ASTR 264 FINAL-URSINO
It took thousands of years for humans to deduce that Earth is spherical. For each of the following alternative models of Earth's shape, identify one or more observations that you could make for yourself that would invalidate the model. (A) a flat Earth (B) a cylindrical Earth, like that proposed by Anaximander (C) a football-shaped Earth
(A) Earth cannot be flat because traveling around the globe, you can tell Earth is not flat because you will not "fall off the edge" of the Earth. (B) Earth cannot be a cylinder because of the proof of what a lunar eclipse shows us. A lunar eclipse is the shadow of the Moon on the Earth, and if Earth were any other shape, the shadows would be different, leaving the idea of the Earth being cylinder shaped to be invalid. (C) Earth cannot be a football shape because of the same reason as stated for the reason the Earth cannot be cylinder shaped. The way the Earth rotates and has an effect on the shadowing of the Moon and Sun (solar and lunar eclipses), it would only make sense that Earth was spherical and not football shaped either.
Describe the conditions that lead to each of the three basic types of spectra. Which type is the Sun's visible-light spectrum, and why?
1. The spectrum of a traditional, or incandescent, light bulb (which contains a heated wire filament) is a rainbow of color. Because the rainbow spans a broad range of wavelengths without interruption, we call it a continuous spectrum. 2. A thin or low-density cloud of gas emits light only at specific wavelengths that depend on its composition and temperature. The spectrum, therefore, consists of bright emission lines against a black background and is called an emission line spectrum. 3. If the cloud of gas lies between us and a light bulb (and the cloud is cooler than the light bulb or other light source), we still see most of the continuous spectrum of the light bulb. However, the cloud absorb light of specific wavelengths, so the spectrum shows dark absorption lines over the background rainbow, making it what we call an absorption line spectrum. Absorption Line Spectrum is the type of spectra that is the Sun's visible-light spectrum. This is because the many dark absorption lines over a background rainbow of color tell us that we are essentially looking at a hot light source through a cooler gas, much like absorption line spectrum. For the solar spectrum the hot light source is the hot interior of the Sun, while the "cloud" is the relatively cool and low-density gas that makes up the Sun's visible surface, or photosphere.
Based on current evidence, which of the following is considered a likely candidate for the majority of the dark matter in galaxies? (a) subatomic particles that we have not yet detected in particle physics experiments (b) swarms of relatively dim red stars (c) supermassive black holes
A
Dark energy has been hypothesized to exist in order to explain (a) observations suggesting that the expansion of the universe is accelerating (b) the high orbital speeds of stars far from the center of our galaxy (c) explosions that seem to create giant voids between galaxies
A
If you observed the redshifts of galaxies at a given stance to be twice as large as they are now, then you would determine a value for Hubble's constant that was (a) twice as large as its current value (b) equal to its current value (c) half its current value
A
The major evidence for the idea that the expansion of the universe is accelerating comes from observations of (a) white dwarf supernovae (b) the orbital speeds of stars within galaxies (c) the evolution of quasars
A
Which of the following best explains why the night sky is dark? (a) The universe is not infinite in space. (b) The universe has not always looked the way it looks today. (c) The distribution of matter in the universe is not uniform on very large scales.
A
Which of the following does inflation help to explain? (a) the uniformity of the cosmic microwave background (b) the amount of helium in the universe (c) the temperature of the cosmic microwave background
A
Much of the Orion Nebula looks like a glowing cloud of gas. What type of spectra would you expect to see from the glowing parts of the nebula? Why?
A glowing cloud of gas would have an emission spectrum. The gas is hot in the glowing parts and electrons are excited and at high energy levels. They will jump to lower levels and emit photons at certain wavelengths, creating an emission line spectrum.
In which type of galaxy would you be most likely to observe a massive star supernova: in a giant elliptical galaxy or in a large spiral galaxy? Explain your reasoning.
A large spiral galaxy is more likely to host a massive star supernova, since an elliptical galaxy has very few if any massive stars remaining.
Suppose you discovered a star made purely of hydrogen and helium. How old do you think it would be?
A star made of only helium and hydrogen would have to be among the first generation of stars ever born, arising out of the primordial mix of elements that came from the Big Bang. The oldest stars we know about are over 12-15 billion years old—a star made of only helium and hydrogen would have to be at least this old. (No star with these conditions has ever been discovered.)
Why is a star's birth mass its most fundamental property?
A star's mass determines surface temperature and luminosity throughout a star's main sequence life which lead to the star's lifetime. Because of this, a star's birth mass is its most fundamental property to studying the star.
For each of the following, which object has more gravitational potential energy, and how do you know? (A) a bowling ball perched on a cliff ledge or a baseball perched on the same ledge (B) a diver on a 10-meter platform or a diver on a 3-meter diving board (C) a 100-kilogram satellite orbiting Jupiter or a 100-kilogram satellite orbiting Earth (assume both satellites orbit at the same distance from their planet's center.)
A. At the same height, a more massive object would have a higher gravitational potential energy compared to a less massive object. The reason is that both objects will fall at the same rate due to gravity, but the larger the object, the more kinetic energy at a particular speed. Hence, the more massive an object, the higher the gravitational potential energy, since its total energy is conserved as it falls. Thus, creating the bowling ball to have more gravitational potential energy. B. The diver has more gravitational potential energy on the higher board because he/she has a greater distance that they can fall. C. The 100-kilogram satellite orbiting Jupiter, because Jupiter has an overall higher gravitational potential energy compared to Earth.
A. The most common form or iron has 26 protons and 30 neutrons. State its atomic number, atomic mass number, and number of electrons (if it is neutral) B. Consider the following three atoms: Atom 1 has 7 protons and 8 neutrons; Atom 2 has 8 protons and 7 neutrons; Atom 3 has 8 protons and 8 neutrons. which two are isotopes of the same element? C. Oxygen has atomic number 8. How many times must an oxygen atom be ionized to create an O^+5 ion? How many electrons are in an O^+5 ion?
A. This atom has atomic number 26, atomic mass 56, and has 26 electrons. B. Atom 2 and Atom 3 are the same element. C. It must be ionized five times; it now has three electrons.
What happens within a contracting cloud in which gravity is stronger than pressure and temperature remains constant? (a) it breaks into smaller fragments (b) thermal pressure starts to push back more effectively against gravity (c) it traps all the energy released by gravitational contraction
A: A contracting cloud in which gravity is stronger than pressure and temperature remains constant breaks into smaller fragments. This is because gravity is pulling down on the cloud that is contracting, and therefore, that pulling causes the cloud to break into smaller fragments.
