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A Galactic glitch

Filed under: — rasmus @ 10 March 2008

Knud Jahnke and Rasmus Benestad

After having watched a new documentary called the ‘Cloud Mystery’ – and especially the bit about the galaxy (approximately 2 – 4 minutes into the linked video clip) – we realised that a very interesting point has been missed in earlier discussions about ‘climate, galactic cosmic rays and the evolution of the Milky Way galaxy.

It is claimed in ‘The Cloud Mystery’, the book ‘The Chilling Stars’, and related articles that our solar system takes about 250 million years to circle the Milky Way galaxy and that our solar system crosses one of the spiral arms about every ~150 million years (Shaviv 2003).

But is this true? Most likely not. As we will discuss below, this claim is seriously at odds with astrophysical data.

Here is a little background on the Milky Way: The arms of spiral galaxies are not constant entities in time. They are results of gravitational instabilities in the disk or are induced by external companions. These instabilities are moving mass ‘overdensities’ containing old stars and gas, but also newly formed stars recently created from local collapse of the overdense gas.

Arms move around a spiral galaxy with a pattern speed that is defined by the mass distribution. This pattern speed differs from the motion of individual stars, just like the speed of an ocean wave differs from the movement of water particles. Estimating the pattern speed is difficult, as it is not coupled to the motion of individual stars but can only be inferred indirectly. For this reason it has not yet been reliably measured for our Milky Way – unlike for some other spiral galaxies, for which our clear and unobstructed view from the outside allows an estimate.

So how did Shaviv come up with this number?

Measuring the rotational velocity of stars in the Milky Way disk or other spiral galaxies is straightforward. The rotation is not rigid, but depends on the encircled mass inside the orbit of a star, including the Dark Matter, a yet unknown but solidly established source of gravitational attraction. It is easy and a standard technique to measure rotation curves of galaxies as a function of radius, and this is also possible for the Milky Way.

The two different rotating velocities of arms and stars have a different radial dependence – to first order the arms get preserved as entities while the stars further out have much smaller angular velocities than stars further inside – so the relative velocity of a star with respect to the nearest spiral arm will depend on its distance from the centre of the galaxy. At a certain radius, the radius of co-rotation, the two velocities are identical and a star at this radius has zero relative velocity with respect to the spiral arm pattern. It stays “forever” in the same spiral arm – or outside of it.

What are the best estimates for the relative velocity of the Sun with respect to the spiral arm pattern of the Milky Way? As mentioned, the pattern speed of the spiral arm in the Milky Way has not been firmly established.

When investigating other spiral galaxies, however, it was found that almost independently of the wide range of possible assumptions on which the pattern speed estimate was based, the radius of co-rotation follows a simple law: rcorot=r0 * (3.0 +/- 0.5), where r0 is the scale length of the exponential disk of the galaxy (the surface brightness of spiral galaxies drops very close to exponentially from the center to the outside, setting a characteristic size scale). This was measured by Kranz et al. 2003.

Since the Milky Way is a completely normal spiral galaxy, we can apply this result to it. The scale length of the Milky Way disk has recent estimates ranging from 2.6 kilo-parsec (kpc, 1pc=3.3 light years) from the SDSS survey (Juric et al. 2008), through 2.8 kpc (Ohja 2001) to 3.5 kpc (Larsen & Humphreys 2003).

We also know the Sun’s distance to the galactic center well, 7.9 +/- 0.4 kpc (Eisenhauer et al. 2003), which means that the range of values for rcorot=9.1 +/- 1.9kpc. In other words, from this calculation the co-rotation radius of the Milky Way is between 7 and 11 kpc, and at 8 kpc our Sun is close to or at the radius of co-rotation. It almost certainly is not 6 kpc further inside, as Shaviv (2003) claims.

Shaviv (2003) lists in his Table 3 a number of values for the pattern speed of the spiral arms, taking from publications ranging from 1969 to 2001, two years before his article. In these papers the derived relative motion of the Sun relative to the arms ranges from Omegarel=+13.5 km/s/kpc to -4km/s/kpc, and includes estimates that are close to zero (-4km/s/kpc < than Omegarel < +7), i.e. a location near the radius of co-rotation in the majority of the publications, and most of the more recent ones. However, he selectively disregards most of these results.

If we add the above evidence that the radius of co-rotation lies at 9kpc distance and not further out, and convert this to relative velocities, e.g. by using the Milky Way rotation curve by Merrifield 1992, we obtain Omegarel =+3.2 km/s/kpc with an error range from -2.5 to +7.1km/s/kpc, and including zero. Shaviv’s derived “period for spiral arm crossing” of p=134 +/- 25Myr for four spiral arms is well outside the range derived from these values.

So it seems that Shaviv’s “periodicity” estimate for crossing of spiral arms by the sun does not hold up under scrutiny when using current astronomical results as the work by Kranz et al. This comes in addition to the previously shown fact that the correlation of cosmic ray flux with paleoclimatic data proposed by Shaviv and Veizer (2003) only arises “by making several arbitrary adjustments to the cosmic ray data” (Rahmstorf et al. 2004).

Note also that the question of current climate change is quite another matter from that over time scales of many millions of years – despite Shaviv’s remarkable press-release claims that “The operative significance of our research is that a significant reduction of the release of greenhouse gases will not significantly lower the global temperature”. As we repeatedly pointed out over the years: that global warming over the past decades is not linked to cosmic rays is clear from the fact that the cosmic ray measurements over the past 50 years do not show any trend (Schiermeier 2007).

Remarkably, the poor scientific basis of the galactic cosmic ray hypothesis seems to be inversely related to the amount of media backing it is getting. At least 3 documentaries (‘The Climate Conflict’, the ‘Global Warming Swindle’, and now ‘The Cloud Mystery‘) have been shown on television – all with a strong thrust of wanting to cast doubt on the human causes of global warming.

References:

Eisenhauer et al. 2003, ApJ, 597, 121; http://adsabs.harvard.edu/abs/2003ApJ…597L.121E

Kranz et al. 2003, ApJ, 586, 143; http://www.journals.uchicago.edu/doi/abs/10.1086/367551

Juric et al. 2008, ApJ, 673, 864; http://adsabs.harvard.edu/abs/2008ApJ…673..864J

Larsen & Humphreys 2003, AJ, 125,1958; http://adsabs.harvard.edu/abs/2003AJ….125.1958L

Merrifield 1992, AJ, 103, 1552; http://adsabs.harvard.edu/abs/1992AJ….103.1552M

Ohja 2001, MNRAS, 322, 426; http://adsabs.harvard.edu/abs/2001MNRAS.322..426O

Rahmstorf, S., et al., 2004: Cosmic rays, carbon dioxide and climate. Eos, 85(4), 38, 41.

