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Beyond The Solar System
Exploring Galaxies, Black Holes, Alien Planets, and More: A History with 21 Activities
By Mary Kay Carson Chicago Review Press Incorporated
Copyright © 2013 Mary Kay Carson
All rights reserved.
ISBN: 978-1-61374-547-2
CHAPTER 1
Prehistory-1600: Stargazers to Scientists
People have been exploring the universe for thousands of years. Even cavemen gazing up at the stars were investigating what lay beyond — in their own way. Early humans believed they lived on a flat world. Each day, a godlike sun crossed the sky overhead. The night sky was filled with traveling lights and a changing moon. Ancient people were wrong about Earth's pancake shape, and they didn't have a clue about black holes. But this didn't keep them from putting what they did know about the universe to very good use.
The Sun, moon, and stars appear to move, disappear, and reappear in the sky in predictable patterns. Figuring out, tracking, and predicting these heavenly patterns made the first clocks, calendars, and navigation tools possible. The waning and waxing moon, as it changes from full to new to full again, marks the passage of 30 sunsets and sunrises — a lunar month. The stars, Sun, moon, and the planets rise and set not because they are moving, but because Earth is. Our mobile planet gives us a constantly changing view of what surrounds us out in space.
Earth's tilted posture as it travels around the Sun each year creates seasons by altering day lengths and the arc of the Sun's daily path across the sky. These changes announce the coming and going of seasons. Since prehistory, the changing seasons helped people know when it was time to plant or harvest, move to winter hunting grounds, or return to summer villages.
Stars, too, are seasonal calendars. Maybe you've noticed this yourself. The pattern of stars we call the Big Dipper changes position throughout the year. Its handle points up in summer and down in winter. Its cuplike end holds water in autumn and empties it in spring.
BIG BEARS, HUNTING GODS
The Big Dipper is part of a constellation called Ursa Major, or the Great Bear. Constellations are groups of nearby stars that people have named after the shapes they make. They are ancient star patterns and so have the names of ancient things — mythical characters and creatures, harps, dragons, unicorns, parts of sailing ships, and now-forgotten tools.
Ursa Major is one of the most ancient of constellations. Humans have recognized and named it for millennia. How do we know that? People in North America as well as Eurasia call the constellation the Great Bear — even though bears haven't lived in the Middle East and Mediterranean since the end of the last ice age! The Great Bear in the sky must have been recognized by northern peoples on both sides of the waterway that was once a frozen land bridge between Siberia and Alaska 15,000 years ago.
Ursa Major was, and is, an important constellation to know if you live in the Northern Hemisphere. Its Big Dipper points out the North Star and can help you find your way. Sailors and travelers can use the stars to navigate their way across oceans and deserts without landmarks.
Constellations also have calendar duties. Virgo, the Maiden, appears in the spring with an armful of grain, telling farmers it's time to sow crops — and watch out for floods. Orion, the Mighty Hunter, is a constellation that heralds winter. In the southern hemisphere, Orion announces summer and looks different since it's flipped over. The Yolngu aboriginal people of Australia call the star grouping Julpan, a canoe filled with brothers who have a fish on the line.
GREEKS, THE ORIGINAL SCIENCE GEEKS
By 1500 BC the Sumerians, Babylonians, Indians, Chinese, and Egyptians all had skilled observers of the heavens. These "star namers" (the meaning of the word astronomer) had important duties in ancient civilizations. But it was the ancient Greeks who put the science in what's celestial. They turned star naming into the science of astronomy.
Greece issued this stamp picturing Hipparchus and an astrolabe to commemorate the opening of the Eugenides Planetarium in Athens in 1965.
activity
Find Polaris
Because our planet moves around the Sun, our view of the backdrop of constellations constantly changes. Autumn night skies feature different stars than springtime ones. But Polaris, the North Star, doesn't move across the sky from season to season; it always remains above us and always points to the north. This is why Polaris has been used in navigation for millennia. Here's how you can spot the North Star for yourself.
YOU'LL NEED
Clear night sky
1. Find the Big Dipper. It's a star grouping in Ursa Major, a constellation in the northern hemisphere. Seven bright stars make up the Big Dipper in the northern or northwest sky. They form the shape of a dipper, or ladle, with a curved handle. Note: The Big Dipper's cuplike end is upright in autumn and overturned in spring, and its handle is pointed up in summer and down in winter.
2. Look at the cup end of the Big Dipper. The side of the cup farther from the handle is its "pouring edge." The two stars that make up this pouring edge of the Big Dipper will point you toward Polaris.
3. Imagine a line that connects the bottom pouring-edge star to the top one and then continues onward. The star that this imaginary line points to is Polaris, the North Star.
