2 ms·

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 coord

by 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.

smeej 2y ago
There wasn't anything intentional about my question. I just didn't understand what thebparebt commenter meant! I don't think I understand how your reply relates to the question either, though, because I was asking what it means to see other galaxies "from above" or "from below," when it seemed like that had to do with which direction they appear to be spinning from here. Your answer is about what we consider "above us" or "below us," but we can still see a galaxy "below us" "from below" relative to it, if it (or we) are "upside down," and I couldn't figure out how we determine the orientation of "upside down" or "backward" for every other galaxy.

by bbor 2y ago

smeej 2y ago

There wasn't anything intentional about my question. I just didn't understand what thebparebt commenter meant! I don't think I understand how your reply relates to the question either, though, because I was asking what it means to see other galaxies "from above" or "from below," when it seemed like that had to do with which direction they appear to be spinning from here. Your answer is about what we consider "above us" or "below us," but we can still see a galaxy "below us" "from below" relative to it, if it (or we) are "upside down," and I couldn't figure out how we determine the orientation of "upside down" or "backward" for every other galaxy.