Traffic Laws of the Planets​—Who Made Them?

IF YOU have ever studied the solar system, you have no doubt marveled at its design. The arrangement of nine planets whirling and spinning around the sun reminds a person of the movements of a fine jeweled watch. The spectacular order and symmetry of the solar system have moved some men to devote much of their lives to investigating the motion of the planets. One such man was a German astronomer of the 16th/​17th centuries by the name of Johannes Kepler. Interestingly, he was motivated in his examination of the planetary movements by a firm belief in a Creator, a Master Architect, and the more he studied these movements, the stronger his faith became. His discoveries, which paved the way for Isaac Newton in uncovering the law of universal gravitation, can strengthen our confidence in the Creator and in his Word, the Bible.

Johannes Kepler was born in the year 1571 in Weil, a small town in Germany. In spite of a lowly background and a sickly nature, he was able to graduate from Tübingen University, one of the foremost colleges in Europe. Originally Kepler intended to enter the Protestant ministry, but his talents in mathematics and astronomy led him in a different direction.

Kepler became a mathematics teacher in the city of Graz, Austria, in 1594, but only six years later he was forced to leave, due to pressures from the religious leaders of the Catholic Church. Kepler and his wife then moved to Prague, where he became associated with the eminent Danish astronomer Tycho Brahe. About a year after Kepler’s arrival, Brahe died and Johannes Kepler was appointed his successor in the office of Imperial Court mathematician to Emperor Rudolf II, and subsequently to Emperor Matthias. While serving at this post, Kepler discovered the three principles actually made by the Creator to govern planetary motion. Consequently, they became known as “Kepler’s Laws.”

Kepler’s Laws

For centuries astronomers had felt that planetary orbits involved some form of circular motion. This belief, however, had not proved true in actual observation, and scientists were led to extremely complex diagrams and equations to explain the discrepancies. Kepler, after years of calculation, primarily with regard to the planet Mars, arrived at the conclusion that this planet’s orbit was not circular but a geometric figure called an ellipse. What is an ellipse? you may be asking. Well, why don’t we make one!

If you wish, go and get the following items: two thumbtacks, a pencil, a piece of cardboard, and a piece of string about 18 inches (46 centimeters) long. First, tie the two ends of the string to make a loop. (See Figure 1.) Next, put the thumbtacks in the cardboard as shown in the diagram and put the loop of string around them. Then put the pencil within the loop, pull taut on the string and trace out the path around the tacks. The figure that you have drawn is an ellipse. The two tacks mark what mathematicians call the focal points of the ellipse.

The farther away these two points are from each other, the flatter our ellipse becomes. If the two focal points are close together, however, the ellipse becomes rounder. Actually, a circle is just a round ellipse that has its two focal points at the same place, namely, at the center of the circle.

Most of the planets travel in orbits that are nearly circular, the earth’s orbit being almost a perfect circle. A few planets, however, have elliptical paths that are quite eccentric, that is, they are flatter or less round. Pluto and Mercury are the most eccentric of the major planets, but some comets, such as the famous Halley’s Comet, have extremely eccentric orbits.

Kepler deduced from a study of the orbit of Mars that all planets travel in elliptical paths. Moreover, he concluded that in every case the sun is at one of the focal points of the planet’s orbit. These conclusions have since been verified, and constitute what has come to be known as Kepler’s first law of planetary motion.

What a remarkable law this is! It shows that the planets do not move in some strange, irregular, and random pattern. Rather, their paths are a smooth mathematical curve. This law certainly points to the conclusion that some very intelligent lawgiver exists, does it not?

From Kepler’s first planetary law it can easily be seen that planets are closer to the sun at certain times than at others. In fact, the Earth, at its closest point to the sun, is 91 million miles (146.450 million kilometers) away, whereas at its farthest point it is over 94 million miles (151.278 million kilometers) away. Halley’s Comet, with its eccentric orbit, is 56 million miles (90.123 million kilometers) from the sun at its nearest approach but over 3,200 million miles (5,149.900 million kilometers) when farthest away.

From the time of the ancient Greeks it was thought that all planetary motion was uniform. In other words, they believed that a planet’s speed was the same at every point in its path. Once again, however, observed facts proved otherwise, and scientists had extreme difficulties in explaining the differences. Johannes Kepler, after combing through mountains of observations made by Tycho Brahe, made another fascinating discovery. Planetary motion is not uniform; a planet travels faster when it is closer to the sun and slower when farther away. Furthermore, Kepler showed that a very curious law holds true: the line drawn between the sun and any planet will sweep out equal areas in equal periods of time. This is somewhat easier to understand by the following illustration: suppose it takes one month for a planet to travel from point T1 to point T2. Suppose it also takes one month from T3 to T4. Then, by Kepler’s second law, the area of the two shaded sections will be equal. (See Figure 2.) From this it can be seen that a planet would travel faster when it is nearer the sun, in order for an equal area to be produced.

Accordingly, we see that the speed of the planets is not some unpredictable, chaotic, jerking motion. While they do move more rapidly at certain times and less rapidly at others, the changes of velocity are smooth and stable and in accordance with mathematical law. Each planet goes swinging back and forth in its orbit in graceful motion. How we marvel at this beautiful design! Surely we must also marvel at its Designer.

By means of his first two planetary motion laws, Kepler had derived formulas for the shape and the speed of a planet’s orbit. The answer to another perplexing question remained: What relation is there between a planet’s distance from the sun and the time it takes to complete a circuit? He knew that planets that are closer to the sun travel at greater speeds than those farther away. After nearly 10 years of labor he discovered a formula that expressed this relationship. This came to be known as his Third Law. This law states that the squares of the periods of revolutions of any two planets are in the same ratio as the cubes of their average distances from the sun.

