Our Galactic Plane

[Turtle]

Originally Posted by freeztar

Interesting thread...

So have there been any new developments?

Where the heck are we?

Indubitably!

None I am aware of.

Quite simply, we are lost in space.

[Qfwfq]

Originally Posted by Turtle

Quite simply, we are lost in space.

We?

I'm not! I know exactly where I am. I'm sitting right here, on a chair, in front of this PC, in a room at a customer's place in Mestre, near the shores of the Venice lagoon...

[Turtle]

Originally Posted by Qfwfq

We?

I'm not! I know exactly where I am. I'm sitting right here, on a chair, in front of this PC, in a room at a customer's place in Mestre, near the shores of the Venice lagoon...

Aha! A zenith. Tant mieux. Taking your upward view, do you see any authoritive reference we have missed that assuredly establishes our Solar system's orientation/situation in regards to the plane of the Milky Way? Over...

[modest]

In:

“The Sun's Displacement from the Galactic Plane from Spectroscopic Parallaxes of 2500 OB Stars”

B. Cameron Reed uses a “model independent” method to get 19.6 (+/-) 2.1 pc from the galactic plane.

The paper also has a table of other determinations of the distance from other sources.

I also found this interesting:

“Variable Oort Cloud Flux Due to the Galactic Tide”

Comparing craters in the geological record to the galactic tide of the ecliptic having an effect on the oort cloud. It sounds very reasonable to me.

-modest

[Turtle]

Originally Posted by modest

In:

“The Sun's Displacement from the Galactic Plane from Spectroscopic Parallaxes of 2500 OB Stars”

B. Cameron Reed uses a “model independent” method to get 19.6 (+/-) 2.1 pc from the galactic plane.

The paper also has a table of other determinations of the distance from other sources.

I also found this interesting:

“Variable Oort Cloud Flux Due to the Galactic Tide”

Comparing craters in the geological record to the galactic tide of the ecliptic having an effect on the oort cloud. It sounds very reasonable to me.

-modest

Thanks Modest! The first paper agrees with our previous findings putting our position within ~20 parsecs.

The second is indeed interesting, if not an outright peach. I think one of the earlier references here hinted at something similar. Anyway, here's the juicy fruit. >>

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).

... Figure 3 shows the results for oscillation models having a
range of plane crossing periods from 25-45 Myr. ...

Looks like we're out of the woods as far as large comet impacts on Earth for the 1,000,000 years or so. My only question now is are we above or below the galactic plane, as none of the sources make mention of it.

[modest]

Originally Posted by Turtle

My only question now is are we above or below the galactic plane, as none of the sources make mention of it.

Would Z⊙ be negative below the galactic plane? I guess not because it’s a distance and not a latitude in the Galactic coordinate system. In any case:

"The Sun's Distance Above the Galactic Plane"

indicates (first paragraph of introduction) that we are above or ‘north’ of the plane. I guess it's in the title of the paper too This would be up if you were facing the direction of galactic rotation (clockwise from north) with the galactic center on your right.

This thread keeps reminding me of:

The Galaxy Song by Monty Python

-modest

[Turtle]

Originally Posted by modest

In any case:

"The Sun's Distance Above the Galactic Plane"

indicates (first paragraph of introduction) that we are above or ‘north’ of the plane. I guess it's in the title of the paper too

Very nice. Before moving to why should North be up, there is a telling bit in the paper regards getting oriented.

... The equatorial plane of the galactic coordinate system, as adopted by the IAU General Assembly in 1958, by definition passes through the Sun. If the Sun were exactly in the midplane, the origin of the galactic coordinate system should coincide with the galactic center. However, it has been shown that the coordinates of Sgr A* imply that the Sun is actually slightly above the plane.

So the equatorial plane of the galactic coordinate system is not the equatorial plane of the galaxy; yes/no? Interesting they make no mention of change in Z, but their ~20 parsec measure is in accord with the others we have rooted out.

Originally Posted by modest

This would be up if you were facing the direction of galactic rotation (clockwise from north) with the galactic center on your right.

Errrhmmm... Since our North is 'up', or 'top', then the galactic top is more-or-less having the same up. Now since the up/down choice is necessary but arbitrary, is there any compelling cultural or other social influence that may have lead to our choice?

Originally Posted by Modest

This thread keeps reminding me of: The Galaxy Song by Monty Python

-modest

Oh yeah! I love the full Monty!

[modest]

Originally Posted by Turtle

So the equatorial plane of the galactic coordinate system is not the equatorial plane of the galaxy; yes/no?

I could see how it would be more convenient to center the thing through earth. Converting between the Equatorial coordinate system and it's galactic coordinate cousin would be harder otherwise. But, it would be more correct to have the axis and the plane centered on Sgr-A. I guess this isn't the case.

Originally Posted by Turtle

Now since the up/down choice is necessary but arbitrary, is there any compelling cultural or other social influence that may have lead to our choice?

I agree it’s completely arbitrary for maps to have north being up. I'm not sure how that became convention in the ancient and middle-age world. Upper and lower Egypt would be an obvious exception. Maybe it was because the sun is further south in the winter. It goes ‘down’ in the winter and comes back ‘up’ in the summer (to a European observer). I’m probably wrong about that - I have no knowledge on the issue. Interesting though. As far as the Milky-Way goes, I guess Australians have one more map to take issue with.

[Buffy]

Originally Posted by Turtle

So we only know our perpindicular position to within 20 pc (parsecs, right?) and our distance from the center of the galaxy within 10,000 light-years, so anyone claiming knowledge of a precise time of our crossing is exagerating the facts...yes?.... The game's still afoot then, if for no other reason than no one seems to have said if we are now above, or below the galactic plane. Then there's that haunting nasty business of extinction....

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?).

Of course there might well be some mass of matter that we pass through that has synchronicity with our revolution about the galaxy that happens to be nearer the approximate Galactic Plane position, that has more to do with the probability of mass increasing as we get closer to the plane, than any devious Creator having it in for us when some geometrically perfect equation reaches zero...

Even a stopped clock is right twice a day, that's numerology!
Buffy

[Turtle]

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?).

We have several sources now in agreement for a Z (distance orthogonal to the galactic plane) of ~20 parsecs, and the last paper Modest offered puts our little Solar whorls above said plane. Table #1 in that paper gives results and the methods to determine them which vary from Z=10pc to Z=42pc. The margin of error for the new 20.5 pc result is 3.5 parsecs.
http://articles.adsabs.harvard.edu/c...;filetype=.pdf

Originally Posted by Buffering

Of course there might well be some mass of matter that we pass through that has synchronicity with our revolution about the galaxy that happens to be nearer the approximate Galactic Plane position, that has more to do with the probability of mass increasing as we get closer to the plane, than any devious Creator having it in for us when some geometrically perfect equation reaches zero...

Even a stopped clock is right twice a day, that's numerology!
Buffy

Yes indeed. Called 'local bubbles' if I recall from another referenced article in post #9, and that we sit near the edge of one.

As nothing is not in motion, there is no such thing as a stopped clock,
Turtle