Faith & Reason Ministries

Science and Christianity: Chapter 2. A Lesson in Astronomy

The Pleiades

Science and Christianity

by John D. Callahan

Third Edition

Copyright © 1985, 1986, 1998 by John D. Callahan

All Biblical quotations are from the Good News translations (3rd or 4th editions) by the American Bible Society.

ISBN 0-9615767-0-7 (2nd edition)
Library of Congress Catalog Card Number: 85-91519 (2nd edition)


It would seem fitting in an attempt to reconcile science and religion to start with what we know of the stars. The facts presented here are questioned by few men. By observation and experimentation mankind has indeed, over the centuries, amassed a wealth of knowledge about the stars. This is especially true when one contemplates what was known in the beginning. In this chapter will be given first an overview of the entire universe with an attempt to give the reader some comprehension of its size. Then will be given a brief discussion about man's experimentation which led to the knowledge.

In our attempt to comprehend the universe let us first start with a man. Consider him to be 6 feet tall. Now shrink the Earth, with a diameter of 8000 miles, down to the size of a meter (around a yard) stick. How big do you think the man would be if he shrunk with the Earth? Well, a meter is divided into centimeters (1/100 of a meter) and millimeters (1/1000 of a meter). Take one millimeter and divide it a thousand more times. This is one millionth of a meter or one micron. Our man is one tenth of this height or .1 microns -- one ten millionth of a meter. This length is a little smaller than a typical vibration of light and about a thousand times bigger than an atom. Next consider the distance between the Earth and sun (93 million miles). Let us shrink this distance down to meter-level and ask how big the Earth is. Well on this scale the diameter of the Earth is .1 millimeter or one ten-thousandths of a meter. Our man has shrunk to .1 angstroms or one hundred-billionth of a meter. This is ten times smaller than the smallest atom -- that of hydrogen.

We might ask next, what is the size of the sun-Earth distance if we shrink the distance from the sun to the nearest star, Alpha Centauri, down to meter length also? Alpha Centauri is 4 light-years away. Now a light-year is the distance it takes light to travel in one year which is 6 trillion miles, so the distance to Alpha Centauri is roughly 24 trillion miles. The distance to the Earth from the sun is 93 million miles or roughly 100 million miles. This means that our Earth is only 4 microns from the sun if Alpha Centauri is 1 meter away! Remember a micron is only one millionth of meter or one thousandths of a millimeter. Our man on this scale has shrunk to half of one quadrillionth of a meter. This is only one thousandth the size of an electron!

Next, let's shrink the size of the diameter of our Galaxy, the Milky Way, down to meter level and ask how big is the sun-Alpha Centauri distance. Remember that the distance to Alpha Centauri is 4 light-years. The diameter of our Galaxy is around 100,000 light-years. Therefore if the diameter of the Milky Way is one meter, the distance to the nearest star from the sun is 40 microns. This is 1/25 of a millimeter. The size of our man is now not even worth mentioning, and on this scale the sun-Earth distance is about 1 angstrom or 1/10 of one billionth of a meter. This is roughly the size of an atom. Imagine, compared to the size of the Milky Way Galaxy, the distance from the sun to the Earth is only the diameter of an atom, if the Milky Way is shrunk to the size of a meter. Recall on top of this that if the sun-Earth distance itself were the size of a meter stick, the size of a man would be that of an atom.

The most logical next step is now to ask how big is the Milky Way Galaxy if we shrink the size of the known universe down to meter level? Can you guess? Well, on this scale the Galaxy is roughly 5 microns or 5 millionths of a meter. This is because the diameter of the known universe is around 20 billion light-years and recall that the size of the Galaxy is 100,000 light-years.

Now that we have an idea of the sizes of things in the universe let's consider numbers. There are 4 billion people on the face of the Earth. This may seem like a large number. Yet when we consider the population of stars in our Galaxy we find that there are 100 billion, or 25 stars for each human being on the Earth. Thinking of our meter stick again, consider shrinking all the stars in the Galaxy so they could all just line up on a meter stick. If this were done each star would be about one tenth the size of an atom! Next, considering that there are 100 billion stars in the Galaxy we might ask how many galaxies there are in the known universe. Well, it's not very well known, but we do know that there are at least 100 billion and perhaps more.

In an attempt to better comprehend the number 100 billion, consider the following. There are approximately 100,000 individual letters in this book. If each one of these letters itself represented another book of 100,000 letters, then it would take 10 books to have 100 billion letters total. This is also roughly equivalent to the total number of letters in all the books of several libraries.

These numbers are truly astounding. It is also astounding that man, a little consciousness on a little planet, was able to ascertain these numbers. When men first attempted to gain knowledge about the universe, think of what they had. They could observe a seemingly flat surface, the Earth, where various points and bodies of light moved above in the sky. However, using methods for obtaining knowledge, which were outlined in the first chapter, man began to increase his knowledge. Today we have the incredible understanding outlined above.

