7 Responses to “CRAM the fifth”

1. 1.   Irishman Says:
   September 24th, 2007 at 2:35 pm

   Read it. Noticed a consistent pattern, perhaps a “feature” of converting web articles to print. Many of the articles seem to truncate just when they’re about to make a point.

   The “Savvy Traveller” article didn’t tell me anything I didn’t already know. Perhaps I’m unusually aware. I was hoping for a tutorial on the finer points of knowing the difference, how to identify a population and whether they are “Arab” or not.

2. 2.   Navneeth Says:
   September 24th, 2007 at 2:43 pm

   And you beat PZ to it! What has the world come to.

3. 3.   occam's comic Says:
   September 24th, 2007 at 4:11 pm

   I just read you blog entry about Mira and i don’t buy your explanation one bit. You did not provide a cogent explanation for why Mira has a 13 light year long tail that is glowing with UV light. You comparison to someone running with a smoke bomb is the silliest thing I have ever heard. Gases in a near vacuum will expand in a near radial fashion they will not form glowing filamentary structures light years long. Show me how diffuse gases can “slam” into the near vacuum of the ISM and produce UV light. You gave us a wonderful “just so” story not a scientific explanation.

   There is a scientific explanation but your bad astronomical paradigm is blinding you from realizing it. The reason why astronomers are amazed to find magnetic fields everywhere they look is because they don’t think that electrical currents exist in space. (moving electric charges are the only things that create magnetic fields)

   A current running through a diffuse plasma will create long filamentary structures and cause the ions to glow in the UV. Look in the radio wave region of the EM spectrum and see if you find magnetic field lines around the long glowing filaments.

4. 4.   The Bad Astronomer Says:
   September 24th, 2007 at 5:04 pm

   Tell you what occam: go and do some research on how gases behave in the ISM, and then come back and tell me again how I’m wrong.

   Here’s a hint: what does “near vacuum” really mean? Put some numbers to it. Read “Astrophysics of Gaseous Nebulae and Active Galactic Nuclei”; there are several chapters in there that will help.

   And astronomers are not “amazed to find magnetic fields everywhere”; that’s a convenient lie put out by people who don’t understand fluid dynamics. The folks out there who put forth the idea that all plasma behavior is dominated by magnetic fields really have no clue what they’re talking about.

5. 5.   occam's comic Says:
   September 24th, 2007 at 6:36 pm

   Ok average reported density of ISM is ~1 atom per cubic centimeter, (that is better than any vacuum that has been created on earth, not quite the “fog” you described in the article.)
   An atom has a volume of less than 1 cubic nanometer (~10 to the 21 times less volume than a cubic centimeter)

   Now, (if i understand you correctly) are you saying that the gases that are coming off Mira have a high enough probability of slamming into the ISM (~1 atom per cubic centimeter) to cause enough of them to form 13 light year long glowing filaments that can be seen ~300 light years away?
   Or am i missing something?

   Now you are not implying in your final comment that magnetic fields don’t effect the movement positive and negative charges in a diffuse medium, are you?

6. 6.   occam's comic Says:
   September 24th, 2007 at 9:12 pm

   I am not sure that I did the calculation correctly but it looks like an atom or molecule of hydrogen has less than 1 in a hundred trillion chance (per cubic centimeter) of hitting another hydrogen from the ISM. So if that probability is roughly correct a gas atom or molecule would typically travel billions of kilometers before it has one interaction with the ISM. And then only some portion of those interactions would cause a photon of UV light to be created, right? Wouldn’t that make for a really diffuse light source?

   (Phil, i reread my initial post and realized I came off more aggressive than I meant to please don’t take it personally, I am genuinely interested in astronomy but honestly skeptical of some of the answers given by astronomers.)

7. 7.   Buzz Parsec Says:
   September 26th, 2007 at 7:40 pm

   Occam -

   I haven’t done the math, but how far is “billions of kilometers” in an interstellar sense? A billion kilometers is about 6AU, or effectively 0.
   If the mean free path of a hydrogen atom is a billion km, then *all* the atoms in the tail would have interacted with the ISM.

   “Near vacuum” is a relative term. When the distances are measured in parsecs and the time scale in centuries or millenia, a “near vacuum” is a poppin’ place!

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