4 ms·
Light rays are effectively parallel at these colossal distances. Everything is in focus. In fact, only 100 years ago this year was the "Great Debate" (https://
by cecilpl2 6y ago
Light rays are effectively parallel at these colossal distances. Everything is in focus.
In fact, only 100 years ago this year was the "Great Debate" (https://en.wikipedia.org/wiki/Great_Debate_(astronomy) https://en.wikipedia.org/wiki/Great_Debate_(astronomy)) about whether Andromeda and other galaxies were outside the Milky Way, or whether they were small internal nebulae.
To determine distances to things, we use the cosmic distance ladder (https://en.wikipedia.org/wiki/Cosmic_distance_ladder https://en.wikipedia.org/wiki/Cosmic_distance_ladder) which is rooted on very close stars whose parallax we can measure over the course of a year.
- peteradio 6y agoThanks for the reply! If we are moving through our galaxy at 220 km/s how long would we have to watch one of these things to determine its precise location (assuming its close) or alternatively set a limit on its distance?
- dnautics 6y agoit's angular motion that you care about, so it could still be a long time. We can put some hard lower bounds on how close it could be, though. For example, it's probably not a wormhole mouth within a few ly of our solar system.