Well, signing in did not work, nor did creating a new log in, so I contacted support here. At first, I thought it was a classic Catch-22 situation-- meaning thst the only way I could let support know I couldn't log in was to log in!
Fortunately, there is a contact form under support, so you can get help without logging in They took care of me quickly and easily. Not sure what is going on with the log in or sign up, but it's a pleasure to receive the usual high quality Sky Safari support (Starry Night; and umbrella org, Simulation Curriculum).
I asked them if there was any chance of bringing over some of the more informative threads, posts, and comments from the Yahoo group. There's a rich archive there that could be helpful to many. They responded in the affirmative-- noting that the Yahoo forums will continue to be maintained and that moving some of the content here would be a good idea.
They also asked me to post the suggestion here! So, I have!