Schiermeier, Q., No solar hiding place for greenhouse skeptics. Nature, 2007. 448: p. 8-9.

Shaviv, N., 2003, NewA, 8, 39; http://adsabs.harvard.edu/abs/2003NewA….8…39S

Shaviv, N. and J. Veizer, Celestial driver of Phanerozoic climate? GSA Today, 2003. 13(7): p. 4-10.


378 Responses to “A Galactic glitch”

  1. 1
    John Gribbin says:

    I agree with the tenor of this post, but I’d like chapter and verse on how we know “the Milky Way is a completely normal spiral galaxy.” It’s only recently been established that it is average sized for as disc galaxy!

    John Gribbin

  2. 2
    Neil B. says:

    Sure, I couldn’t understand in those claims why the sun would move much relative to spiral arms – isn’t it part of the stars making those arms? But in any case, we have to take dark matter into account (or MOND if that offbeat theory turns out to be true) whenever we talk about rotation in galaxies. BTW, how about the idea that now the sun is primed for a cool spell, and that will compensate to whatever extent for global warming stimuli? It had a big splash recently, but I haven’t heard much since.

  3. 3
    Arch Stanton says:

    Thank you for addressing this issue.

    It amazes me how quickly and unquestionably the skeptically hopeful accept the minimally substantiated claims of Svensmark, yet refuse to believe science that has been much better substantiated.

  4. 4
    Gsaun039 says:

    It seems that a couple of years ago, that new evidence suggested that the Milky Way was likely a barred spiral type.

    Also something else that I seem to remember is that our Solar system is likely slightly inclined from the galactic plane ecliptic. The slight pertubations of the gravitational field as the solar system make’s it’s transit through the plave could be a good source of comets from the Oort cloud.

  5. 5
    Nick says:

    The two different rotating velocities of arms and stars have a different radial dependence – to first order the arms get preserved as entities while the stars further out have much smaller angular velocities than stars further inside – so the relative velocity of a star with respect to the nearest spiral arm will depend on its distance from the centre of the galaxy. At a certain radius, the radius of co-rotation, the two velocities are identical and a star at this radius has zero relative velocity with respect to the spiral arm pattern. It stays “forever” in the same spiral arm – or outside of it.

    Actually, it doesn’t. You’ve made a whooping assumption that the star stays in the glactic plane

    In the case of the sun, it doesn’t. It ossilates from above to below the galactic plane over time.

    As such it periodically passes though the plane, and that’s where the gasses are concentrated.

  6. 6
    John P says:

    I am reminded of Pauli’s comment when showed a paper – “This isn’t right. This isn’t even wrong.” Denialists such as Shaviv and the producers and broadcasters of this piece of drek have serious ethical issues. They don’t have a standard of proof, they merely spread disinformation with an agenda. The bar for publication of denialist nonsense is set far lower than that for publication of science in a respected journal such as Nature or Geophysical Letters.

  7. 7
    gusbob says:

    Knud Jahnke and Rasmus Benestad says “The rotation is not rigid, but depends on the encircled mass inside the orbit of a star, including the Dark Matter, a yet unknown but solidly established source of gravitational attraction.”

    I am curious when something is unknown and close to impossible to measure, what does it mean to be solidly established.

    Dark matter was created because current explanations regarding orbital velocities were missing the required mass for gravitational calculations to work. Now every time there is a gravitational anomaly it becomes “verification” of this unknown dark matter.Dangerous circular reasoning, and not very scientific.

    [Response: You are confusing matters quite seriously. The point is simply the gravitational attraction of dark matter (whatever it is) is known, and so can be used in calculations. See #33 below for a more detailed explanation from an astronomer.--eric]

  8. 8
    Craig Allen says:

    Going out on a limb here:

    An analogy for how galaxy arms and stars can move at different speeds can be found found in weather patters. I have noticed on my local online weather radar loop that clouds and storms move a lot faster than the cloud bands in which they form. I assume that the cloud bands are troughs in atmospheric pressure waves and that clouds and storms form as air mass passes across the waves. Obviously the physics of the weather patters has no connection with the dynamics of galaxies, but it demonstrates how structures at different scales in a medium such as air, water or space can move at different speeds.

  9. 9
    Hank Roberts says:

    > barred
    Perfectly normal, innit?

    “Bars in spiral galaxies seem to be ubiquitous in our local universe. Up to two-thirds of all spirals contain bars. …”
    http://www.space.com/scienceastronomy/astronomy/hubble_bar_010302.html

    > ossilates
    Oscillates? We assume this? or we know this how?
    Cite, please?

  10. 10
    Walt Bennett says:

    Amazingly,

    Still no post on the differences between Hadley and GISS anomalies.

    Instead, a steady stream of “Why the debunkers are full of it” posts.

    Is RC in the business of discussing climate science, or being the repository for anti-denialist rebuttals?

    It’s almost as though you guys sit around exclaiming “Look what they wrote about us TODYAY! Let’s get right to work on that one…”

    Quit taking your eyes off the ball, please. There are no doubt legitimate topics worthy of your brainpower and expertise.

    In the 2 years I’ve been coming here, your focus on refuting what “the other guys” say has never been narrower, and you are attracting an enormous crowd who want nothing more than to bash denialists. This is ceasing to become a “climate science” blog and becoming just another back-and-forth blog, as if we (a) could afford to lose the former and (b) needed another of the latter.

    [Response: Hey you know what? I have a real job as well and sometimes things just need to be done. This is on my to do list because it's of interest - but the nature of a volunteer spare time blog is that one doesn't get to devote unlimited resources to it. Sorry about that, but he who pays the piper... - gavin]

  11. 11
    Ben M says:

    I could buy Shaviv’s argument to a point, but it doesn’t change the fact that human influence is causing warming as well. If anything, it means we picked a really lousy time to start heating up our planet.

