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«1. Define and describe “galaxy”.

a. A is a very large cluster of stars (tens of millions to trillions of stars) gravitationally bound together.
b. There are billions of galaxies in the observable .
c. The various types of galaxies include:

* galaxies, which are typically disk-shaped with a somewhat greater concentration of stars near their centers, often containing arms of stars extending from their central nucleus
*Barred spiral galaxies, a type of spiral galaxy that has the stars arranged in the shape of a , which rotates as a rigid system
*Elliptical galaxies, the most abundant type, which have an shape that ranges to nearly spherical, and lack spiral arms
*Irregular galaxies, which lack symmetry and account for only 10 percent of the known .

d. Galaxies are not randomly distributed throughout the . They are grouped in galactic clusters, some containing thousands of galaxies. Our own, called the Local , contains at least 28 galaxies.

«2. Locate the Sun’s position in the Milky Way Galaxy.

a. The Sun is one of the 200 billion that make up the Milky Way galaxy.
b. The Milky Way galaxy is a large, disk-shaped, galaxy about 100,000 light-years wide and about 10,000 light-years thick at the center (central “bulge”).
c. There are three distinct spiral of stars.
d. The is positioned in one of these arms about two-thirds of the way from the galactic center, at a distance of about 30,000 light-years.
e. Scientists suspect that a super massive – an immensely dense area of space that sucks up matter and light – lies at the galaxy’s center
f. It takes about 200 million years for the to revolve around the galactic center.
g. Surrounding the galactic disk is a nearly spherical halo made of gas and numerous globular clusters (nearly spherically shaped groups of densely packed ).
h. We see the as a bright band of stars across the sky. It looks like spilled milk!
i. Most of the points of light in the night sky are in the Milky Way

SECTION 2 SLIDES (Question 1) (Question 2) (Question 3) (Question 4) (Question 5) (Question 6) (Question 7) (Question 8) (Question 9) (Question 10)

«3. Understand why light years are used to measure distances in space.

a. A light-year is a unit of (NOT TIME!!!). It is the distance that can travel in one year.
b. Light moves at a velocity of about 300,000 km each (in a vacuum). So in one year, it can travel about 10 trillion km. More precisely, one light-year is equal to 9,460,500,000,000 kilometers (5,880,000,000,000 miles).
c. Why would you want such a big unit of distance? In the Universe, the kilometer is just too to be useful. For example, the distance to the next nearest big galaxy, the Andromeda Galaxy, is 21 quintillion km. That is 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance.
d. In our solar system, we tend to describe distances in terms of the (AU). The AU is defined as the average distance between the Earth and the . It is approximately 150 million km (93 million miles). Mercury can be said to be about 1/3 of an AU from the Sun and Pluto averages about 40 AU from the Sun. The AU, however, is not big enough of a unit when we start talking about distances to objects outside our .
e. For distances to other parts of the Milky Way Galaxy (or even further), astronomers use the . Using the light-year, we can say that:

*The Milky Way Galaxy is about 150,000 light-years across.
*The Andromeda Galaxy (one of our nearest neighboring galaxies) is 2.3 million light-years away.
*Proxima Centauri, the star, is 4.24 light years away.
*Sirius the “dog star” (the brightest star in the sky) is 8.6 light years away.
*Center of the galaxy is approximately 30,000 light years away.
*The most distant observed are more than 12 billion light years away.

f. Light minute- the distance light travels in a vacuum in one , approximately 18 million kilometers. The Sun is 8.3 light-minutes away.
g. Light second- the distance light travels in a vacuum in one , approximately 300,000 kilometers. The Moon is about 1.3 light-seconds away.
h. When we look up, we see the Moon and sun, not as they are now, but as they 1.3 seconds and 8.3 minutes ago.
i. Since it takes light to reach us, the further out we look into space, the farther we see into time.

