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But rotation direction depends on the observer. If i see galaxy spinning clockwise, this means someone observing galaxy from behind it sees it rotating counter

But rotation direction depends on the observer. If i see galaxy spinning clockwise, this means someone observing galaxy from behind it sees it rotating counter clockwise. So are we just located so in the universe that we see 2/3 spinning clockwise and another counter?

Patient0 2y ago
The actual paper makes more sense: "the number of galaxies in that field that rotate in the opposite direction relative to the Milky Way galaxy is ∼50 per cent higher than the number of galaxies that rotate in the same direction relative to the Milky Way."
- floatrock 2y ago
  So 1/3 MilkyWay-Wise, 2/3 Counter-MWW? Or is it? I hate these percent-relative word games things... - Let x = "num MWW" - then "num CMWW" = 1.5x ("50% higher than x") - x + 1.5x = 1 - x = 0.4 So 40% is MWW, 60% CMMW?
  - wruza 2y ago
    Correct, I guess. 40/100 x 1.5 = 60/100. For 1/3 and 2/3 it must have been 100% higher.
permo-w 2y ago
this is a hard one for me to instinctively understand spatially, so I’m imagining myself stood in a room with arrows pointing left and right. if I have 3 arrows facing left in front of me and behind me I have 3 arrows facing left -- from my perspective when I turn around -- then I step past one of the arrows and now I have 2 left facing on one side and then in front of me what was now a left arrow is a right arrow, so now there's 5 lefts and 1 right. so extrapolating that, the observation is possible, but it still doesn't explain the imbalance, does it? you would expect most places in the universe to have a roughly even distribution from any perspective, I think?
- jncfhnb 2y ago
  No I don’t think so Once you have a few dimensions on a normal or other distribution there’s not a lot of content that’s in the middle.
rob74 2y ago
It just occured to me that "rotation direction" is a pretty coarse measurement. Actually, you could look at the angle of a galaxy relative to ours, where (let's say) 0° is viewed exactly from "above" (rotating clockwise), 180° is viewed exactly from "below" (rotating counterclockwise), 90°/270° is viewed side-on etc. How about some stats based on this parameter?
- q_andrew 2y ago
  This is actually why rotational math is more complicated in 3d than you would expect. It's something game developers get used to, because accessing and modifying a rotation requires knowing what the orientation is relative to a fourth axis. That's what a quaternion is. In the situation of this story, it's in reference to the milky way's vertical axis.
- smeej 2y ago
  What does "above" or "below" even mean in the context of something without a top or bottom? Or are you defining "above" to mean "the vantage point from which the galaxy appears to be rotating in the direction of earth clocks" for the purpose of this question?
  - bbor 2y ago
    Not to disagree with your justified Socratic questioning, but this sparked my interest and I figured I'd share my (novice!) TIL: it appears the IAU uses a coordinate system based on our solar system on January 1st 2000, 00:00 AM, or "J2000.0". Thus (0, 0, 0) is at the ~center of Sol and the x and y are within Earth's orbital plane, which means the z axis is orthogonal to that. In other words, it seems like "above"/"up" in a astronomical sense denotes the same approximate direction as "Northward"/"North", which is pretty fascinating! Of course as an arrogant computer scientist I think they're downright kooky for not basing it on the galaxy, but ce la vie. Presumably there's one of those too, and this just wins for boring social inertia reasons as much as for any technical ones. image: https://geoscienceaustralia.github.io/ginan/images/ICRF-75pc-20250121.png https://geoscienceaustralia.github.io/ginan/images/ICRF-75pc... wiki: https://en.wikipedia.org/wiki/International_Celestial_Reference_System_and_its_realizations https://en.wikipedia.org/wiki/International_Celestial_Refere... Of course this doesn't really matter for the above musing since top/bottom would purely be conventional based on our viewpoint, but otherwise illuminating on the issue of understanding rotation directions across the universe.

Patient0 2y ago

The actual paper makes more sense: "the number of galaxies in that field that rotate in the opposite direction relative to the Milky Way galaxy is ∼50 per cent higher than the number of galaxies that rotate in the same direction relative to the Milky Way."

floatrock 2y ago
So 1/3 MilkyWay-Wise, 2/3 Counter-MWW? Or is it? I hate these percent-relative word games things... - Let x = "num MWW" - then "num CMWW" = 1.5x ("50% higher than x") - x + 1.5x = 1 - x = 0.4 So 40% is MWW, 60% CMMW?
- wruza 2y ago
  Correct, I guess. 40/100 x 1.5 = 60/100. For 1/3 and 2/3 it must have been 100% higher.

permo-w 2y ago

this is a hard one for me to instinctively understand spatially, so I’m imagining myself stood in a room with arrows pointing left and right. if I have 3 arrows facing left in front of me and behind me I have 3 arrows facing left -- from my perspective when I turn around -- then I step past one of the arrows and now I have 2 left facing on one side and then in front of me what was now a left arrow is a right arrow, so now there's 5 lefts and 1 right. so extrapolating that, the observation is possible, but it still doesn't explain the imbalance, does it? you would expect most places in the universe to have a roughly even distribution from any perspective, I think?

jncfhnb 2y ago
No I don’t think so Once you have a few dimensions on a normal or other distribution there’s not a lot of content that’s in the middle.

rob74 2y ago

It just occured to me that "rotation direction" is a pretty coarse measurement. Actually, you could look at the angle of a galaxy relative to ours, where (let's say) 0° is viewed exactly from "above" (rotating clockwise), 180° is viewed exactly from "below" (rotating counterclockwise), 90°/270° is viewed side-on etc. How about some stats based on this parameter?

q_andrew 2y ago
This is actually why rotational math is more complicated in 3d than you would expect. It's something game developers get used to, because accessing and modifying a rotation requires knowing what the orientation is relative to a fourth axis. That's what a quaternion is. In the situation of this story, it's in reference to the milky way's vertical axis.
smeej 2y ago
What does "above" or "below" even mean in the context of something without a top or bottom? Or are you defining "above" to mean "the vantage point from which the galaxy appears to be rotating in the direction of earth clocks" for the purpose of this question?
- bbor 2y ago
  Not to disagree with your justified Socratic questioning, but this sparked my interest and I figured I'd share my (novice!) TIL: it appears the IAU uses a coordinate system based on our solar system on January 1st 2000, 00:00 AM, or "J2000.0". Thus (0, 0, 0) is at the ~center of Sol and the x and y are within Earth's orbital plane, which means the z axis is orthogonal to that. In other words, it seems like "above"/"up" in a astronomical sense denotes the same approximate direction as "Northward"/"North", which is pretty fascinating! Of course as an arrogant computer scientist I think they're downright kooky for not basing it on the galaxy, but ce la vie. Presumably there's one of those too, and this just wins for boring social inertia reasons as much as for any technical ones. image: https://geoscienceaustralia.github.io/ginan/images/ICRF-75pc-20250121.png https://geoscienceaustralia.github.io/ginan/images/ICRF-75pc... wiki: https://en.wikipedia.org/wiki/International_Celestial_Reference_System_and_its_realizations https://en.wikipedia.org/wiki/International_Celestial_Refere... Of course this doesn't really matter for the above musing since top/bottom would purely be conventional based on our viewpoint, but otherwise illuminating on the issue of understanding rotation directions across the universe.