Galileo and the Telescope Galileo and the Telescope Questions The science of astronomy took a huge leap forward in the first decade of the 1600s with the invention of the optical telescope and its use to study the night sky. Galileo Galilei did not invent the telescope but was the first to use it systematically to observe celestial objects and record his discoveries. His book, Sidereus nuncius or The Starry Messenger was first published in 1610 and made him famous. In it he reported on his observations of the Moon, Jupiter and the Milky Way. These and subsequent observations and his interpretations of them eventually led to the demise of the geocentric Ptolemaic model of the universe and the adoption of a heliocentric model as proposed in 1543 by Copernicus. Galileo's drawings of phases of the Moon. Question: What features are visible here that cannot be seen with the unaided eye? Galileo's Telescopes The basic tool that Galileo used was a crude refracting telescope. His initial version only magnified 8x but was soon refined to the 20x magnification he used for his observations for Sidereus nuncius.

It had a convex objective lens and a concave eyepiece in a long tube. The main problem with his telescopes was their very narrow field of view, typically about half the width of the Moon. Galileo's drawing of the optical path of his telescope The earliest known sketch of a telescope, August 1609. One of Galileo's telescopes. The focal length is 1330 mm with a 26 mm aperture, it magnifies 14x. It has an objective bi-convex lens and a plano-concave eyepiece. Galileo's Observations Galileo made several key discoveries through his systematic use and refinement of the telescope. The Moon According to Aristotelian principles the Moon was above the sub-lunary sphere and in the heavens, hence should be perfect. He found the "surface of the moon to be not smooth, even and perfectly spherical,...,but on the contrary, to be uneven, rough, and crowded with depressions and bulges. And it is like the face of the earth itself, which is marked here and there with chains of mountains and depths of valleys." He calculated the heights of the mountains by measuring the lengths of their shadows and applying geometry.

One of Galileo's lunar drawings. Note the craters, mountains and mare or "seas". The terminator between lunar day and night is clearly seen down the centre. Moons of Jupiter Observations of the planet Jupiter over successive night revealed four star-like objects in a line with it. The objects moved from night to night, sometimes disappearing behind or in front of the planet. Galileo correctly inferred that these objects were moons of Jupiter and orbited it just as our Moon orbits Earth. For the first time, objects had been observed orbiting another planet, thus weakening the hold of the Ptolemaic model. Today these four moons are known as the Galilean satellites; Io, Europa, Ganymede and Callisto. Galileo's drawings of the moons of Jupiter of successive nights The Phases of Venus Venus was observed to go through a sequence of phases similar to the Moon. This could not be explained in the Ptolemaic model but could be accounted for by either the Sun-centered Copernican model or the Earth-centered Tychonic model that had the other planets orbiting the Sun as it orbited the Earth.

Galileo rejected Tycho's model as an unnecessary hybrid and used the discovery to consolidate his support of the Copernican model. Sunspots Along with contemporaries such as Thomas Harriot, David Frabicius and Christoph Scheiner, Galileo observed dark regions that appeared to move across the surface of the Sun. Debate centered on whether these were satellites of the Sun or actual spots on its surface. Galileo, in his Letters on Sunspots supported the sunspot interpretation and used it to show that the Sun was rotating. Its blemishes and imperfections again undermined the Aristotelian ideal of a perfect cosmos. "Appendages" on Saturn Galileo noted two appendages from the sides of Saturn. These disappeared then later reappeared. It was not until 1656 that the Dutch scientist, Christiaan Huygens correctly described them as rings. Stars in the Milky Way Even through a telescope the stars still appeared as points of light. Galileo suggested that this was due to their immense distance from Earth. This then eased the problem posed by the failure of astronomers to detect stellar parallax that was a consequence of Copernicus' model.

On turning his telescope to the band of the Milky Way Galileo saw it resolved into thousands of hitherto unseen stars. This posed the question as to why there were invisible objects in the night sky? More stars are resolved in this drawing by Galileo of the Pleiades than are visible to the unaided eye. Further Information An excellent online source for all things related to Galileo is: The Galileo Project. It is hosted by Rice University and includes his writings, details on his experiments and observations and links. It is also the source for the image of Galileo at the top of this page. Another worthwhile site is The Art of Renaissance Science: Galileo and Perspective . It has a wealth of diagrams matched with clear. concise text. There are some animations of his experiments. The Institute and Museum of the History of Science in Florence has a wealth of detail on the history of astronomy including Galileo's work. Their new website is worth exploring. Much of it is in English although some sections, including an excellent simulation of early telescopes, is only available in Italian at present. They also have an excellent new site: Galileo's Telescope, the Instrument that Changed the World .