Which of these stars is the most massive? (a) a main-sequence A star (b) a main-sequence G star (c) a main-sequence M star
A: A main-sequence A star is the most massive because, once again, that is what is shown on the H-R diagram. (Masses decrease from the upper left to the lower right on the main sequence).
Which of these stars has the hottest core? (a) a white main-sequence star (b) an orange main-sequence star (c) a red main-sequence star
A: A white main-sequence star
The age of our solar system is about (a) one-third of the age of the universe (b) three-fourths of the age of the universe (c) two billion years less than the age of the universe
A: One-third of the age of the universe -- You can calculate this by taking the age of our solar system and dividing it by the age of the universe.
Why do sunspots appear darker than their surroundings? (a) they are cooler than their surroundings (b) mathematical models of the sun (c) laboratories that create miniature versions of the Sun
A: Sunspots are actually hot. They have average temperature of 4000 Celsius. They appear darker only because they are cooler than surrounding photosphere, which has average temperature 6000 Celsius.
If you heat a rock until it glows, its spectrum will be (a) thermal radiation spectrum (b) an absorption line spectrum (c) an emission line spectrum
A: Thermal Radiation Spectrum -- This is because thermal radiation deals with heat, therefore, if a rock was heated until it glowed it is known as the thermal radiation spectrum.
Compared to red light, blue light has higher frequency and (a) higher energy and shorter wavelength (b) higher energy and longer wavelength (c) lower energy and shorter wavelength
A: This is because blue light is farther away from us, than what red light is, creating it to be shorter in wavelength and have higher energy.
What do we need to measure in order to determine a star's luminosity? (a) apparent brightness and mass (b) apparent brightness and temperature (c) apparent brightness and distance
A: We need to know a star's apparent brightness and distance to determine a star's luminosity, because with those, we can plug in the correct numbers into the appropriate formula to find a star's luminosity.
Beijing and Philadelphia have about the same latitude but different longitudes. Therefore, tonight's night sky in the these two places will (a) look about the same (b) have completely different sets of constellations (c) have partially different sets of constellations.
A: Will look about the same -- This is due to the positioning of the Earth and the night sky. Because they have the same latitude, they have the same positioning towards the night sky, causing the two places to have similar skies at night.
Which of these objects has the largest radius? (a) a 1.2Msun white dwarf (b) a 0.6Msun white dwarf (c) Jupiter
A: a 1.2Msun white dwarf -- A 1.2Msun white dwarf is the biggest of these three. This is because on the H-R diagram, that is where the white dwarves fall in comparison to the other two.
Which of these stars does not have fusion occurring in its core? (a) a red giant (b) a red main-sequence star (c) a blue main-sequence star
A: a red giant
Which of these clouds light passes most easily through interstellar clouds? (a) red light (b) green light (c) blue light
A: red light -- Red light is the color that most easily passes through interstellar clouds because on the infrared scale, it is the brightest color, allowing it to pass through the easiest.
What happens to a low-mass star after it exhausts its core helium? Why can't it fuse carbon into heavier elements?
After a low-mass star exhausts its core helium, fusion ceases and the star core contracts. Because degeneracy pressure halts the collapse before the carbon becomes hot enough to sustain carbon fusion, the core becomes inert. The layers about the core, where shells of hydrogen and helium both continue fusing, will keep generating heat, causing the star to expand further than in the red giant phase. But this fusion cannot last long, perhaps a few million years, and then the star is dead, leaving behind a white dwarf.
In which of these galaxies would you be least likely to find an ionization nebula heated by hot young stars? (a) a large spiral galaxy (b) a large elliptical galaxy (c) a small irregular galaxy
B
The current temperature of the universe as a whole is (a) absolute zero (b) a few K (c) a few thousand K
B
The rate at which supernovae explode in a starburst galaxy that is forming stars 10 times faster than the Milky Way is (a) about the same as the rate in the Milky Way (b) about 10 times the rate in the Milky Way (c) about 0.1 times the rate in the Milky Way
B
Which of the following does inflation help to explain? (a) the origin of hydrogen (b) the origin of galaxies (c) the origin of atomic nuclei
B
Which of these statements is a key assumption in our most successful models for galaxy formation? (a) the distribution of matter was perfectly uniform early in time (b) some regions of the universe were slightly denser than others (c) galaxies formed around supermassive black holes
B
Why do disk stars bob up and down as they orbit the galaxy? (a) because the gravitational pull of other disk stars always pulls them toward the disk (b) because of friction with the interstellar medium (c) because the halo stars keep knocking them back into the disk
B: Because of the gravitational pull of other disk stars always pulls them toward the disk, the disk stars bob up and down as they orbit the galaxy. That gravitational pull is what creates the motion of them moving up and down as if they were bobbing.
The set of spectral lines that we see in a star's spectrum depends on the star's (a) interior temperature (b) chemical composition (c) rotation rate
B: Chemical Composition -- The chemical makeup of the stars creates different colors when they react, therefore, based on the chemical composition, that is how we see stars and their spectrums.
Earth is closer to the Sun in January than in July. Therefore, in accord with Kepler's second law, (a) Earth travels faster in its orbit around the Sun in July than in January (b) Earth travels faster in its orbit around the Sun in January than in July (c) it is summer in January and winter in July
B: Earth travels faster in its orbit around the Sun in January than in July -- 2nd Law States: a planet moves faster in the part of its orbit nearer the sun and slower when it is farther from Sun, sweeping out dual areas in equal times.
What is the typical percentage (by mass) of elements other than hydrogen and helium in stars that are forming right now in the vicinity of the Sun? (a) 20% (b) 2% (c) 0.02%
B: It is 2% because hydrogen and helium makeup the other 98%. This is typical for your average star makeup.
Compared to their values on Earth, on another planet your (a) mass and weight would both be the same (b) mass would be the same but your weight would be different (c) weight would be the same but your mass would be different
B: Mass would be the same but your weight would be different -- This is because the mass of the planet would be the same, because mass always stays the same, however, the amount of gravitational pull and "weightlessness" feeling would vary depending on what planet it was.
When we say the universe is expanding, we mean that (a) everything in the universe is growing in size (b) the average distance between galaxies is growing with time (c) the universe is getting older
B: The average distance between galaxies is growing with time -- Using the "raisin cake baking in the oven" analogy, one understands that overtime galaxies are moving away from each other, causing the universe to expand.
In the Greek geocentric model, the retrograde motion of a planet occurs when (a) Earth is about to pass the planet in its orbit around the Sun (b) the planet actually goes backward in its orbit around Earth (c) the planet is aligned with the Moon in our sky
B: The planet actually goes backward in its orbit around Earth -- A planet following a circle-upon-circle motion would trace a loop as seen from Earth, with the backward portion of the loop mimicking apparent retrograde motion.
