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Why do comets have tails ?

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  1. Feb 1, 2015 #1
    Just having a think about comets this morning .

    Im guessing the tails associated with comets are fragments of rock and ice from the surface of the comets but
    what is causing them to come off the surface if the comet is traveling through no medium to cause a force to move the bits that a make up the tail?

    I may have the wrong idea of what is going on but thought someone here might be able to clear it up :)
     
  2. jcsd
  3. Feb 1, 2015 #2
    The dust tail is caused by the radiation pressure from the sun and is curved because of the different orbital speeds of the particles.
    The ion tail points straight away from the sun. It caused by the elecric force between ions in the comet and ions in space caused by the sun's radiation.
     
  4. Feb 1, 2015 #3

    phinds

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    https://www.physicsforums.com/threads/very-little-excuse-to-ask-a-question-cold.765735/
     
  5. Feb 1, 2015 #4

    davenn

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    That's all OK ... but it didn't answer the OP's question why do comets have tails ?

    Hi discosucks .... I guess you weren't a older teenager in the '70's ;)

    Comets only get their tails as they come closer to the sun and start to heat up. For the most part, comets are just big dirty snowballs with or without a hard rocky core.
    The heat from the sun melts and vaporises the volatiles, eg icy water and methane etc and they then stream away from the comet in a direction opposite to the direction of the sun. Also is released are lumps of dust and rocks etc that have been trapped in that ice.

    One cool observation is that after the comet has come around the sun and is heading back out, the tail will be leading the comet nucleus instead of trailing it


    Dave
     
  6. Feb 1, 2015 #5
    Dave, nice work identifying that comets only have tails in their inner orbits. It is an important distinction that the ion tail points straight away from the sun. The dust and debris tail is curved as per Kepler's law.
     
  7. Feb 1, 2015 #6

    davenn

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    I have observed/photo'ed a few comets in my time ....
    there a pic or 2 in the astronomy forum section on the latest one I imaged ... Comet Lovejoy
    https://www.physicsforums.com/threads/comet-lovejoy-finder-charts.792205/

    cheers
    Dave
     
  8. Dec 12, 2015 #7

    Dotini

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    From today's edition of Spaceweather.com:

    MAGNETIC STORM ON COMET CATALINA:
    Earth isn't the only place with geomagnetic storms. Comets can have them, too. Such a storm appears to be in progress right now in the sinuous ion tail of Comet Catalina (C/2013 US10). Note the blobs of plasma circled in this Dec. 11th photo taken by Michael Jäger of Jauerling, Austria:

    catalina_strip.jpg

    These blobs are a sign of stormy space weather. Observers of comets frequently witness plasma blobs and 'disconnection events' in response to CMEs and gusts of solar wind. In extreme cases, a comet's tail can be completely torn off.

    The underlying physics is akin to terrestrial geomagnetic storms. When magnetic fields around a comet bump into oppositely-directed magnetic fields in a CME, those fields can link together or "reconnect." The resulting burst of magnetic energy can make waves, blobs, or even ruptures in the comet's tail. When CMEs hit Earth, a similar process takes place in the planet's magnetosphere powering, among other things, the aurora borealis.

    Comet Catalina is brightening in the eastern pre-dawn sky, not yet visible to the naked eye, but an easy target for backyard telescopes.
     
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