Required Reading
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As incredible as it might sound, astronomy covers objects spanning sizes from the nucleus of an atom to the farthest reaches of the visible universe: from less than 1 picometer (10–12 meter), to 1026 meters, or equal to a full range of 38 powers of ten. Lesson One covers the major structures of the Universe and the basics of observing the night sky, including the vocabulary, and concludes with brief overview of the history of astronomy.
After completing this lesson, you should be able to
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The prologue section of the text gives an introduction to the nature of astronomy and the nature of science. Let's combine this to the "science of astronomy." Astronomers are rarely, if ever, concerned with naming stars, as the title literally means. Astronomy today is applying the physics we know and understand here on Earth to the Universe in general. Except for the most extreme cases (space and time around black holes and at speeds approaching that of light), the physics of Sir Isaac Newton suits us just fine. We use concepts such as the conservation of angular momentum (the reason an ice skater speeds up as she pulls in her arms) and the conservation of energy (why you break a bone when you fall off a tall ladder) to explain how the Milky Way galaxy formed a disk of stars and why the interior of the Sun gets so hot that fusion starts. It is amazing that it all works and it is all tied together.
At the introductory level, it would not be prudent to start talking in detail about nebulae, supergiant stars, and even black holes if you haven't been taught where to look for some of these objects in the sky. It is one thing to read about the Ring Nebula and know that our Sun will soon resemble this remnant of a star that was once much like our Sun; it is quite another thing to peer at a white, hazy, donut-looking object in the telescope and think, "Wow! I know what you are! I know where you came from and what you will become." So, although much of the professional field of astronomy is involved in digital processing, mathematical analysis, and the writing of grant proposals, as beginning amateur astronomers we can start with the "frosting" and build our appreciation of the physics step-by-step.
As you will soon note from the text, astronomy and astrology parted ways hundreds of years ago. You will not learn to cast horoscopes in this class, nor will you learn to be a storyteller of mythological creatures or gods banished forever to the starry realm. You will not need to memorize the names of stars, nor the locations of constellations and what they mean. These areas (except for the horoscopes) will come as a natural part of your increasing interest in your cosmos and how it all works.
One of the common areas of confusion for students is the distinction among the "levels" of the Universe. Many students confuse the solar system with the universe, thinking that there are multiple stars, other galaxies, even quasars in our solar system. Answers are marked wrong because universe is put down when solar system is meant, or vice versa. Perhaps this is oversight and inattention, but let's make absolutely sure we can identify each level as we move from North America to the edge of the visible universe.
Contrary to what we would like to believe, we are not the center of the Universe. What if we were to jump aboard a spaceship that could travel at unlimited speeds? What would we see? As you go through the following slideshow, pretend you are looking out the rear window and visualize your trip away from the planet Earth. Each step is many powers of ten greater than the one preceding it.
Your TurnNow that you've traveled to the edge of the Universe, address a postcard home. Don't forget to put down the complete cosmic address!Check your answer here. |
Slideshow: Levels of the Universe
Can we pull so far away that eventually we reach the very edge of the Universe?
We look up at the stars on a clear night, and they look like sparkling gems on an inverted crystalline bowl. From the northern hemisphere, we are assured that when we look to the north, we will always see the Big Dipper (which is, technically, an "asterism"; the constellation is Ursa Majoris). We probably know and recognize the constellation Orion because of its prominence in the sky; but do we know exactly when to look? In what season does it appear? Why are some constellations always seen, and others only periodically?
For ancient people, the motions of the sky and the seasons on the Earth were intimately related. The appearance at midnight of Sirius, the Dog Star, heralded the coming of winter; Arcturus signaled winter's end. In the glare of today's light pollution, we have lost that intuitive sense of our place in the Universe. To stand back and imagine the grander architecture of the cosmos often takes an almost impossibly difficult level of abstraction.
As you read Chapter 1, in your text, try to move your mind from the images in the text to the real night sky. On a clear night, go out and look for the North Star, Polaris, and recognize it as lying close to the north celestial pole. Imagine you are able to walk directly to the North Pole on Earth. Where would Polaris be then, and how would its position in the sky change during your journey?
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Classically, there were only 48 constellations, formed from the brightest stars in the sky, and located mostly in the northern hemisphere. We believe they were named by peoples of the Middle East thousands of years ago, but we have lost much of the history of these constellations with the passage of time. The names of the constellations passed on to the Greeks and the Romans; but not all astronomers resided in that part of the world. Ancient astronomers from all lands named distinct patterns in the sky after important parts of their culture. The constellations represented animals, gods, or tools of daily living, and did not necessarily have to actually look like that person or object. To the Greeks, the pattern making up Cassiopeia represented the Queen on her throne; to Pacific Northwest native peoples, the pattern represented an elk skin; to fourth graders at a summer camp at the Pacific Science Center, in Seattle, the pattern represented McDonald's golden arches; to Husky fans at the University of Washington, it is the "Big W" in the sky.
