The Earth is round because gravity pulls it into a round shape. Gravity also holds the atmosphere on the Earth – and us too!
The Earth is 12,700 kilometres across, but the core in the middle of the Earth is only 2,400 km across. So the core of the Earth is only one-fifth the size of the whole planet.
Although the sky looks solid and blue to us from Earth, this is actually just an effect of the way the light scatters from the Earth’s atmosphere. Therefore from space you can’t see what we think of as the sky at all!
That depends on exactly what you mean by the core. The inner core of the Earth (the solid part of the core) has a radius of 760 miles. The radius of the Earth is 3959 miles, or about 5 times the radius of the core. Volume is proportional to the cube of the radius, so the Earth is about 125 times bigger than the core.
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