early sailors discovered a gradual change in position of the north star. this discovery helped to prove that?

Question

A:Earth is round
B:Earth is flat at its poles
C:Earth rotates on its axis
D:Earth is approxmately 40,074 kilometers in circumference

Answer 1

The axis, and therefore, poles, gravitational pull is slowly changing. (Therefore changing due Norths position.) That's alot of observant Sailors.

Answer 2

Wow. This is a classic example of a horrible multiple choice question.

If the way the sailors discovered the change in position of the north star was by sailing north and south, then the answer is "A", that the earth is round. When you sail away from the north pole, the pole star appears lower and lower in the sky, and higher and higher as you sail north. This is because of the shape of the earth. At the pole, the north star is straight up, and at the equator it is on the horizon. Thus: The earth is round. (A)

(B) doesn't work. The fact that the earth is an oblate sphere comes from much more complex measurements.

(C) _is_ a possible answer, as others have posted, since the pole star is not EXACTLY at the north celestial pole, and it _does_ inscribe a tiny circle in the sky every night. --- BUT ---- (C) is not a good answer since every OTHER star does the same thing, and this movement is in no way unique, and it isn't observed due to traveling. So, it would not be unique to sailors.

(D) has a shot... the circumference of the earth CAN be determined by measuring the change in elevation of the pole star, but you have to know how many miles north-and-south you have traveled. This is best done then, on LAND not at sea. So, while (D) is a possibility, it isn't as good an answer as (A) was.

Answer 3

E. None of the above. The changing position of the North Celestial Pole, (which is really what you mean, I believe) demonstrates the phenomenon of Precession of the Equinoxes caused by the wobble of the Earth's axis, which takes 25,000 years to complete one circle

Answer 4

It demonstrates, more precisely than the way C is expressed, the precession of the Earth's rotational axis. Precession refers to a change in the direction of the axis of a rotating object.

The Earth goes through one complete precession cycle in a period of approximately 25,800 years, during which the positions of stars as measured in the equatorial coordinate system will slowly change; the change is actually due to the change of the coordinates.

Over this cycle the Earth's north axial pole moves from where it is now, within 1° of Polaris, in a circle around the ecliptic pole, with an angular radius of about 23.5 degrees (exactly 23 degrees 27 arcminutes). The shift is 1 degree in 180 years, where the angle is taken from the observer, not from the center of the circle.

The precession of the equinoxes was first discovered in antiquity by the Greek astronomer Hipparchus, and was later explained by Newtonian physics.

Crucially, as a consequence, the star that is regarded as the pole star changes, over time. As navigation at sea is steering the ship vis-a-vis the Pole Star, this is what sailors would have noticed.

Polaris has a visual magnitude of 1.97 (second magnitude). In 3000 BC (early sailors were certainly sailing the oceans in 3000 BC) the faint star Thuban in the constellation Draco was the North Star. At magnitude 3.67 (fourth magnitude) it is only one-fifth as bright as Polaris. The first magnitude star Vega will be the North Star by AD 14,000.

Due to the precession of Earth's rotational axis, Thuban was the naked-eye star closest to the north pole from 3942 BC, when it moved farther north than Theta Boötis, the previous "holder" of that role, until 1793 BC, when it was superseded by Kappa Draconis. It was closest to the pole in 2787 BC, when it was less than two and a half arc-minutes away from the pole. It remained within one degree of true north for nearly 200 years afterwards, and even 900 years after its closest approach, was just five degrees off the pole. Thuban was considered the pole star until about 1900 BC, when the much brighter Kochab began to approach the pole as well.

Having gradually drifted away from the pole over the last 4,800 years, Thuban is now seen in the night sky at a declination of 64° 20' 45.6", RA 14h 04m 33.58s. After moving nearly 47 degrees off the pole by 10000 AD, Thuban will gradually move back toward the north celestial pole. In 20346 AD, it will again be the pole star,

THETA BOOTIS

Theta Boötis has apparent magnitude +4.04 and belongs to the spectral class F7V. It is approximately 47 light years from Earth. From about 4300 BC until 3942 BC, it was the closest star to the celestial north pole visible to the naked eye, although it was still too dim to be regarded as a pole star.

KAPPA DRACONIS

Kappa Draconis is a blue giant star located in the constellation Draco. It has an apparent magnitude of 3.88, is approximately five times as massive as our Sun, is 1,400 times as luminous as the Sun and is located approximately 490 light-years away from us.

Kappa is thought to be just entering its red giant phase. Over the next several thousand years, the star will expand. Tens of thousands of years from now, Kappa Draconis will appear much brighter as seen from Earth, likely shining with a reddish hue.

Kappa Draconis was the nearest star to the North Celestial Pole visible to the naked eye from 1793 BC to approximately 1000 BC. However, because it is so much dimmer than nearby Kochab, Kochab was considered the pole star during that time instead.

KOCHAB

Kochab (Beta Ursae Minoris) (β UMi / β Ursae Minoris) is the second brightest star in the bowl of the "Little Dipper." It has a magnitude of 2.1. It is 16 degrees from Polaris. The star is a yellow giant and is 110 light years from Earth. It is 130 times more luminous than the Sun.

Kochab and its neighbor Pherkab are both naked-eye stars. They served as twin pole stars, Earth's North pole stars, from 1500 B.C. until 500 A.D. Neither star was as proximitous to the pole as Polaris is now.

Due to precession of the equinoxes, the previous holder of the title was Thuban, and the next was the present-day Polaris.

The "title" will change hands twice more again before Vega becomes the Pole Star. Polaris will cease to be the Pole Star by about 4000 AD.

That means that there will have been at least six other Pole Stars by the time Thuban resumes the role 25,000 years after its last tenure of the post. Which is something I never knew, and makes the claims of the Ptolemaic Model that there is a rigid firmament of fixed stars with the earth staying still in the middle, look rather silly.

Answer 5

The only answer that fits is A.

Answer 6

C

Answer 7

C