Afocal CCD Images Through a Galilean Telescope is an excellent resource that provides CCD images that approximate what the human eye would see through a Galilean telescope. It has images of the Sun, Moon, Venus, stars and nebulae. The site provides historical background and technical details. Galileo's Sidereus nuncius or The Sidereal messenger is available in translation by A. van Helden from University of Chicago Press, 1989. The Cambridge Illustrated History of Astronomy, ed Michael Hoskin, Cambridge University Press, 1997 provides a wealth of information and diagrams and is an authoritative yet readable guide to the topic. The Sleepwalkers by Arthur Koestler is a classic book dealing with the development of astronomical thought up to the time of Newton. There are numerous other books and web sites covering Galileo's work and the history of astronomy. Questions Why was the telescope an advance over naked-eye astronomy? What did Galileo's observations of the Moon reveal? What was the significance of Galileo observing phases of Venus? How did Galileo's observations help undermine the existing paradigm of the Ptolemaic model of the Universe and Aristotle's physics? Who Invented the Telescope? Who Invented the Telescope?

By Lauren Cox, SPACE.com Contributor | July 13, 2013 11:40am ET MORE The telescope is one of humankind's most important inventions. The simple device that made far away things look near gave observers a new perspective. When curious men pointed the spyglass toward the sky, our view of Earth and our place in the universe changed forever. But who invented the telescope? The answer remains a mystery today. It is highly probable that as glassmaking and lens-grinding techniques improved in the late 1500s, someone held up two lenses and discovered what they could do. Hans Lippershey, credited with invention of the telescope. Credit: Public domain The first person to apply for a patent for a telescope was a Dutch eyeglass maker named Hans Lippershey (or Lipperhey). In 1608, Lippershey tried to lay claim on a device with three-times magnification. His telescope had a concave eyepiece aligned with a convex objective lens. One story goes that he got the idea for his design after observing two children in his shop holding up two lenses that made a distant weather vane appear close.

Others charged at the time that he stole the design from another eyeglass maker, Zacharias Jansen. Jansen and Lippershey lived in the same town and both worked on making optical instruments. Scholars generally argue, however, that there is no real evidence that Lippershey did not develop his telescope independently. Lippershey, therefore, gets the credit for the telescope, because of the patent application, while Jansen is credited with inventing the compound microscope. Both appear to have contributed to the development of both instruments. Compounding the confusion, yet another Dutchman, Jacob Metius, applied for a patent for a telescope a few weeks after Lippershey. The government of the Netherlands eventually turned down both applications because of the counterclaims. Also, officials said, the device was easy to reproduce, making it difficult to patent. In the end, Metius got a small reward, but the government paid Lippershey a handsome fee to make copies of his telescope. A 1754 painting by H.J. Detouche shows Galileo Galilei displaying his telescope to Leonardo Donato and the Venetian Senate.

Credit: Public domain Enter Galileo In 1609, Galileo Galilei heard about the "Dutch perspective glasses" and within days had designed one of his own — without ever seeing one. He made some improvements on his initial design and presented his device to the Venetian Senate. The Senate, in turn, set him up for life as a lecturer at the University of Padua and doubled his salary, according to Stillman Drake in his book "Galileo at Work: His Scientific Biography" (Courier Dover Publications, 2003). Galileo's ink renderings of the moon: the first telescopic observations of a celestial object. Credit: NASA Galileo was the first to point a telescope skyward. He was able to make out mountains and craters on the moon, as well as a ribbon of diffuse light arching across the sky — the Milky Way . He also discovered the sun had sunspots, and Jupiter had its own set of moons . The British ethnographer and mathematician Thomas Harriot also used a spyglass to observe the moon. Harriot became famous for his travels to the early settlements in Virginia to detail resources there.

His August 1609 drawings of the moon predate Galileo's, but were never published. The more he looked, the more Galileo was convinced of the sun-centered Copernican model of the planets. Galileo wrote a book “Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican” and dedicated it to the Pope Urban VIII. But his ideas were considered heretical, and Galileo was called to appear before the inquisition in Rome in 1633. He struck a plea bargain and was sentenced to house arrest where he continued to work and write until his death in 1642. Elsewhere in Europe, scientists began improving the telescope. Johannes Kepler studied the optics and designed a telescope with two convex lenses, which made the images appear upside down. Working from Kepler's writings, Isaac Newton reasoned it was better to make a telescope out of mirrors rather than lenses and built his famous reflecting telescope in 1668. Centuries later the reflecting telescope would dominate astronomy. Exploring the cosmos The largest refracting telescope ever built opened at Yerkes Observatory in Williams Bay, Wis., in 1897.

But the 40-inch wide glass lens at Yerkes was soon made obsolete by larger mirrors. The Hooker 100-inch reflecting telescope opened in 1917 at Mount Wilson Observatory in Pasadena, Calif. It was there that the astronomer Edwin Hubble determined the distance of the Andromeda Nebula — far beyond the Milky Way. With the development of the radio, scientists could start to study not just light, but other electromagnetic radiation in space. An American engineer named Karl Jansky was the first to detect radio radiation from space in 1931. He found a source of radio interference from the center of the Milky Way. Radio telescopes have since mapped the shape of galaxies and the existence of background microwave radiation that confirmed a prediction in the Big Bang Theory . In April 1990, the Hubble Space Telescope sailed into orbit. The reflecting telescope took advantage of digital cameras and satellite communications to give jaw dropping views of space free from the interference of the earth's atmosphere and light pollution. More than 200 years after Galileo pointed his telescope skyward, people could see space from the heavens.

