How does no one not know what stars are?

THey've been in there 140-something years right? Some people would have been in their teens when they entered that silo 140 years ago and a few would have lived to 100. So they would have only died a maybe 50 years prior to the current timeline, how did the current residents not know what stars were and how life was like outside? Some of the current elderly must have had grandparents who lived outside prior to the catastrophe.

I understand physical knowledge was repressed but unless they killed anyone who moved into the silo it feels like it would be common knowledge?