We take it for granted today that in our science books we can read about the vast universe, learn about Jupiter and its rings, or look at images of distant galaxies. However in the 1600s, the scientific community didn't know astronomical facts that we hold to be commonplace. However, this situation was to soon change. In 1629 Galileo, an astronomer and scientist, published a book called Dialogue Concerning the Two Chief World Systems. In this work he compared Ptolemy's and Copernicus's ideas on how the solar system was organized. Galileo defended Copernicus's idea of a heliocentric solar system based upon the observations Galileo had made with his telescope. The ideas he set forth were new and amazing. The image of the solar system in his book can be compared with a picture, taken by the Royal Observatory in Edinburgh in 1979, of the Horse Head Nebula. These two images exhibit many striking similarities in their origins, purposes, and uses. This is intriguing because these two images were not only released four hundred years apart, but also into vastly different social and political climates.

The first of these similarities is that the image from the Dialogue and the picture of the Horse Head Nebula were instrumental to the advance of astronomy. In the 1600s the scientific community knew about the heliocentric ideas of Copernicus, the data Brahe collected, and Kepler's three laws of planetary motion. Despite these advances, the scientific community of Galileo's time was still hindered by dogma. Studying to be an astronomer, Galileo began to do experiments and take observations. This was revolutionary, because usually astronomers just learned through the interpretations of ancient and outdated texts. When he peered into the night sky with his telescope, Galileo saw images that were to upset the theories on which astronomy was based. He could see the moon's craters and maria (the darker regions), sunspots on the sun, and Saturn's rings. These discoveries proved that the heavenly bodies were not perfect. He also saw the phases of Venus, which confirmed the heliocentric view of the solar system. Furthermore, he observed the moons that orbit Jupiter. More importantly, this observation of Jupiter's moons shook the foundations that were the basis of astronomy during those times.

These observations, which challenged the accepted beliefs, are shown in his image in the third day from the Dialogue. Previously it was taught, based on what Aristotle and Ptolemy had observed, that all heavenly bodies orbited the Earth. As Pasachoff states, "the discovery proved that all bodies did not revolve around the Earth, and also, by displaying something that Aristotle and Ptolemy obviously had not known about, showed the Aristotle and Ptolemy were not omniscient."1 The fact that one of their ideas had been proved wrong brought up the question of whether the rest of their theories were accurate. Studying the image in Galileo's book, you can see how the ancient ideas were false. Not only did Galileo set forth ground breaking ideas, but also he began to advance astronomy through the gridlock of dogma. To us the findings of Galileo seem commonplace. We find it hard to believe that one might not know that Jupiter had moons or that Saturn had rings. However, we can understand the exhilaration of discovering something new when we compare Galileo's image to a modern day picture of space.

The pictures of space that we now have access to would have startled any astronomer from Galileo's time. Every day, astronomers see images through their telescopes that help advance our knowledge of the universe. One of these images is of the Horse Head Nebula. Nebulae are only one of the many objects that exist in the interstellar medium. This particular grouping of interstellar gas exhibits a shape that resembles a horse's head, from which it receives its name. The image is particularly useful to astronomers because it shows multiple types of nebulae. It consists of an absorption nebula (one that absorbs light) in front of an emission nebula (one that produces its own light). However, nebulae are especially important, because within these objects astronomers can observe the births of stars. As shock waves from other parts of the universe, such as supernovas, reach the gas, the pressure pushes the material together to create new stars and ignite their cores. In the image of the Horse Head Nebula, we can see new stars lighting up the surrounding clouds. Thus it is easy to see how both the diagram drawn by Galileo and the picture of the Horse Head Nebula were important to the advance of science when placed in their respective times.