  12. 12
    Arch Stanton says:

    Re Nick @ #5:

    Actually Rasmus is right. Even if is a body oscillates “up and down” through the galactic plane (as our sun does) if the body is located at “the radius of co-rotation” it will remain indefinitely (essentially ‘forever’ for the purposes of this discussion) within (or without) of a spiral arm. Perhaps he could have been more accurate by saying “aligned with”. A body can remain in the spiral arm even as it oscillates up and down thorough the center of it. The “arm” is not limited to the “plane” within it.

  13. 13

    Do we really have to know all about this? I got to “But is this true? Most likely not,” and took your word for it. Not even looking further to see what it had to do with global warming.

    Seems to me a good old ploy of the denialists is to come up with far-flung, convoluted hypotheses that side-track us to such an extent, we don’t have time to deal with the real issue of GW.

    So while scientists may have to be on hand to refute these hypotheses, it seems to me a waste of precious time for the laypersons out there who need to keep on (or start) reducing their GHGs.

    So if a denialist crosses my path using this “galactic cosmic ray hypothesis,” I’ll just say I don’t have time for those kind of far-fetched hypotheses, but I know it’s been roundly refuted at RealClimate, and here is their webpage…..

  14. 14
    Henry says:

    What happened to your paper submitted to A&A in 2005 that also criticized Saviv’s work?
    http://de.arxiv.org/abs/astro-ph/0504155
    Was it rejected by A&A or is it still being revised?

    I think that New Astronomy has reasonable standards in general (although I never published or referred anything for that journal myself).

  15. 15
    Vern Johnson says:

    Astrophysics, gentlemen, is in it’s infancy. What is unknown far exceeds what is “known”. Cosmic rays, for example, are unknown as to source or what accelerates them. Gravity waves from theorized radiative sources like black holes have never been confirmed to exist and thus black holes themselves have never been triangulated as to location, not one. Leonard Krause extrapolates 100 billion years into the future and boldly states that our local group of galaxies will have coalesced into an “island universe” ( with nothing else in sight) and forecasts that the whole kit and kaboodle will eventually collapse into a black hole! We think we do know something about interstellar dust that is now flowing thru our solar system in larger amounts because of the reversed polarity of the sun that cyclically occurs. I would like to see this apparent fact discussed if it is true because that dust could have cooling effects?

  16. 16
    Jim Galasyn says:

    Re Nick’s suggestion in 5, claiming that oscillation above and below the galactic plane causes variation in GCR flux:

    If find it hard to believe that the amplitude of this oscillation is great enough to significantly vary the galactic magnetic field incident on Earth. Do you have any evidence that this is the case?

  17. 17
    Walt Bennett says:

    Re: #10 inline,

    Gavin,

    I appreciate the entirety of your comment, and I look forward to that post.

    My point this time was about what has become of the orientation of this blog: pugnacious, defensive, and heavily “interested” in debunking denialism. Less and less original commentary on the work you and others do.

    I miss that, personally.

  18. 18
    Paul Middents says:

    Perhaps the post by Tamino on his blog “Open Mind” might satisfy Walt’s impatient demand:

    http://tamino.wordpress.com/2008/01/24/giss-ncdc-hadcru/#more-556

  19. 19
    Henry says:

    f find it hard to believe that the amplitude of this oscillation is great enough to significantly vary the galactic magnetic field incident on Earth.

    Possibly of relevance is this paper:

    http://arxiv.org/abs/astro-ph/0602092
    Do extragalactic cosmic rays induce cycles in fossil diversity?
    Authors: Mikhail V. Medvedev, Adrian L. Melott

    Abstract: Recent work has revealed a 62 (+/-) 3-million-year cycle in the fossil diversity in the past 542 My, however no plausible mechanism has been found. We propose that the cycle may be caused by modulation of cosmic ray (CR) flux by the Solar system vertical oscillation (64 My period) in the galaxy, the galactic north-south anisotropy of CR production in the galactic halo/wind/termination shock (due to the galactic motion toward the Virgo cluster), and the shielding by galactic magnetic fields. We revisit the mechanism of CR propagation and show that CR flux can vary by a factor of about 4.6 and reach a maximum at north-most displacement of the Sun. The very high statistical significance of (i) the phase agreement between Solar north-ward excursions and the diversity minima and (ii) the correlation of the magnitude of diversity drops with CR amplitudes through all cycles provide solid support for our model. Various observational predictions which can be used to confirm or falsify our hypothesis are presented.

  20. 20
    Khebab says:

    What’s the point in looking a the hypothetical impact of the galaxy given the stated lack of a trend in the GCRs with the climatology (http://www.realclimate.org/index.php/archives/2004/12/recent-warming-but-no-trend-in-galactic-cosmic-rays/)!!

  21. 21
    Nick says:

    Nothing like giving you a reference or two

    http://en.wikipedia.org/wiki/Milky_Way

    Sun’s location

    The Sun (and therefore the Earth and Solar System) may be found close to the inner rim of the Galaxy’s Orion Arm, in the Local Fluff or the Gould Belt, at a hypothesized distance of 7.62±0.32 kpc from the Galactic Center.[28][29][30][31] The distance between the local arm and the next arm out, the Perseus Arm, is about 6,500 light-years.[32] The Sun, and thus the Solar System, is found in what scientists call the galactic habitable zone.

    The Apex of the Sun’s Way, or the solar apex, is the direction that the Sun travels through space in the Milky Way. The general direction of the Sun’s galactic motion is towards the star Vega near the constellation of Hercules, at an angle of roughly 60 sky degrees to the direction of the Galactic Center. The Sun’s orbit around the Galaxy is expected to be roughly elliptical with the addition of perturbations due to the galactic spiral arms and non-uniform mass distributions. In addition the Sun oscillates up and down relative to the galactic plane approximately 2.7 times per orbit. This is very similar to how a simple harmonic oscillator works with no drag force (dampening) term.

    It takes the Solar System about 225–250 million years to complete one orbit of the galaxy (a galactic year),[33] so it is thought to have completed 20–25 orbits during the lifetime of the Sun and 1/1250th of a revolution since the origin of humans. The orbital speed of the Solar System about the center of the Galaxy is approximately 220 km/s. At this speed, it takes around 1400 years for the Solar System to travel a distance of 1 light-year, or 8 days to travel 1 AU.[34]

    http://www.americanscientist.org/template/AssetDetail/assetid/21173/page/2

    a bit longer quote, because of some of the details

    Our sun is also in motion. Relative to the average motion of the most commonly measured nearby stars, the sun moves with a speed of about 16.5 kilometers per second, or nearly 50 light-years per million years. The sun’s path is inclined about 25 degrees to the plane of the galaxy and is headed toward a region in the constellation of Hercules near its border with Lyra. The sun oscillates through the plane of the galaxy with an amplitude of about 230 light-years, crossing the plane every 33 million years. However, the sun’s motion relative to the local stellar neighborhood should not be confused with its movement around the center of the galaxy, since the whole solar neighborhood (including the sun) orbits the galactic center once every 250 million years. Just as we do not include the earth’s velocity around the sun when calculating the speed of an airplane (we are only interested in the ground-speed), astronomers do not include the sun’s galactic orbital velocity when describing its local motion.