— Lauren Cox, SPACE.com Contributor Galileo's Moon- Then and Now Galileo's Moon-- Then and Now Galileo's Work When Galileo first turned his telescope to the moon, he had no idea that he was about to see something that would cast doubt upon centuries-old beliefs. At the time of Galileo, science was based upon the teachings of Aristotle. According to Aristotle, the Earth was the center of the universe. All heavenly bodies, including the moon, were perfect spheres that moved around the Earth with circular motions (or combinations of circular motions), and the Earth was the only source of imperfection in the universe. The dark spots on the moon that been visible to man throughout the ages were explained away as parts of the moon that absorbed and emitted light differently than other parts-- the surface itself was perfectly smooth. Copernicus's theory that the sun rather than the Earth was the center of all motion had moved the Earth into the realm of heavenly bodies. However, Copernicus's theory went against fundamental beliefs of the time, and therefore was dismissed by most learned people. One of the unacceptable notions was that of the imperfect Earth existing in the realm of the perfect heavens.

However, in November 1609 Galileo pointed his improved telescope with 20x magnification to the moon for the first time. He had decided to make an in-depth study of the moon. From November 30 until December 18 of that year, he examined and drew the moon and described that research in his book Sidereus Nuncius. Galileo's observations led him to the startling conclusion that the moon is anything but perfect. With his telescope, he noticed small dark spots that had never been seen before on the illuminated part of the moon's surface, along with similar light spots in the dark area. He observed that as time passed, these and other spots changed, either getting lighter and eventually disappearing or getting darker and more distinct. The interface between the light and dark sides of the moon was rough and uneven, rather than smooth as would be expected on a perfectly smooth sphere.

Galileo also observed that the spots all "have a dark part on the side toward the Sun while on the side opposite the Sun they are crowned with brighter borders like shining ridges." (Sidereus Nuncius, p 41) From these and many other observations, Galileo concluded that the moon's surface consists of valleys, plains and mountains much like the surface of the Earth (Sidereus Nuncius p 48-49). The dark spots are shadows cast by these mountains and valleys as the sun falls on them. As the moon's position relative to the sun changes, the shapes and intensities of these shadows change. Galileo's conclusion was a shocking one-- how can the moon, a heavenly body, not be perfect and spherical? If the moon is imperfect, could there be other imperfect heavenly bodies as well? If heavenly bodies can be imperfect, why can the Earth not be a heavenly body? Galileo's conclusions about the moon did not give solid proof of Copernicus' theory, but his observations paved the way for the theory's eventual acceptance. [Note: The page numbers in Sidereus Nuncius cited above refer to Sidereus Nuncius or the Sidereal Messenger.

Translated with introduction, conclusion, and notes by Albert Van Helden. Chicago: University of Chicago Press, 1989. AVH] Galileo's Work Today I am a member of the Spring 1995 History 333 ("Galileo in Context") class at Rice University. Our assignment was to study Galileo's work in a particular field and then recreate his work as closely as possible. The Astronomy Group built Galilean telescopes and used them to study the same heavenly bodies that Galileo did 375 years ago. Our group experienced many of the exciting discoveries and frustrating problems that Galileo himself may have encountered. We used modern materials to make replicas of Galileo's telescopes (click here for more information on our Galilean telescopes). One fundamental difference between our telescopes and Galileo's is the fact that ours had only about 9x magnification while Galileo used telescopes with magnifications of up to 20 to study the moon. Our attempt to rigorously recreate Galileo's work was also thwarted by the uncooporative Houston spring weather.

The skies were clear for only about five nights during the semester, making it impossible to observe all the phases of the moon as Galileo did. During my first attempt at observing the moon, I encountered problems, both expected and unforeseen. I was initially frustrated in trying to find the moon due to the small field of view the telescope. The best technique, I found, was to search until a bright light (the light of the moon) was visible on the interior surface of the tube. By moving the telescope so that this light moved down the length of the tube towards my eye, I was able to bring the moon into view. After securing the mounting so that the telescope was fixed on the moon, I was ready to begin viewing. Before my work on this project, I had had very little experience observing the heavens with a telescope. Therefore, on my first night of observing, I felt much of the same amazement and excitement that Galileo must have felt when he first saw the detail of the moon that is invisible to the naked eye. This is my drawing of the moon as seen through a Galilean telescope at 11pm on April 26, 1995.

The 9x magnification of our telescope brought out numerous small shadows in the lower left face of the moon, along with a distinctly rough interface between the dark and light sides of the moon. The telescope also made it possible to see the variations in the darkness of the shadows, which gave the moon the distinct three-dimensional look. Galileo's conclusions about the imperfect surface of the moon may have been revolutionary, but they are not surprising once one has looked at the moon through a telescope. Before Galileo made his 20x telescope, the strongest telescopes people had been able to make had only about 3x or 4x magnification. Presumably these telescopes were not strong enough to bring out the details of the moon as Galileo's did; It was this high magnification that allowed Galileo to make his discoveries before others. Galileo's effort to examine the moon through all its phases also played a big role in enabling him to discover and interpret the changing shadows. As I continued my observations, a number of other problems with our telescope and mounting became obvious. At least one of these problems was one with which Galileo probably had to deal.

