inspired by Selden's initiative, I now composed a locations file with lots of observatories, (radio) telescopes, Sternwarten, VLA's on our beloved planet

http://www.shatters.net/~t00fri/earth-obs.ssc.zip
As an interim solution, I have throughout assigned 'Importance 5' . This needs some improvement, since in certain favorable places (Hawaii, Andes) there are LOTS of telescopes/observatories very nearby! So again there is overlap of labels in a few favorable astro-spots

Since I have assigned the Type "Observatory" to all of them, you can now just display these labels without being swamped by City labels. In KDE at least, you may activate the labels separately for each type. I am sure in Windows it works analogously...
Enjoy,
Bye Fridger