The question of what the exact distance around the Earth is has concerned humanity since we realized the sphericity of our planet. This is not just an abstract figure from geography textbooks, but a fundamental parameter that affects navigation, cartography and even calculations in satellite systems. Many people mistakenly believe that the Earth is a perfect sphere and therefore the circumference is the same in any direction. However, the reality is much more complex and interesting than it seems at first glance.
The length of the equatorial circle is approximately 40,075 kilometers. This is the distance you would have to travel if you could follow the equator around the planet. However, if your path passes through the North and South Poles, the distance will change. The meridional circle passing through the poles is shorter and approximately equal to 40,008 kilometers. This difference, although it seems small in percentage terms, is about 67 kilometers, which is comparable to the distance between two major cities.
Understanding these differences is critical to modern technology. Systems GPS and GLONASS use complex ellipsoidal models of the Earth for precise positioning. If navigators considered the planet a perfect sphere, the error in determining the coordinates would accumulate with each kilometer of travel, making accurate navigation impossible. Therefore, knowledge of the real parameters of our planet is a matter of not only scientific interest, but also of practical necessity.
Why is the Earth not a perfect sphere?
The shape of our planet is determined by physical laws that have been in effect for millions of years. The rotation of the Earth around its axis creates a centrifugal force, which “flattens” the planet at the poles and “inflates” it at the equator. This form in science is called geoid or, more precisely for calculations, reference ellipsoid. That is why the distance around the Earth along the equator will always be greater than through the poles.
The difference between the equatorial and polar radii is about 21 kilometers. The equatorial radius is approximately 6378 km, while the polar radius is about 6357 km. It would seem that against the background of the overall diameter of the planet this is an insignificant error, but it is precisely this that dictates the conditions for the gravitational field and the shape of the oceans. If the Earth rotated faster, the oblateness would be much more noticeable, like the planet Saturn.
⚠️ Attention: When planning long-distance flights, pilots take into account the oblateness of the Earth. Laying out a route along the shortest path (orthodrome) on the map may look like a curved line, but in reality it is the most economical path along the surface of the ellipsoid.
To visualize the scale, here is a list of facts about the shape of our planet:
- 🌍 If you reduced the Earth to the size of a billiard ball, it would be smoother than the highest quality bowling ball, despite the mountains and depressions.
- 📏 The difference in circumference length (equatorial and meridional) is less than 0.2%, which makes the Earth very close to a sphere, but not ideal.
- 🛰️ Satellites in geostationary orbit must take into account the unevenness of the gravitational field caused by the shape of the planet.
The study of the shape of the Earth continues today. Satellite data allows us to refine geoid models with centimeter accuracy. This is essential to understanding climate change, as sea levels are also not uniform across the planet due to differences in gravity.
History of measurements: from Eratosthenes to satellites
The first known scientific measurement of the Earth's circumference was carried out in the 3rd century BC by the ancient Greek scientist Eratosthenes. He used an ingeniously simple method based on geometry and observation of the sun. Eratosthenes knew that in the city of Syene (modern Aswan) on the day of the summer solstice, the sun at noon was strictly at its zenith and illuminated the bottom of deep wells. At the same time, in Alexandria, located to the north, the sun deviated from the zenith at a certain angle.
Having measured this angle and knowing the distance between the cities, the scientist calculated the length of the full circle. His calculations were amazingly accurate for that time, differing from modern values by less than 1-2%. Of course, he did not use complex tools, but relied on camel steps and simple goniometric instruments. This proves that logic and observation can give results comparable to high technology.
How exactly did Eratosthenes take measurements?
Eratosthenes measured the angle of the shadow in Alexandria to be approximately 7 degrees (1/50th of a circle). By multiplying the distance between cities (about 800 km according to his data) by 50, he obtained the circumference. The accuracy of his method depended on the accuracy of knowing the distance between cities, which was then measured in days of caravan travel.
In the Middle Ages and during the Age of Discovery, knowledge of the Earth's circumference became a practical tool. Navigators such as Magellan empirically confirmed the calculations of the ancients by traveling vast distances. However, exact figures appeared only with the development of triangulation in the 17th-18th centuries. French academics then went on expeditions to the equator and to the pole to measure the length of the meridian degree.
The modern era began with the launch of space satellites. Laser ranging and interferometry technologies have made it possible to measure the distance around the Earth with an accuracy of millimeters. We now know that the planet is dynamic: its shape changes slightly due to tides, melting glaciers, and even the redistribution of water masses after strong earthquakes.
Equatorial and meridional circle: what is the difference
When we talk about how many kilometers around the Earth, it is important to clarify exactly what circle we are talking about. As mentioned earlier, the planet is flattened at the poles. The equatorial circle is the longest line that can be drawn around the planet without changing latitude. The meridional circle passes through the poles and connects them.
The difference of 67 kilometers is due to rotation. Centrifugal force is maximum at the equator and zero at the poles. This causes the planet's matter (especially liquid magma and water) to shift toward the equator. To the average person, this difference may not seem significant, but to engineers laying transoceanic cables or calculating the trajectories of ballistic missiles, these numbers are critical.
Let's look at the main parameters in the table for a visual comparison:
| Parameter | Equatorial | Polar (Meridional) |
|---|---|---|
| Radius (km) | 6 378,1 | 6 356,8 |
| Diameter (km) | 12 756,2 | 12 713,6 |
| Circumference (km) | 40 075,0 | 40 008,0 |
| Surface area (million km²) | 510.07 (total) | - |
It is interesting to note that because of this difference, the highest point on Earth, measured from the center of the planet, is not the summit of Everest, but the summit of the Chimborazo volcano in Ecuador. Chimborazo is located almost on the equator, and thanks to the "hump" of the equatorial bulge, its peak is further from the center of the Earth than the peak of Everest, although Everest is higher above sea level.
Rotation speed and travel time
Knowing the circumference, it is easy to calculate how fast the Earth's surface is moving. At the equator, the rotation speed is about 1670 kilometers per hour. It's faster than the speed of sound! However, we do not feel this movement because the atmosphere and all objects on the surface move at the same speed. If the Earth suddenly stopped moving, the inertia would destroy everything at the equator, but, fortunately, this is physically impossible in the foreseeable future.
As latitude decreases, the rotation speed decreases. At the latitude of Moscow or New York it is already about 1000-1200 km/h, and at the poles it is zero. This is important to consider when launching rockets: it is more profitable to launch them closer to the equator and in the direction of the Earth's rotation in order to get free acceleration.
When planning a trip around the world by plane, remember that due to the Earth's rotation and jet streams, flying east (in the direction of rotation) often takes less time than flying west.
How long would it take to travel around the Earth using different methods? Let's look at approximate calculations for the equatorial route:
- 🚶♂️ On foot (at a speed of 5 km/h without stopping): about 333 days of continuous walking. In reality - for many years.
- 🚗 By car (at a speed of 100 km/h): about 400 hours of pure travel time, or roughly 17 days.
- ✈️ By jet plane (900 km/h): approximately 44-45 hours. Record holders do it faster, using supersonic speeds.
- 🚀 In low Earth orbit (28,000 km/h): about 1 hour 25 minutes. This is how long one day lasts for astronauts on the ISS.
Of course, these calculations are theoretical. In reality, the journey by car or on foot is complicated by the presence of oceans, mountain ranges and state borders. But for aviation and shipping, these numbers are the basis of logistics.
Practical value of equator length
Knowing the exact distance around the Earth is not only necessary for scientists. The metric system of measures, which is used by most countries in the world, was originally tied to the size of the Earth. A meter was defined as one forty-millionth of the length of a meridian. Although the standard meter is now defined in terms of the speed of light, the historical connection remains.
In navigation, the concept of "nautical mile" is used. One nautical mile is equal to one minute of meridian arc. Since the length of the meridian is known, it is easy to calculate that 1 nautical mile is approximately 1852 meters. This allows sailors and pilots to easily convert angular coordinates (latitude and longitude) into real distance.
☑️ What you need for a trip around the world
⚠️ Attention: When using GPS navigators near the poles, accuracy may decrease due to the convergence of meridians and the geometry of the satellite constellation. At high latitudes, relying only on electronic maps is risky.
Also, the length of the equator is important for telecommunications. Ocean cables and communications satellites must take into account the curvature and length of the signal path. The signal delay (ping) directly depends on the distance it travels. For high-frequency trading on exchanges, where milliseconds count, even extra kilometers of fiber can cost millions of dollars.
Interesting facts and records
There are many myths and interesting facts surrounding the topic of the size of the Earth. For example, many are surprised to learn that it is possible to fly around the Earth on an airplane faster than it was once around it on ships. The first flight around the world by plane took several months in 1924, but now it can be done in less than two days with transfers.
There is also the concept of "antipodes" - points on opposite sides of the Earth. If you pierce the planet right through at any point, you will come out at the antipode. Interestingly, most of the land is in the northern hemisphere, so if you dig from many points in Europe or the United States, you will end up in the waters of the Pacific or Indian Oceans. A straight tunnel through the center of the Earth would have a diameter of about 12,742 km.
Accurate knowledge of the Earth's parameters allows us to create global communication, navigation and logistics systems, turning the planet into a single connected space.
In conclusion, it is worth noting that the Earth is a dynamic system. Due to tectonic processes and climate change, its shape and size may vary slightly over geological time scales. However, for human life these parameters remain a constant that determines our existence.
Why is the length of the equator greater than the length of the meridian?
This occurs due to the centrifugal force that occurs when the Earth rotates around its axis. The force is greatest at the equator and “pulls” the planet’s matter outward, creating a bulge. There is no rotation at the poles, so the planet is more flattened there.
Does the distance around the Earth change over time?
Yes, but very slowly. Tectonic movements of plates, melting glaciers (postglacial rebound) and even large earthquakes can change the shape of the planet by millimeters or centimeters. Also, the tidal forces of the Moon cause permanent deformations of the Earth's solid body.
Who was the first to accurately measure the circumference of the Earth?
It is believed that Eratosthenes was the first to do this quite accurately in the 3rd century BC. Later, in the 17th century, the French scientists Picard and others refined the measurements using the triangulation method, and in the 20th century, satellites gave final accuracy.
How long does it take to walk around the Earth?
Theoretically, moving non-stop at a speed of 5 km/h, it will take about 333 days. In reality, taking into account sleep, food and overcoming obstacles (oceans), such a journey would take the expedition several years. Record holders spend 2-3 years on this.