cassandra santiago's List: astronomy

• • page includes questions or things that need to be discovered about comets.
    
• Comets are dark, solid bodies a few kilometers across that orbit the Sun in eccentric paths
• Some of the icy material — perhaps less than 1 percent — evaporates as the comet nears the Sun, creating an envelope of gas and dust that enshrouds the solid body. This envelope, called the coma, may be up to 620,000 miles (1,000,000 kilometers) across. Swept back by the solar wind and the radiation pressure of sunlight, this material forms the comet's tail. Comet tails can span a distance greater than that separating the Earth from the Sun.
• Within the coma, and invisible to both the naked eye and the most powerful telescopes, lies the small icy body responsible for this grand apparition — the comet's nucleus.
• The two most important considerations in assessing the visibility of a comet are its distance from the Sun at closest approach, which controls the comet's activity, and its distance from Earth, preferably after the intense heating of it closest approach to the Sun.
• A typical comet might move across the sky by a degree or so a day, too slowly for the eye to notice.
• Astronomers believe comets may be the best-preserved remnants of the cloud of dust and gas in which the Sun and planets formed. In the deep-freeze of the outermost solar system, they have remained largely unchanged during the 4 billion years the solar system has existed. Planetary scientists study comets for the same reason paleontologists study fossils: to catch a glimpse of the most ancient past.
• And what better way to scrutinize comets than by visiting them directly
• ? Japan, the European Space Agency (ESA), and the Soviet Union began the direct exploration of comets in 1985 by sending separate missions past Halley's Comet. The ESA probe, Giotto, returned the first detailed images of a comet's nucleus, revealing a dark, peanut-shaped body, a hint of hills and craters, and several bright jets spewing streams of gas and dust.

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• Did comets help create Earth's seas?
• Where do comets come from?
• Comets so close to the sun?

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• • 2350 bc - comet impact[s] brought civilizations down. wide spread environmental problems in the east.
    
    how to capture them in space to stop them from striking earth.
    most comets will appear and just grow brighter, not hit the earth.
    

• • dust 
  • ice (water, ammonia, methane, carbon dioxide) 
  • some carbon-containing (organic) materials (e.g., tar) 
  • a rocky center (some comets)
• Comets are thought to be made from the earliest materials of the solar system. When the sun first formed, it blew lighter material (gases, dust) out into space

• • fragments tore into the planet @ 60km a second.
    after each hit, astronomers had to wait til the planet rotated and the impacts were in view.
    1908, forest flattened in siberia due to comet.

• • comets - dislodged by gravitational twitch by neighboring star [unsure], they round the sun and are captured in an eliptical orbit.
    comets grow two tails; blue-gas, yellow-dust.
    blue can be blown off by gust in solar wind and reattached. [stretch 100,000,000 km from comets head], dust tail is pushed outward by radiation pressure of sunlight.
    tails disappear as comet goes back to the freezing part.
    tail points away from the sun always.
    grains streak and burn up into the upper atmosphere on earth when a comet moves closer to earth and it is seen as "shooting stars" or meteor showers.
    some don't make it to the sun.
    they have random orbits. can be influenced by not only the sun but other planets. they can come from all directions because they start in all directions.
    halley is the most famous comet. it was captured by jupiter and returns to the skies once every 76 years. edmund halley predicted the return of the comet. halley is a short period.
    probes flew through halleys comet.
    1998, space thing to explore a short period comet.
    long periods - appear unexpectedly.
    probe stardust - collects comet filled stuff, the dust is returned to earth for analysis.
    comet grains are dissected.
    russian probe orbitted a comet.
    ---launch a probe at a comet to make an impact the size of a stadium so scientists are able to see what's inside.
    comets hold clues to its birth, could have put water on earth, sparked life. 100 billion comets could be awaiting to travel to the sun.
    

• As a comet approaches the sun, it warms up. During this warming, you can observe several distinct parts: 
   
  • nucleus 
  • coma 
  • hydrogen envelope 
  • dust tail 
  • ion tail
• The nucleus is the main, solid part of the comet. The nucleus is usually 1 to 10 kilometers in diameter, but can be as big as 100 kilometers. It can be composed of rock.