Hacker News Reader

Comment by MetaWhirledPeas | Hacker News Reader

> To be honest it's not clear if it's from our point of view or not, since they don't mention it explicitly in the paper, but it seems to be the case since they start from observations made by the Apache Point Observatory, which is on Earth

Would the perspective difference be significant even if it were far out into the solar system?

View on HN

Yes, of course, a 2D circle could appear as a line from a certain perspective in 3D space.

I don't think a ring of galaxies is going to look very different from anyplace within the solar system. Anyway I think moralestapia's point is that the circle might not be centered on us, so the redshift of the galaxies would not be the same. We could still determine that a circle exists by plotting the galaxies in 3D.

No, I mean, a 2D circle could appear as a line from a certain perspective in 3D space.

Spin up your mental model of a circle in 3D space, look at it from a vector perpendicular from its diameter, rotate it 90 degrees in any other axis but the one you're looking at it; on that 2D projection, it will be a line.

>No, I mean, a 2D circle could appear as a line from a certain perspective in 3D space.

Right, and as a matter of fact that's exactly what we DO see with the Milky Way galaxy. It can be conceived of as a circular disc, more or less, but in our sky we see it from the side, as a streak or a band rather than a disc.

But of all perspectives in 3D space, there are only a fraction of perspectives that see it as a line. Most other perspectives see it as a circle/ellipse. So, the earth's perspective is not that unique—in fact, it's the most common.

Reply on news.ycombinator.com