Hipparchus was born around 190 BC. He was a weather watcher as a young man, making records of rainfall and winds. For much of his life, Hipparchus spent his time on the Greek isle of Rhodes, observing the stars. He recorded the position, size, and brightness of many hundreds of stars. Another ancient Greek astronomer updated Hipparchus's work. Ptolemy (c. 100 AD–C.170) wrote the first astronomy textbook, called The Almagest. It had a catalog of all the known stars — more than 1,000. The book also explained why Earth is at the center of the universe.
An Earth-centered, or geocentric, view of the universe was already accepted among ancient Greek philosophers. The Greeks saw the universe as a series of nested shells. The stars were located in the outermost shell, rising and setting in the night sky as it turned around the Earth. The Sun, moon, and five known planets — Mercury, Venus, Mars, Jupiter, and Saturn — also orbited our motionless world. What Ptolemy added was an explanation that cleared up the theory's trouble spots. Until Ptolemy, no one could explain some of the movements of the five visible planets.
The word planet means "wanderer" because these lights in the night sky wander across the background of stars in odd ways — speeding up, moving backward, changing brightness, etc. The Ptolemaic system explained these oddities with mini-orbits within orbits, called epicycles. Mars, for instance, didn't just loop around Earth. It also moved in circles (its epicycle), bringing it a bit closer and farther from Earth as it looped around — sort of like a carousel ride on which you sit in a spinning car as the whole thing goes around. Ptolemy sealed the deal on his theory with some impressive and convincing geometry.
Few had trouble with the unmoving Earth aspect of Ptolemy's system. Humans don't feel Earth spinning or hurtling through space around the Sun. "Those who think it paradoxical that the Earth, having such a great weight, is not supported by anything and yet does not move, seem to me to be making the mistake of judging on the basis of their own experience instead of taking into account the peculiar nature of the universe," wrote Ptolemy.
Ptolemy tapped into the belief systems of the time. No one expected the heavens to play by the same rules as Earth. After all, the heavens were the domain of gods, goddesses, and forces that controlled lives and fates. Even though it was awkwardly complicated, the Ptolemaic system was popular for 15 centuries, or 1,500 years.
ALLAH'S PATH OF UNDERSTANDING
Ptolemy's ideas went far beyond Greece. He worked in the Egyptian city of Alexandria. Islamic and European astronomers through the 16th century accepted his theories as fact. The name of his book, The Almagest, is not even a Greek word. It comes from the Arabic name al-majisti, which means "the greatest." Ninth-century Arab translations of Ptolemy's book fueled Islamic astronomy. Meanwhile, The Almagest remained lost to Europe until the Dark Ages ended.
activity
Ptolemy on a Plate
Ptolemy's invention of epicycles made his Earth-centered system seem to work. Epicycles are the mini-orbits that the "planets" (not Earth) make around an invisible point as they circle Earth in orbits called deferents.
This system of epicycles within deferents is complicated. But it seemed right because it matched the observable movements of the planets in the night sky. The theory wrongly accounted for why Mars moves backward in retrograde or why Jupiter moves slower or faster depending on the time of year.
In this activity, you'll see for yourself how Ptolemy's grand illusion matched these variations in the night sky.
YOU'LL NEED
* Poster board, index card, or heavy paper
* Ruler
* Scissors
* Markers or colored pencils
* Small balls (optional)
* Glue (optional)
* 2 paper plates, one large and one small, or one large and one small circle of cardboard
* 2 brads (paper fasteners)
* Liquid correction fluid (optional)
1. Cut out a small circle from an index card or heavy paper about 2 inches (5 cm) in diameter. This circle represents an epicycle. Draw a red circle on its edge to represent Mars. If you're using the small balls, glue a small red ball near the edge of the circle. Label it Mars.
2. If your two plates are the same size, cut one down to make it slightly smaller than the other plate. Set the 2-inch-wide circle (5 cm) near the edge of the smaller plate. Push a brad through both plates and fold it back to attach them. Make sure it turns freely. This spinning circle is the epicycle on the edge of the deferent. (You can use liquid correction fluid to blot out the epicycle's fastener. It's an invisible point.)
3. The small plate is the deferent, Mars's orbit around Earth. Turn the large plate over, center the smaller plate on top of it, and push a brad through to attach them. Make sure it turns freely. The paper fastener in the center is Earth. Draw a little blue circle around it or glue down a blue ball. Label it Earth.
4. Put Ptolemy's universe into motion! Turn the larger deferent circle while simultaneously turning the epicycle. Think about being on Earth and how Mars would move in the night sky over time. Use a ruler or pencil to create a line of sight between Earth and Mars at different positions of the deferent's and epicycle's orbits.
One of the most important astronomers of this time was Abd al-Rahman al-Sufi. The Persian scientist spent years updating Ptolemy's star list for his own Book of Fixed Stars. Al-Sufi's star catalog named the stars differently than Ptolemy. The Greeks based star names on their constellations. An individual star might be referred to as "the top right star in constellation Lyra." Al-Sufi called this star Vega, giving each star its own Arabic name, separate from its constellation.