(Question 1) (Question 2)

«4. Explain the composition of the Sun and other stars and the process of fusion.

a. The Sun is actually a of about medium size. It appears larger than the other stars because it is closer to the earth.
b. By mass, the Sun is 73% and 25% .
c. The can be divided into four parts 1) the solar interior, 2) the photosphere (visible surface), and the two layers of its atmosphere, 3) the chromosphere and 4) corona.
d. The photosphere radiates most of the we see. Unlike most surfaces, it consists of a layer of glowing gas less than 500 kilometers (300 miles) thick with a grainy texture consisting of numerous, relatively small, bright markings called granules.
e. Just above the lies the chromosphere, a relatively thin layer of hot, glowing gases a few thousand kilometers thick.
f. At the edge of the uppermost portion of the solar atmosphere, called the corona, gases (mostly protons and electrons; plasma) escape the pull of the Sun and stream toward Earth at high speeds producing the solar .
g. Numerous features have been identified on the active Sun. are dark blemishes with a black center, the umbra, which is rimmed by a lighter region, the penumbra. The number of sunspots observable on the solar disk varies in an 11-year . Sunspots are dark because they are than the surrounding areas.
h. Prominences, huge cloudlike structures best observed when they are on the edge, or limb, of the Sun, are produced by gases trapped by fields that extend from regions of intense solar activity.
i. The most explosive events associated with sunspots are solar flares. Flares are brief outbursts that release enormous quantities of energy that appear as a sudden brightening of the region above sunspot clusters. During the event, radiation and fast-moving atomic particles are ejected, causing the wind to intensify. When the ejected particles reach and disturb the atmosphere, radio communication is disrupted and the auroras, also called the northern and southern lights, occur.
j. The source of the Sun's energy is nuclear . Deep in the solar interior, at a temperature of 15 million K, nuclear fusion converts four atoms into one atom. During the reaction some of the matter is converted to the of the Sun. (The weight of four hydrogen atoms is slightly than the weight of one helium atom. This “missing weight” is converted to , making the Sun shine!)
k. A the size of the Sun can exist in its present stable state for 10 billion years. Since the Sun is already 4.6 billion years old, it is a "middle-aged" star.

SECTION 4 SLIDES (Question 1) (Question 2) (Question 3) (Question 4) (Question 5)

«5. Explain the how stars are plotted on the Temperature/ Luminosity Diagram (H-R Diagram).

a. This diagram (ESRT p.15) is a graph of stars plotted with and along the vertical axis and (decreasing) and along the horizontal axis.
b. Its real name is the (Hertzsprung-Russell) Diagram.
c. The differ from each other in size, temperature, and age.
d. Luminosity =
e. The has a luminosity of 1. A star with a luminosity of 100 is times brighter than the Sun, etc.
f. More stars are usually brighter.
g. Hot stars are . Cool stars are .
h. Typically, as a star gets hotter, it gets . These stars are the stars.
i. A is a cool star, but it is bright because it is so big.
j. A is a hot star, but it is dim because it is small.
k. The Sun is an size star. It is located near the of the graph. Its surface is 5,500°C, which makes it .
l. Plotting stars on this graph causes certain types and ages of to cluster together.

SECTION 5 SLIDES (Question 1) (Question 2) (Question 3) (Question 4) (Question 5) (Question 6) (Question 7) (Question 8) (Question 9) (Question 10) (Question 11) (Question 12) (Question 13) (Question 14) (Question 15) (Question 16) (Question 17) (Question 18) (Question 19)

«6. Describe the evolution of the Sun and different kinds of stars.

a. A typical star (one like the Sun) lives (produces nuclear energy) for about 10 billion years. This incredible length of time is greater than 100 million lifetimes.
b. A of dust in space (a nebula) begins to contract due to .
c. As it contracts, pressure and temperature inside this “protostar.”
d. When the temperature gets hot enough, begins, and a main sequence star is born.
e. A star loses during fusion as energy is released. This decreases the star’s gravity.
f. A star will expand, becoming a red giant, when the outward force of is greater than the inward force of .
g. As fuel runs out in a star, fusion slows down. When the force of fusion is less than the force of gravity, the star will shrink in size, becoming a white .
h. A star like the Sun will run out of fuel, and die, becoming a dwarf.
i. - An explosion that marks the end of a very massive star's life. When it occurs, the exploding star can outshine all of the other stars in the galaxy in total for several days and may leave behind only a crushed core (perhaps a neutron star or black hole). All of the heavy (heavier than iron) were created in supernova explosions.
j. A larger, more massive star will collapse violently, becoming a star.
k. star- an imploded core of an exploded star made up almost entirely of neutrons. A teaspoonful of their material would weigh more than all the automobiles in the United States put together.
l. The largest stars collapse so violently that they become .
m. - the remains of the death and collapse of an extremely massive star. The pull of a black hole is so strong that light itself cannot .