What causes the cycle of solar activity? (a) changes in the Sun's fusion rate (b) changes in the organization of the Sun's magnetic field (c) changes in the speed of the solar wind
B: There are many features that are created by magnetic fields which help to cause the cycle of solar activity. All of those features are created by magnetic fields, which form and change easily in the convecting plasma in the outer layers of the Sun.
Which of these stars has the hottest core? (a) a blue main-sequence star (b) a red supergiant (c) a red main-sequence star
B: a red supergiant
What would you be most likely to find if you returned to the solar system in 10 billion years? (a) a neutron star (b) a white dwarf (c) a black hole
B: a white dwarf
Why do we say that light is an electromagnetic wave? Describe the relationship among wavelength, frequency, and speed for light.
Because visible light is on the electromagnetic spectrum. Wavelength: distance from one peak to the next (or one trough to the next) Frequency: number of peaks passing by any point each second Speed: waves tells us how fast their peaks travel across the pond
A photograph of a cluster of galaxies shows distorted images of galaxies that lie behind it at greater distances. This is an example of what astronomers call (a) dark energy (b) spiral density waves (c) gravitational lensing
C
Dark matter is inferred to exist because (a) we see lots of dark patches in the sky (b) it explains how the expansion of the universe can be accelerating (c) we can observe its gravitational influence on visible matter
C
Strong evidence for the existence of dark matter comes from observations of (a) our solar system (b) the center of the Milky Way (c) clusters of galaxies
C
The primary source of a quasar's energy is (a) chemical energy (b) nuclear energy (c) gravitational potential energy
C
When the ultraviolet light from hot stars in very distant galaxies finally reaches us, it arrives at Earth in the form of (a) X rays (b) slightly more energetic ultraviolet light (c) visible light
C
When we observe a distant galaxy whose photons have traveled for 10 billion years before reaching Earth, we are seeing that galaxy as it was when the universe was about (a) 10 billion years old (b) 7 billion years old (c) 4 billion years old
C
Which of these stars has the coolest surface temperature? (a) an A star (b) an F star (c) a K star
C: A K star has the coolest surface temperature because that is what is shown on the H-R diagram. (Surface temperature decreases from left to right on the x-axis of the diagram).
Why is a sunflower yellow? (a) it emits yellow light (b) it absorbs yellow light (c) it reflects yellow light
C: A sunflower absorbs every other color but yellow, and reflects the color yellow to appear to the human eye as yellow.
Which kind of star is most likely to be found in the halo? (a) an O star (b) an A star (c) an M star
C: An M star is most likely to be found in the halo because the size of the star (the mass) and the luminosity and temperature of it fit the conditions to be formed in the halo.
Where do gamma-ray bursts tend to come from? (a) neutron stars in our galaxy (b) binary systems that also emit X-ray bursts (c) extremely distant galaxies
C: Extremely distant galaxies -- Gamma-ray bursts tend to come from extremely distant galaxies because of the pressure that is in those extremely distant galaxies that are forced into being gamma-ray bursts.
Which kinds of stars are most common in a newly formed star cluster? (a) O stars (b) G stars (c) M stars
C: M stars -- This is because they are formed on the right side of the main-sequence, meaning that they would be M stars first that would then develop into other lettered stars overtime.
What happens to a cloud's thermal pressure if its temperature falls while its density rises? (a) Thermal pressure goes up (b) Thermal pressure goes down (c) More information is needed to determine what thermal pressure does.
C: More information is needed to determine what thermal pressure does.
Which of these groups of particles has the greatest mass? (a) a helium nucleus with two protons and two neutrons (b) four electrons (c) four individual protons
C: Proton and neutron have the same mass. However, when they combine to form a nucleus, some of their mass is converted to energy.
Compared to its angular momentum when it is farthest from the Sun, Earth's angular momentum when it is nearest to the Sun is (a) greater (b) less (c) the same
C: The same -- It is the same because it is on the same axis and no matter its position, the angular momentum does not change.
What is the shape of the Milky Way's halo? (a) round like a ball (b) flat like a disk (c) flat like a disk but with a hole in the center
C: There is a black hole in the center of the Milky Way Galaxy, which name is Signus X-1. This absorbs all of the light and interstellar gas and other objects that would be absorbed in the black hole.
Where would you be most likely to find an ionization nebula? (a) in the halo (b) in the disk between spiral arms (c) in a spiral arm
C: You would most like find an ionization nebula in the spiral arm because that is where the conditions are met to most easily form the ionization nebula.
Describe some of the consequences of galaxy collisions. Why were collisions more common in the past?
Collisions could result in gas being stimulated to form stars. It could also remove gas from galaxies, through tidal interactions, ram pressure events, or (indirectly) by inciting more stellar winds and supernovae. We expect collisions between galaxies to be relatively common (while star-star collisions are rare) because the typical distance between galaxies is comparable in scale to the size of the galaxies themselves. Galaxy collisions should have been even more common in the past than they are today because the density of galaxies was greater in the past. Since a similar number of galaxies (compared to today) existed in closer proximity to each other, they were more likely to encounter each other.
What was the Copernican Revolution, and how did it change the human view of the universe?
Copernican Revolution: The ideas introduced by Copernicus fundamentally changed the way we perceive our place in the universe. The story of this dramatic change, known as the Copernican Revolution, is in many ways the story of the origin of modern science. It is also the story of several key personalities beginning with Copernican himself. Copernicus's created a Sun-centered model of the solar system designed to replace the Ptolemaic model. This model changed people's perception on the overall universe, however, it was later proven that it was no more accurate than Ptolemy's because Copernicus still used perfect circles. Although, it was very influential at the time, and changed the people's perception on the universe being sun-centered rather than Earth-centered.
Define dark matter and dark energy, and clearly distinguish between them. What types of observations have led scientists to propose the existence of each of these unseen influences?
Dark matter is matter that gives off little or no light. Dark energy is the name given to whatever it is that is causing the universe's expansion to accelerate. While they have similar names, they are not similar in nature. Dark matter is massive, behaves like something that has gravitational effects, and is really dark in the sense that we do not see it. Dark energy is not matter, and it is dark in the sense that we can't see it. Dark matter has been detected by carefully observing the gravitational effects on matter we can see in clusters of galaxies and in galaxies. Dark energy has been detected by observing the rate of expansion of the universe, from studies of white dwarf supernovae. (There is also less direct evidence for dark energy that goes beyond the scope of the course.)
How do the galaxy types found in clusters of galaxies differ from those in smaller groups and those of isolated galaxies?
Elliptical galaxies are much more common in large galaxy clusters than they are among isolated galaxies. Half of the large galaxies in large clusters are ellipticals, while among isolated galaxies they make up only about 15%.
