# The Naked Scientists Forum

### Author Topic: How was the radius of Earth calculated?  (Read 7638 times)

• Guest
##### How was the radius of Earth calculated?
« on: 08/06/2010 08:30:02 »

How did scientists calculate the radius of the Earth and Sun?

What do you think?
« Last Edit: 08/06/2010 08:30:02 by _system »

#### LeeE

• Neilep Level Member
• Posts: 3382
##### How was the radius of Earth calculated?
« Reply #1 on: 08/06/2010 18:16:32 »
Eratosthenes, c. 276 BC – c. 195 BC, is believed to be the first person to calculate the circumference, and thereby the radius, of the Earth.

From: http://en.wikipedia.org/wiki/Eratosthenes

Quote

Once the radius of the Earth, and thereby its curvature was known, the distance to the Sun could be measured by parallax from two separated points on the Earth's surface (although in theory, you only need to know the baseline length between the two observation stations, this assumes that the two stations are on a flat surface.  Over the length of the baseline required though, the curvature of the Earth became significant and had to be allowed for).  Once the distance to the Sun was known, it was then just basic trigonometry to work out its absolute size from its apparent angular size.

#### The Naked Scientists Forum

##### How was the radius of Earth calculated?
« Reply #1 on: 08/06/2010 18:16:32 »