Beginning to understand the heavens

Beginning to understand the heavens

Debi Prasad Choudhary

Los Angeles, 02/05/2014

The rhythmic march of the sun, moon, planets and star patterns on the sky and occasional fireball shower and the appearance of sword shaped comets of different color made ancient wise man accept their influence on major earth events especially the fate of kings and emperors. When I was in 2^nd or 3^rd grade, I remember curiously listening to my father chatting with his friends about the death of an honest prime minister of India in 1966. Many were saying they know some thing like this was going to happen as the bright comet Ikeys-Seki appeared a year earlier in 1965. Now, I understand their anxiety. They were growing up in a country that got freedom from British about a decade and half ago, already fought two wars and already lost two big leaders that included Mahtma Gandhi, during which there was both a comet and an eclipse!! They knew that King Edward VII of England died in 1910, when Halley’s comet appeared in the sky. They were quoting Homer, “Like the red stars, that from his flaming Hair, shakes down diseases, pestilence and war.” I wondered, why no such thing happened for the death of our villagers that I witnessed all the time!! Well in the word of Shakespeare, “When the beggars die, there are no comets seen; the heavens themselves blaze forth the death of princes”. But, our villagers were no beggars, or princes either. Later, when my PhD supervisor suggested me to work on Comet Halley, I joked if we will survive through and he laughed and still healthy after 15 years of retirement.  

Ancient rulers built gigantic monuments such as Stonehenge, Newgrance, and Fajada Butte that served as a tool to keep track of the movement of heavenly bodies. Many years ago, I visited such a monument, a sun temple Konark, situated 90 miles from my town. The three doors of this huge temple were precisely aligned to allow entering of the sunlight into the temple throughout the year and illuminate the spokes of the wheels like a sundial. This demonstrates the precision of the observations of the north-south movement of the sun.

Such careful observations of the motion of heavenly bodies produced two important results that may be considered as the base of modern astronomy. One: The no shadow day at different locations of the earth used by Greek scholar Eratosthenes (200BC) to determine the earth’s radius. Two: Apart from the sun and moon, five bright objects (planets) in the sky did not follow the pattern of stars.  The planets shift position progressively eastward in the sky with respect to the background stars, which would sometimes slowdown, stop and reverse direction making westward swing. The westward swing is known as retrograde motion. For different planets the amount of eastward and westward shift are different. The first attempt to visualize the celestial sphere, in which all objects including earth, planets, stars, sun and moon are arranged, was made by Claudius Ptolemaeus (Ptolemy 140 AD), all heavenly bodies move around the earth. If we consider circular path of these objects around the earth, it is not possible to explain the retrograde motion and predict the position of a planet with respect to the background stars for a particular day of the year. So, Ptolemy proposed that the planets move on small circles (called epicycles) the center of which slide on larger circles that surround the earth (deferent). In spite of the complexity of mathematical calculations, this idea prevailed for more than 1000 years until Copernicus (1473 AD) proposed that the planets, including the earth move around the sun, NOT around the earth. This heliocentric universe could explain the retrograde motion of the planets easily without invoking complex geometry of circles moving on circles, but could not predict the location of planets correctly enough.

Major breakthrough happened when Tycho Brahe (1546) gathered accurate positional information of planets in the sky for several years using a sophisticate instrument that was periodically calibrated. Tycho was a wealthy nobleman who could maintain such an instrument and perform these measurements. He had a silver nose after losing on a sword duet with his cousin to settle an argument over the legitimacy of a mathematical formula! He hired Kepler to work on the data, but never shared until his death due to bladder failure after refusing to leave a banquet to relieve him (to go to restroom!). Founded on theological believe, Kepler (1571) looked for the cosmic harmony designed by God’s geometrical plan in the Tycho Brahe’s data leading to three laws of planetary motion. First law states: the planets move around the sun in an elliptical orbit, NOT circular. Ellipse is a flattened circle that has two focal points one of which is occupied by the sun. Unlike a circle, which has only one radius, an ellipsis has two axes major and minor. The second law states: while going around the sun the planets swipe equal area of ellipse in equal time. This means during same period of time the planet must move more distance when situated near the sun compared to the furthest location. The third law states: the square of the period during which planets go around the sun is equal to the cube of half major axis. Since these laws were empirically determined, they were only good for the planets moving around the sun. In 1621, Kepler applied his law to the moons of Jupiter and found that period square was not exactly equal to one unlike for the planets.

Around the same time, Galileo (1564) made a number of discoveries that had profound effect on the progress of our understanding of heavens. Using the telescope, he showed that objects move around planets like Jupiter similar to the planets moving around the sun. He dropped two balls of different mass from the tower of Pisa in Italy and found that both arrived on the ground simultaneously.  While falling, the distance increased as the square of time. If in the first minute the ball covered 2 meter, in the second minute it would cover 8 meter. Because, when a body falls freely without any air resistance, the speed changes by about 10 meter per second per second as if something is pulling from below.

This pulling force is the gravitational force, discovered by Sir Isaac Newton (1642), who said two bodies with mass m1 and m2 separated by a distance r would attract each other by a force that would increase as their mass and decrease rapidly as they are separated. Mathematically: the gravitational force F= G (m1 x m2)/r². G is called gravitational constant, which is same no matter what material we are considering or where we are testing this law. This was a profound discovery. The consequence of this law is that if we consider the sun and the earth, both attract each other with a force that depend on their mass and separating distance. Actually, because of this mutual force they circle a common center located nearer to the heavier mass. So careful observation shows that the earth and other planets do not circle the sun but around a point located near it’s surface. This is the same force that cause ocean tides.  Using mathematics he showed that such paths would be elliptical. In fact, Kepler’s laws are consequence of this force. It was so obvious to Newton that when Edmond Halley visited with the observations of the positions of a comet, immidiately he told the path around the sun must be an ellipse and it would come near the sun after every 76 years. Halley was so impressed with this work that he sold some of his property to publish all these findings in the famous book “Philosophiæ Naturalis Principia Mathematica “. This book also deals three other famous laws of motion. The first law says, if some thing is not moving or moving with constant speed it will maintain such situation until forced to change. The effect of this is experienced everyday in the form of a jerk due to sudden break or pushing the accelerator of the car. The second law states that when we apply force a heavier body is pushed with less speed compared to a lighter body. More the force, speeder the body moves. The third law states for every force we apply on a body, it exerts back equal and opposite force. Many modern technologies starting from designing a car to launch of rockets depend on these laws. But the most important achievement is that Newton’s discoveries demonstrated the universality of physical processes – the same laws of nature govern the motion of objects on earth and in havens.

Almost 300 years later, Albert Einstein (1879) said that the space, time and mass are related. When you place a mass on a flat space the geometry around it changes such that it is no longer flat. But the effects are really very small so you never notice such changes around you while walking. But, if you replace yourself with a huge object like the sun, you will notice the changed geometry of the space. This was confirmed by two important observations in early 20^th century. One of them was total solar eclipse photograph that showed some stars located behind the sun due to the light travelling from them on a path that was curved near the sun.  The other observation was the pattern of motion of mercury, which is very near the sun. Mercury becomes closer to the sun sooner than expected from the Kepler’s laws as it moves in a distorted space caused by the mass of the sun. Today, there are many more examples of this effect observed with space telescope and other advanced instruments.

Over these years, the fear of the heavens for me is replaced by curiosity and wonderment, as I am equipped with the tools of science. The sky still amazes but throwing challenges for understanding. Our civilization is in a unique position that is equipped with a plethora of scientific theories and technological innovations to enjoy the creation. We must invent different stories to entertain our next generation that cannot base on fearing the heavenly bodies.