What are the four major ways light and matter can interact? Give an example of each from everyday life.
Emission: A light bulb emits visible light; the energy of the light comes from electrical potential energy supplied to the light bulb. Absorption: When you place your hand near an incandescent light bulb, your hand absorbs some of the light, and this absorbed energy warms your hand. Transmission: Some forms of matter, such as glass or air, transmit light, which means allowing it to pass through. Reflection/Scattering: Light can bounce off matter, leading to what we call reflection when the bouncing is all in the same general direction or scattering when the bouncing is more random.
Describe the energy levels that we find for electrons in atoms. Under what circumstances can energy level transitions occur?
Energy levels in an atom: There are only some possible energies in atoms, and those possible energies that are possible are known as the energy levels of an atom. The energy level transition of an electron either raising from a low energy level to higher one or fall from a high level to a lower one, is created because energy might be conserved. Energy level transition can occur only when an electron gains or loses the specific amount of energy separating two levels.
Non-Science or Evaluated Scientifically: Several kilometers below its surface, Jupiter's moon Europa has an ocean of liquid water.
Evaluated Scientifically: You can do the research and can scientifically test this hypothesis, whether the result is true or false.
What evidence suggests that supermassive black holes really exist?
Evidence for the existence of supermassive black holes can be found in the orbits of gas clouds and accretion disks in galaxies like M87 and NGC 4258. Their orbital speeds show that they are orbiting extremely massive objects. The central objects must also be quite small for their masses in these cases. We do not know of any objects that could be so massive and so small apart from a supermassive black hole.
True or False: If you had X-ray vision, you could read this entire book without turning any pages.
False: A book doesn't emit x-rays so you wouldn't see anything.
True or False: Because of their higher frequencies, X rays must travel through space faster than radio waves.
False: All light travels through space at the same speed of light.
True or False: It's the year 2030, and scientists have just learned that there is a 10Msun black hole lurking near Pluto's orbit.
False: An object of that magnitude that close to the Sun would've (at the very least) destabilized every last orbit in the solar system.
True or False: Someday soon, scientists are likely to build an engine that produces more energy than it consumes.
False: Engines can only be so powerful, because energy that is transferred creates less energy, but it cannot become more powerful.
True or False: Galaxies that show redshifts must be red in color.
False: For distant galaxies, the light spectrum is wrong. The frequency lines of the spectrum are all too low. One possible explanation of the incorrect spectrum is that those stars and galaxies are moving away from us, and that the spectrum is shifted toward the red end of the color spectrum because of the Doppler effect.
True or False: I wear a lead vest to protect myself from solar neutrinos.
False: It would take only an inch of lead to stop an x-ray but would require lead more than a light-year thick to stop any average neutrino. Many neutrinos pass through our body everyday all day but do not cause any damage at all.
True of False: The universe is billions of light-years in age.
False: Light years is a measure of distance, not of age. Yes, the universe is approximately 14 billions of years in age, however, you would not denote that with the measure of light years, but rather just regular years.
Stars that begin their lives with the most mass live longer than less massive stars because they have so much more hydrogen fuel.
False: Massive stars lives have shorter lifetimes as they burn through their fuel faster.
True or False: NASA will soon launch a spaceship that will photograph our Milky Way Galaxy from beyond its halo.
False: NASA will not soon launch a spaceship that will photograph our Milky Way Galaxy from beyond its halo, because our science is not developed enough to reach science/a spaceship out that far.
True or False: Protostars are generally best observed in ultraviolet light because their surfaces have to get very hot before fusion can begin.
False: Protostars are best observed in the infrared part of the spectrum. The dust in the collapsing cloud surrounding the protostar will cause some of the radiation and the dust to be heated, but will not be the same temperature as the star. The emission from the dust instead will be in the far infrared.
True or False: The constellation Orion didn't exist when my grandfather was a child.
False: The constellation Orion has existed for approximately 32,000 to 38,000 years, therefore it would have existed when your grandfather was a child.
Some of the stars on the main sequence of the H-R diagram are not converting hydrogen into helium.
False: The main-sequence is defined as the phase of a star's file when it burns hydrogen into helium.
True or False: The current mass of any star is the same as the mass it had when it first became a protostar.
False: The mass of a protostar changes until the star is no longer a protostar and has evolved into a main-sequence star.
True or False: The white dwarf at the center of the Helix Nebula has a mass three times the mass of our Sun.
False: The maximum mass of a white dwarf is the Chandrasekhar mass, about 1.4 solar masses.
True or False: We know that a black hole lies at our galaxy's center because numerous stars near it have vanished over the past several years, telling us that they've been sucked in.
False: The orbital velocities of stars at the galactic center are what indicate a black hole. None of these stars have vanished from sight.
True or False: If Earth's orbit were a perfect circle, we would not have seasons.
False: The seasons are created because of the tilt of Earth's axis, not the distance from the sun, so it would not matter if Earth's orbit was a perfect circle or not.
True or False: Our Solar System is bigger than some galaxies.
False: This is false because our solar system is a minuscule part of a vast galaxy. Although there are various sizes of galaxies, our solar system is still smaller.
True or False: Cepheid variables make good standard candles because they all have exactly the same luminosity.
False: This statement does not make sense. Cepheids are good standard candles because their light curve pattern tells you what their luminosity is.
True or False: Dark energy is the energy associated with the motion of particles of dark matter.
False: This statement does not make sense. Dark matter is matter, dark energy is a name for an energy field; the two are not related to each other.
True or False: If dark matter consists of WIMPs, then we should be able to observe photons produced by collisions between these particles.
False: This statement does not make sense. Since WIMPs are "weakly interacting," they do not interact via the electromagnetic force, and therefore do not collide in the same way that charged particles can collide.
True or False: We can't see galaxies beyond the cosmological horizon because their light is too dim.
False: This statement does not make sense. We can't see beyond the cosmological horizon because that boundary is defined by the time light has had since the Big Bang to travel to us.
According to the Big Bang theory, most of the helium in the universe was created by nuclear fusion in the cores of stars.
False: This statement is false. According to the Big Bang theory, most of the helium in the universe was created by fusion in the uniform gas that filled the universe during the first few minutes after the Big Bang.
True or False: According to the hypothesis of inflation, large-scale structure in the universe may have originated as tiny quantum fluctuations.
False: This statement is false. Inflation posits that the universe is flat because it experienced a huge expansion event shortly after the Big Bang. This exponentially huge expansion wiped out whatever curvature might have been in place before.
True or False: Clusters of galaxies are the largest structures that we have so far detected in the universe?
False: This statement is false. Superclusters and voids are much larger than clusters of galaxies.
True or False: Observed characteristics of the cosmic microwave background can be explained by assuming that it comes from individual stars and galaxies.
