Meridian arc facts for kids
A meridian arc is a special measurement used to understand the shape of our planet, Earth. Imagine a line that goes from the North Pole to the South Pole, passing through a specific place. This line is called a meridian (or line of longitude). A meridian arc is the distance along this line between two points.
In simple terms, it's like measuring a piece of a very long, imaginary rope laid out on the Earth's surface. This rope follows a straight line from north to south. Scientists use these measurements to figure out how round or flat the Earth is.
Contents
What is a Meridian Arc?
A meridian arc is a part of a meridian, which is a line of longitude. All points on a meridian have the same longitude. Think of longitude lines as slices of an orange, all meeting at the top and bottom (the poles).
When we talk about a meridian arc, we are measuring the distance along one of these lines. This measurement helps us understand the Earth's true shape. It's not a perfect ball, but a bit squashed.
Measuring the Earth's Shape
Early scientists used meridian arcs to find the size and shape of the Earth. They would measure the distance between two places on the same longitude. Then, they would use astronomy to figure out the angle between these two points from the Earth's center.
By doing this, they could calculate the Earth's circumference. Modern methods use satellites and advanced tools. These help us get a very accurate picture of the Earth's shape. This shape is called a geoid or a reference ellipsoid. It's like a slightly squashed sphere.
Eratosthenes' Amazing Idea
Around 240 BC, an ancient Greek scientist named Eratosthenes made a clever calculation. He found a good estimate for the Earth's circumference. He knew that in the city of Syene (now Aswan, Egypt), the Sun was directly overhead at noon on the summer solstice. This meant no shadows were cast.
At the same time in Alexandria, which was north of Syene, he measured the Sun's angle. It was 1/50th of a full circle (7.2 degrees) away from being directly overhead. Eratosthenes believed Alexandria was straight north of Syene. He then figured the distance between the two cities must be 1/50th of the Earth's total circumference. His calculation was very close to what we know today!
Newton's Discovery
In 1687, the famous scientist Isaac Newton published his book, Principia. In it, he showed that the Earth is not a perfect sphere. Instead, it is an oblate spheroid. This means it is slightly flattened at the poles and bulges a bit at the equator.
Newton calculated that the Earth was flattened by about 1/230. This means its diameter from pole to pole is slightly shorter than its diameter across the equator. This idea was later proven by more measurements.
Related Pages
See also
In Spanish: Arco de meridiano para niños