The small field diameter of our telescopes (my telescope had a calculated field diameter of 964.8 arcseconds, or 16 arcminutes) made it impossible to see the whole face of the moon at once. In the picture above , the concentric circles indicate the field of view visible at one time. The outer circle shows the total view possible with the telescope, while the inner circle roughly indicates the maximum field I was able to get in focus. The small field of view made it necessary to move the telescope around in order to see the whole moon when observing and drawing it. Many of Galileo's drawings of the moon indicate that he had to deal with the same problem. His pictures seem to have been drawn more as representations of the moon than as accurate replicas of what one sees through a telescope. For example, in the picture below, the size of the circular crater on the terminator (perhaps Albategnius) is greatly exaggerated. It is speculated that Galileo represented it this way in order to emphasize the effect of shadowing in creating a three-dimensional image. From Galileo's Sidereus Nuncius (p 44) Keeping the image withing the field of view also became a problem.

In spite of our efforts to make the mounting as stable as possible, we could not entirely eliminate the wobble from the telescope. Any slight wind or shakiness of the viewer's hand, coupled with the tiny field of view, would move the telescope enough for the object under study to move out of the field. This effect made observing somewhat more difficult, although it had a more detrimental impact on observations of the more distant (and therefore smaller) planets than on observations of the moon. Full moon observed and drawn March 16, 1995 by Nicole Peterson. One final problem that future groups will find easily correctable is the height of the eyepiece of our telescope. Once I got the telescope angled at the moon, I discovered that the eyepiece was too high for my eye to reach while I was sitting, yet too low to see into while kneeling. The half-crouch position that I finally had to settle for became uncomfortable and made the observing much more difficult. A suggestion for the future is to design each person's mounting so that the eyepiece sits where it is most comfortable for that person in order to eliminate this annoying problem.

The Moon - Facts About The Moon For Kids The Moon Planets >> The Moon the Moon was probably made 4.5 billion years ago when a large object hit the Earth and blasted out rocks that came together to orbit round the Earth. They eventually melted together, cooled down and became the Moon. For another 500 million years pieces of rock kept striking aginst the surface of the Moon. You can see the surface of the Moon by using a pair of binoculars or a small telescope. The Moon’s surface shows the damage caused by these large pieces of rock hitting it billions of years ago. The surface is covered in craters, pits and scars. From the Earth we can only see one side of the Moon; the other side is always turned away from us. Photographs from space show a similar scarred surface on the other side. The Earth has a much greater surface than the Moon and was also hit by debris (the rocks from explosions and collisions) but over time the damage has disappeared. The wind and rain in the Earth’s atmosphere has helped to erode the pits and craters. The Moon has no atmosphere and so we can still see the damage caused billions of years ago.

If you look at the Moon when it is nearly full you can see the dark areas which are known as the seas. (They are all given Latin names, such as Mare Serenitatis – the Sea of Serenity, or Mare Frigoris – the Sea of Cold).These are not really seas but are huge expanses of smooth dark lava. Figure 1. A map of the Moon. All parts of the Moon are lit in turn by the Sun. As it rotates round the Earth we see different fractions of the sunlit half, or hemisphere, of the Moon. These are known as the phases of the Moon, or lunar phases. The Moon changes from a thin crescent to a full moon and back again to a crescent in one month (actually 29 days, which is a lunar month). Figure 2. The Phases of the Moon. This diagram shows the phases of the moon, from a new moon, which you can hardly see at all, round to a full moon and back again in just over four weeks. Follow the phases in an anticlockwise direction(the opposite way from how the hands of a clock move). The waxing Moon. “Waxing” means growing.

After the new moon appears in the sky as a tiny sliver of light the moon waxes. It grows into a crescent, curving to your left as you look at it and then into a half moon. This takes a week and so the period is described as the Moon’s first quarter. The waxing gibbous Moon. Gibbous means humped and describes the shape of the Moon as it grows from a half moon to a full moon. Another week has passed and this is the Moon’s second quarter. The waning Moon. “Waning” means shrinking. Now the Moon begins to get smaller again – it “wanes”. The third quarter takes us from a full moon to a half moon again, but this time it is the right hand side of the moon that shines. The waning crescent Moon. The last quarter takes us from a half moon back to a crescent moon, facing right, and to a point where the moon disappears. When the Moon is a crescent and only the crescent is being illuminated by the Sun, you can often see the shadow of the rest of the Moon. This is caused by reflection of sunlight from the Earth.