False: This statement is false. The cosmic microwave background is extremely smooth across the sky, and its blackbody spectrum corresponds to a very precise temperature. The characteristics of this background would not be so uniform if it came from many different objects.
True or False: Humanity will eventually have to find another planet to live on, because one day the Sun will blow up as a supernova.
False: This statement is not sensible. The Sun will eject a planetary nebula and fade away as a white dwarf. It is not massive enough to explode as a supernova. However, if humanity survives that long, we will probably have to find another place to live.
True or False: We did not understand the true size and shape of our galaxy until NASA launched satellites into the galactic halo, enabling us to see what the Milky Way looks like from the outside.
False: We have never seen what the Milky Way looks like from the outside. Any picture that you see of the Milky Way is an artist's rendition based on the limited amount of information we do have about the structure of the galaxy and photographs of galaxies like Andromeda.
True or False: I've never been to space, so I've never experienced weightlessness.
False: You can experience weightlessness in a simulator on land, or on a thrill ride, such as a rollercoaster. (also on an airplane)
Briefly describe how gravitational contraction generates energy. When was it important in the Sun's history? Explain.
Gravitational contraction is the process in which gravity causes an object to contract, thereby converting gravitational potential energy into thermal energy. It was important to get the Sun's core to start fusion. It generates energy by converting gravitational potential energy into thermal energy. An example of this would be heat.
In broad terms, explain how the life a high-mass star differs from that of a low-mass star. How do intermediate mass stars fit into this picture?
High-mass stars go through their lives more quickly than low-mass stars. Part of the reason for this is that during their main-sequence lifetimes, they fuse hydrogen to create helium via the CNO cycle, which produces more energy. After their main sequence lifetimes, high-mass stars begin fusion reactions involving a series of heavier and heavier elements in their cores. But eventually, high-mass stars reach a stage when they have iron cores and cannot fuse any elements together to produce more energy. When this happens, the star explodes as a supernova. Intermediate-mass stars have similar lives up through the phase where the cores create carbon and oxygen. At this point, the intermediate-mass stars can no longer fuse elements to produce energy and die as white dwarfs.
Many people incorrectly guess that the phases of the Moon are caused by Earth's shadow falling on the Moon. How would you convince a friend that the phases of the Moon have nothing to do with Earth's shadow? Describe the observations you would use to show that Earth's shadow cannot be the cause of the phases.
I would first start by explaining that the phases of the Moon are not created by Earth's shadow, but rather by the positioning of the Sun in relation to the Moon. The sun shining on the moon is what causes people on Earth to be able to see the Moon at nighttime. As Earth rotates, one sees more or less of the Moon depending on where they are on Earth. There are times that you could be completely opposite of the sun, you can be directly facing it, or you could be somewhere in between. This is what causes the phases of the moon. As you stand in one position on Earth, and Earth continues to rotate around the Sun, the Sun "lights up" the Moon, and depending on your position is what determines how much of the Moon you can or cannot see. This could be demonstrated with a tennis ball, a penny, and a flashlight. It would be similar to the observations we saw in class.
What do we mean by inflation, and when do we think it occurred?
Inflation refers to the dramatic expansion of the universe that brought it from the size of an atom to the size of the solar system in a mere 10-36 second. We think that this occurred at the end of the GUT era when the strong force froze out of the GUT force, at around 10-38 second into the universe's history.
When Einstein's theory of gravity (general relativity) gained acceptance, it demonstrated that Newton's theory had been (a) wrong (b) incomplete (c) really only a guess
It had showed that Newton's theory had been incomplete.
Describe the laws of conservation of momentum, of angular momentum and of energy. Give an example of how each is important in astronomy.
Laws of Conservation of: (A) Momentum: the principle that, in the absence of net force, the total momentum of a system remains constant/Importance: it helps us understand the current understanding of the universe (jumping up and down example) (B) Angular Momentum: the principle that, in the absence of net torque (twisting force), the total angular momentum of a system remains constant/ Importance: it helps us understand that astronomical objects can have angular momentum due to both rotation and orbit (C) Energy: the principle that energy (including mass-energy) can be neither created nor destroyed, but can only change from one form to another/Importance: it helps us understand the story of the universe and how it is a story of the interplay of energy and matter: all actions involve exchanges of energy or the conversion of energy from one form to another
Briefly describe the Moon's cycle of phases. Can you ever see a full moon at noon? Explain.
Moon Phases: a. New Moon: rises and sets with sun b. Waxing Crescent: rises mid-morning, highest mid-afternoon, set late evening c. First Quarter: rises at noon, highest at sunset, set at midnight d. Waxing Gibbous: rises mid-afternoon, highest late evening, set before dawn e. Full Moon: rise at sunset, highest at midnight, set at sunrise f. Waning Gibbous: rises late evening, highest before dawn, set mid-morning g. Third Quarter: rise at midnight, highest at sunrise, set at noon h. Waning Crescent: rises before dawn, highest mid-morning, set mid-afternoon You cannot see a full moon at noon because it rises and sets between the hours of 6pm and 6am approximately.
Suppose you live on the Sun (and could ignore the heat). Would you still see the Moon go through the phases as it orbits Earth? Why or why not?
No you would not, because the phases are determined by your position on Earth and the shadows that are created from the Sun are what determines the Moon's phases.
Non-Science or Evaluated Scientifically: The Yankees are the best baseball team of all time.
Non-Science: This cannot be tested because it is an opinion (unless you look at factual evidence and stats).
What is the difference between between nuclear fission and nuclear fusion? Which one is used in nuclear power plants? Which one does the Sun use?
Nuclear fusion and nuclear fission are two different types of energy-releasing reactions in which energy is released from high-powered atomic bonds between the particles within the nucleus. The main difference between these two processes is that fission is the splitting of an atom into two or more smaller ones while fusion is the fusing of two or more smaller atoms into a larger one. Nuclear fission is used for nuclear power plants. Nuclear fusion is used by the sun.
What is the overall nuclear fusion reaction in the Sun? Briefly describe the proton-proton chain.
Nuclear fusion is the source of all energy the Sun releases into space. If the fusion rate is varied, so would the Sun's energy output, and large variations in the Sun's luminosity would almost surely be lethal to life on Earth. Fortunately, the Sun fuses hydrogen at a steady rate, thanks to a natural feedback process that acts as a thermostat for the Sun's interior. Solar energy production remains steady because the rate of nuclear fusion is very sensitive to temperature. A slight increase in the Sun's core temperature would mean a much higher fusion rate. The proton-proton chain is the chain of reactions by which low-mass stars (including the Sun) fuse hydrogen into helium.