«7. Explain why larger/hotter stars burn their fuel faster and live shorter lives than the Sun.

a. Large, more massive stars have much more than the sun.
b. The great internal pressures, due to the higher gravity, cause the fusion reaction to occur more .
c. This causes the largest stars to burn their fuel, and eventually run out, much more .
d. Larger stars live shorter .
e. Bigger stars are brighter and hotter due to the rapid rate of .

SECTION 7 SLIDES (Question 1)(Question 2) (Question 2 pic BIG) (Question 3)

«8. Explain why stars are considered to be “factories” which create elements needed for future stellar generation.

a. Stars of all masses spend the majority of their lives their lives fusing into : we call this stage the main sequence.
b. When all of the in the central regions of a star is converted into helium, the star will begin to "burn" helium into carbon.
c. However, the helium in the stellar core will eventually run out as well; so in order to survive, a star must be enough to fuse increasingly heavier elements, as the lighter ones become used up one by one.
d. Stars heavier than about 5 times the mass of the can do this with no problem: they burn hydrogen, and then helium, and then carbon, oxygen, silicon, and so on... until they attempt to fuse iron.
e. Iron is special in that it is the lightest element in the periodic table that doesn't release when you attempt to fuse it together. In fact, instead of giving you energy, you end up with less energy than you started with! This means that instead of generating additional pressure to hold up the now extended outer layers of the aging star, the iron fusion actually takes thermal energy from the stellar core. Thus, there is nothing left to combat the ever-present force of from these outer layers. The result: collapse!
f. The lack of outward pressure generated by the iron-fusing core causes the outer layers to fall towards the of the star. This implosion happens very, very quickly: it takes about 15 seconds to complete. During the collapse, the nuclei in the outer parts of the star are pushed very close together, so close that elements heavier than are formed.

«9. Explain the importance of the electromagnetic spectrum in identifying some objects in the universe.

a. We have only recently been able to look at the over the entire electromagnetic spectrum. Our Universe contains objects that produce a vast range of radiation with either too short or too long for our eyes to see.
b. Some astronomical objects emit mostly infrared radiation, others mostly visible light, and still others mostly ultraviolet radiation. determines the type of electromagnetic radiation emitted by astronomical objects.
c. Type of radiation radiated by objects and typical sources:

*Gamma-rays: accretion disks around holes
*X-rays: gas in clusters of galaxies; supernova remnants; stellar corona
*Ultraviolet: supernova remnants; very hot stars
*Visible: planets, stars, some satellites
*Infrared: cool clouds of dust and gas; planets
*Microwaves: Sun, comets, planets, molecular clouds, galaxies, quasars and the cosmic radiation
*Radio: radio emission produced by electrons moving in magnetic fields

SECTION 9 SLIDES (Question 1) (Question 2) (Question 3) (Question 4) (Question 5) (Question 6) (Question 7) (Question 8) (Question 9) (Question 10) (Question 11) (Question 12) (Question 13) (Question 14) (Question 15)

«10. Describe the Big Bang theory of the origin of the universe.

a. The Big Bang Theory is the leading scientific theory about the of the universe.
b. According to the Big Bang, the universe was created around 15 years ago from a cosmic explosion that hurled matter and energy in all directions.
c. The universe was originally a single tiny dense sphere of that exploded into a gigantic expanding cloud that eventually condensed into separate galaxies.
d. After the Big Bang, matter, energy, and time came into being.
e. By "running the film backward'' (theorizing the galaxies' motions backward in time) astronomers can estimate when the universe was .

«11. Explain how red shift (the Doppler Effect) and background radiation are evidence for an expanding universe.