    The interstellar cloud currently surrounding the solar system—often referred to as the Local Interstellar Cloud—is warm, tenuous and partially ionized. Like all interstellar clouds, our local cloud is made of dust and gas, with the dust fraction making up about one percent of the cloud’s mass. The elemental composition of interstellar clouds is much like that of the sun, about 90 percent hydrogen and 9.99 percent helium. The heavier elements make up the remaining 0.01 percent.

    The sun is on the edge of what is sometimes called the Local Bubble, a great void in the distribution of interstellar gas in the nearby galactic neighborhood. As voids go, the Local Bubble interior is one of the most extreme vacuums yet discovered. The very best laboratory vacuum is about 10,000 times denser than a typical interstellar cloud, which in turn is thousands of times less dense than the Local Bubble. The Local Bubble is not only relatively empty (with a density of less than 0.001 atoms per cubic centimeter); it is also quite hot, about one million degrees kelvin. By comparison, the interstellar cloud around the solar system is merely warm, about 7,000 degrees, with a density of about 0.3 atoms per cubic centimeter.

    The Local Bubble lies within a ring of young stars and star-forming regions known as Gould’s Belt. The Belt is evident in the night sky as a band of very bright stars that sweeps in a great circle from the constellations Orion to Scorpius, inclined about 20 degrees relative to the galactic plane. The north pole of Gould’s Belt lies close to the Lockman Hole, a region in the sky with the least amount of intervening interstellar gas between the sun and extragalactic space. Star formation regulates the distribution of interstellar matter, including the boundaries of the Local Bubble. The closest star-forming region on the outskirts of the Local Bubble is about 400 light-years away in the Scorpius-Centaurus association. The molecular clouds from which stars are formed are both cooler (less than 100 degrees) and denser (over 1,000 atoms per cubic centimeter) than the Local Interstellar Cloud.

    A plot of the sun’s course through our galactic locale shows that the sun has been traveling through the Gould’s Belt interior in a region of very low average interstellar density for several million years. The sun is unlikely to have encountered a large, dense interstellar cloud in this relatively benign region during this time. Although our solar system is in the process of emerging from the Local Bubble, the sun’s trajectory suggests that it will probably not encounter a large, dense cloud for at least several more million years. The consequences of such an encounter for the earth’s climate are unclear; however, one wonders whether it is a coincidence that Homo sapiens appeared while the sun was traversing a region of space virtually devoid of interstellar matter.

    Despite the absence of massive clouds within 100 light-years, it seems likely that the local galactic environment changes in subtle ways on much shorter time scales. The low density of the Local Bubble permits the products of supernova explosions—such as superbubbles and shock fronts—to expand easily into the void and sweep past the sun. Indeed, within the past 250,000 years the sun has entered the outward flow of material from the star-forming region of the Scorpius-Centaurus association. There is even some suspicion that the interstellar environment may have changed within the past 2,000 years! This is uncertain, however, because astronomers have an incomplete understanding of the structure of the local interstellar cloud complex.

  22. 22
    Hank Roberts says:

    This is rather old — 1984.

    “… the time needed for the Solar System to oscillate vertically about the plane of the Galaxy, which is 33 plus/minus 3 Myr according to the best current astronomical evidence.”

    Has anyone the time to follow citing publications forward in time, or to find another cite to look into?

    http://www.nature.com/nature/journal/v308/n5961/abs/308709a0.html

  23. 23
    tom ward says:

    Papers on solar variability and cosmic-rays continue to surface even though many would prefer they go away from the climate variability debate. We find yet another case for solar variability and cosmic rays in an article in Physics Today March, 2008, pgs 50-51, “Is Climate sensitive to solar variability?” by Nicola Scafetta and Bruce West. References therein detail considerable work in progress. I would like to see a discussion of the method these folks are using who come to the conclusion that 15-70% of the warming is due to solar variability.

  24. 24
    Arch Stanton says:

    Lynn (13) This is significant due the galactic cosmic ray (GCR) hypothesis popularized by Svensmark and others (and popular with some denialists). Accordingly; as our solar system passes through the more dense parts of the Milky Way galaxy found in the arms and along the center of the galactic plane, it is subject to increasing amounts of GCRs. According to the hypothesis; during these increased periods of terrestrial GCR bombardment the earth experiences increased high clouds (and subsequent cooling) because the GCR- ionized atoms in the upper atmosphere (allegedly) make dandy cloud droplet/crystal nuclei.

    The timing of these events is very significant to the hypothesis.

    Fans of the GCR hypotheses often tend to cite them as gospel and are frequently not aware of the tenuousness of the components they are based on are.

  25. 25
    Nick says:

    Seems a comment went missing.

    http://en.wikipedia.org/wiki/Milky_Way

    he Sun (and therefore the Earth and Solar System) may be found close to the inner rim of the Galaxy’s Orion Arm, in the Local Fluff or the Gould Belt, at a hypothesized distance of 7.62±0.32 kpc from the Galactic Center.[28][29][30][31] The distance between the local arm and the next arm out, the Perseus Arm, is about 6,500 light-years.[32] The Sun, and thus the Solar System, is found in what scientists call the galactic habitable zone.

    The Apex of the Sun’s Way, or the solar apex, is the direction that the Sun travels through space in the Milky Way. The general direction of the Sun’s galactic motion is towards the star Vega near the constellation of Hercules, at an angle of roughly 60 sky degrees to the direction of the Galactic Center. The Sun’s orbit around the Galaxy is expected to be roughly elliptical with the addition of perturbations due to the galactic spiral arms and non-uniform mass distributions. In addition the Sun oscillates up and down relative to the galactic plane approximately 2.7 times per orbit. This is very similar to how a simple harmonic oscillator works with no drag force (dampening) term.