When men first considered the nature of the Earth, many considered it to be flat, for so it appeared. Only a few men had the insight to propose that the Earth was instead round. Men had these two theories about the Earth: flat and round. To prove which theory was correct and establish the theory as a fact, men experimented and made observations. The flat-Earth side contended that anyone could see that the Earth was obviously flat just by looking at it. Yet they failed to conceive of a round Earth so big that it appeared flat. The Earth is about 6 million meters in radius. On the surface, the difference between a flat Earth and the true round Earth over a 1000 meter distance, roughly 500 times a man's height, is only .06 meters! This is not a perceptible difference to the naked eye. But as is so often the case, men were not considering a bigger picture but were rather assuming the obvious.

Even from antiquity, however, there were strong evidences that the Earth was indeed round. Ships sailing off toward the horizon would disappear from the bottom up, implying a round Earth. The shadow the Earth cast upon the moon during a lunar eclipse was that of a circle, implying a round Earth. Note that this conclusion was based on a theory and not a fact. It was many years before man could prove that a lunar eclipse was caused by the shadow of the Earth.

Another test for the curvature of the Earth involved two sticks and the sun. Assuming that light from the sun travels in parallel or nearly parallel rays, the curvature of the Earth may be measured as follows. Imagine two sticks placed perpendicular in the ground and separated from each other by a significant distance (several miles). If at a given time the sun is shining directly over one of the sticks, no shadow will of course be cast by it. However, if the Earth is round, then at this same time the sun will not be directly over the other stick, and a shadow will be cast. Measuring the length of this shadow and doing some arithmetic will give the radius of the Earth. Just such an experiment was performed by the Egyptian astronomer Eratosthenes (276-195 BC). He measured the Earth's circumference to within a few percentages of its actual value of 24,000 miles. This was truly a brilliant feat. It is unfortunate that mankind did not universally accept the idea that the Earth was round until many centuries later -- not until the Renaissance.

The next most logical question to ask is how far away are the sun, moon, and planets, and what is the nature of their motions? For a long time it was believed that the Earth was the center of the universe, and that sun, moon, planets, and stars all revolved around the Earth. This seemed to be the obvious answer to anyone who observed the sky. However, just as with a flat Earth, there was evidence to the contrary. For instance the motions of some of the planets were not regular but would change direction periodically.

With the help of some great thinkers during the Renaissance, man was able to improve his model of the universe. Copernicus proposed that the sun, not the Earth, was the center of the solar system. Galileo's telescopic observations of the planets strongly supported Copernicus's theory. Kepler meticulously showed that the observational data for the planets was best explained if they moved in ellipses about the sun. And finally Newton's brilliant theory of gravitation consolidated the whole picture and put the sun unmistakably at the center of the solar system.

Kepler was able to calculate the relative distances of the planets from the sun. For instance if the distance from the sun to the Earth is 1.0, then the distance from the sun to Mars is 1.5. Therefore if the distance from the Earth to Mars could be measured, then one would also know the distance of the Earth from the sun and the dimensions of the solar system. But how was this first done? Well, it is a well known fact that objects in the foreground appear to change their position with respect to background objects as an observer changes position. This is called parallax.

Since the Earth is roughly 8000 miles in diameter, it is not too difficult to make simultaneous astronomical observations from two points on the Earth separated by thousands of miles. The planets are close enough that such observations will show a parallax with respect to the fixed stars. The observations cannot be made with the naked eye. However, they can be made with only fair telescopes, and it was not long before man knew the dimensions of the solar system.

Once the distance from the sun to the Earth was known it became possible to determine the distances to the nearer stars. As the Earth moves in its orbit we observe the stars from different angles. Although the Earth is 93,000,000 miles from the sun, most stars are still too distant for us to observe any parallax. However, a handful of the closest stars do exhibit parallax and seem to move with respect to the more distant background stars. It is more than 10 times more difficult to see the parallax of nearby stars due to the motion of the Earth in its orbit, than it is to see the parallax of nearby planets due to different observations made from widely separated points on the Earth.

As we have seen, the distance to the nearest star (other than the sun) is 24 trillion miles. But how do we determine the distances to the distance stars and with this knowledge understand the size and dimensions of the Milky Way Galaxy? Well, astronomers studied carefully the light emitted by the representative sample of stars for which we have parallax measurements. Then astronomers studied the light of distant stars. This revealed that in many cases the distant stars looked very similar to the nearby ones. It is a well known fact that an object decreases in brightness with distance, according to mathematical principles. Assuming that the distant stars were similar to the nearby stars, distances could be calculated. Hence man was able to extend his knowledge of the universe.

