Isaac Newton was born on January 4, 1643, at Woolsthorpe Manor in the United Kingdom. Newton became a mathematician, physicist and astronomer, and is now world-renowned as a scientist who helped us understand the universe through his discoveries that became the basis of many scientific principles.

Newton published his insights in three well-known volumes collectively titled the *Philosophae Naturalis Principia Mathematica* (Mathematical Principles of Natural Philosophy), often referred to as simple *Principia*, which is, by all accounts, a masterpiece. In this work, Newton notes his *three laws of motion*, which today forms the foundation of classical neural mechanics. *Principia* also notes Newton’s revelations about gravity.

Best New Year’s Gift Ever! EarthSky lunar calendar for 2017

**Newton’s Three Laws of Motion.** They are called *laws*, but they are really descriptions of basic truths about our physical universe.

1. An object at rest will remain at rest unless acted upon by an external force. A moving object continues to move at the same speed and in the same direction unless exerted by an external force. This law is often called *the law of inertia*. Click here to read more about Newton’s First Law of Motion.

2. When a force acts on mass, *acceleration* is produced. The greater the mass of the object being accelerated, the greater the force needed to accelerate the object. Click here to read more about Newton’s Second Law of Motion.

3. There is an equal and opposite reaction for every action. Click here to read more about Newton’s Third Law of Motion.

**Newton’s revelations about gravity.** Do you remember the story of the apple falling on Newton’s head? Although not necessarily true in all its details, Newton probably observed an apple fell from a tree and began to think that, in order to fall on the ground, the apple was *acceleration* of zero when it hung on the tree.

According to his Second Law of Motion, acceleration is produced when a force acts on an object. Newton must have wondered, what is that force? He came to understand this power as what every schoolboy today knows *gravity*.

Newton’s major revelation was that the force of gravity does not extend to the tops of apple trees alone. If an apple tree were as high as a mountain, for example, the apple would still fall. The police would still act. Newton’s insight was that the force of gravity extends much further … to the moon. He recognized that the moon’s orbit around the Earth is due to the force of gravity.

Indeed, the force of gravity extends throughout space. Today, physicists refer to Newton’s ideas about gravity as the universal law of gravity.

Others who followed Newton – especially Albert Einstein – refined our understanding of gravity. The most accurate description of gravity today can be found in Einstein’s general theory of relativity, he claims *gravity is the result of space-time curvature*.

Intrigued by Newton’s revelations about gravity? Check out this 15 minute video:

Had Newton only contributed his three Laws of Motion and his understanding of universal gravity, we would have remembered him as one of the world’s greatest scientists. But Newton didn’t stop there. He also built one of the first practical reflection telescopes, contributed to the invention of calculus, and explored how a prism can be divided into a spectrum of colors, thus laying the foundation for much of modern astronomy.

Yet Newton himself knew how much more was left to be discovered. He is known to have said:

I don’t know what I might look like to the world, but to myself it seems like I’m just a boy playing by the seaside, diverting myself in now and then finding a stone smoother or more beautiful than average shell, while. the vast ocean of truth lay everything undiscovered before me.

One strange fact about Isaac Newton is that you can say he had two birthdays, ten days apart. You may have seen Newton’s birthday before as December 25, 1642. That address is beginning to change, and now it is more common to see Newton’s birthday as January 4, 1643. ‘ The difference is due to the fact that when Newton, England was born in the middle of a 150 year period of using a different calendar from the rest of Europe. The rest of the continent had already adopted the Gregorian calendar, which is the same calendar we use today. However, at the time of Newton’s birth, the English were still using the Julian calendar, which was still ten days behind due to a flawed account of leap years. (Coincidentally, 1642 was the year that Galileo died.)

So Newton himself would have said his birthday was December 25. But everywhere outside England he was born on January 4. Read more about Newton’s birthday anomaly.

Bottom line: Isaac Newton could claim two dates of birth, but his birthday is now largely recognized as January 4, 1643. Newton’s work in gravity and motion laws underlies much of today’s understanding of physics and astronomy.