DEFINE LIGHTYEAR AND POLESTAR.

Solution,
Lightyear: It is the distance ravelled by light in 1 year. It is normally used to represent far-off distances of the celestial bodies.
$1 Lightyear=ct=3\times {10}^8 \times 365\times 24\times 60\times 60=9.461\times {10}^{15}m$
Polestar is the North star that lies closely with the rotation axis of the earth above its north pole. Pole star is the only star in the sky which appears stationary to an observer on Earth.