When a celestial body interposes between two others blocking its light, an eclipse occurs. On Earth we have two types: eclipses of the Sun and eclipses of the Moon.
Eclipses of the Sun
A solar eclipse it consists of the total or partial obscuration of the Sun that is observed from a planet by the passage of a satellite, such as the passage of the Moon between the Sun and the Earth.
An eclipse of the Sun is only visible in a narrow strip of the Earth's surface. When the Moon interposes between the Sun and the Earth, it casts a shadow on a certain part of the Earth's surface, and a certain point on Earth can be immersed in the shadow cone or the penumbra cone.
Those who are in the area in which the shadow cone is projected will see the disk of the Moon overlap entirely with that of the Sun, and in this case there will be a total solar eclipse. Those who are in an area intercepted by the penumbra cone, will see the disk of the Moon overlap only in part with that of the Sun, and there is a partial solar eclipse.
There is also a third case, when the new Moon is in the node at a greater distance from the average, then its apparent diameter is smaller than usual and its disk does not cover exactly that of the Sun. these circumstances, on a certain strip of the Earth the shadow cone does not affect but its prolongation, and there is an annular solar eclipse, because around the lunar disk a luminous ring is visible.
As one of these situations occurs in the eclipses, there is talk of areas of totality, partiality or annularity, referring to the type of eclipse that can be observed from any point on the earth's surface.
Because of the moon movements around the Earth and the movement of the Earth around itself, the shadow of the Moon on the earth's surface moves at about 15 km / s. The entire phase for a given geographical point does not therefore exceed eight minutes. This area can have a maximum width and length of 200 and 15,000 km respectively.
Eclipses of Luna
A lunar eclipse it consists of the passage of a planetary satellite, like the Moon, by the shadow cast by the planet, so that the direct illumination of the satellite by the Sun is interrupted.
Lunar eclipses take place only near the full moon phase, and can be observed from large areas of the earth's surface, particularly throughout the hemisphere that is not illuminated by the Sun, provided the Moon is above the horizon.
Normally the disappearance of the Moon is not total; its disk is illuminated by the light scattered by the Earth's atmosphere and acquires a reddish halo. The total shadow or umbra produced by the earth is surrounded by a region of partial shade called penumbra. In the initial and last stages of lunar eclipse, the moon enters darkness.
Depending on whether or not the moon enters the umbra zone completely, the total lunar eclipses can be distinguished, when the satellite is completely submerged in umbra, the partial lunar eclipses, when it penetrates only partly in umbra and only part of the Lunar surface is visibly obscured, and penumbra eclipses, when the Moon passes only through the penumbra cone, hardly noticeable to the naked eye and only evident by suitable photographic techniques.
The maximum duration of the total lunar eclipses is 3.5 hours. The magnitude of a lunar eclipse is defined as the length of the lunar path through the umbra divided by the apparent diameter of the Moon.
The study of the lunar eclipses, in addition to allowing astronomical measures such as the verification of the contact moments between the disk of our natural satellite and the shadow cone, is useful to indirectly analyze the conditions of the Earth's atmosphere, since the Density and coloration of the umbra and penumbra cones are greatly influenced by the presence of ozone and suspended dust in the various strata of the atmosphere.
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