The ancient or classical constellations are human-made patterns imposed on groupings of stars in the sky. They represented items that were important in each culture, and did not necessarily always look like the object they were named after. As mentioned in your textbook, today constellations represent distinct segments of the sky, 88 in all, much like counties represent parts of states, or states part of our country. Astronomers use these constellations as we would use an atlas to locate stars, nebulae, galaxies, and other celestial objects. For example, under the Bayer system for naming stars, each star is given a Greek designation (roughly in order of brightness) along with the name of the constellation. The brightest stars in a constellation thus get named alpha, beta, gamma, delta, and so on, plus the possessive form of the name of the constellation in Latin. For Orion, Betelgeuse is alpha Orionis; Rigel is beta Orionis; Bellatrix is gamma Orionis; and Mintaka is delta Orionis. The spiral galaxy also known as Messier 31 is found in the constellation of Andromeda, and thus is called the Andromeda Galaxy.
The naked eye can see stars down to about 6th magnitude. Binoculars can take us down a couple more magnitudes; a good 8-inch telescope down to 13th magnitude (or more than 100 times fainter than the naked eye). "Deep sky objects" include nebulae (interstellar gas, star-forming regions, star-death remnants) and galaxies, even a few relatively "nearby" quasars. The following thumbnails show a variety of objects that can be termed deep sky. All are found in our galaxy, except one.
Examine each of the following objects. These are just a representative sample of things in our galaxy that we will be studying in this course. As you look at the pictures, do you see individual stars? Do you see anything that looks like substructure: streaks, arms, openings, dark clouds? Guess what each object might be. After examining each image, click on it to find out more.
Number |
Image
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Object Name |
| 1 |  |
Eta Carinae |
| 2 |  |
Horsehead Nebula |
| 3 |  |
47 Tucanae |
| 4 |  |
Orion Nebula |
| 5 |  |
Ring Nebula |
| 6 |  |
Sol |
| 7 |  |
Bubble Nebula |
| 8 |  |
Crab nebula |
| 9 |  |
h & chi Persei |
| 10 |  |
Eclipse |
| (Images Copyright National Optical Astronomy Observatory/Association of Universities for Research in Astronomy/National Science Foundation (NOAO/AURA/NSF). See list at end of lesson for individual image credits.) | ||
For images and a plethora of information of over one hundred famous, deep sky objects (many in glorious color!), you should take a look at the Messier Catalog put together by SEDS: Students for the Exploration and Development of Space (hosted by the Lunar and Planetary Laboratory and the University of Arizona).
Sometime between 12 and 15 billion years ago, there was an occasion to celebrate: the Humongous Space Kablooie (a name coined by Calvin of "Calvin and Hobbes" fame; also known as the Big Bang). The Universe was incredibly hot and dense. Matter and antimatter were being created out of pure energy, and then annihilating each other and producing energy. As the Universe expanded over the next 100,000 years or so, it cooled, and there was a period when protons, neutrons, and electrons formed. This period was followed by the period of nucleosynthesis where the fusion of hydrogen nuclei (protons) formed helium and trace amounts of deuterium, lithium, and boron.
As the Universe continued to expand, it cooled to below the temperatures needed for fusion. Atoms formed as the nuclei captured electrons, and radiation and matter went their separate ways—this era is known as decoupling. The Universe is still bathed in the radiation from its violent beginning—radiation known as the Cosmic Background Radiation. Disconnect your cable, and turn on your TV set to a channel with no signal; one percent of the static you hear comes from the birth of the Universe.
Although this background radiation appears to be uniform in every direction, there are miniscule but significant differences in temperatures. These differences must trace regions where the temperature of the Universe was lower and thus the density was slightly higher. From these regions, stars and galaxies formed; structure became apparent; massive stars, made only of hydrogen and helium, were born and cooked heavier elements in their cores: carbon, nitrogen, oxygen, neon, magnesium, silicon, iron. These stars exploded magnificently, spraying their innards back into the interstellar region, where, millions of years later, the material would cool, clump, and new stars would form.
Run the clock forward about 10 billion years, and we see our Sun forming from a galactic cloud enriched with heavy elements: not only those mentioned already, but aluminum, lead, copper, nickel, uranium, gold, and silver as well. How many massive star explosions had to happen before the material was gathered together and collapsed into our Sun, its planets, us?
As we look out in space with ever more powerful telescopes, we look back in time. As we look beyond the Local Group we notice something amazing: everything is expanding away from us! The farther away we look, the faster the galaxies are receding! Our conclusion: the Universe is still expanding.
For this introductory course in astronomy, you will find that you have more than enough to study and learn about this quarter with our covering just our solar neighborhood of stars and the contents of our galaxy, The Milky Way. However, there is a whole universe out there, and the distances to objects within it are truly unfathomable! But, being the astute students we are, we are going to try.
Visit the following web site (and some related links as necessary) and answer the questions that follow. This is not to be turned in; it is just for your educational enjoyment!
Visit http://hometown.aol.com/nlpjp/cosmo.htm and gather the information needed to answer the following questions (click on the "cosmology" link):
Your TurnVocabulary of Astronomy Review |
Think you have a basic grasp of the vocabulary used in describing the sky? Try this simple review of the vocabulary of astronomy. If you have trouble with most of the words and concepts, then more review is called for.
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