Observing with Street Lights

Observing with Street Lights
Dark sky sites not always necessary to see the Milky Way (This image was taken ouside of a B&B in Julian, CA)

Friday, September 29, 2017

Ocean streaks and Langmuir's observation and theory; Approaching Quebec and the end of our Viking cruise; Some insights into relativistic simulation paradoxes; Extragalactic source of cosmic rays

Greetings from Palmia Observatory (offsite closing in on our last cruise night in Quebec, Canada),

Well our In the Wake of the Vikings cruise comes to an end the day after tomorrow and we were only able to photograph the northern lights on two separate days.  Nonetheless we had a great time and meet some great folks and saw some great scenery.  One image that turned out to be steeped in physics was the following one of long parallel streaks in the Saguenay River, Quebec, Canada.
the image below shows one example of the long parallel streaks in the water.  What causes those streaks?  It's not ship wakes or animals?  Apparently they are just caused by the wind and were first explained by Langmuir in 1927, who went on to win the Nobel prize for his work in surface chemistry in 1932.

Long parallel white streaks observed in the Saguenay River (Source:Palmia Observatory)
Great bands of long white parallel streaks in the Saguenay River (Source: Palmia Observatory)

Now this was pretty neat.  My first introduction to Langmuir was through his work and development of what is now called the Langmuir probe for measuring the electron density in plasmas.  But Langmuir was very observant during a crossing of the Atlantic Ocean, where he noticed the strange parallel streaks in the water, and worked out how the wind could stir up counter rotating vortices, which would form in the surface waters and would be visible and even sometimes trap seaweed in those long parallel rows.  They tend to be tilted just a bit more than at right angles to the direction of the wind.  We saw many instances of these long white streaks in the river.  They seemed to be quite stable and even on occasion they could be seen to be twisted and curved to match the bends in the river.  If you want to read more of the story check out this article:

Hey, we're crossing the Atlantic Ocean, maybe I can think up something too?  I've stared in my martini glass on many occasions, looked for patterns in the cold mixture, and pondered the nature of the universe but have yet to come up with some interesting results.  Maybe I just have to practice observing more often?

Ok, ok, let's get back to some real astrophysics.  You probably had read in other articles about trying to identify the source of high energy cosmic rays.  Remember these are very energetic particles, such as high speed protons, that come streaming in from many different angles and strike the Earth.  When they do, they cause many secondary showers of other particles as the energy of the incoming cosmic ray excites many other particles.  This process is illustrated in the following photo from Astronomy Magazine.

Cosmic ray showers (Source: Astronomy Magazine, September 29, 2017)
Illustration of shower resulting from cosmic ray interaction with atmosphere (Source: Astronomy Magazine,, Sept 29, 2017)

Initially after observing many of these showers it seemed that the cosmic rays were coming toward the Earth from just about every direction and the source of the rays could not be pinned down.  But after many years of observing these showers, the statistics has now started to show that the source of the cosmic rays is not within the Milky Way galaxy and instead the source is indeed extragalactic.

Now to me me this result is sort of disappointing.  Yes, ok, so the source of the high energy cosmic rays is found to be mostly extragalactic in origin.  That part is completely acceptable and understandable.  This means that the source is maybe, perhaps rare enough that it doesn't occur very often in a particular galaxy, such as the Milky Way.  But, when you examine the statistically significant over flux region from which cosmic rays appear to come, why does it appear to come from the location identified?

After many years of observation, the source of high energy cosmic rays appears to be extragalactic (Source: Astronomy Magazine)
Excess cosmic ray flux with position of source (Source: Astronomy Magazine, Sept 29, 2017)

What you can see is that the excess flux comes from a region not in the plane of the Milky Way disk.  At one time the source was thought to be from out per own galaxy, like the central bulge of the Milky Way, but this is not the case.  The cosmic rays can be deflected by galactic magnetic fields which is why this study only considers the highest energy cosmic rays, which will suffer the least direction changing effects of the magnetic fields.  For more of the details, check out the source article at: 

My unease with this analysis, not because the authors have done something wrong, I'm in no position to criticize their paper, but can wonder why the source of high energy cosmic rays should have any identifiable location other than just random position around the galaxy.  It's great that they can show that the major sources of cosmic rays are outside of our own galaxy.  But other measurements, such as that of the cosmic background radiation, shows that it is mostly uniformly distributed and there is no preferred direction.  So, I am quite perplexed as to why the statistical significance establishes what to me seems like a preferred direction for the source of the high energy cosmic rays.  Why should this be the case?  This seems to violate the basic assumptions of homogeneity and isotropy?  What is going on?

Finally, we should go over some of my insights into the paradox described in the the September 27, 2017 post, covering the relativistic simulations demonstrated in the www.edX.com course: Astrophysics: The Violent Universe.  Remember that one of the simulations showed what an observer, accelerating close to the speed of light, would see regarding the objects in front of him, and the simulation first showed the object in front moving away from the observer and then finally being caught up with.  If you are moving at velocities close to the speed of light, yes, you would notice length contraction and time dilation for object in front of you.  But why would these objects appear to move away from you?  Well, my insight is that the simulations included not only special relativity, but also general relativity.  In that case as the observer accelerates toward the object, general relativity predicts that the observers clock will run slow and the measured radial distances would stretch.  The simulation accelerated the observer from standstill to the speed of light in say 20 seconds.  So during the first second the velocity would increase from 0 to about 5% of the speed of light.  This represents an acceleration of about 0.05 * 300,000,000 / 9.8 = 1,500,000 gees, which would result in some serious time dilation and distance stretching.  So, yes, it seems the observed object would indeed be found to move away from the observer until the speed had increased enough that the observer could not be accelerated any more and then the effects predicted by special relativity would dominate over the effects predicted by general relativity.  So, yes, it seems the observed object would indeed seem to move away from the observer as the observer accelerated towards the object.  Pretty neat, assuming my understanding and analysis is correct!

Until next time,
Resident Astronomer George

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1 comment:

  1. Astronomy is quite hard to understand and quite a rough subject too but at the same time it is really an informative subject on can get a lot of good info's about the planets and other stuff. Great share