Click here to see an example of a secure and flexible seat in trot. Watch closely as the rider's hips, pelvis, and legs flex freely with the horse's movement. Horse's willingly raise their back up under a seat like this, probably because it feels a bit like getting a gentle back rub with each step.
The celestial sphere is divided by the celestial equator. In astronomy and navigation, the celestial sphere is an imaginary sphere (ball) of a very large unspecified size. The sphere is concentric with the Earth. This means that the celestial sphere and the earth have the same centre. They also rotate upon the same axis.
As Vaibav has so clearly stated, the celestial north pole is just an extension of the earth's rotational axis onto the celestial sphere. The North Star, or Polaris, is the bright star that is nearest to this imaginary point.