Question

Why the earth is spherical?​

Answer 1

1)time zones

we observe different times during day and night in different places

2)stars

The Star formation(orion) is upside down in south

3)photographic evidences

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Answer 2

1. Ships and the horizon

The horizon is the line at which the Earth’s surface and the sky appear to meet. When ships sailing away disappear into the horizon, they do so bottom-first. The top vanishes later, which creates the illusion that the ship is sinking. Similarly, when ships appear from the horizon, the top appears first, and then the rest of the ship.

2. We cannot see very far away

Let’s say that you are standing on the West coast of North America on a clear day. While you are able to see the sun and moon in the sky, which are quite far away, you cannot see Japan if you look to the west. The reason you cannot see that far away on Earth is that light travels in a straight line and hence cannot follow Earth’s curve.

3. Visibility and elevated areas

Many sailors are aware of the fact that elevated areas of land are visible at greater distances than those less elevated. Moreover, if one is standing on an elevated area, they are able to see farther away into the distance compared to if they were standing at a lower altitude. The curvature of the Earth is responsible for these observations.

4. Other planets are spherical

Mercury, Venus, Mars, Jupiter and Saturn can all be seen with the naked eye. In 1781, William Hershel used his telescope to observe Uranus’ motion and discovered that it was a planet, not a star as was previously thought. Based on small perturbations in Uranus’ orbit, it was then predicted that a more distant planet also existed. In 1846, Neptune was discovered to be that planet (it was also previously thought to be a star). If the other planets in our solar system can be observed to be spherical, why should ours be any different?

5. Most things are spherical

If a spherical object is rotating, the rotation flattens out the middle, making the sphere wider across the equator and narrower across the poles. This is because, in the case of rapid spinning, the centripetal force overcomes the gravitational attraction trying to create a spherical shape. Earth is an example of this, hence the oblate spheroid shape. Jupiter is the fastest spinning planet in our solar system and therefore is more flattened than Earth. The sun rotates slowly, but there are other stars that spin rapidly and also have flattened shapes. Rapid spinning is also the reason black hole accretion disks, solar systems, and galaxies exhibit flattened disk shapes.