Day 3 | Day 4 | Day 5 |
Reading Assignment 2
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What is the shape of our galaxy? |
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Read this standardized test practice passage and answer the questions.
You have seven minutes to complete the assignment. |
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Astronomer |
The physical sciences seek to understand matter and its relationship with energy. Understanding matter and energy is sometimes difficult, but most of the time we have concrete data to work with. To answer questions like "where does matter come from?" and "how was the earth made?" are much harder to answer. There is very little direct data available to answer questions like these. The best we can do is rely on current scientific "theories". To make things even harder, there are several theories for many of these questions.
As a science student, it is your responsibility to examine conflicting theories, compare the data supporting each theory, and make you own decision about which seems more credible. |
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Your assignments for the next few days ask you to write paragraphs. Since you are asked to write less than three paragraphs, these assignments are not essays. A paragraph can only contain one topic, so you must construct them carefully. Remember, good paragraphs begin with a topic sentence. Each assignment is expected to be made up of your own words. Do not "cut and paste" from a research reference. Never lose sight of the fact that your purpose is to convey information and your ideas about that information. |
Astronomers and cosmologists usually specialize in physics, but they must be experienced in geology and chemistry as well. The universal abundance of the chemical elements is one of five fundamental pieces of evidence supporting the cosmological model of the Big Bang Theory. 
Each element has a characteristic spectroscopic "signature", a complex pattern of wavelengths of light emitted when the element is excited. These patterns can be seen in light from stars and other astronomical objects. By comparing their relative brightness, scientists have estimated that the universe is nearly 75% hydrogen and nearly 25% helium. Only 1 to 2 percent is made up of all the other elements together.
The Universe has been expanding since the time of the Big Bang, spreading the available energies over greater distances. Don't think of the Big Bang as an explosion that sent bits of the cosmos in all directions into a preexisting space. A more accurate model is an expanding balloon. If you think of space as the surface of the balloon, and the galaxies as dots of ink on that surface, the recession of the galaxies (moving away from one another) is due to the expansion of space, not the distribution of debris through space.
The table below is based on a combination of today's best theories about the life of the Universe. The table assumes maximum concentrations of energies at the point of the Big Bang.
| ERAS OF OUR UNIVERSE | ||
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| Era | Time After The Big Bang |
Particles and Forces Formed |
| Chemical | 10 to 20 Billion years | enriched stars, planets, molecules, life |
| Galactic | 5 Billion years | supernovas, heavy atoms galaxies, quasars, stars light atoms, free photons |
| Nuclear | 300,000 years | light nuclei (helium, etc.), plasma |
| Hadron | 3 minutes | hadrons, electrons, neutrinos, electromagnetic force |
| Quark | 1 X 10 -10 seconds | quarks, leptons, weak force |
| GUT (Grand Unified Theories) |
1 X 10 -34 seconds | space, time, gravity, fermionic force, bosonic force |
| Planck | 1 X 10 -43 seconds | pregeometry (superstrings)
quantum physics  begins to work |
| Big Bang | ||
The Universe includes all the stars 
galaxies and material between them. As the galaxy rotates, the Sun completes a circuit of the galaxy about every 240 million years. Obviously, the Milky Way Galaxy covers an enormous amount of space. Since galaxies are so large, how many can there possible be?
This picture 
was taken with the Hubble telescope. The bright white object below and to the left of the center is a star in our galaxy. All other objects in the picture are galaxies! If a dime is held 75 feet in front of your eyes, the dime would cover the area of the sky in this picture.
This assignment must be turned in by the end of class today to receive credit.
Scoring criteriaOne theory about the beginning of the Universe is called the Big Bang Theory.
- Write a paragraph detailing what the Big Bang theory says about the future of the Universe.
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What conditions are needed to form elements heavier than iron? |
(18 min)
Our Sun is one of about 1 X 1011 (100 billion) stars located in the rotating, spiral-shaped galaxy we call the Milky Way. The Sun contains more than 99.8% of the total mass of our solar system, which is located about two thirds of the way out on one of the arms of the galaxy, about 30,000 light years from the center.
Life Cycles of Stars:
A star's life cycle is determined by its mass. The larger its mass, the shorter its life cycle. A star's mass is determined by the amount of matter available in the giant cloud of gas and dust, nebula, from which forms. Stage 1 Dust and gas is pulled together by gravity to form a protostar inside a nebula. This gravitational contraction causes heating as potential energy is converted to kinetic energy. The picture above shows stars beginning to form at the edges of a nebula.Stage 2 When the star is hot enough,15,000,000 oC, nuclear fusion (converting hydrogen to helium) starts in the core of the newly formed star, and it begins to emit light and heat. The star becomes a main sequence star.Stage 3 After many millions of years, the main sequence star runs out of hydrogen in its core. The core becomes unstable and contracts, while the outer shell of the star, which is still mostly hydrogen, starts to expand. As it expands, it cools and glows red. The star has now become a red giant. Stage 4 has two possibilities depending on mass: Stage 4 (low mass stars) The star will contract, becoming a white dwarf, which slowly cools, changing color as it does, until it can no longer be seen, a black dwarf.Stage 4 (high mass stars) Massive stars may glow brightly again as they undergo further fusion reactions, expanding and contracting several times and forming the nuclei of heavier elements before becoming a supernova. |
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Creation of Heavy Elements:
Once stars that are several times more massive than our Sun reach the red giant phase, their core temperature increases as carbon atoms are formed from the fusion of helium atoms. Gravity continues to pull carbon atoms together as the temperature increases and additional fusion produces elements from nitrogen to iron. Fusion in the core of a red giant star ceases when the core is mostly iron. Since energy is no longer being released from the core, the star begins the final phase of gravitational collapse. The core temperature rises to over 100 billion degrees as gravity crushes the iron atoms together. The repulsive force between the nuclei overcomes the force of gravity, and the core recoils out from the center in an shock wave called a supernova explosion. As this energy encounters material in the star's outer layers, the material is heated, fusing to form heavier elements and radioactive isotopes.