    It takes the Solar System about 225–250 million years to complete one orbit of the galaxy (a galactic year),[33] so it is thought to have completed 20–25 orbits during the lifetime of the Sun and 1/1250th of a revolution since the origin of humans. The orbital speed of the Solar System about the center of the Galaxy is approximately 220 km/s. At this speed, it takes around 1400 years for the Solar System to travel a distance of 1 light-year, or 8 days to travel 1 AU.[34]

  26. 26
    Nick says:

    More references

    http://www.nature.com/nature/journal/v308/n5961/abs/308712a0.html

    Raup and Sepkoski1 have recently reported evidence fora 26-Myr periodicity in the occurrence of mass extinctions based on a study of marine fossils. The data baseline of 250 Myr suggests events of variable amplitude, with some of the strongest peaks associated with boundaries between major geological periods which have been defined by previous palaeontological studies. In a more limited quantitative study, Fischer and Arthur2 earlier cited evidence for a 32-Myr period of major extinction events. Hatfield and Camp3 were among the first to suggest that mass extinctions might be correlated with periodic galactic phenomena, noting intervals of 80−90 Myr between major mass extinctions with an exceptionally strong mass extinction every 225−275 Myr. Here we point out a possible correlation between the 26-Myr extinction period and the Sun’s oscillation about the galactic plane.

  27. 27
    Eyal Morag says:

    As Mach as I like to find mistake in shaviv theory the last paragraph is enough.
    I can live without paleozoic climate and skip the mesozoic. I guess that if someone will put error bars on the radiation in that time they will fill the the page.

    as a Hebrew climate blogger who write 10% of what I would like I can’t complaint But I’l be glad to have more on non deniers things.

    P.S. Surely I will put link to this post in my shaviv post

  28. 28
    dws says:

    Re 10) Hadley and GISS anomalies
    I’m not familiar with the history of your prior posts but the
    subject is discussed well at:
    http://tamino.wordpress.com/2008/03/02/whats-up-with-that/#more-614

    Seems ok!

  29. 29
    Ray Ladbury says:

    Vern Johnson–It would appear that you know neither what we know, nor what we do not know. We have seen black holes, and we know GCR are accelerated by supernovae. We know that the density of interstellar dust is infinitesimal and has no effect on solar irradiance (which we can measure), and we know that GCR fluxes are not varying appreciably. What nobody knows is how you would take a putative tiny variation in said GCR flux measuring on average 6 particles per cm^2 per second and turn it into a global effect–especially one that only made clouds during the daytime. Neat trick, that.

  30. 30
    Jon Gradie says:

    The orbital inclination of the solar orbit is about 5.5 deg with respect to the galactic plane. Simple trig gives an “oscillation” amplitude such that the solar system moves +2,600 l.y. above and -2,600 l.y. below the galactic plane at the semimajor axis of the solar system during its 250 million galactic year. Two import points derived from orbital mechanics: (a) the sun spends most of its time above or below the galactic plane and transitions only twice (up one, down once) per galactic year and (b) the “velocity” of the sun perpendicular to the galactic plane is highest during the transit through the galactic plane which means the sun spends very little time passing through the disk. We would expect two “short” periods of increased GCR exposure every 250 m.y.

    Dark Matter: the presence of dark matter was known ever since astronomers in the early 20th century recognized the odd orbits of the stars around the Milky Way and eventually other galaxies (via Doppler spectroscopy of the “gross” spiral arms — stars do not need to be resolved). The Dark Matter was known to be large quantities of mass exterior, but in close proximity, to the galaxy that was not luminous (hence “dark”). The issue has always been “what is it?” Not, is it really there. 20th century theories included dark (nonluminous) H regions, nonluminous substars (e.g., MACHOs), neutrinos, etc., but not until cosmology and particle physics began to converge in the late 20th century (and the other theories were ruled out by observation) did the “weirdness” of dark matter come to the forefront (weird in that it does not interact with the rest of the mass in the universe except through gravity. We can see evidence of dark matter, as a primordial substance, in galactic cluster collisions, thanks to the Great Observatories (Hubble, Chandra, Spitzer and Compton) combined with ground-based radio astronomy (e.g., http://www.nasa.gov/audience/forstudents/postsecondary/features/F_NASA_Great_Observatories_PS.html)

    Astrophysics as an immature science: age is relative. Read both the history and current status — not in popular science, but in the real world, and you will find a robust, young adult.

  31. 31
    Lawrence Brown says:

    Regarding comment #10. This is an unjust accusation(about ‘being the repository for anti-denialist rebuttals’). Several of the most recent posts didn’t take issue with the basic premise and/or the conclusions of the paper reviewed- e.g. ’536 AD and all that’,The papers on Tropical Cyclone History, and ‘A Day When Hell Was Frozen’, to name a few.

    On this particular topic, the astronomers gave their results and conclusions based on their findings and Rasmus and Knud Jahnke, gave theirs in more mathematical detail than presented in the film. The latter presenters are on more solid ground in rebutting the spike in temperatures over the last 2 and a half decades than the cosmic ray people.

    If you disagree with this, present your findings and conclusions, or establish a site where you can choose the subject matter. Don’t expect volunteers working without remuneration to march to the beat of your drummer.

    When I was sick a while back, the Dr. asked my wife what my main symptoms were and she answered “Whining and complaining.” Instead of that, set up your own site and pick your own topics.

  32. 32
  33. 33
    Ralph says:

    I am an astronomer, so I hope I can help clear up some of the confusion here.

    Post #1: “I agree with the tenor of this post, but I’d like chapter and verse on how we know “the Milky Way is a completely normal spiral galaxy.” It’s only recently been established that it is average sized for as disc galaxy!”

    Chapter and verse are way too specific — you need a whole book. Try Galactic Astronomy by Binney & Merrifield. The size scale of the Milky Way has been established for many decades — the existence of spiral arms was discovered over 40 years ago and has been confirmed numerous times since then. Pulsars, molecular gas, and atomic gas all trace the spiral structure very nicely (and independently). As for the galaxy being a disk, look for a google image of “COBE galaxy” to put the nail in that coffin. That the Milky Way is a typical-sized spiral is beyond dispute at this point. It’s not a “new” result.

    Post #2:”Sure, I couldn’t understand in those claims why the sun would move much relative to spiral arms – isn’t it part of the stars making those arms? But in any case, we have to take dark matter into account (or MOND if that offbeat theory turns out to be true) whenever we talk about rotation in galaxies.”

