BrooklynVariety t1_j4lvzg4 wrote on January 16, 2023 at 5:20 PM

Reply to comment by [deleted] in How do we know that we are in a certain place inside our galaxy? and how do we know how big it is just by looking at the cross section we are in? by friday_panda

> Stuff farther away moves faster away than stuff closer to us. So we know relative distances to us.

I blame this on poor science communication, but I see people talking about redshift being used to measure distances in all the wrong contexts.

Redshift ONLY works when measuring the distances to GALAXIES outside our local group. So relative velocities are meaningless even when talking about andromeda, much less stars in the milkyway.

Puppy-Zwolle t1_j4mxv09 wrote on January 16, 2023 at 9:15 PM

I was not talking red shift. This is just one of the methods. Not for our neighborhood but does paint a picture we can apply to our neck of the woods.

BrooklynVariety t1_j4n0tdd wrote on January 16, 2023 at 9:34 PM

Not really, the whole “things moving faster further away from us” only applies to the things furthest away from us, not at all our neck of the woods. The physics that governs that phenomenon is irrelevant within the local group and certainly within our galaxy, so it doesn’t really tell us anything about how we map our own galaxy.