It is sometimes called “the old moon in the new moon’s arms”. Figure 3. The effect of earth shine on the moon. The gravity of the Moon, the pull which it exerts on the Earth, causes two high tides on the Earth every day – one every 12 hours and 25 minutes. The first man to make proper maps of the moon was Galileo. Galileo did not invent the telescope but by 1609 he had developed a telescope that could magnify objects to 20 times, and with this telescope he began his careful study of the Moon’s surface. The first person to walk on the Moon was the American astronaut, Neil Armstrong, who stepped out of his space landing craft, the Eagle, on 21 July 1969 with these famous words, “That’s one small step for man, one giant leap for mankind”. Figure 4. A photograph of the Earth taken from the surface of the Moon. The Moon is 239,000 miles, or 384,000 kilometres away from the Earth.

The Moon is much smaller than the Earth, with a diameter of 2159 miles, or 3476 kilometres. It is airless, waterless and lifeless. History Corrected by 400-year-old Moon Map History Corrected by 400-year-old Moon Map By SPACE.com Staff | January 14, 2009 11:43am ET MORE The first drawing of the Moon through a telescope, dated July 26, 1609, by Thomas Harriot. This crude but historic sketch roughly delineates the terminator, the line that marks the boundary between day and night on the lunar surface. The original image is a little more than 15 cm across. The dark patches correspond to Mare Crisium (at the top), Mare Tranquilitatis and Mare Foecunditatis. Credit: © Lord Egremont Galileo Galilei is often credited with being the first person to look through a telescope and make drawings of the celestial objects he observed. While the Italian indeed was a pioneer in this realm, he was not the first.

Englishman Thomas Harriot made the first drawing of the moon after looking through a telescope several months before Galileo, in July 1609. Historian Allan Chapman of the University of Oxford details that 400-year-old breakthrough in astronomy in the February 2009 edition of Astronomy and Geophysics, a journal of the Royal Astronomical Society. Chapman explains how Harriot preceded Galileo and went on to make other maps of the moon's surface that would not be bettered for decades. The story Harriot lived from 1560 to 1621. He studied at St Mary's Hall (now part of Oriel College), Oxford, achieving his BA in 1580. He then became a mathematical teacher and companion to the explorer Sir Walter Raleigh. In the early 1590s Raleigh fell from royal favor and was imprisoned in the Tower of London. Harriot was passed to the patronage of Henry Percy, the Ninth Earl of Northumberland who was himself imprisoned as one of the Gunpowder Plotters in 1605 but continued to support Harriot in his residence at Sion (now Syon) Park, in what is now west London.

Harriot became a leading force in mathematics, Chapman explains, working on algebraic theory and corresponding with scientists across Europe. By 1609, Harriot had acquired his first "Dutch trunke" (telescope), which had been invented in The Netherlands in 1608. He turned it on the moon on July 26, becoming the first astronomer to draw an astronomical object after viewing it through a telescope. The crude lunar sketch shows a rough outline of the lunar terminator (the line marking the division between night and day on the moon, as seen from the Earth) and includes a handful of features like the dark areas Mare Crisium, Mare Tranquilitatis and Mare Foecunditatis. Harriot went on to produce more maps from 1610 to 1613, Chapman said in a statement released today. Not all of these are dated, but they show an increasing level of detail. By 1613 he had created two maps of the whole moon, with many identifiable features such as lunar craters that crucially are depicted in their correct relative positions.

The earliest telescopes of the kind used by Harriot (and Galileo) had a narrow field of view, meaning that only a small portion of the moon could be seen at any one time and making this work all the more impressive. No better maps would be published for several decades. Cush job Despite his innovative work, Harriot remains relatively unknown. Unlike Galileo, he did not publish his drawings. Unlike Galileo, Harriot is not being widely celebrated during 2009, dubbed the International Year of Astronomy as a commemoration of the telescope's 400th year. Chapman attributes this to his comfortable position as a "well-maintained philosopher to a great and wealthy nobleman" with a generous salary, said to be "several times the level of the Warden of Wadham College, Oxford." Harriot had comfortable housing and a specially provided observing chamber on top of Sion House, all of which contrasted with Galileo's financial pressures. Galileo, interestingly, was unable to buy a telescope. So he figured out the optics of it and built his own. He also examined the moon, and then found that the Milky Way was composed of individual stars.

Galileo also discovered four moons around Jupiter and spent much time observing and drawing sunspots. "Thomas Harriot is an unsung hero of science," Chapman said. "His drawings mark the beginning of the era of modern astronomy we now live in, where telescopes large and small give us extraordinary information about the universe we inhabit." Professor Andy Fabian, President of the Royal Astronomical Society, agrees. "As an astrophysicist of the 21st century, I can only look back and marvel at the work of 17th century astronomers like Thomas Harriot," Fabian said. "The world is right to celebrate Galileo in the International Year of Astronomy – but Harriot shouldn't be forgotten!" Skywatcher's Guide to the Moon Image: Englishman Thomas Harriot NASA - Telescope History Telescope History 09.12.03 Galileo's ink renderings of the moon: the first telescopic observations of a celestial object. In 1609 an Italian physicist and astronomer named Galileo became the first person to point a telescope skyward.

