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Comets

Comets. The Oort cloud is a “cloud” of icy planetismals that extends from Neptune’s orbit to 150,000 AU To the very edge of the solar system. Most of these orbit in the same plane as the planets forming a “belt”. that extends from Neptune to about 50 AU called the Kuiper Belt ( in green).

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Comets

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  1. Comets

  2. The Oort cloud is a “cloud” of icy planetismals that extends from Neptune’s orbit to 150,000 AU To the very edge of the solar system. Most of these orbit in the same plane as the planets forming a “belt” that extends from Neptune to about 50 AU called the Kuiper Belt ( in green) The Oort Cloud and Kuiper Belt

  3. Composition These planetismals are made of mostly water ice with some CO₂ or Dry Ice, with traces of other gas ices They also contain small rocks and dust, including carbon compounds These are what become comets They are often called “Cometary Bodies”

  4. The Origin of Comets Occasionally the gravity of a passing star changes the orbit of some of these icy planetismals so that they go closer to the Sun. When the icy planetismal, a comet nucleus, usually about 10 km in diameter reaches Jupiter’s orbit it begins to melt and a cloud of gas and dust called a coma which grows to as much as 1,000,000 km across. Sunlight breaks down water into hydrogen and oxygen and forms a dim hydrogen envelope up to 10,000,000 km across.

  5. Two tails As it gets closer to the Sun the solar wind and radiation push on the coma and create two “tails.” The solar wind pushes Ionized Gases directly away from the Sun forming an blue Ion or Gas tail. Radiation pressure pushes the dust forming a yellow-white dust-tail that points between directly away from the Sun and the comet’s path. The Tails can be as much as 1 AU long!

  6. Comets in History Comets are spectacular celestial objects. They appear suddenly are there for a few weeks or months And then disappear. Until the 1700’s Comets were thought to be unique events, often believed to be omens of disaster….such as the death of Kings For example the Normans used the appearance of a comet to justify their invasion of England (The comet meant God wanted the English king to die!)

  7. Halley’s Comet In 1705 English Astronomer Edmund Halley realized that a comet seen in 1681 was the same one that appeared in 1607 and 1531. He calculated that it was on an orbit with a period of 75-76 years and predicted its reappearance in 1758 It has been recorded as early as 240 BCE, and as recently as 1986 when a probe imaged its nucleus

  8. Short period comets Comets that orbit with a period of less than 200 years are called short period comets. Each time a comet nears the Sun it loses mass. Gradually it evaporates leaving only dust and rock… a meteor shower

  9. Long Period and Other Comets Some comets take much longer….up to 5000 years or more to complete one orbit… a “Long Period” Comet. Some are “One-timers” When knocked out of the Oort cloud they took an hyperbolic path thus passing close to the Sun and then heading out into interstellar space…forever!

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