1
$\begingroup$

How was the size of the earth determined 100/200/300 years ago? I know that by then the had better methods then the simple sticks and shadow experiment.

$\endgroup$
1

1 Answer 1

8
$\begingroup$

The same principle, but with better equipment.

To measure the size of the Earth you need to know the angular distance between two points (in degrees) and the curved distance (in km). If you choose two points that are on the same meridian of the Earth (ie due North and South) then measuring the angular difference is relatively easy. You choose a reference star, and measure its angle of elevation as it passes due South. With simple sticks, you can achieve an accuracy of less than a degree. With a telescope, you can get arc-minute accuracy or less. At these levels of accuracy, considerations of refraction by the atmosphere must be taken into account

In fact, the hard part is to determine the distance between the two points in km, and determine that they are truly on the same Meridian. Much of the effort in determining the size of the Earth was therefore the triangulation of the land.

By 300 years ago, these measurements had progressed to the point that the non-spherical shape of the Earth was becoming apparent and so the matter changed from determining the size of the Earth to determining its shape.

Around the time of the French Revolution, there was a concerted effort to measure the size of the Earth, not least because the metre had been defined as 1/10000000 of the distance from the equator to the pole. But the essential techniques remained the same: measure the angles from the stars, and measure the distance by surveying.

You can read more about the History of geodesy. and there are also multiple wikipedia pages about (for example) the Paris meridian

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .