**Earth is the third planet in the Solar System, formed 4.6 billion years ago and the only planet to have life.** **But how to measure the size of the Earth?**

Currently, **there are two main methods for calculating Earth's mass** . The simplest way is to measure the weight of an object on the surface of the Earth and then derive the mass by the famous formula of Isaac Newton in 1687 on the law of universal gravitation, connecting the distance and mass of two objects. imagine the gravity they create.

. (1643 - 1727) was a prominent British physicist, astronomer, philosopher, mathematician, theologian and alchemist, argued by many to be a great scientist and influence is greater than Einstein.

By Newton's method, the Earth's mass is about 6,102 x 10 ^ 24kg.

In the treatise Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) published in 1687, he describes the law of universal gravitation and gives three Newton's laws, considered to be the basis of mechanics. Learn classical, dominated the concept of physics, science during the next 3 centuries.

By Newton's method, **the Earth's mass is about 6,102 x 10 ^ 24kg** . However, **this measurement is only approximate** , because the Earth is not completely spherical, so the radius is not uniform. Therefore, this volume figure is currently only used as a reference for researchers.

The second method is more complicated, based on **Kepler's third law** since the seventeenth century. (1571 - 1630), was a German mathematician, astronomer and astrology. As one of the representatives of the 17th-century scientific revolution, Kepler is best known for his laws of celestial motion named after him. This method connects the satellite's orbital parameters (travel time and shape of orbit) to the mass of the object it orbits.

To do this, in 1976, NASA put on Lageos-1 satellite orbit, a large sphere of copper alloy - zinc covered with reflecting concave surfaces with a diameter of 60 cm. The delay time between the transmission path and the laser's reflection is recorded in order to deduce the distance of the satellite with the Earth is almost exactly correct to help establish the value of **the Earth** 's **mass exactly 5,972 x 10 ^ 24. kg.**

According to Kepler's calculation, the Earth's mass is exactly 5,972 x 10 ^ 24kg.

However, for science, absolute numbers are always needed, so new methods of measurement are still being studied. Because it is important to get the exact number of Earth's mass, so it is possible to understand the inner structure of the Earth, the interaction between planets together or predict the orbit of the Earth. satellite.

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