Utente:Mirandolina/Prove2

GrassettoContents [hide] 1 Eclipses in the Earth-Moon system 1.1 Types of eclipse 1.2 Eclipse phases 1.3 General phases of a solar eclipse 1.4 Local phases of a solar eclipse 1.5 Phases of a lunar eclipse 1.6 The eclipse in mythology 2 Eclipses elsewhere in the solar system 3 See also 4 External links

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[edit] Types of eclipse

1999 Total solar eclipse seen from the Mir space stationThe most dramatic eclipses visible from Earth are:

Lunar eclipses - the Earth obscures the Sun, from the Moon's point of view. The Moon moves through the shadow cast by the Earth. This can only happen at full moon. Solar eclipses - the Moon occults the Sun, from the Earth's point of view. The Moon casts a shadow that touches the surface of the Earth. This can only happen at new moon. Eclipses can be divided into different types:

The ratio between the apparent sizes of the eclipsing body and that of the luminary is called the magnitude of the eclipse. For solar eclipses, the ratio varies around 1, being sometimes more than 1, sometimes less. For lunar eclipses, the magnitude is much larger than 1; they never appear annular (viewed from the Moon).

[edit] Eclipse phases These were used in occult ceremonies.[citation needed]

[edit] General phases of a solar eclipse The general eclipse begins when the Moon's penumbra cone starts to sweep across the Earth's disc. The total or annular eclipse begins when the Moon's umbra starts to sweep across the Earth's disc. The centrality begins when the axis of the Moon's shadow cone starts to sweep across the Earth's disc. The eclipse's maximum occurs when the terrestrial surface within the umbra reaches its largest area. The centrality ends when the axis of the Moon's shadow finishes its sweep across the Earth's disc. The total or annular eclipse ends when the Moon's shadow finishes its sweep across the Earth's disc. The general eclipse ends when the Moon's penumbra finishes its sweep across the Earth's disc.

The French 1999 eclipse[edit] Local phases of a solar eclipse First contact (also called first exterior contact) is the instant when the Moon's disc starts to cover the Sun's. Second contact (also called first interior contact) is the instant when the Moon's disc is entirely surrounded by the Sun's (for an annular eclipse) or the instant when the Sun's disc disappears completely behind the Moon's (for a total eclipse). Third contact (also called second interior contact) is the instant when the Moon's disc starts to come out of the Sun's (for an annular eclipse) or the instant when the Sun's disc reappears from behind the Moon's (for a total eclipse). Lastly, fourth contact (also called second exterior contact) is the instant when the Moon's disc clears the Sun's. [edit] Phases of a lunar eclipse There are three types of lunar eclipses: penumbral, when the Moon crosses only the Earth's penumbra; partial, when the Moon crosses partially into the Earth's umbra; and total, when the Moon crosses entirely within the Earth's umbra.

The progression of a lunar eclipseFirst contact (also called first exterior contact) is the instant when the Moon starts to enter into the Earth's umbra. Second contact (also called first interior contact) is the instant when the Moon enters completely into the Earth's umbra. This is the beginning of totality. The maximum of the eclipse occurs when the angular distance between the centre of the Moon's disc and the centre of the shadow cone is at its smallest value. Third contact (also called second interior contact) is the instant when the Moon starts to come out of the Earth's umbra. This is the end of totality. Lastly, fourth contact (also called second exterior contact) is the instant when the Moon clears the Earth's umbra completely. [edit] The eclipse in mythology

Han Dynasty CarvingBefore modern astronomy arose there were long-standing explanations for eclipses in many cultures. These would typically involve conflicts between mythic forces. For example, in Hindu mythology, the two demons Rahuand Ketu were believed to be the cause of eclipses.However Aryabhata gave an accurate explanation of the eclipse in his scientific treatise Aryabhatiya dated 499 AD .

Similarly in China, at the Imperial observatory in Beijing, is a carved stone with the following explanation:

"This carved stone chart explained the cause of solar eclipses. The center of the golden bird (the symbol of the sun) was covered by the toad (the symbol of the moon). The people of the Han Dynasty called the phenomenon a good combination of the sun and the moon." In this explanation we see a recognition of the celestial realities and a cheerful outlook regarding the event. In other cultures an eclipse could be both a surprising and a terrifying event.

[edit] Eclipses elsewhere in the solar system

A picture of Jupiter and its moon Io taken by Hubble. The black spot is Io's shadow.Eclipses are impossible on Mercury and Venus, which have no moons.

On Mars, only partial eclipses are possible, because neither of its moons is large enough to cover the Sun's disc. Martian eclipses have been photographed from both the surface of Mars and from orbit. See Transit of Phobos from Mars and Shadow of Phobos on Mars.

The gas giants, which have many moons, frequently display eclipses. The most striking involve Jupiter, which has four large moons and a low axial tilt, making eclipses more frequent. It is common to see the larger moons casting circular shadows upon Jupiter's cloudtops.

Pluto, with its large moon Charon, is also the site of many eclipses.

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