You can try to guess. I also don't know the answer

I』m tall when I』m young, I』m short when I』m old, and once a year, I make heavy pumpkins light. What am I?

I don』t have eyes, but once I did see. Once I had thoughts, but now I』m white and empty. What am I?

I am scary, and when you have more of me, you will see only less. What am I?

I sleep upside down and I fly through the night. I live in dark places and I don』t have good eyesight. What am I?