Early sailors discovered a gradual change in position of the North Star. This discovery helped to prove tha?

Question

Early sailors discovered a gradual change in position of the North Star. This discovery helped to prove tha?

Answer 1

The earth wobbles as it rotates

Answer 2

Pole stars change over time because stars exhibit a slow continuous drift with respect to the Earth's axis. The primary reason for this is the precession* of the Earth's rotational axis that causes its orientation to change over time. If the stars were fixed in space, precession would cause the celestial poles to trace out imaginary circles on the celestial sphere approximately once every 26,000 years, passing close to different stars at different times. However, the stars themselves exhibit motion relative to each other, and this so-called proper motion is another cause of the apparent drift of a pole star.

*The orientation of the Earth's axis is slowly but continuously changing, tracing out a conical shape in a cycle of approximately 25,765 years (the so called Great or Platonic year, and also the determining factor in the length of an astrological age). This movement is caused by the gravitational forces of the Sun and the Moon, and to a lesser extent other bodies, on the equatorial bulge of the spinning Earth.

If you had the patience to read all this, you now know maybe more than you wanted about pole star drift!

Answer 3

This exact question has been asked and answered several times before.   Try typing in "Early sailors" in the search box.

I don't think that early sailors would have discovered precession. It takes about 72 years for the north pole to move 1 degree. Hipparchus of Rhodes (c. 160 BC) is generally given the credit for discovering precession, and he used star maps that were about 150 years old.

What early sailors, and travelers in general, would have noticed was that the distance of the north star above the horizon changes as you move north and south -- this is about 1 degree for every 60 miles you travel.

One degree is about what humans can remember. As in, "Hey, wasn't the north star about 1 degree lower a week ago, when we were 60 miles south of here?"

This was evidence that the Earth was round.