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?