Don't panic, but a big Chinese rocket will make an uncontrolled re-entry this weekend

Sometime over the weekend, the 30-meter long 20+ ton first stage core booster of a Chinese Long March 5B rocket will re-enter Earth's atmosphere in an uncontrolled manner, with pieces of it crashing somewhere on the planet.

The thing is, we don't know where.

Now, don't panic. It's a big planet, and the odds of it hitting anyone are low… but not zero. To be more clear, this is a worrisome event but not one to be freaked out about.

Why don't we know where it will hit? There are several factors ...