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Because the Earth is not perfectly spherical, no single value serves as its natural radius. Distances from points on the surface to the center range from 6,353 km to 6,384 km (≈3,947-3,968 mi). Several different ways of modeling the Earth as a sphere each yield a convenient mean radius of 6371 km (≈3,959 mi).
While "radius" normally is a characteristic of perfect spheres, the term as employed in this article more generally means the distance from some "center" of the Earth to a point on the surface or on an idealized surface that models the Earth. It can also mean some kind of average of such distances. It can also mean the radius of a sphere whose curvature matches the curvature of the ellipsoidal model of the Earth at a given point.
This article deals primarily with spherical and ellipsoidal models of the Earth. See Figure of the Earth for a more complete discussion of models.
The first scientific estimation of the radius of the earth was given by Eratosthenes.
Earth radius is also used as a unit of distance, especially in astronomy and geology. It is usually denoted by
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What is circumference of the universe?
There are many things man can not prove. This is one of them.
How many digits of pi would you need to calculate the circumference of the known universe to a precision the radius of an atom?
39 decimal places.
What is the size in square miles of the Universe?
First, you would measure the diameter of the Universe in miles, or its volume in cubic miles; but what would you want to measure in square miles?Second, the size of the Universe is not currently known. The observable Universe has a radius of about 46 billion light-years. Convert that to kilometers or miles if you like. One light-year is about 10 million million kilometers. But the entire Universe is probably much, much bigger.First, you would measure the diameter of the Universe in miles, or its volume in cubic miles; but what would you want to measure in square miles?Second, the size of the Universe is not currently known. The observable Universe has a radius of about 46 billion light-years. Convert that to kilometers or miles if you like. One light-year is about 10 million million kilometers. But the entire Universe is probably much, much bigger.First, you would measure the diameter of the Universe in miles, or its volume in cubic miles; but what would you want to measure in square miles?Second, the size of the Universe is not currently known. The observable Universe has a radius of about 46 billion light-years. Convert that to kilometers or miles if you like. One light-year is about 10 million million kilometers. But the entire Universe is probably much, much bigger.First, you would measure the diameter of the Universe in miles, or its volume in cubic miles; but what would you want to measure in square miles?Second, the size of the Universe is not currently known. The observable Universe has a radius of about 46 billion light-years. Convert that to kilometers or miles if you like. One light-year is about 10 million million kilometers. But the entire Universe is probably much, much bigger.
If you calculated the circumference of a circle the size of the known universe requiring that the answer be accurate to within the radius of one proton how many decimal places of pi would you need?
39
Is radius half radius?
No. Radius is half of the diameter.
