How can we tell the earth is round?

Question

Besides the obvious lunar eclipse, ships on the horizon, and space photos, how do we know?
Oh, and serious answers only.

Yes, I KNOW the earth is round! I'm not stupid! I'm just wondering. I said SERIOUS answers!!!

congratu l, do I look like a billonare? If you're so rich, go up there yourself and take some pictures for me!

Answer 1

The Sun is so distant from us that all the rays that strike our planet approach us along essentially parallel lines.

Eratosthenes noticed that on the first day of summer at Syene, Egypt (near modern Aswan), sunlight struck the bottom of a vertical well at noon. This indicated that the sun was right over the well (that Syene was on a direct line from the center of the Earth to the Sun). At the corresponding time and date in Alexandria, he observed that the Sun was not directly overhead but was slightly south of the zenith, so that its rays made an angle with the vertical equal to about 1/50 of a circle (7º). Since the Sun's rays striking the two cities are parallel to one another, why would the two rays not make the same angle with the Earth's surface? Eratosthenes reasoned that the curvature of the Earth meant that "straight up" was not the same in two cities.

The Sun's rays come in parallel, but because the Earth's surface curves, a ray at Syene comes straight down, while a ray at Alexandria makes and angle of 7º with the vertical.

Answer 2

1. The moon and the constellations look upside down from the SOuthern hemisphere compared with the Northern Henisphere

2. Time zones change evenly and gradually around the world - can only happen on a round world.

3. If the world was flat, how are night and day explained? The night shadow would not creep around the world like it does, but would suddenly flip from one side to the other, as this flat world turned its other face to the sun

Answer 3

The ancient Egyptians planted two vertical sticks in two towns at some distance. They waited until the sun cast the shortest shadow at one stick (astronomical Noon) and checked if it was at the same time at the other stick, It wasn't. By calculating the time difference between the two occurences of Noon at each site and using the distance between the two locations they came up with a roughly accurate size of a round Earth.

Answer 4

The most obvious example of the Earth's shape is ancient. As we view a ship sailing away, the bottom of the ship starts to disappear as the ship approaches the horizon. The ship appears to be sinking into the sea as it sails away. If the Earth was flat, the ship would just appear smaller and smaller as it sailed away.

If the Earth was flat, you could see tall mountains on a distant shore.

Answer 5

Shoot a tangent from anywhere on earth and it always goes off the horizon.

Answer 6

Because as we explore the planet, and search for the edge, we find ourselves arriving back where we started. No matter what direction we choose, we always get back to our starting point.

Answer 7

Good question, I was going to say what you said, but you said it. I'm not sure how they know, but isn't that proof in itself?

Answer 8

Even pictures from space can't convience you?

Answer 9

Because it keeps rolling around heaven all day.

Answer 10

hey man, try to go to moon and watch the earth.