    No, the Sun is not part of the stars that make up the spiral arms. Spiral arms are obvious because the brightest stars are formed in them. These stars have very short lives, however, compared to the pattern speed of the arms. There are almost as many stars between the arms as in them (the Sun is between arms right now). The arms trigger star formation, which creates bright, short lived stars, which quickly burn out. When the arm moves on, the bright stars go away.

    No, you don’t need to worry about dark matter here (or MOND, which has been repeatedly shown to be an inaccurate description of gravity, despite its success in limited applicaitons). The rotational velocity of the Galaxy is well measured for both the stars and the gas. It is what it is — WHY it has that speed doesn’t change the arguments made in the main post. You don’t have to buy that dark matter is an exotic weakly interacting massive particle to believe that the Sun orbits the Milky Way every 250 million years.

    #4:”It seems that a couple of years ago, that new evidence suggested that the Milky Way was likely a barred spiral type.

    Also something else that I seem to remember is that our Solar system is likely slightly inclined from the galactic plane ecliptic. The slight pertubations of the gravitational field as the solar system make’s it’s transit through the plave could be a good source of comets from the Oort cloud.”

    Current evidence of the kinematics of stars near the Galactic Center indeed suggests the Milky Way is a barred spiral. It also could be the case that as the Sun bobs up and down through the Galactic plane it may encounter more stars during plane crossings, which may induce more comets. It’s not clear if this is a strong effect, though.

    #5:”Actually, it doesn’t. You’ve made a whooping assumption that the star stays in the glactic plane
    In the case of the sun, it doesn’t. It ossilates from above to below the galactic plane over time.
    As such it periodically passes though the plane, and that’s where the gasses are concentrated.”

    It’s true that the gases are concentrated in the plane, but it’s very patchy (and concentrated in the arms) — most of the time the Sun will pass through the plane without encountering much molecular gas.

    #7:”I am curious when something is unknown and close to impossible to measure, what does it mean to be solidly established.

    Dark matter was created because current explanations regarding orbital velocities were missing the required mass for gravitational calculations to work. Now every time there is a gravitational anomaly it becomes “verification” of this unknown dark matter.Dangerous circular reasoning, and not very scientific.”

    The existence of a smooth source of gravity in galaxies is overwhelming. This conclusion is completely scientific. We know that the stars in the Galaxy orbit at a rate that cannot be explained by adding up the gravity of the stars themselves. This is not a small effect. Either gravity operates differently at large scales, or there is matter that isn’t bright. Evidence for the former option is strongly lacking. Evidence for the latter option is ubiquitous and self-consistent (not circular — there’s a difference). If there dark matter in the Universe, then our models of cosmology, galaxy clusters, and the Galaxy itself are essentially complete and very simple. Occam’s razor dictates that the easiest explanation is that there is simply matter we cannot see. The alternative is that, although Einstein’s theory of General Relativity has been demonstrated to amazing levels of accuracy in some places, it somehow fails spectacularly in others. This would be very hard to understand. Dark matter requires no new physics. Neptune was the original dark matter (look up the story of its discovery). The neutrino was another.

    #8: I don’t know much meteorology, but that sounds like an excellent analogy.

    #9:”> barred
    Perfectly normal, innit?

    “Bars in spiral galaxies seem to be ubiquitous in our local universe. Up to two-thirds of all spirals contain bars. …”
    http://www.space.com/scienceastronomy/astronomy/hubble_bar_010302.html

    > ossilates
    Oscillates? We assume this? or we know this how?
    Cite, please?”

    Yes, barred spirals are common, as large galaxies go.
    The bobbing of the Sun through the Galactic plane is firmly established by measurements of what is known as the “local standard of rest”. The Sun has significant velocity in the direction perpendicular to the plane of the Galaxy (as most G stars do). This is expected from stellar dynamics, and produces a small, slow oscillation. We are now about 30pc or so from the plane, although that number has big error bars.

    #15:”We think we do know something about interstellar dust that is now flowing thru our solar system in larger amounts because of the reversed polarity of the sun that cyclically occurs. I would like to see this apparent fact discussed if it is true because that dust could have cooling effects?”

    The dust in the Galaxy is nothing like “dust” that would effect climate for several reasons. 1) It’s not “dust” like in your room. It’s many times finer than cigarette smoke. 2) It’s incredibly sparse. There isn’t nearly enough of it to have any effect on the atmosphere compared to the amount of much bigger particles in the atmosphere naturally, to say nothing of the man-made contribution.

    #16: The magnetic field near the Earth is dominated by the Earth’s own field. This field is strongly distorted by the magnetic field and “wind” of the Sun. The galactic field is stopped many billions of miles away by the Sun’s field. The Voyager and Pioneer spacecraft are just now starting to find this boundary (called the “heliopause”). The galactic field cannot penetrate the heliopause (far beyond the orbit of Pluto) so the galactic field is not important here.

    [Response: Ralph, thanks for stopping by RealClimate. Your helpful and clear responses are much appreciated. --eric]

  34. 34
    Ray Ladbury says:

    Gusbob, your “dangerous circular reasoning” is the same type of reasoning that Enrico Fermi employed to posit the neutrino. It is the same sort of intuitive leap Newton made from the falling apple to the motion of the planets. In a self-correcting discipline like science, being wrong is not the greatest sin–and taking the risk of being wrong is the only way to fundamentally advance understanding.

  35. 35
    Gary says:

    Interesting. But I am hard pressed to figure out why if astrophysicists should not be commenting on climate, why climatologists (physicist for Rasmus) should be commenting on astrophysics?

  36. 36

    Let’s clarify a couple things.

    Re #5, 9, 12, 16: The vertical oscillation of the sun is moderate. It results in a ~50% change in local galactic density at the extreme vertical displacement relative to the plane of the disk. This is enough to matter, but one would have a semantic argument about whether a 50% drop is really large enough to say that the sun ever meaningfully leaves the disk of the galaxy. Medvedev and Melott, writing after Shaviv and for entirely different reasons, suggest that this much oscillation translates to as much as a factor of 5 change in cosmic ray flux with a 50-80 Myr timescale. (For those keeping track, this factor of 5 change would actually be larger and on a different timescale than the factor of ~3 that Shaviv and Veizer suggested occurs on a 140 Myr timescale.) I’m not entirely convinced Medvedev and Melott are right about the magnitude, but it is a point to be aware of.