If Earth were twice as far from the Sun, the force of gravity attracting Earth to the Sun would be (a) twice as strong (b) half as strong (c) one quarter as strong
One quarter as strong. This is because gravity follows an inverse square law in proportion to distance.
What is a photon? In what way is a photon like a particle? In what way is it like a wave?
Photon: We say that light comes in individual "pieces," called photons, that have properties of both particles and waves. Like waves, each photon is characterized by a wavelength and a frequency.
What is a protostar? How does it form? Why does its mass increase with time?
Protostar: A forming star that has not yet reached the point where sustained fusion can occur in its core A protostar is formed when the thermal energy can no longer escape from the cloud. The temperature of the cloud rises and the thermal pressure begins to push back against the push of the gravity slowing down the cloud's collapse. It's mass increases with time because a molecular cloud fragment contracts in an "inside-out" fashion. Gravity is strongest near the protostar, where the gas density is greatest. The gas in the outer part of the cloud fragment feels a weaker gravitational pull, so it initially remains behind as the protostar forms. However, because the gas beneath has already contracted to make the protostar, the outer regions of the cloud fragment are left with little pressure support from below. Like something that was reacting on a trapdoor that has just opened, the gas from these outer regions begins to rain down onto the protostar, gradually increasing its mass.
Suppose Earth were smaller. Would solar eclipses be any different? If so, how? What about lunar eclipses?
Solar Eclipse: occurs when the Moon gets between the Earth and the Sun, and the Moon casts a shadow on the Earth (Moon is between Sun and Earth) Lunar Eclipse: occurs when the Moon is directly behind the Earth, and the Earth is in between the Sun and the Moon Solar eclipses would still be the same, because they are created by the Moon's shadow on Earth. Because of this, the size of Earth does not matter, just the size of the Moon does. Lunar eclipses would be a bit different. They would still occur, however, they would not be as frequent, and they would not last as long because the shadow that is being created is smaller.
How can we use emission or absorption lines to determine the chemical composition of a distant object?
Spectroscopes are attached to telescopes to separate the spectral lines. Then, the wavelengths and intensities indicate the elements and amount of the elements in that object (star, or in some cases, planet atmosphere). You have to have an idea of a prism or diffraction grating being able to separate the wavelengths of the light into their constituents, and that specific elements emit or absorb light or a particular set of wavelengths.
Why is mass so important to a star's life? How and why do we divide stars into groups by mass?
Star mass is important because larger stars have higher temperatures in their cores, making fusion proceed more rapidly and allowing fusion of heavier elements in their cores. We categorize stars by mass into three groups: low-mass stars (less than 2 solar masses), intermediate-mass stars (between 2 and 8 solar masses), and high-mass stars (above 8 solar masses).
Summarize the Star-Gas-Star Cycle Shown in Figure 19.3.
Stars are born when gravity causes the collapse of molecular clouds. They shine for millions or billions of years with energy produced by nuclear fusion, and in their deaths they ultimately return much of their material back to the interstellar medium.
Explain what we mean by the Big Bang theory.
The Big Bang theory is the scientific theory that describes the universe's earliest moments. The theory is based on the idea that the universe began as an incredibly hot and dense collection of matter and radiation. Everything we can observe today was crammed into a tiny space. The expansion and cooling of this unimaginably intense mixture of particles and photons could have led to the present universe, and this idea explains several aspects of the present universe with impressive accuracy.
Why did ancient peoples study astronomy? Describe an astronomical achievement of at least three ancient cultures.
The ancient peoples studied astronomy because of inherent curiosity as humans, but also because ancient cultures also discovered that astronomy had practical benefits for time keeping, keeping track of seasonal changes, and navigation. Astronomical Achievements: (1) People of Central Africa: learned to predict rainfall patterns by making careful observations of the moon (2) Egyptians: divided daytime and nighttime into twelve hours each of the morning and of evening (am and pm) / they also created and used star clocks (3) Ancestral Pueblo People: created the Sun dagger to mark a special cycle of the moon that had ritual significance (4) Chinese: built a great observatory in Beijing that still stands today, in the 15th century (5) Pawnee People of Kansas: built lodges that featured strategically placed holes for observing the passage of constellations that figure prominently in Pawnee folklore
In winter, Earth's axis points toward the star Polaris. In spring, the axis points toward (a) Polaris (b) Vega (c) the Sun
The axis also points toward Polaris.
Explain how the color of an old elliptical galaxy has changed during the last 10 billion years. How might you be able to use the galaxy's color to determine when it formed?
The color of an elliptical changes as the population of stars, most of which formed at some early time, ages together. So like a globular cluster, an elliptical's color gets redder as the high-mass stars evolve off the main sequence to become red giants.
When a star exhausts its core hydrogen fuel, the core contracts but the star as a whole expands. Why?
The core of a red giant contracts because there is no more hydrogen fusion to heat the core and raise thermal pressure to resist gravity. However, the shell of hydrogen outside the core heats up to very high temperatures (hotter than the core during the main-sequence phase), and hydrogen fusion is occurring quickly. The star as a whole expands because the energy transport cannot keep up with the shell's increasing energy generation rate, so the thermal energy is trapped in the star and builds up, pushing the surface outward.
Distinguish between the disk component and the halo component of a spiral galaxy. Which component includes cool gas and active star formation?
The disk component of spiral galaxies is a flat disk in which stars follow orderly, nearly circular orbits around the galactic center. The disk contains cool gas and active star formation. The halo component of spiral galaxies has a round shape with stars orbiting at many different inclinations.
What do the large-scale structures of the universe look like? Explain why we think these structures reflect the density patterns of the early universe.
The large-scale structure of the universe shows galaxies arranged in huge chains and sheets that span millions of light-years. Between the chains and sheets are giant voids. This structure probably mirrors the original distribution of dark matter in the early universe. The more dense regions in the early universe would have gone on to collapse and form galaxies, clusters, and superclusters, while the less dense regions would have gone on to form the voids.
How are the luminosities of galaxies related to their colors?
The most luminous galaxies in the universe are more likely to be red galaxies, occupying the bright end of the "red sequence" in galaxy luminosity-color diagrams. Galaxies of somewhat lower luminosity split between "blue cloud" galaxies and galaxies at the faint end of the red sequence.
Compared to the Sun, a star whose spectrum peaks in the infrared is (a) cooler (b) hotter (c) larger
The star would be cooler than our Sun.
Describe two ways in which conditions in a protogalactic-cloud system might lead to the birth of an elliptical rather than a spiral galaxy.
There are two possible differences that could lead to an elliptical galaxy forming rather than a spiral: • Protogalactic spin—Rapidly spinning clouds tend to form a disk as they collapse, leading to a spiral galaxy. Clouds with little or no spin may not form a disk, and would instead form elliptical galaxies. • Protogalactic density—Denser clouds collapse faster, causing stars to form more quickly. If the star formation is sufficiently rapid, the gas will never have a chance to settle into a disk, making the galaxy an elliptical rather than a spiral.