Abd al-Rahman al-Sufi (AD 903–986)
Isfahan, Persia, where al-Sufi lived his life, is today part of Iran. The Persian astronomer was known in Europe as Azophi, and his star map was used there for centuries. In his famous Book of Fixed Stars, the scientist cataloged 1,018 stars according to their brightness, positions, and colors.
Al-Sufi also recorded the first celestial object outside our galaxy in the book. Al-Sufi described and drew what we today know is the Andromeda galaxy. He called it "a little cloud" lying before the mouth of an Arabic constellation named the Big Fish.
Al-Sufi used a tool called an astrolabe to locate stars and other celestial objects. The instrument has movable parts to set the time and date and gives the observer a picture of how the sky looks at his or her latitude. Al-Sufi wrote about the many possible uses of the astrolabe, including timekeeping and navigation.
Many star names we use today are Arabic — Rigel, Fomalhaut, Aldebraran — and most can be traced back to al-Sufi's book. One of the most unusual names is Betelgeuse, the reddish star in constellation Orion. Its original Arabic name was likely Yad al-Jauza, but it got miscopied and repeatedly changed as it was translated from Arabic script to Medieval Latin and then to Italian and German.
Al-Sufi and the other Islamic astronomers believed they were fulfilling their creator's wishes. The Muslim holy book, the Qur'an, encourages exploring the universe, saying: "In the creation of the heavens and the earth ... there are indeed signs for men of understanding." Apparently those signs did not include questioning the Ptolemaic system. Al-Sufi accepted that an unmoving Earth was at the universe's center because it meshed with Muslim beliefs. The Qur'an also states, "It is not for the Sun to overtake the Moon. ... They all float, each in an orbit." It would be another five centuries before the Sun found its way to the center of things.
COPERNICAN REVOLUTION
News of Christopher Columbus landing on a continent unknown to Europe spread quickly — at least by 1492 standards. Nicolaus Copernicus was among the University of Kraków students amazed by the historic voyage. Europe's idea of the world was changing. But Copernicus would change the world's view of the universe itself.
Copernicus caught the astronomy bug while studying in Poland. He left to study church law in Italy but was lucky enough to get lodgings with the astronomy professor there. Astronomy was never Copernicus's profession, but it was his lifelong obsession. His day job was being a church business manager, called a canon, in a small town on the Baltic Sea. "This very remote corner of the Earth," is what Copernicus called what is today Frombork, Poland. Copernicus filled his free time with stargazing — and lots of reading.
Copernicus studied the texts of Ptolemy's ancient geocentric system. He read what the great thinkers and philosophers had written about it. Over the centuries, they'd added odd bits and pieces to the Ptolemaic system in order to get it to match what they saw in the night sky. All of the ridiculously complicated circles inside orbits within spheres troubled Copernicus. All the added-on circles and adjusted orbits needed to explain the Earth-centered system were to him like putting together a person from random feet, hands, and a head. "Since these fragments would not belong to one another at all, a monster rather than a man would be put together from them," Copernicus wrote. Why create a Frankenstein if you don't need to? For Copernicus, the question of how celestial objects moved could be simply explained by putting the Sun in the center, with all of the planets — including a spinning Earth — orbiting around it.
activityMake an Astrolabe
Astrolabe means "star-taker," as in taking the measurement of the stars. It's an ancient instrument that measures the angles of space objects such as stars and planets above the horizon.
Take your own star measurements after making this simple astrolabe.
YOU'LL NEED
* String or heavy thread, 12 inches (30 cm) long * Metal washer, bolt, or other weight * Protractor, 6 inches (15 cm) with hole at the center * Wide drinking straw * Heavy tape
1. Tie a washer or other weight to one end of the string.
2. Attach the other end of the string to the hole in the middle of the protractor's straight edge. Knot the string at the back of the protractor to hold it in the hole. If the hole is big, a bit of tape can help. Hold up the protractor, ruler side on top, and check that the string swings freely along the printed side of the protractor.
3. Set the straw against the ruler edge of the protractor and secure it there with tape. Your astrolabe is ready!
4. Test it out by using it to find your latitude. Find Polaris (see page 3) and then look at it through the straw. Note what degree the string lines up with on the protractor. (Your eye is at 0°.) Subtract that zenith angle from 90° to get your latitude. For example, if your astrolabe reads 42° with Polaris sighted (at zenith), then 90° – 42° = 48°.
5. Use your astrolabe to measure the latitude of the moon, planets, and stars. Make sure to write down the date and time with your measurements.
(Continues...)
Excerpted from Beyond The Solar System by Mary Kay Carson. Copyright © 2013 Mary Kay Carson. Excerpted by permission of Chicago Review Press Incorporated.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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