    Re #1: If the Milky Way is really a four armed spiral (as opposed to the more mundane two armed variety), then we are actually living in a fairly rare type of galaxy. That has no bearing on the validity of the co-rotation argument however.

    Re #2: The spiral pattern is created by a “supersonic” “shock wave” in the gas of the galaxy. The shock front moves at its own speed seperate from the velocities of stars, much the same way that ripples on a pond move faster than the water itself. In fact, the concentrations of stars we see in spiral arms are actually created that way. The passage of the shock front leads to compression that squeezes the gas just enough that some of it collapse to form new stars, and it is this concentration of new stars that make the spiral arms appear brighter. After the shock wave passes, the normal motions of the stars will cause them to disperse. (Note: both “supersonic” and “shock wave” have technical meanings that aren’t really important to the qualitatively understanding.)

    Re #4: The solar system is highly inclined relative the galactic plane, making an angle of nearly 60 degrees.

  37. 37
    Ray Ladbury says:

    Scafetta and West have been eviscerated on RC previously:
    http://www.realclimate.org/index.php/archives/2007/11/a-phenomenological-sequel/

    http://www.realclimate.org/index.php/archives/2006/03/solar-variability-statistics-vs-physics-2nd-round/

    http://www.realclimate.org/index.php/archives/2006/10/how-not-to-attribute-climate-change/

    The biggest problem with this work is that it completely ignores the known physics of greenhouse forcing and adopts a “blackbox” approach of comparing time series–epidemiology applied to physics devoid of a mechanism.
    It is numerology. I look forward to the future editorials in Physics Today on astrology, phrenology and other pseudoscientific topics. I would have expected better.

  38. 38
    William Astley says:

    The article above presents a link to this paper,

    http://www.nature.com/nature/journal/v448/n7149/full/448008a.html

    , which purports to show that solar changes were not responsible for a significant portion of the 20th century warming. The paper in question looks at only two of the three mechanisms by which solar changes affected planetary temperature. These are the three mechanisms.

    1)Solar irradiation changes. (No the sun did not get hotter in the 20th century.)

    2)Solar heliosphere modulation of Galactic Cosmic Rays. (No, for the time period in question, GCR changes did not cause global warming. The strength and the extent of the solar heliosphere changes throughout the solar cycle, which modulates the amount of GCR that strikes the atmosphere. Changes in GCR has been shown to affect planetary cloud cover. More GCR more clouds colder planet and visa versa.

    3)Electroscavenging. Yes that is mechanism by which the solar magnetic field is purported to have caused a significant portion of the warming in the 20th century. Solar wind bursts (caused by coronal holes moving towards the solar equator for example, particularly at the end of the solar cycle.) create a space charge in the ionosphere which removes cloud forming ions. Less ions, less clouds. Less clouds warmer planet.

    Look at figure 12 in the attached which shows the number of solar magnetic storms per year, from 1865 to present and the solar cycle number. There is roughly a 10 times increase in the number of magnetic storms at the end of the solar cycles, when comparing the 20th century to the 19th century. It is not just the number, but the magnitude of the solar storms.

    http://www.geomag.bgs.ac.uk/earthmag.html#_Toc2075558

    This paper by Brian Tinsley and Fangqun Yu “Atmospheric Ionization and Clouds as Links Between Solar Activity and Climate” outlines solar mechanisms 2) and 3), if you are interested in more details concerning the mechanisms.

    http://www.utdallas.edu/physics/pdf/Atmos_060302.pdf

    Now as the sun appears to be entering a long term minimum the solar wind bursts should drop off, in frequency and magnitude. There will therefore be less electroscavenging to remove cloud forming ions. In addition, with the solar magnetic cycle in a minimum, the large scale magnetic field and solar heliosphere should be reduced. A reduced solar heliosphere should result in increased GCR.

    The following is a link that shows GCR has increased by about 12%.

    http://cosmicrays.oulu.fi/Request.dl…=00&mR=00&PD=1

    If there was more cloud forming ions, there should be more clouds over the ocean which should over time result in colder ocean surface temperatures. What are your thoughts?

    http://www.osdpd.noaa.gov/PSB/EPS/SST/data/anomnight.3.10.2008.gif

  39. 39

    #10, Walt, I find debunking contrarians just as instructive as any other topic here. A contrarian stance is always seriously flawed in one way or another, and knowing this error is just as good as being taught about climate reality in some topical way… Keep up the good work RC!

    Surface temperatures should be taken with the idea that they represent the bottom of an ocean of air. It is hardly possible to determine what is going on from just surface information, or to say that surface temperature leads and what happens above follows.

  40. 40
    gusbob says:

    Ralph said, “The existence of a smooth source of gravity in galaxies is overwhelming. This conclusion is completely scientific. We know that the stars in the Galaxy orbit at a rate that cannot be explained by adding up the gravity of the stars themselves. This is not a small effect. Either gravity operates differently at large scales, or there is matter that isn’t bright. Evidence for the former option is strongly lacking. Evidence for the latter option is ubiquitous and self-consistent (not circular — there’s a difference).”

    Ralph thank you for your thoughtful post. However I must disagree that it is not circular reasoning. I agree that the Dark Matter hypothesis is scientific but only in the sense that it is a hypothesis to explain current astronomical conundrums. And I agree that the missing gravity is not a small effect. It is huge! But what we are observing in outer space is evidence of “attractive forces” that can not be explained by the calculations of observable mass. Yes, the evidence is indeed ubiquitous, that this force is accounted for by visible mass.

    However it is most definitely circular reasoning to hypothesize this missing force is the result of dark matter and then every time you observe the missing force to claim it must be the very same hypothesized dark matter.

    I find it easier to believe, and eventually prove or disprove, that the missing force results from electromagnetic interactions. The electromagnetic force is at least a trillion, trillion, trillion, times more powerful than gravity. Occam’s razor suggests to me, that a theory that incorporates electromagnetic forces is an easier explanation than creating a new form of matter that has not been observed and so far is impossible to observe.

    The idea of Birkeland currents (http://en.wikipedia.org/wiki/Birkeland_current) connecting the sun to the earth and elsewhere in outer space was believed to be impossible because space was believed to be a vacuum. It seems then Occam’s razor made it was easier to deny their existence than let go of the erroneous idea of the “space vacuum”. Dark matter only serves Occam’s razor because we need not re-think our theories. Electromagnetic ideas do not replace gravitational effects or nuclear effects but fills in the holes with a force that is observable and testable.

