Chapter 2 - Commets and Meteor

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  • Astronomy - Chapter 2 - Planetary System - Comets and Meteors
    • Comet orbits
      • The orbit of a comet is elliptical, with a high eccentricity (a planet has a near circular orbit by comparison, with a low eccentricity)
    • Kuiper Belt and Oort Cloud
      • Short-period comets have comets periods less than 200 years and originate from the KUIPER BELT
        • The Kuiper Belt is a thick disc-shaped region of icy bodies that lies beyond Neptune (between 30 - 50 AU)
        • A famous short-period comet is Comet Halley with a period of 76 years
      • Long-period comets originate from the Oort Cloud
        • The Oort Cloud is a spherical distributionof cometary nuclei at the outer reaches of the Solar System (50,000 AU from the Sun)
        • Even though there is no evidence for the Oort cloud there is strong support for its existence
          • Their paths around the Sun are in either sense (clockwise or anticlockwise)
          • Orbits are often highly inclined to the ecliptic
          • A high percentage of them originate at vast distances (typically 50,000 AU) from the Sun
        • A famous comet is the Comet Hale-Bopp in 1997
    • Comet facts
      • Comet tails
        • As a comet approaches the sun, the temperature rises and gas and dust form an extremely rarefied spherical COMA that surrounds the nucleus up to 100,000 km across
        • A comet can develop two (or more) tails:
          • A blue coloured, straight ION tail consisting of atoms and molecules of gas (carbon monoxide) that have been ionised by the solar wind and when they de-excite atoms emit light by fuorescence
          • A lighter coloured shorter boader and slightly curved DUST tail produced by radiation pressure that pushes particles out of the nucleus; this tail of dust and git shines by reflecting sunlight and its curvature is due to the individual dust particles
        • Comet tails can be several millions of kilometres long
        • The comet tail enlarges as it approaches the Sun
      • Comets are balls of rock and ice (often called 'dirty snowballs' or icy dirtballs')
      • The  nucleus is rock and ice and dust
    • Origin of Meteoroids, Meteorites and Micrometeorites
      • Meteoroids are pieces of dust or rock that orbit the Sun with many entering the Earth’s atmosphere
        • The origin  varies - some are broken fragments of colliding asteroids whereas others are formed through impacts with the surface of Moon or Mars
      • Many are so small MICROMETEORITES, weighing just a few milligrams. They dont burn but sink into Earth
      • If a meteoroid survives its passage into Earth and lands its called a METEORITE; there are 3 major categories
        • stones
        • Iron
        • Stony-irons
    • PHOs - Potentially Hazardous Objects
      • Near-Earth Objects (NEOs) might come closer to Earth than 0.3AU (45 million km)
      • NEOs have projected orbits that might bring them even closer to our planet
      • These POTENTIALLY HAZARDOUS OBJECTS(PHOs) have orbits that bring them closer to us than 0.05AU (7.5 million km)
      • Like the richture scale for earthquakes the TORINO SCALE goes from 0-10 on the likelihood of an collision and the estimated kinetic energy
        • From 0-1 indicate likely misses or collisions
        • However 8,9 and 10 show a certain collision capable of inflicting world-wide devastation
          • Such as global change, natural disasters but extreme that could threaten the future civilisatio
    • Impacts with the Solar System
      • Research of craters/impacts on the surface of Earth
      • Direct viewing of impacts using telescopes
      • Simulating impacts – as with the Deep Impact mission to study the effect of an impactor on the formation of craters and the structure of a comet
      • Seisomology experiments left in the ALSEPs package on the Moon
      • Study of lunar rocks brought back to Earth by the Apollo astronauts
      • Research and the use of computer simulations using data and images gained by space missions
    • Meteor showers
      • At certain times in the year there is a massive increase in the number of meteors
      • This occurs when when the Earth passes through a meteor stream left in the wake of a comet
      • The increased number of dust particles entering and burning up in the atmosphere causes a meteor shower
    • Meteors
      • When they enter our atmosphere, friction causes the meteoroid and surrounding air to heat up producing a short streak of incandescentlight - a METEOR or shooting star
      • Meteors with a magnitude of -3 or brighter are called FIREBALLS


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