A bit about site overlaps
Firstly: Sites can have overlap regions. In such cases, posts only get migrated if:
- The OP asks for migration
- The question does not get (good) answers for some number of days
As a mod on both Physics and Chem, I come across this fairly regularly — there are posts which are on topic on two sites.
However, this isn't a matter of overlap of scope, it is a matter of being a complete subset.
Do such sites succeed?
Depends. Mathematica.SE succeeded even though it was a subset site because there were a staggeringly huge number of MMA users on SO who had no interest in the rest of SO. But TheoreticalPhysics (and, more recently, Arduino) didn't. There are a lot of situation-specific reasons for these failures, though. However, when there's an established place where you can ask stuff, there.
Note that the last Astro.SE was not a full subset of Physics.
Will Astro.SE succeed?
I don't know. Last time it failed due to low activity, and there's a high chance it will this time as well. Physics is a much larger site and tends to attract people better. I personally predict that it will be closed in private beta, but I could be grossly wrong.
Is it a threat?
No, not really. If it does succeed, it wouldn't really harm our site. Our scope would not change, so questions asked here would stay here. Maybe the number of questions we receive in the topic would be halved. Not much of an issue -- though the astronomy subcommunity (@ChrisWhite, you, etc) may be split. (When Mathematica.SE was launched in beta, the whole SO community moved over. This did not happen with Arduino or TheoreticalPhysics).
It's something that you, as an astrophysicist, may even want to look forward to. Currently it is not immediately clear that Astronomy is on topic for Physics.SE. Astrophysics — yes, but astronomy is not really a part of physics (in the minds of the general public).
If it fails, Physics.SE would be happy to accept their posts as we did the last time.
Can we do anything about it?
I posted this. Not that I want the site to fail, but if that was enough justification for the proposal to be closed (before it wasted a lot of time), so be it.
The banner you see on the top is because one of us pinged a community team member about the scope subset
This would help test if the site will be able to stand on it's own later -- if Physics.SE is a more lucrative option for those willing to commit, then this makes the site less likely to succeed. The community team is good at helping sites succeed, but they also are good at identifying ones which won't. They generally give such iffy cases a chance: they at least let them have a week of private beta.
There's not much more we can do: You can always post your own answer on that discussion thread.