The second similarity between the images is that both where created for scientific purposes and intended to be seen by those who were studying the topic. However, both were and can be presented in such a way that any layman could understand them. In Galileo's time, books, specifically scientific ones, were written in Latin, because it was the language of the learned. As a result the common people were not exposed to many of the scientific advances of their day. Galileo did not follow this age-old rule. In the preface of The Dialogue, the translator remarks, "The Dialogue was written in colloquial Italian rather than in Latin (into which it was shortly translated) in order to reach the widest possible audience."² Since the image was a supplement to the dialogue, it was necessary to have access to the text, so printing in Italian allowed a greater number to understand the image. Likewise, the image of the nebula was taken with the intent of being studied by astronomers to gain more insight on the universe. Yet the image of the Horse Head Nebula has been printed on posters and in many other forms that lay-people are in contact with everyday. Additionally it has been reproduced in textbooks as an instructional tool to teach those learning about the universe.

Both of the images are better understood if they are accompanied by the relevant text. In the Dialogue, the picture was introduced as an explanatory aid, to be referred to while reading the text. In the surrounding text Galileo proves this arrangement of the planets based on the observations he made with his telescope. Galileo places Venus in the orbit before the Earth, because of the phases that he witnessed. He puts the moon in an orbit around the Earth. The moon is positioned here so it could cause an eclipse. Then Galileo proceeds to place the rest of the planets, putting Mars past our orbit, because it must orbit the sun and it did not have phases. Throughout the passage Galileo names the orbits with letters, "this first one, for Jupiter, I mark EL; the other, higher, for Saturn, is called FM,"³ so that it is easier for one to understand how the illustration relates to the text. The image would most likely not have been understood if it were not placed with the text, because these ideas were new and contrary to those held by most of Europe. Similar to Galileo's image, the image of the Horse Head Nebula would not have been easily understood without the text of the book in which it is presented. Non-astronomers would have been unable gain knowledge about space and nebulae without the image being in conjunction with any text. They would be able to recognize it as a picture from space, but would not know that it was a star nursery. However, scientists could look at the picture and gain insight concerning the composition of the nebula, material surrounding it, and the neighboring stars without an accompanying text.

Another comparison that can be made between the two images is the fact that they were both obtained by telescopes. Galileo was the first to really make scientific observations through a telescope. Before he turned his lens on the sky, astronomers used to make observations with their unaided eyes. The resolution of the images Galileo saw was not as clear as the ones that we see today. Yet they were clear enough that he was able to make his exciting discoveries. Today the telescope has become an integral part of observational astronomy. Like Galileo, we still use reflecting telescopes. However, they are made with lenses, so they cannot be bigger than about a meter. The larger the surface, the more light a telescope can gather, so refracting telescopes were invented. Refracting telescopes are manufactured with mirrors, so they can be much larger and produce images with more detail. Telescopes have even moved off of the earth and into space where they are present on satellites. However, the difference between the social climates that were present during Galileo's time and ours, becomes evident when discussing telescopes. The technology of the telescope was new in the sixteenth century, and people were skeptical of the images seen through the new machine. This was because they were not able to directly see the images that Galileo claimed to have seen. As a result there was a question about the accuracy of his observations. Today the same question of accuracy exists because we are still dealing with objects invisible to the naked eye. Yet today, the public has greater access to viewing with telescopes, and telescopes have come to be regarded as truthful sources.

It is amazing that images that had so much in common and were both important to science were received with such different attitudes. Similar to the difference in the reliability of telescopes, this was due to the different political and social climates in which they were released. During Galileo's time, the Catholic Church controlled much of what the scientific community could print. The Inquisition had begun, and to hold the view that we lived in a heliocentric world was considered heresy. When Galileo published his book, most people thought that it was a great work of science. However, Galileo made some rude remarks about a Jesuit named Scheiner who claimed to have discovered sunspots twenty-two years before. As a result of this, the Jesuit Fathers went after Galileo and his Dialogue, working to have the book banned. They were so ingenious in their methods that they were able to convince Pope Urban VIII, that Galileo had mocked of him. As Reston states,