Although that telescope was small and the images fuzzy, Galileo was able to make out mountains and craters on the moon, as well as a ribbon of diffuse light arching across the sky -- which would later be identified as our Milky Way galaxy. After Galileo's and, later, Sir Isaac Newton's time, astronomy flourished as a result of larger and more complex telescopes. With advancing technology, astronomers discovered many faint stars and the calculation of stellar distances. In the 19th century, using a new instrument called a spectroscope, astronomers gathered information about the chemical composition and motions of celestial objects. Twentieth century astronomers developed bigger and bigger telescopes and, later, specialized instruments that could peer into the distant reaches of space and time. Eventually, enlarging telescopes no longer improved our view… all because of the Earth's atmosphere. A Telescope in the Sky? Why? The next time you gaze up at the night sky, you're likely to spot a twinkling star. But is it really twinkling? What looks like a twinkling star to our eyes is actually steady starlight that has been distorted, or bent, by the Earth's atmosphere. The visual effect of this distortion is like looking at an object through a glass of water.

Telescopes here on the ground -- which also must peer through Earth's atmosphere -- are equally vulnerable to our atmosphere's visual tricks. That's why astronomers around the world dreamed of having an observatory in space -- a concept first proposed by astronomer Lyman Spitzer in the 1940s. From a position above Earth's atmosphere, a telescope would be able to detect light from stars, galaxies, and other objects in space before that light is absorbed or distorted. Therefore, the view would be a lot sharper than that from even the largest telescope on the ground. Vision Becomes Reality In the 1970s the European Space Agency and the National Aeronautics and Space Administration began working together to design and build what would become the Hubble Space Telescope. On April 25, 1990, five astronauts aboard the space shuttle Discovery deployed the eagerly anticipated telescope in an orbit roughly 380 miles (600 km) above the Earth's surface. That deployment and, later, the unprecedented images that Hubble delivered represented the fulfillment of a 50-year dream and more than two decades of dedicated collaboration between scientists, engineers, contractors, and institutions from all over the world.

The Hubble Space Telescope in Lockheed's Cleanroom. Hubble's Job Description Stargazing with Galileo - Sky & Telescope Sky & Telescope Download Your Free Astrophotography Primer Now from Sky & Telescope! * Portrait of Galileo Galilei, from the National Maritime Museum, London S&T Imagine the thrill of looking through a telescope and making a new discovery as soon as you peer into the eyepiece. Although spotting some never-before-seen celestial object can happen, it’s rare these days because so many professional and amateur astronomers are combing the sky every night. But four centuries ago the telescope was a revolutionary new invention, and when the great scientist Galileo Galilei first pointed a telescope skyward in late 1609, he was astounded by what he saw night after night. All the unexpected sights revealed through his instrument transformed his life and the world at large. You can follow the same path as Galileo, observing the same celestial sights that he did  from craters on the Moon to the miniature solar system encircling Jupiter.

As you “rediscover” some of the night sky’s many marvels, you’ll gain skill as an observer and get an appreciation for the profound insights revealed to Galileo’s inquisitive eyes. Before the telescope came along, most educated people still accepted concepts about the universe first popularized by Aristotle and his contemporaries in the 4th century BC. In their view, Earth sat motionless at the center of the universe, with the Sun, Moon, planets, and stars affixed to nested crystalline spheres like the layers of an onion. The spheres spun at various rates, such that the Sun completely encircled Earth in just one day while the stars took an entire year. And, unlike earthly matter, the spheres and all they contained consisted of a perfect, changeless, and eternal “aether.” In the 2nd century AD, the influential astronomer-geographer Ptolemy introduced an even more elaborate crystalline-clockwork scheme that prevailed unchallenged for nearly 1,500 years. It takes a bit of imagination, but look up at the night sky and think about how it must have appeared to people who lived before Galileo.

Try to see the stars not as distant suns, but as points of light shining from the edge of the universe. Imagine the planets as perfect bits of aether instead of worlds with moons of their own. Of course, not everyone accepted the ideas of Aristotle and Ptolemy. In 1543 Nicholas Copernicus published a fundamentally different concept that placed the Sun at the center of the universe with Earth and other planets moving in orbits around it. It was a radical departure  most authorities continued to accept the Ptolemaic system. Only two of Galileoâ€™s many telescopes survive. Shown here is the skyward end of a museum-grade replica that, once completed, will be displayed at Griffith Observatory in Los Angeles. Steven A. Simpson But all that would eventually change. In October 1608 a Dutch eyeglass maker named Hans Lipperhey filed a patent application for an invention he called a kijker (“looker”). It was a tube with a convex lens in the front and a concave lens at the eyepiece end, a combination that made distant objects appear much closer.

