Our satellite, however, does not disappear because of the eclipse but takes on a red color. The sun’s rays, in fact, are refracted by our atmosphere, which subtracts the blue component of light.
The result was definitely spectacular. The Moon entered the Earth’s shadow cone after 7 pm and 9:30 pm the total eclipse began, which ended at 11.13pm. The eclipse is therefore back to be partial until 01.30.
But why was this eclipse the longest of the twenty-first century? There are three reasons that, combined, have made this event possible:
- The Moon was at its apogee, that is at its point of the orbit farthest from the Earth, about 400,000 km away. By Kepler’s laws, a celestial body at the farthest point of the orbit moves more slowly.
- In July the Earth reached aphelion, or the point of the orbit farthest from the Sun. Since the Sun was farthest away, the shadow cast by the Earth was longer.
- Finally, the Sun – Earth – Moon alignment was perfect and the Moon passed right in the center of the shadow cone of our planet.
But how come we do not see two eclipses every month, one of the Sun and one of the Moon? The reason lies in the fact that the orbital plane of the Moon is inclined 5° to that of the Earth, and the two orbits meet at two points called nodes. Eclipses can occur only when the Moon is in one of the two nodes and these are aligned with the Earth and the Sun, an event that happens every 173 days.