The exact number is not possible to derive without knowing the average spacing of the hand holders.
If you were standing on the Moon, it would be easy to notice a solar eclipse; the Earth would block out the Sun, all over the Moon, for an hour or so. On the Earth, we would have called it a lunar eclipse. From the Moon, it would be difficult to notice an Earth eclipse; the shadow of the Moon on the Earth, so obvious when you're in the dark at midday, wouldn't be so obvious from 250K miles away; a small dark circle on the Earth.
This comparable to the perimeter of a circle.
The height of typical pencil is about 15cm. Laid end to end you would need 66,791,933 to circle the Earth at the equator.
When it occurs, a solar eclipse is visible over only a portion of the earth. In order to see it, you must stand: -- at a place on earth where the eclipse will be visible, -- outdoors -- in the daytime, i.e. between the hours of sunrise and sunset
At or very near the surface it would take almost 34 hours.
Below your feet.
Somewhere around the Arctic Circle would be a pretty good guess.
If you are standing on the full moon you would be facing the earth at night.
If you experience 24 hours of daylight in the summer, you would be located in regions north of the Arctic Circle or south of the Antarctic Circle. This phenomenon is known as the midnight sun, where the sun remains visible for the entire 24 hours due to the tilt of the Earth's axis.
If you were standing on the Moon, it would be easy to notice a solar eclipse; the Earth would block out the Sun, all over the Moon, for an hour or so. On the Earth, we would have called it a lunar eclipse. From the Moon, it would be difficult to notice an Earth eclipse; the shadow of the Moon on the Earth, so obvious when you're in the dark at midday, wouldn't be so obvious from 250K miles away; a small dark circle on the Earth.
it would look small
It would take about a month.
No, it is not possible for two people to stand on opposite ends of the Earth without being on water. The Earth is mostly covered by water, so if two people were on opposite ends of the Earth, at least one of them would have to be standing on water.
a sphere or 3D circle
The Earth's atmosphere moves right along with the Earth. If it didn't, then anybody standing on the equator would be standing in a 1,000 mph wind !
we would have no tides and night would be pitch black
because a square or a triangle would not rotate properly