ADVANCES

1)I’m your uncle’s brother,
But I’m not your uncle.
What am I?
2)I am between mountain and valley.
What am I?
3)You can see nothing else
When you look in my face
I will look you in the eye
And I will never lie.
4)Until I am not measured I am not known. Yet, how you miss me when I have flown. Who am I?
5)Which letter is a part of the body?