    And now we know that space is filled with plasma and our Local Bubble of plasma is being investigated by CHIPS. And Themis cinfirms what Birkeland suggested 100 years ago: “”The satellites have found evidence for magnetic ropes connecting Earth’s upper atmosphere directly to the Sun,” says Dave Sibeck, project scientist for the mission at the Goddard Space Flight Center. “We believe that solar wind particles flow in along these ropes, providing energy for geomagnetic storms and auroras.”

    http://science.nasa.gov/headlines/y2007/11dec_themis.htm

    Magnetic fields are caused by electric currents and as Themis and Ulysses reveal, the evidence mounts that electromagnetic forces must be incorporated into our cosmological understanding. Much of the electromagnetic ideas can be demonstrated and tested in plasma labs and are scalable. meanwhile the actuality of dark matter remains a fairy tale, a nice story of inferences but not testable and nor falsifiable. And thus it is not science. It is a galactic glitch.

  41. 41
    gusbob says:

    RL,

    “Gusbob, your “dangerous circular reasoning” is the same type of reasoning that Enrico Fermi employed to posit the neutrino. It is the same sort of intuitive leap Newton made from the falling apple to the motion of the planets. In a self-correcting discipline like science, being wrong is not the greatest sin–and taking the risk of being wrong is the only way to fundamentally advance understanding.”

    In my above post I relate why I think the risk of exploring an electrical idea of the universe is at least as valid as seeking a dark matter solution. And it would be in keeping with Fermi and Newton’s risk taking.

    I responded to your aggressive denunciation of the electric universe on the Antartica thread but those posts were deleted. So perhaps you missed the 3 questions I asked you to answer w(ithout evoking elctromagnetic forces). I think the elctromagnetic answers to those questions are plausible and testable.

    First why does the solar wind accelerate away from the suns and past the planets. Gravitational theory alone suggests it should decelerate.

    Second why does the temperature beginning at the photosphere,5800K , drop in the chromosphere and then jump to over 1 million K in the corona. Shouldn’t we get cooler as we stand further from the fireplace.

    And 3rd if Themis’ magnetic ropes are not Birkeland currents then what are they?

    And since you mention the neutrino, why are we missing the predicted neutrinos postulated for a strictly nuclear sun?

  42. 42
    cce says:

    If we could shift the discussion to clouds, Nexus6 pointed out over a year ago with the problems with the ISCCP cloud dataset. That the decrease in cloud cover is either mostly or entirely due to the addition of satellites, improving the field of view. This is described in this paper:
    http://cimss.ssec.wisc.edu/clavr/amato/2006GL028083.pdf

    Joel Norris recently did a presentation on cloud cover, i.e. satellite vs surface observations:
    http://meteora.ucsd.edu/~jnorris/presentations/12469 (real video)

    This data is described in this paper:
    http://meteora.ucsd.edu/~jnorris/reprints/NorrisGwattRevised.pdf

    In particular, look at the graphs on page 4 (figure 1) and the map of the cloud cover anomalies on page 6 (figure 2). I don’t see how anyone can still cling to the cosmic ray theory of climate change (at least as an explanation for current warming) given these facts.

  43. 43
    Jim Galasyn says:

    Thanks to Ralph in 33 for helpful explanations. Re my suggestion about the galactic magnetic field, this was the only relevant variable I could imagine that would affect the GCR flux as the Sun oscillates about the galactic plane.

    Very interested to know what other effects might modulate the GCR flux. Surely not dust and gas…?

  44. 44
    Peter Erwin says:

    #36:
    Re #2: The spiral pattern is created by a “supersonic” “shock wave” in the gas of the galaxy. The shock front moves at its own speed seperate from the velocities of stars, much the same way that ripples on a pond move faster than the water itself. In fact, the concentrations of stars we see in spiral arms are actually created that way. The passage of the shock front leads to compression that squeezes the gas just enough that some of it collapse to form new stars, and it is this concentration of new stars that make the spiral arms appear brighter. After the shock wave passes, the normal motions of the stars will cause them to disperse. (Note: both “supersonic” and “shock wave” have technical meanings that aren’t really important to the qualitatively understanding.)

    Actually, the spiral pattern is probably a combination of this and a gravitational density wave in the old and young stars. Many young stars are indeed born in the compressed gas, and their light makes the arms stand out, especially in blue light (young stars are generally hot, and thus blue).

    But the arms in many spirals can still be seen when one looks in the infrared, where the light comes more from older stars. Faint spiral arms can even be seen in disk galaxies that lack gas and young stars entirely (and such arms also produced in gravitational n-body simulations of galaxies, without needing gas).

    A gravitational density wave like a spiral arm can be thought of as something like a traffic jam: it’s a moving region of higher density, which stars join and then leave.

  45. 45
    vijay says:

    Sorry I do not belive on the astronomy.

  46. 46
    pete best says:

    Re#1 is this John Gribbin of popular science writing fame in the UK and quantum theorist / scientist ?

  47. 47

    Shouldn’t that r0 * 3 be r0 ^ 3? If it were a scalar coefficient it would come before the variable, not after it. I’m pretty sure the 3 should be an exponent.

  48. 48

    gusbob says:

    [[I am curious when something is unknown and close to impossible to measure, what does it mean to be solidly established.]]

    Dark matter is easily measured by its gravitational effect.

  49. 49

    The idea that the Sun “oscillates” above and below the galactic plane seems to me to defy celestial mechanics. What would make it do that?

    If it has a nonzero orbital inclination, it would pass the galactic midplane exactly twice per orbit — once on the way down and once on the way up — at the descending and ascending “nodes,” respectively. For a galactic orbital period of 225 million years, that would be once every 113 million years. And Shaviv’s 250 MY (which I think is too high) => once in 125 MY, not 150.

  50. 50

    gusbob writes:

    [[I find it easier to believe, and eventually prove or disprove, that the missing force results from electromagnetic interactions. The electromagnetic force is at least a trillion, trillion, trillion, times more powerful than gravity.]]

    Doesn’t matter how powerful it is if the electric charges involved are balanced, and they are. There is no good evidence for huge charge differences on a galactic scale. Enough to account for the galaxy’s differential rotation would have other noticeable effects which we don’t see (e.g. the galaxy either expanding or contracting).


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