Several months later news of Lipperhey’s invention reached Galileo in Italy, who quickly fashioned an instrument of his own. In August 1609 Galileo presented the Venetian Senate with an 8-power telescope. Impressed, the senators doubled his salary and guaranteed his job for life! The newly promoted professor then made a 20-power telescope for his own use and began studying the night sky in October or November. By contrast to modern refracting telescopes, Galileo’s instrument was not very capable. Its front lens was only 37 mm (1½ inches) in diameter, and the field of view was restricted to 15 inches at 100 yards  much narrower than most instruments now. Still, this modest telescope was good enough to make discoveries as important as any in the history of astronomy. As most new stargazers do, Galileo began by studying the Moon. Lunar Landscape Step outside to gaze at the next full Moon, and try to forget all the photographs you’ve seen of the lunar landscape. To Galileo’s contemporaries, the Moon appeared to be a perfect sphere. The mottled gray patterns, they imagined, were areas of different densities. Messenger (1610).

His sketch of a first-quarter moon, shown here, called attention to the details visible along the day-night terminator. The prominent crater below center, which he probably drew overly large for emphasis, is most likely the one known today as Albategnius, 71 miles across." credits="S&T" width="" height="" align="right"] Now think about that as you look at the Moon through binoculars or a telescope. The view is most impressive along the terminator, the line separating day from night, where long shadows make it easier to see the terrain. When Galileo looked at the terminator, he realized that the lunar landscape is a jumble of mountains, valleys, and craters  visual proof that the Moon’s face was far from perfect. Galileo continued to view the Moon night after night, following the progress of the terminator as it swept across the landscape and sketching what he saw so he could share his discoveries with others. Sketching what you observe is still a good idea: trying to record what you see accurately teaches you to perceive more details whenever you look.

Galileo’s drawings conveyed the jagged nature of the Moon’s terrain, and one sketch in particular exaggerated the prominence of a single lunar crater straddling the terminator, most likely the one now called Albategnius. The best time to look for Albategnius is when the Moon’s phase is around first or last quarter. Jupiter’s Revelations After the Moon, the most alluring objects in the night sky are planets. Jupiter shone brightly in the evening sky when Galileo began observing, so it was an obvious target for his telescope. You should have no difficulty finding Jupiter either  during summer it’s in the southern part of the sky after sunset, and on the moonless evenings nothing else is brighter. Use the Sky & Telescope sky charts in our issues or on our Web site if you’re unsure about where to look. Even a small telescope shows that Jupiter is truly a world, not just another starlike pinpoint of light. Jupiter also comes with “extras”: its four largest moons are relatively bright and easy to spot. Their positions shift noticeably as they move around Jupiter, and because their orbits are edge-on from our perspective, they form a more-or-less straight line running east to west.

When Galileo first viewed Jupiter through a telescope  on January 7, 1610, he discovered that the planet was accompanied by three "stars" in a line. Imagine his surprise the next night, when he found that the trio had shifted in position. On later nights he spied a fourth moon as well. The Sidereal Messenger At first, Galileo believed that the four pinpoints of light near Jupiter were simply background stars. However, his nightly observing sessions soon revealed that they shifted in position but never strayed far from the planet (illustrated in the image at right). Galileo realized he was tracking four moons. Nothing in the teachings of Aristotle or Ptolemy could account for Jupiter’s companions, and Galileo quickly deduced that he’d found new evidence for Copernicus’s theory. Showing that Jupiter and its system of moons orbit the Sun together made it easier to accept that the Earth and Moon do, too.

(Critics of Copernicus had claimed that if Earth were in motion it would eventually leave the Moon behind.) Galileo wrote: ”Here we have a fine and elegant argument for quieting the doubts of those who, while accepting with tranquil mind the revolutions of the planets about the Sun in the Copernican system, are mightily disturbed to have the moon alone revolve about the Sun. Some have believed that this structure of the universe should be rejected as impossible. But now we have not just one planet rotating about another while both run through a greater orbit around the Sun; our eyes show us four stars which wander about Jupiter as does the moon around the earth, while all together trace out a grand revolution about the Sun in the space of twelve years.” Today, you likely own a telescope powerful enough to reveal far more detail than Galileo ever saw. At magnifications as low as 50×, you can see two dark bands of clouds girding Jupiter’s midsection. If your timing is right and the air above you is steady, you might even glimpse the hurricane-like oval called the Great Red Spot.

Galileo apparently couldn’t see Jupiter’s cloud bands, which weren’t discovered until others reported seeing them a generation later, in 1664. We know that Galileo also observed Saturn. But his telescope wasn’t powerful enough to reveal the planet’s rings for what they truly are: a thin, flat disk of small particles. Initially he thought the rings were two separate bodies alongside Saturn. And in 1612, when the ring system was oriented edge-on as seen from Earth, he was convinced that they had disappeared entirely. “I do not know what to say in a case so surprising, so unlooked for, and so novel,” he wrote. There’s no evidence that Galileo saw the then-undiscovered planet Uranus, but his sketches prove that he saw Neptune in the vicinity of Jupiter and mistook it for a star. Neptune moves slowly in its orbit, taking nearly 165 years to complete one trip around the Sun. The apparent motion of the outer planets among the stars slows to a stop and even reverses at predictable times each year, and Neptune wasn’t drifting noticeably when Galileo saw it.