An example of this relationship can be seen in the case of the planet Jupiter. Jupiter is approximately 5.2 times as far from the sun as is the Earth. Correspondingly, it takes Jupiter about 11.8 earth years to make one orbit around the sun (called its “period” in the chart below), which is one Jupiter year. Let us prove the accuracy of the Third Law by applying it in the case of the planet Jupiter.

To square a number is to multiply it by itself; to cube a number is to multiply this result again by the original number. So going back to the example of Jupiter, what do we find? If we square the period (Jupiter’s period of orbit around the sun is 11.8 earth years), we get 11.8 times 11.8, which equals nearly 140. Now, if we cube the distance, we get 5.2 times 5.2 times 5.2, which also equals approximately 140. This equality holds true for each one of the planets. You can easily prove this for yourself by carrying out the same calculation for the rest of the planets on the accompanying chart.

Kepler called his third law the “harmonic law” because he believed that it revealed the harmony that the Creator had manifested in the solar system. After discovering this law, Kepler exclaimed: “I feel carried away and possessed by an unutterable rapture over the divine spectacle of the heavenly harmony.” Indeed, we also feel a sense of awe as we think about the heavenly Musician and the harmony that he has composed.

It was this third planetary motion law, the harmonic law, that started Isaac Newton toward his discovery of the law of universal gravitation. Newton desired to know what sort of force would produce the curious relationship between the distances and the periods of the planets. His discovery was that all bodies generate a gravitational force just like the one that makes an apple fall to the ground. He demonstrated that the gravitational field of the sun is what governs the planet’s movements and that Kepler’s laws are based on this phenomenon.

Kepler’s three laws of planetary motion have proved very useful to men in the scientific field. These laws are essential, along with the law of gravitation, in calculating the position and velocity of any planetary body.

In 1976 American space technologists successfully landed the Viking I and Viking II spacecrafts on the surface of Mars. They were able to do this because they could determine exactly where Mars would be and at what speed it would be traveling when touchdown was made. If Johannes Kepler were alive today, he certainly would be amazed to see the startling feats that men have performed, using the laws he discovered!

Interestingly, it has been proved over the years that the three laws of planetary motion hold true in many more cases than just in those involving the nine major planets of the solar system. These laws also describe the elliptical orbits of the asteroids, a group of nearly 2,000 small planet-like masses lying in a belt between Mars and Jupiter. Also, the motion of comets, fiery balls of matter that periodically sweep across the heavens, can be determined by applying the laws of Kepler. Even in the vast spiral galaxies, unimaginably remote from our solar system, the shape of the arms reveals a tendency to conform to these laws. Shifting our focus from the incomprehensibly great to the infinitesimally small, we find that the movements of electrons in an atom can also be described mathematically as following elliptical paths, like tiny planets in orbit around the nucleus.

Kepler’s laws of planetary motion, therefore, serve as celestial traffic laws that must be obeyed throughout the universe. Who set up these traffic laws? There is no question but that one majestic Sovereign, familiar with the workings of everything from the submicroscopic atom to the astronomically huge galaxies, is the Originator of them.

Kepler’s Belief in God

Johannes Kepler himself realized that God was responsible for these remarkable laws that he discovered. Kepler remarked on one occasion: “Just like a human architect, God has approached the foundation of the world according to order and rule.” He appreciated, too, that God’s laws and regulations work for the good of man. As Kepler expressed it: “Most causes for the things in the world can be derived from God’s love for man.” Moreover, unlike many scientists today, Kepler was confident that the Bible is in harmony with true science. On one occasion he wrote a paper demonstrating the agreement between the Scriptures and scientific fact, but because of pressure from the clergy, the paper was not published.

In contrast with the harmony of the heavenly world that Kepler studied, the human world of his day was in constant discord. Kepler lived during the opening years of the Thirty Years’ War in which Catholic and Protestant factions fought bitterly with each other. Unable to agree fully with either side, Johannes Kepler lived his life in unending turmoil. Several times he and his family had to flee their home to avoid persecution. Amid such circumstances Kepler died in 1630 at the age of 59.

Like Johannes Kepler, we can appreciate the glorious harmony manifest in the creation around us. The laws he discovered vividly testify to the order and symmetry of the movements of the planets. If this motion were the product of blind chance, the result would be chaos and disorder. Only a Supreme Lawgiver, a Master Architect, would have composed this harmony. Our hearts should be filled with the deepest love and respect for him. Should we not be moved to serve him with every fiber of our being and give him the honor he deserves? Yes, and if we do, he will reward us with life in a new order that will bring to the human race the order and harmony it so greatly needs.

[Chart on page 19]

Planet Distance from Sun Period

Mercury  .39  .24

Venus  .72  .61

Earth 1.0 1.0

Mars 1.5 1.9

Jupiter 5.20 11.86

(Earth, as 1.0, is the unit of measurement used. Distances and periods are here carried to one or more decimal figures. Therefore calculations with these figures will give only approximate results. A period equals one revolution around the sun in proportion to earth’s at 1.0.)

[Diagram on page 17]

(For fully formatted text, see publication)

MAKE AN ELLIPSE

To draw an ellipse, put two thumbtacks into a piece of cardboard. Put a loop of string around them, draw the string taut with a pencil, and move the pencil around the tacks. The thumbtacks will be at the two focal points of the ellipse

Fig. 1

Fig. 2

KEPLER’S 2ND LAW

If it takes the same amount of time for a planet to travel from T1 to T2 as it does from T3 to T4, then shaded sections will have equal areas

T2

T1

Sun

Planet

T3

T4