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Study this timeline of mankind's facination with the heavens. The telescope was the first invention to improve our observations. Today, devices like the Hubble telescope and probessent to other planets help us better understand the universe. But most of our scientific data about stars and other planets is still "indirect" and open to interpretation. There are many theories about the universe based on these indirect observations.
Astronomy: study of objects in the universe.
Cosmology: study of the universe as a whole.
(27 min)
Patterns in the stars as seen from the Earth are called constellations. In 1922, the International Astronomical Union (IAU) officially adopted the list of 88 constellations that we use today. Definitive boundaries between constellations, which extend out beyond the star figures, were set in 1930, so that every star, nebula, or galaxy, no matter how faint, now lies within the limits of one constellation. For today's astronomer, constellations refer not so much to the patterns of stars, but to precisely defined areas of the sky.
The constellations in the diagram above represent the signs of the zodiac. These particular constellations are used in astrology, which is something less than an exact science. Different constellations are visible in different places in the sky as the Earth moves around the sun. Star charts 
may be used to locate the constellations.
Constellation identification:
Orion
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Ursa Major
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Sagittarius
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Cygnus
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Cassiopeia
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Leo
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Taurus
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This assignment must be turned in by the end of class today to receive credit.
Scoring criteria
- In many science fiction stories, the aliens have machines that are made out of wonderful elements that we don't have on Earth. Based on what you have learned about the way elements form, write a paragraph giving your ideas about the possibility of these "alien elements".
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What causes Earth's seasons? |
(15 min)
The apparent path of the Sun in the sky is known as the ecliptic and is actually the intersection of the plane of the Earth's orbit with the celestial sphere. Because the rotation axis of the Earth (which defines the celestial sphere) is tilted at an angle of 23.5o with respect to the plane of the Earth's orbit, the ecliptic is inclined at an angle to the celestial equator, as shown in the diagram.
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The ecliptic and the equator intercept at two points:
The spring or vernal equinox: This point is defined as the point where the Sun, moving along the ecliptic, crosses the celestial equator from south to north. Occuring on March 21, when day and night are of equal length, this marks the beginning of spring. The altitude of the Sun in the sky increases from the spring equinox to a maximum (farthest North) on June 21 - the summer solstice - marking the beginning of summer.The fall or autumnal equinox: This point is defined as the point where the Sun, moving along the ecliptic, crosses the celestrial equator from north to south. Occuring on September 21, when day and night are again of equal length, this marks the beginning of fall. The altitude of the Sun in the sky decreases from the autumnal equinox to a minimum (farthest South) on December 21 - the winter solstice - marking the beginning of winter. |
Distance Radius Mass Name Orbits (000 km) (km) (kg) --------- ------- -------- ------- ------- Sun 697000 1.99 x 1030 Jupiter Sun 778000 71492 1.90 x 1027 Saturn Sun 1429000 60268 5.69 x 1026 Uranus Sun 2870990 25559 8.69 x 1025 Neptune Sun 4504300 24764 1.02 x 1026 Earth Sun 149600 6378 5.98 x 1024 Venus Sun 108200 6052 4.87 x 1024 Mars Sun 227940 3398 6.42 x 1023 Ganymede Jupiter 1070 2631 1.48 x 1023 Titan Saturn 1222 2575 1.35 x 1023 Mercury Sun 57910 2439 3.30 x 1023 Callisto Jupiter 1883 2400 1.08 x 1023 Io Jupiter 422 1815 8.93 x 1022 Moon Earth 384 1738 7.35 x 1022 Europa Jupiter 671 1569 4.80 x 1022 Triton Neptune 355 1353 2.14 x 1022 Pluto Sun 5913520 1160 1.32 x 1022 |
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This assignment must be turned in by the end of class today to receive credit.
Scoring criteria
- Show the calculation of the density of Jupiter in kilograms per cubic kilometer.
Research links:
Our galaxy has a spiral shape.
The unstable conditions of a supernova explosion are required to form elements heavier than iron.
Earth is located near the end of an arm at the outer edge of the Milky Way galaxy.
While many of the lighter elements are made by nuclear fusion in the cores of stars, it takes the unstable conditions of a supernova explosion to form elements heavier than iron.