Now many of these distant stars are embedded in clusters of stars; so we know the distances to the clusters. Some of the members of these clusters are very brilliant, and we have no nearby counterparts for them. However, since we know the distances to these clusters we can analyze and classify the bright stars anyway. Many of these stars are very massive giants burning brightly. Others are abnormal stars exhausting their last gasp of energy in death throngs. Anyway, observing similar bright stars in the far reaches of our Galaxy gave us a pretty clear picture of the nature of it. As we have seen, our Galaxy is roughly 100,000 light-years across and contains approximately 100 billion member stars.

At first it was thought by many that our Galaxy constituted the entire universe. However, there were fuzzy objects observed in the night sky which might be outside the Galaxy and galaxies in their own right. There were other theories to explain these objects also, but for a long time there was not enough evidence to prove which theory was correct. Experiments were run in an effort to gain the necessary facts, but nothing was shown conclusively until the 1920's. Then using the newly constructed 100 inch Mount Wilson telescope, the largest in the world at the time, astronomers were able to identify individual stars in these fuzzy objects. This proved they were galaxies outside of our Galaxy. In order to obtain distances, astronomers used bright stars which displayed periodic variations in brightness. These stars are called Cepheid variables and had been observed in clusters in our own Galaxy. There is a direct relationship between absolute brightness and period for these stars.

Observing the periods of Cepheid stars in other galaxies and therefore knowing their absolute brightness allowed astronomers to determine the distances to the nearby galaxies. For instance a galaxy very similar to our own and close to it is the Andromeda Galaxy. This galaxy is 2.5 million light-years away and contains a hundred billion stars like our own Milky Way. It also has about the same shape as the Milky Way (a spiral).

Now observing very bright stars in galaxies, to determine their distances, only works for nearby galaxies. For the more distant galaxies it is impossible to resolve individual stars. So how do we determine their distances? Well one method, as with stars, is to make use of the obvious fact that the more distant an object is, the dimmer it is bound to be. Since we know the distances to the nearby galaxies we may calculate their true brightness. Just as with stars, there are also different types of galaxies. Knowing the true brightness of a certain type allows astronomers to calculate a distance whenever that type is observed. However, the correlation between types of galaxies and brightness is not so nearly as strong as between types of stars and brightness.

Another method employed by astronomers to determine the distances to the distant galaxies is to make use of a fact discovered by the astronomer Hubble. He observed that the farther away a galaxy was, the faster it was speeding away from us. The speed of a galaxy can be determined by analyzing its light in a certain way and determining the light's "red shift." This is the amount colors of light are shifted toward the red. The effect is predicted by the theory of relativity for objects traveling at significant fractions of the speed of light.

Using red shifts astronomers are able to look out to the very edge of the known universe (10 to 20 billion light-years) by observing highly luminous objects called quasars. Quasars are very bright and very compact and their light is very red shifted. Exactly what they are is still a mystery. The universe at the distances of the quasars, however, is not like that near our Galaxy. Quasars are billions of light-years from us. This means of course that it took billions of years for the light they emitted to reach us even traveling, as light does, at 186,000 miles per second. Therefore we are observing the quasars not as they appear today but rather as they appeared billions of years ago.

The methods outlined above do not exhaust those used by astronomers to calculate distances. However, they are some of the major methods and should give the reader a good idea of "how it was done."

So now we know a little about the size and contents of the universe. It is truly staggering, and one might ask could man have ever conceived of such a universe without observation and experimentation? Could man, using just his own reasoning powers, have imagined such a universe? Hardly, for without the evidence, man thought the universe consisted of a flat Earth at the center, with the sun and planets revolving around at unknown distances. The stars were fixed to celestial spheres which also rotated about the Earth. And who ever pictured galaxies and quasars?

Astronomers also know not only the nature of the universe, but ages of various bodies in it and how it has changed with time. For instance, we know that the universe probably started with a "Big Bang" 10 to 20 billion years ago. This explosion is the cause of the rapidly receding galaxies we see today. Also our Galaxy is about 10 billion years old, and our sun and solar system are about 5 billion years old. The solar system formed from dust and gas within the Milky Way. The Earth is approximately 4.5 billion years old. These facts were also arrived at by observation and experimentation, and they are questioned by almost no scientists.

Now it took man many years to form the accurate model of the universe we have today. It took steady refining of models. Old and incorrect ideas were replaced by better ones based on the evidence. The process is continuing today. One very significant question which is still unanswered is whether or not the universe will some day stop its expansion and start to collapse. The answer to this question awaits better experiments and collection of facts until the evidence becomes sufficient to make a conclusion. However, at present, the evidence appears to favor an ever expanding universe.


Make a selection

  • Introduction & Chapter 1. Is the Bible Perfect?

  • Chapter 2. A Lesson in Astronomy

  • Chapter 3. Who Are God and Satan, Really?

  • Chapter 4. A Lesson in Life Upon the Earth

  • Chapter 5. Who is Man, Really?

  • Summary & About the Author

  • Return to Home Page