Describe the three hallmarks of science and how we can see them in the Copernican revolution. What is Occam's razor? Why doesn't science accept personal testimony as evidence?
Three Hallmarks: (1) Modern science seeks explanations for observed phenomena that rely solely on natural causes. (2) Science progresses through the creation and testing of models of nature that explain the observations as simply as possible. (3) A scientific model must make testable predictions about natural phenomena that will force us to revise or abandon the model if the predictions do not agree with observations. Occam's Razor: the idea that scientists should prefer the simpler of two models (Copernican view over the geocentric view) that agree equally well with observations. Why not accept your personal testimony? (1) because you cannot retest their findings if you wanted to (there is no concrete evidence? (2) also, people cannot agree on what exactly they saw, making it less believable
True or False: Gamma-ray bursts are more likely to be observed in galaxies that are rapidly coming new stars than in galaxies containing only old stars.
True
True or False: A "white hot" object is hotter than a "red hot" object.
True: An object must emit a red color from heat before it can emit a white color, because white is all of the colors combined.
True or False: Some of the stars in a star cluster live their entire lives and then die off before many of the cluster's stars initiate fusion.
True: Because each individual star has its own span of lifetime, there are stars that could die off before many of the cluster's stars initiate fusion. Some stars have short life spans, and some have long, and all are susceptible to dying off before the cluster's of stars initiate fusion.
True or False: I live in the United States, and during a trip to Australia I saw many constellations that I'd never seen before.
True: Compared to the United States, Australia has a different viewpoint of the sky. Although you will see some similar constellations, you will not be able to see all of the same constellations. What constellations you see are based on your location on the Earth (the longitude and latitude of your location). With that being said, because there are different longitude and latitude points in the two different countries, you would be able to see constellations you've never seen before in Australia on a vacation.
True or False: Planets like Earth probably didn't form around the very first stars because there were so few heavy elements back then.
True: Earth formed through the accretion of smaller, rocky objects made from heavy elements.
True or False: A temperature rise in the Sun's core is nothing to worry about, because conditions in the core will soon return to normal.
True: Gravitational equilibrium will stabilize the temperature of the Sun's core.
True of False: If the Sun were magically replaced with a giant rock that had precisely the same mass, Earth's orbit would not change.
True: It would not change because gravity is based on mass, therefore, if it had the same mass, Earth's orbit would not change.
All giants, supergiants, and white dwarfs were once main-sequence stars.
True: Main-sequence stars evolve to become giants and supergiants based on their mass and eventually end up as white dwarfs.
True or False: The walls of my room are transparent to radio waves.
True: Radio waves pass through most walls, which is why you can receive radio broadcasts and cell phone callers inside a house, and in your bedroom.
True or False: The gold in my wedding band was made by the merger of two neutron stars.
True: Scientists have caught two neutron stars in the act of colliding. They have found that heavy elements can be found in everything from weeding brings to cellphones to nuclear weapons.
True or False: If we could watch a time-lapse movie of a spiral galaxy over millions of years, we'd see many stars being born and dying within the spiral arms.
True: Spiral arms are bright because they contain many short-lived blue stars that shine for only a few million years.
True or False: If the Sun's magnetic field somehow disappeared, there would be no more sunspots on the Sun.
True: Sunspots occur because the Sun's magnetic field prevents hot gas from entering into them. If the magnetic field disappear, there can't be any more sunspots.
True or False: Because of their higher frequencies, X-rays must travel through space faster than radio waves.
True: The speed of different types of light is determined by the wavelength and the frequency. If the wavelength has a higher frequency, like X-rays do versus the radio waves then that wavelength will travel faster through space.
True or False: When I drive my car at 30 mph, it has more kinetic energy than it does at 10 mph.
True: The speed of different types of light is determined by the wavelength and the frequency. If the wavelength has a higher frequency, like X-rays do versus the radio waves, then that wavelength will travel faster through space.
True or False: If there are few sunspots this year, we should expect many more in about 5 years.
True: The sunspot cycle has average period of 11 years or sometimes 22 years. Assuming we are at the lowest point of the cycle, the number of sunspots should increase in the next 5 years.
Sirius looks brighter than Alpha Centauri, but we know that Alpha Centauri is closer because its apparent position in the sky shifts by a larger amount as Earth orbits the Sun.
True: This is true because Sirius is a much brighter star, regardless of the distance. It is so much brighter than Alpha Centauri that it appears brighter even from a greater distance.
True or False: Most of the supernova explosions that occur in a star cluster happen during its first 100 million years.
True: This statement is sensible only if you mean all the massive star supernovae explosions, since most of the stars with 8 solar masses will have evolved away from the main sequence by this time.
True or False: If the Andromeda Galaxy someday collides and merges with the Milky Way, the resulting galaxy may be elliptical.
True: This statement is sensible, because computer simulations of collisions between two large spiral galaxies show that these collisions create elliptical galaxies.
True or False: Elliptical galaxies are more likely to form in denser regions of space.
True: This statement is sensible, because unlike spiral galaxies, elliptical galaxies appear to be more common in the cores of clusters, which are denser regions of space.
True or False: If you could look inside the Sun today, you'd find that its core contains a much higher proportion of helium and a lower proportion of hydrogen than it did when the Sun was born.
True: This statement is sensible. Because the Sun is about halfway through its core hydrogen-fusing life, it has turned about half the core hydrogen into helium.
True or False: The black hole at the center of our own galaxy may once have powered an active galactic nucleus.
True: This statement is sensible. The active nuclei in other galaxies appear to be powered by accretion of matter onto supermassive black holes, so it is quite possible that our own galaxy underwent a similar episode of nuclear activity.
True or False: The iron in my blood came from a star that blew up more than 4 billion years ago.
True: This statement is sensible. The iron in the solar system was created before our Sun was formed about 4.6 billion years ago. Because iron is created in high-mass stars and delivered into interstellar space by supernova explosions, the supernova (or supernovae) responsible for creating the solar system's iron must have occurred before the Sun formed.
True or False: Strange as it may sound, most of both the mass and the energy in the universe may take forms that we are unable to detect directly.
True: This statement is true, because the amount of dark matter seems to far outweigh the ordinary matter and the inferred mass-energy of dark energy is even greater.
True or False: According to the Big Bang theory, the early universe had nearly equal amounts of matter and antimatter.
True: This statement is true. According to the Big Bang theory, the universe was hot enough to generate matter-antimatter pairs of particles very early in time, ensuring that the amounts of matter and antimatter were virtually equal.
