twinkle because their light passes through various levels of our atmosphere, as the air moves at different levels or layers, the light is bent, which looks like twinkling to those of us on the ground? Pictured from space, do you think stars twinkle?
If you were aboard the space shuttle or International Space Station, you would not see the stars twinkle.
The light from planets also travels through that same atmosphere to you, but light from the wider disks of planets is not as disturbed as the changes between atmospheric levels cancel each other out. That's why, as seen from Earth, planets shine with a steady light.