If he’d watched it a bit longer, he’d surely have noticed its motion and realized it wasn’t a star. The Phases of Venus From Earth's perspective, Venus completes an entire cycle of phases in 19 months. With a backyard telescope and a magnification of at least 50×, you can watch Venus slowly change appearance from week to week. S&T By December 1610, Galileo had already published Sidereus Nuncius (The Sidereal Messenger), an account of his initial telescopic observations, and was continuing his reconnaissance of the known solar system. He next took aim at Venus, which was then blazing brightly in the evening sky. If you’re observing during May and June (when this article was first published) you’ll have to get up early to spot Venus. In those months the planet sits low in the east just before dawn. You might find Venus a disappointing subject for observation through a telescope  it’s shrouded in thick clouds that hide all details of the surface. But the most important thing to notice is that the planet’s disk is not perfectly round. Instead, it looks like a tiny elongated football, mimicking a gibbous Moon.

Watch carefully over the next few weeks, and you’ll see the disk getting fuller (more circular) and smaller. Those changes confirm an especially important discovery made by Galileo: Venus goes through phases, just like the Moon, and this cycle of change proves that it must be orbiting the Sun. If you imagine the motion of Venus as explained by Copernicus, you can visualize how it should appear from Earth. Depending on its position relative to the Sun, Venus can look like a crescent, a semicircle, or a full globe. The planet appears biggest during its crescent phase (when it’s between Earth and the Sun) and smallest when full. The shape is especially easy to see when Venus displays a thin, bright crescent. Truth and Consequences As you retrace the steps Galileo took in his wanderings around the night sky, it’s worth thinking about the effect his observations had 400 years ago. The Sidereal Messenger was a sensation, transforming Galileo into a scientific celebrity and sparking public interest in telescopes and astronomy.

He used this opportunity to curry favor with the rich and powerful Medici family, dedicating the book to Grand Duke Cosimo II de Medici and naming the moons of Jupiter “Medician stars.” Flattered, the Grand Duke appointed Galileo his chief physicist, subsidized his work, and protected him from critics. The telescope enriched and transformed Galileo’s life in way he could not have imagined on the night he first pointed it toward the sky. Yes, he endured a harrowing clash with church officials, who ultimately convicted him of heresy for promoting Copernican theory. But that happened 22 years after publication of The Sidereal Messenger, and in the interim Galileo repeatedly capitalized on his famous discoveries and built the scientific legacy we remember today. Perhaps you too have been (or will be!) personally transformed by a first look at Jupiter, the lunar landscape, or the crescent Venus through a telescope. For some of us, the telescope sparks a lifelong interest in science. For others, it ignites a passion for discovery and knowledge. And for most everyone, it offers a keener appreciation of the universe and our place in it. Observing the heavens changed Galileo’s life profoundly.

If you follow in his footsteps and join the observing tradition he started four centuries ago, it will change your life, too. Learning Technologies' kit for constructing a 16× refracting telescope using low-plastic lenses for $9. Craig Michael Utter Build a Galilean Telescope! Making a working replica of Galileo’s telescope is the best way to appreciate the accomplishments of this great observer. It’s an easy, affordable project that provides a good introduction to optics. Modern suppliers don’t offer perfect matches for the lenses that Galileo used, but it’s possible to get a pair that are nearly so for less than $50. For the objective, you’ll want a convex lens with a diameter of no more than 40 mm and a focal length of about 1,000 mm; for the eyepiece, choose a concave lens with a focal length of about 50 mm. Used together, these will yield a magnification of roughly 20×. Once you have suitable lenses, you’ll need something to mount them in. You can use nested cardboard mailing tubes with plastic end caps, or for something sturdier try PVC plumbing parts.

Either way, spray the inside of your tubes with flat-black paint to reduce internal reflections and increase contrast. Securely mount the objective lens in the wider, outer tube and the eyepiece lens in the inner tube. You can try to improvise lens holders using plumbing gaskets, hardware bushings, or auto parts. Otherwise, use a hobby knife to make cardboard disks sized to hold the lenses. Then shim the drawtube until it slides smoothly. Duct tape provides the perfect shim material. Galileo sometimes wrapped his wooden telescope tubes in leather. An outer wrap of brown self-adhesive vinyl (sold in craft stores) will give your telescope a better, more accurate appearance than a simple coat of paint. Once it’s all assembled, you’ll discover immediately that your telescope is impossible to hold steady enough while observing. It’s not clear what kind of mount Galileo himself used, so feel free to be creative. A camera tripod and rubber bands or bungee cords will certainly work, or you can simply steady the tube against a stout pole, a tree, or the corner of a building. Jim Quinn’s footsteps can be found all over his backyard in North Canton, Ohio.

He’s a freelance writer associated with the National Inventors Hall of Fame in nearby Akron. This article first appeared in the May/June 2006 issue of Night Sky. CATEGORIES

Question: Who was the first person to report seeing craters on the moon using a telescope?
Answer: Galileo