## How did Eratosthenes measure the circumference of the earth?

Eratosthenes then measured the angle of a shadow cast by a stick at noon on the summer solstice in Alexandria, and found it made an angle of about 7.2 degrees, or about 1/50 of a complete circle. Eratosthenes then used this to calculate the circumference of the Earth to be about 250,000 stadia.

## How did Eratosthenes measure the distance to the sun?

Eratosthenes could measure the angle of the Sun’s rays off the vertical by dividing the length of the leg opposite the angle (the length of the shadow) by the leg adjacent to the angle (the height of the pole). This gave him an angle of 7.12 degrees.

**How is the circumference of the earth measured?**

Eratosthenes sent a man to Syene from Alexandria on foot to measure the distance between Alexandria and Syene. Thus, Eratosthenes measured the distance between the two cities is 800 km. He multiplied by 800 km to 50 and calculated that the Earth’s circumference is 40,000 km.

**Who first calculated distance to Sun?**

astronomer Aristarchus

Historically, the first person to measure the distance to the sun was the Greek astronomer Aristarchus around the year 250 B.C. He used the phases of the moon to measure the sizes and distances of the sun and moon. During a half moon, the three celestial bodies should form a right angle.

### How was the size of the Earth first measured?

On the day the Sun shone on the bottom of the wells in Syene, Eratosthenes measured the Sun’s position in the sky over Alexandria. It was seven degrees away from the zenith, meaning Syene must be seven degrees away from Alexandria as measured on the circle that is Earth’s circumference.

### What is the length of world?

However, from pole to pole — the meridional circumference — Earth is only 24,860 miles (40,008 km) around. Our planet’s shape, caused by the flattening at the poles, is called an oblate spheroid. Those numbers make Earth just slightly bigger than Venus, whose equatorial radius is about 3,761 miles (6,052 km).

**How did Eratosthenes calculate the circumference of the Earth?**

Eratosthenes calculated the distance between Alexandria and Syene using records involving camel caravans. The distance he used was 5000 stadia. Thus, the circumference of the Earth is 250,000 stadia, which translates to somewhat less than 25,000 miles (depending on how ancient units convert to modern units).

**How did Eratosthenes calculate the distance between Alexandria and Syene?**

Since he assumed that Alexandria and Syene both lay on a meridian (half a great circle), it followed that the distance between these two locations was 1/50 th of the circumference of the Earth. Eratosthenes calculated the distance between Alexandria and Syene using records involving camel caravans. The distance he used was 5000 stadia.

#### What was the size of the Stadion Eratosthenes used?

The exact size of the stadion he used is no longer known (the common Attic stadion was about 185 m), but it is generally believed that Eratosthenes’ value corresponds to between 39,690 km and 46,620 km. The circumference of the Earth around the poles is now measured at around 40,008 km.

#### How old was Eratosthenes when he died?

Eratosthenes also measured tilt of the Earth’s axis, and wrote at length of the eight year lunar-solar cycle. He is remembered by history as a great contributor to the field of astronomy. He would die in Alexandria in c. 194 BC at the age of 82.