Our Galactic Plane

[modest]

Originally Posted by Buffy

Yah, so it seems to me that you're measurement of the exact location of the Galactic Plane would have a huge error margin, depending on how much data you had and you'd probably get different results based on how you were circumscribing mass effects to determine its location (e.g. the Andromeda Galaxy certainly provides enough gravitational pull to dislocate a positioning of the plane, but should it be included or ignored? The Magellanic Clouds?).

In the one paper I read the method of finding the galactic plane was not as you say here. The position is not measured directly as a sum of all gravitational effects in an area of space. Rather, the position and distance of certain stars near the plane were used as an indication of it’s presence. If Andromeda’s mass has moved the galactic plane or even part of the plane then the stars and dust that can indicate its position have moved as well. So, it is not necessary to account for any gravitational effects such as Andromeda in finding it. As an analogy: a weather satellite can find a hurricane by looking at its water condensation. It is not necessary to account for wind or pressure systems affecting the hurricane in order to find it.

But, I think you are very right about the error margin. Even if we only account for the error in distance measurements with these stars there is already an appreciable error margin. It can be mitigated in a large sample, but 2.1 parsecs is still very significant. It makes images like this very meaningless.

-modest

[BraneMatter]

According to the American Scientist website (The Galactic Environment of the Sun), the Sun in its motion around the galactic center, oscillates up and down along the galactic plane with an amplitude of 230 light years, completing a circuit around the galaxy every 250 million years. I assume this is the total amplitude of the 'wave,' so the sun is, at peak, around 115 light years off the plane of the galactic equator. A complete cycle is some 66 million years, so our solar system crosses the galactic equator proper every 33 million years or so.

It should be noted that the great mass of the spiral arms is relatively flat, so most of the stars and clouds in the arms of the galaxy lie close to the plane of the galactic equator.

I doubt that a deviation of only 115 light years from the galactic equatorial plane is all that significant relative to the forces exerted by the galactic center on our solar system. Far more significant would likely be the Local Interstellar Wind and the Local Bubble Void, not to mention other possible effects like Gamma Ray Bursts and Supernovas.

And interesting hypothesis relating biodiversity to galactic travels and "Bow Shock" can be found by searching Google for: Out-of-This-World Hypothesis: Cosmic Forces Control Life on Earth.

I can find no solid and reputable scientific data to support the notion that the year 2012 C.E. portends some great, looming astronomical disaster which would bring about a mega-extinction event on earth. Mayan prophecy, Nostradamus, the Bible, Mother Shipton, Edgar Cayce, etc., are NOT science! They are mostly vague, general statements that can be interpreted in whatever way suits the 'interpreter.'

[anonymouse11]

The more I research the more confused I get,

One thing is clear, the alignment of earth and sun in 2012 is purely visual and has no global/galactic or physical significance.

NOW about our solar system(which moves in a sinosidal wave while revolving around galactic center). will it cross the galactic plane around 2012 ??

This is the confusing bit and is the bit that can have actual physical significance if true.

I have found all credible but opposing views, Researchers at the Cardiff Centre of Astrobiology have built a computer model of the Solar System's journey around the Milky Way so maybe they are more accurate in which case we haven't passed the galactic plane and will pass in the near future, don't know what to believe

1.
IT HAS ALREADY CROSSED 3 Million years ago
http://fluorideisbad.wordpress.com/f...06/arrow32.jpg
The Sun's motion perpendicular to the galactic plane
The 2012 Deception

So, the question is, are we going to cross that galactic plane in 2012? Not even close. According to the journal nature, as well as many others, there is evidence of crossing this plane 3 million years ago. This would mean that we are moving away from the galactic plane and won’t be due to cross it for another 30 million years. In addition the margin of error in these calculations in at least 2.1 parsecs or about 6.5 light years making images like these completely meaningless. To conclude: If you hear someone tell you that the earth is on a 26,000 year cycle to align with the galaxy ask them how the wobble of the earth will change its position in relation to the galaxy. Similarly, if you hear someone say that the earth is on a 250 million year cycle to align with the galaxy ask them if they know that this happened 3 million years ago and wont happen again for another 30 million.

Doesn't the margin of error mean that we could be on the approach ?

