The Earth's rotation axis precesses in space, completing a full cycle every 26,000 years or so. Each year, the axis is pointed at a slightly different location for 'Celestial North' Which is a coordinate system we humans have invented which is tied to the Earth's equator and Greenwich England. The celestial coordinates of stars much be corrected by this precession. Epoch 1950 and 2000 differ by the direction of the North Celestial Pole during these two epochs of the coordinate calculation. Since we are 4 years away from 2000, the coordinates you read from star maps more accurately reflect where you ought to point your telescope based on your computer latitude, longitude and time of day.