I may cross once, I may cross twice, I may cross never, but never thrice. When starting up, I finish down, I finish up, when starting down. I have three parts, some friends would say, One straight, one curved, one same all day. With time and place and rate of flight, I’ll tell you where you’ll be tonight. And when you throw a ball up high, I’ll tell you when to close your eye. I’ll use my shape to bend the light, And take you close to stars at night, And if you want to talk to friends, Transmit/Receive, I’m on both ends. Now if my name you still can’t state, Just draw a line, then integrate. What am I?