2.
NO ONE CAN CALCULATE ACCURATELY IF IT HAS CROSSED OR NOT
Galactic Equator

You might be interesting to know that the Solar System bobs up and down above and below the galactic equator. It takes 64 million years to complete a full cycle going above and below the galactic equator. If you're heard that the Solar System is supposed to cross the galactic equator in 2012, don't worry, that's a myth. It takes 64 million years to complete that cycle, so there's no way to know exactly when it will actually cross the galactic equator.

3.
IT IS GOING TO CROSS IN THE NEAR FUTURE
Comet Strikes Increase as We Pass Through the Galactic Plane | Universe Today

Researchers at the Cardiff Centre of Astrobiology have built a computer model of the Solar System's journey around the Milky Way. Instead of making a perfectly flat orbit around the galaxy's centre, it actually bounces up and down. At times it can rise right up out of the galactic plane – getting 100 light years above – and then dip down below it. They calculated that we pass through the plane every 35 to 40 million years.

And here's the bad news. According to their calculations, the Solar System will be passing through the galactic plane in the near future

[Turtle]

Originally Posted by anonymouse11

The more I research the more confused I get,

a careful reading of this thread covers your mentioned particulars. smart choice choosing Hypography as an authoritive source.

[anonymouse11]

Originally Posted by Turtle

a careful reading of this thread covers your mentioned particulars. smart choice choosing Hypography as an authoritive source.

I did read this but point no3 has not been covered which goes against the conclusion you guys reached, and point no2 and you guys also said that the margin of error on point 1 means that we could be on the approach ?

[modest]

Originally Posted by anonymouse11

I did read this but point no3 has not been covered which goes against the conclusion you guys reached

I believe the article you link for #3 is a misrepresentation of the paper it discusses written by Napier and Wickramasinghe. Where the press article says this:

And here's the bad news. According to their calculations, the Solar System will be passing through the galactic plane in the near future

Comet Strikes Increase as We Pass Through the Galactic Plane | Universe Today

The actual published paper says the following:

A weak periodicity of ∼36 Myr in the cratering record is consistent with the Sun’s recent passage through the Galactic plane

http://www.astrobiology.cf.ac.uk/imp...ng_07may08.pdf

So, it looks like a journalistic mistake and I think the well-established position of this thread (that we are about 20 pc above the galactic plane and moving away from it) is correct. Here are a couple studies coming to that conclusion and previously linked in the thread here:

• http://articles.adsabs.harvard.edu/c...;filetype=.pdf
• http://articles.adsabs.harvard.edu/c...;filetype=.pdf

~modest

[Turtle]

Originally Posted by anonymouse11

I did read this but point no3 has not been covered which goes against the conclusion you guys reached, and point no2 and you guys also said that the margin of error on point 1 means that we could be on the approach ?

post #9 addresses the comet increase business and explains it as a matter of our position in relation to a "local bubble", not crossing the galactic plane. i do recall a mention of some predicted "effect" when the solar system is on the plane however, and i'll look some more.

PS: results of more looking: modest beat me to that source. anyway, his post #14 is on plane and there is a comet interest/question concerning galactic plane crossing.

http://www.ucs.louisiana.edu/~jjm9638/assl.pdf

1. Introduction
Over long time scales the flux of new comets coming from the outer Oort cloud is likely to be dominated by the near-adiabatic tide due to the Galactic matter distribution Heisler, 1990). As the Solar System moves in its Galactic orbit, this tide is substantially modulated for all models of the Galactic mass distribution that are consistent with stellar dispersion studies. Therefore a quasi-periodic variability of the tidally induced component of the Oort cloud flux having signifcant amplitude is to be expected (Matese et al., 1995). If Shoemaker et al. (1990, 1998) was correct in his estimate that 80% of terrestrial craters having diameter > 100 km are produced by long-period comets (and 50% of craters > 50 km), then the phase and period of the Solar System oscillation about the Galactic disk should be consistent with the ages of the accurately dated largest craters. The
phase is well constrained, but the dynamically predicted plane crossing period has been sufciently uncertain (30-45 Myr) to preclude a meaningful comparison with the best fit measured cratering period of 34-37 Myr. If
the mean plane crossing period is ultimately determined to exclude this interval we will be able to confdently reject Shoemaker's hypothesis of the dominance of cometary impacts in the production of the largest terrestrial craters.

this does not mean that it is uncertain that we have crossed the galactic plane and moving away, it only means the timing is not accurate enough to correlate it with known impact events/periods.