a. The Big Bang was initially suggested because it explains why distant are traveling away from us at great speeds.
b. - the lengthening (or "stretching") of light waves coming from a source moving away from us.
c. If a source of light is moving toward us, the opposite effect — called a " Shift"— takes place.
d. Light from galaxies outside our Local Group is "red-shifted," indicating that they are moving away from us (and from each other).
e. Actually, it is the that is expanding, carrying the galaxies along with it! This phenomenon is called the "expansion of the ."
f. Spectral lines are -shifted from distant galaxies, indicating that the galaxies are moving away from us due to the expansion of the Universe.
g. The Big Bang Theory also predicts the existence of cosmic (the glow left over from the explosion itself).
h. The Big Bang Theory received its strongest confirmation when Arno Penzias and Robert Wilson, who later won the Nobel Prize for this discovery, discovered this radiation in 1964. They detected background noise using a special low noise antenna. The strange thing about the noise was that it was coming from every and did not seem to vary in intensity much at all. If this static were from something on our world, like radio transmissions from a nearby airport control tower, it would only come from one , not everywhere. The scientists soon realized they had discovered the cosmic microwave background radiation. This radiation, which fills the entire , is believed to be a clue to it's beginning: The .

SECTION 11 SLIDES (Question 1) (Question 2) (Question 3) (Question 4) (Question 5) (Question 6) (Question 7) (Question 8) (Question 9) (Question 10) (Question 11) (Question 12) (Question 13)

«12. Understand that scientists are searching for invisible mass that will explain continued expansion, implosion (Big Crunch), or oscillation of the universe.

a. The fate of the universe depends upon the balance between the force of expansion, and the pull of gravity.
b. The inward pull of gravity depends on the total amount of in the universe. More matter has more and greater .
c. If there is not enough matter in the universe, the outward force of will be greater, and the universe will expand forever. It will get colder and darker.
d. The “Big ,” the opposite of a big bang, will occur if there is enough matter (and therefore ) in the Universe to slow down and reverse its present expansion. Everything will come back together again.
e. matter is material that is believed to make up more than 90% of the mass of the universe, but is not readily visible because it neither emits nor reflects electromagnetic radiation, such as light or radio signals. Its composition is unknown. It can be detected by its effect on objects in space.
f. If we can determine the amount of in the universe, we can predict its future.
g. The universe may oscillate. This means that it may go through of Big Bangs and Big Crunches, over and over again (almost like the universe is breathing!).

«13. Describe how the Sun/Solar System formed 4.6 billion years ago from the gas and dust (nebula) left behind by a previous star’s supernova.

a. The nebular hypothesis describes the formation of the solar .
b. The planets and Sun began forming about 4.6 years ago from a large cloud of dust and gases composed of hydrogen and helium, with only a small percentage of all the other elements.
c. As the contracted, it began to rotate and assume a disk shape.
d. Material that was gravitationally pulled toward the became the protosun.
e. Within the rotating disk, small centers, called , swept up more and more of the cloud's debris.
f. The characteristics of the planets of the solar system are affected by each planet’s location in relationship to the Sun.
g. The inner planets are denser. The lighter elements were blown, by the solar , to the outer planets, making them less dense. substances like metals, oxides and silicates stayed near the Sun, forming the inner planets.

«14. Explain how the planets were formed by accretion.

a. The concept of planetary development by accretion is a theory that cosmic lumped together (gravity) to form particles, particles became gravel, gravel became small balls, then big balls, then tiny planets, or planetesimals, and, finally, dust became the size of the moon.
b. As the planetesimals became larger, their numbers , and the number of collisions between planetesimals, or meteorites, decreased.
c. Fewer items available for accretion meant that it took a long time to build up a planet. One calculation suggests that about 100 million years would pass between the formation of an object measuring 10 kilometers in diameter and an object the size of the Earth.

(Question 1) (Question 2)

«15. Explain the theories of the origin of the moon.

a. Most scientists believe that the Moon was formed from the ejected material after the collided with a Mars-sized object.
b. This ejected material clumped together to form the , orbiting around the Earth.
c. This catastrophic collision occurred about 4.3 billion years ago. The age of the Moon is determined by the dating of Moon rocks.
d. Another theory is that the Moon was captured by Earth’s .

(Question 1)

«16. Explain why astronomers say, “we are made of star dust.”

a. The that make up your body come from the Earth itself. (You are what you eat!)
b. The atoms that make up the Earth came from the cloud of dust ( ) in space that formed our Solar System.
c. Where did this cloud come from?
d. The fact that there are many elements here on Earth is evidence that a supernova occurred in the past. (Remember: any elements heavier than can only form during a supernova, when a massive star explodes.)
e. This indicates that a different once existed that ended its life with a bang (supernova) leaving behind a cloud of dust in space.
f. The dust, from a star that exploded in the , is where the atoms in your body came from.