how big is the earth?

Answer 1

Mean radius: 6,372.797 km = 3.9 million miles, mean diameter = 7.8 million miles

Mean circumference: 40,041.47 km ≈ 25 million miles

Surface area: 510,065,600 km² ≈ 3 *10^11 miles²

Answer 2

This question was first solved by Eratosthenes [air-are-toss-thin-ease] in 235BC.

I know, it's an amazing thought isn't it. We've known for 2200years how big the earth is.

Best of all, he used a protractor, a stick and a piece of rope to work it out.

In Alexandria in North Egypt, where he lived, the sun casts a shadow of 7.2 degrees at midday on a stick stuck vertically in the ground on midsummers day.
On the same day, in Aswan, you can see the sun reflected in a well. That means it is direcly overhead and not 7.2 degrees away.

Not only does it mean the earth is round, but that Aswan is 7.2 degrees round the earth from Alexandria.

So he tied a rope between his legs [to make sure his paces were all the same size] and walked from Alexandria to Aswan and worked it out as 500miles.

Since 7.2 degrees is 1/50th of a circle, the size of the earth must be 50x500 miles.

Eratosthenes worked out that the circumference of the earth is 25000 miles.

The real value is 24980 [ish]

over 2000 years ago.

Yet in the 15th century, when Christopher Columbus set off to find India by sailing west, he did so because he didn't know how big the earth was. [nobody really thought the earth was flat. This is a myth begun by the New York Times in the 1850s].
Yet over 1700 years earlier, a bloke in a Toga had worked it out
So next time you think we are smarter than the people back then....think again.

Answer 3

It is THIS big. No, wait, it is even bigger...

Sorry.

Earth's diameter (at the equator) is 12,756 km (almost 8,000 miles).
Earth's circumference (going all the way around a meridian) is a tiny bit more than 40,000 km (25,000 miles).

In a car at 100 km/h (highway speed a bit higher than 60 mph), it would take 400 hours (almost 17 days non-stop) to go all the way around (which we can't, unless they build roads across the poles and the oceans).

Earth mass is almost 6 x 10^21 tonnes
6,000,000,000,000,000,000,000 tonnes
(You may have to place your mouse on the number -- without clicking -- to see the entire number).

The Earth is very small compared to the Sun.

Answer 4

Great question! I'd like to know the answer to that too.

Answer 5

3.9 million miles in diameter