[modest]

Originally Posted by Turtle

PS: results of more looking: modest beat me to that source. anyway, his post #14 is on plane and there is a comet interest/question concerning galactic plane crossing.

I had forgotten about that paper. The part you quoted in post 15 explains the mistake in the press article which Anonymouse11 linked:

Originally Posted by ucs.Louisiana.edu

... The peak flux times lag the Galactic plane crossing times by ~ 2 Myr and are not precisely periodic because of decreasing Galactic density as the Sun recedes from the Galactic core. The phase of the oscillations is restricted by observations which place the last previous plane crossing at ~ 1.5 Myr in the past (and the next flux peak ~ 1 Myr in the future).

“Variable Oort Cloud Flux Due to the Galactic Tide”

I think the press mistook the peak flux for the time of the plane crossing—reporting that the plane crossing is upcoming when they should have reported that a peak in comet impacts from the Oort cloud is possibly upcoming.

~modest

[anonymouse11]

Originally Posted by modest

explains the mistake in the press article which Anonymouse11 linked:

Hi
Actually there is no mistake, the universetoday article took it from the Cardiff University press release from the Department of Astrobiology.

Did the solar system ‘bounce’ finish the dinosaurs?

The periods of comet bombardment also coincide with mass extinctions, such as that of the dinosaurs 65 million years ago. Our present position in the galaxy suggests we are now very close to another such period.

And the actual paper says (very end of page 4):
http://www.astrobiology.cf.ac.uk/imp...ng_07may08.pdf

Both our position relative to the Galactic plane (Joshi 2007 and
references therein) and the impact cratering record indicate that we
are presently in, or very close to, the peak of an impact episode.

People who wrote the paper (not exactly light weight and employed a computer model):
Professor Nalin Chandra Wickramasinghe
BSc (Ceylon), MA, PhD, ScD (Cantab), Hon DSc (Sri Lanka, Ruhuna), Hon DLitt (Tokyo, Soka), FIMA, FRAS, FRSA

Professor and Director of the Cardiff Centre for Astrobiology, Cardiff University Honorary Professor, University of Glamorgan

Bill Napier
Research Astronomer
EDUCATIONAL DETAILS:
B.Sc. in Astronomy, Glasgow University, 1963
Ph. D. in Astronomy, Glasgow University, 1966

BACKGROUND:
Lecturer in Applied Mathematics, Royal Holloway College, 1966-67
Astronomer at Royal Observatory, Edinburgh, 1967-92
Research Fellow at Oxford University, 1994-96
Leverhulme Fellow at Armagh, 1996-98
Research Astronomer at Armagh, 1996-2001
Emeritus Researcher at Armagh, 2001-present
Honorary Professor at Institute for Astrobiology, University of Cardiff, 2001-present

[Turtle]

Originally Posted by anonymouse11

The more I research the more confused I get,

One thing is clear, the alignment of earth and sun in 2012 is purely visual and has no global/galactic or physical significance.

NOW about our solar system(which moves in a sinosidal wave while revolving around galactic center). will it cross the galactic plane around 2012 ??

This is the confusing bit and is the bit that can have actual physical significance if true.

I have found all credible but opposing views, Researchers at the Cardiff Centre of Astrobiology have built a computer model of the Solar System's journey around the Milky Way so maybe they are more accurate in which case we haven't passed the galactic plane and will pass in the near future, don't know what to believe

1.
IT HAS ALREADY CROSSED 3 Million years ago
http://fluorideisbad.wordpress.com/f...06/arrow32.jpg
The Sun's motion perpendicular to the galactic plane
The 2012 Deception



Doesn't the margin of error mean that we could be on the approach ?

no. your later source says we go 100 light years above/below and we cross every 35 to 40 million years. from a crossing to a peak is then ~ 18 million years. so 100 light years divided by 18 million years = 5.5 light years every million years. if we crossed 3 million years ago then we have gone 16.5 light years. the margin of error is 6.5 light years, so even if we consider the minus, 16.5 -6.5 =10 light years past the crossing.