True or False: The energy from supernova explosions can drive a large proportion of the interstellar gas out of a small galaxy.
True: This statement makes sense because the escape speed from a small galaxy is less than the speeds generated by a supernova explosion. [Note: Another issue is how much the ejecta slow down because of encounters with other gas clouds.]
True or False: If someone in a galaxy with a lookback time of 4.6 billion years had a super powerful telescope, that person could see our solar system in the process of its formation.
True: This statement makes sense because the light travel times between two galaxies should be nearly symmetric, that is, the same whether light travels from galaxy 1 to galaxy 2 or from galaxy 2 to galaxy 1. So a galaxy 4.6 billion light-years away would see our solar system as it was 4.6 billion years ago.
True or False: After measuring a galaxy's redshift, I used Hubble's law to estimate its distance.
True: This statement makes sense since Hubble's law gives the relationship between redshift and distance, as calibrated by various standard candles.
True or False: Galaxy A is moving away from me twice as fast as galaxy B. That probably means it's twice as far away.
True: This statement makes sense, since Hubble's law says that a galaxy's distance is proportional to its recession velocity.
True or False: Patterns in the cosmic microwave background tell us abut conditions in the early universe that ultimately led to galaxy formation.
True: This statement makes sense, since the cosmic microwave background is a primary source of information about how the density of the universe varied from one place to another 380,000 years after the Big Bang.
True or False: If you want to get a more accurate count of the number of stars in our galaxy, use an infrared telescope to observe them instead of a visible-light telescope.
True: Using an infrared telescope gives us the ability to see further in the spectrum and, therefore, we are then able to see through the dust particles that are in the galaxy that may block us from seeing the light of stars.
True or False: Suppose you could enter a vacuum chamber (a chamber with no air in it) on Earth. Inside this chamber, a feather would fall at the same rate as a rock.
True: We did an experiment in class that proved this. Air resistance is what creates the feather and rock to fall at different times, and with no air in a tight vacuum, that would not happen.
True or False: If you want to find a pulsar, you should look near the remnant of a supernova described by ancient Chinese astronomers.
True: When a massive star explodes in a supernova explosion, it can leave a pulsar behind. So, it is accurate for one to look for pulsars near supernova remnants.
What do we mean by WIMPs? Why does it seem likely that dark matter consists of these particles, even though we do not yet know what they are?
WIMPs, or weakly interacting massive particles, are a form of dark matter that is made up of particles that do not generally interact with baryonic matter much, except through their gravitational influence. These particles need to be more massive than neutrinos and therefore move more slowly so that mutual gravity could hold clumps of them together. Such matter seems the best candidate for the dark matter in the universe since it meets the requirements for dark matter well and because there are other reasons to think that such (nonbaryonic) matter should exist in the universe.
In what sense are we "star stuff"?
We are essentially "star stuff" because our galaxy consists of 2% original hydrogen and helium, that was converted into heavier elements, from earlier generations of stars. Because of this, the cloud that "birthed" our solar system, was made of 98% Hydrogen and Helium (roughly) and 2% other elements. That 2% then went on to form Earth, and then on Earth, other elements became the raw ingredients of life, which blossomed into the great diversity of life on Earth today.
Briefly explain how we can learn about the lives of stars even though their lives are far longer than human lives.
We can examine clusters of stars and can compare younger and older stars to see how they look at various stages of life. By doing this, we can predict what is going to happen in the future and use our knowledge to know about what has happened in a star's life in the past. Because of this we can use our observations to form models that are used today to learn about the lives of stars.
Briefly describe the three different ways of measuring the mass of a cluster of galaxies. Do the results from the different methods agree? What do they tell us about dark matter in galaxy clusters?
We can measure the masses of clusters of galaxies in three ways. The first method is to measure the speeds and positions of the galaxies in a cluster as they orbit. Applying Newton's law of gravitation to the speeds, we can deduce the mass of the cluster. The second method for finding the mass of a cluster is to measure the temperature of the gas between galaxies in the cluster and the approximate size of the cluster. The pressure of the gas must balance the pull of gravity from the mass in the cluster, so the temperature and size lead us to the mass. The final method of finding the mass of a galactic cluster is gravitational lensing. This technique measures the amount that a beam of light is bent as it passes near the cluster and uses Einstein's theory of general relativity to determine the mass of the cluster. The results from all three methods agree on the masses of the clusters, and these results tell us that the clusters hold substantial amounts of dark matter.
In this first chapter, we have discussed the scientific story of the universe but have not yet discussed most of the evidence that back it up. Choose one idea presented in this chapter-such as the idea that there are billions of galaxies in the universe, or that the universe was born in the Big Bang, or that the galaxy contains more dark matter than ordinary matter-and briefly discuss the type of evidence you would want to see before accepting the idea.
When trying to research a new topic, such as the idea that there are billions of galaxies in the universe, one would look for specific information. A specific piece of evidence that one would look for is factual data, such as photos. If there was a specific photo of billions of galaxies in our entire universe, then it would be easy for a scientist to fully accept the idea. Another piece of evidence would be the findings of factual documentation that scholars have created, and other scientists have accepted. With the idea of scientists exploring the research together, more people are going to want to "jump on board," because it is going to seem more reliable. If the information that was being stated had been peer reviewed and accepted by other scientists, it would be hard for one to not fully accept the idea that they were researching.
When we observe the cosmic microwave background, at what age are we seeing the universe? How long have the photons in the background been traveling though space? Explain.
When we observe the cosmic microwave background, we are seeing the universe as it was when it was 380,000 years old. The photons we see have been traveling for about 14 billion years, since not long after the Big Bang.
The 2006 decision to call Pluto a "dwarf planet" still generates controversy. Gather and summarize information about the results from the New Horizons mission to Pluto and the Dawn mission to the dwarf planet (and large asteroid) Ceres. Where did you get your information? How do you know it is reliable? Has this information shed any light on the classification of Pluto, Ceres, and other solar system bodies? Overall, what is your opinion about the appropriate classification of these bodies?
Where: NASA.gov How: NASA is a supported science organization, and its biggest astronomical company in the United States. They do all kinds of thorough space research and study aero space extensively. Influenced: I don't necessarily think that this information has shed any light on the classification of Pluto, Ceres, and other solar system bodies because the mission just occurred recently in 2015. I believe that there is still research being done on the scientific information that was found, and so a direct, specific classification has not been made yet. Opinion: Overall, I think that the appropriate classification of these bodies, because they are still somewhat unknown, is up to the scientists at this point. Making Pluto a "dwarf planet" after it had been a planet for many years is somewhat controversial, however, scientists have proven with facts and evidence as to why the concurred this, therefore, I think it is important to leave it up to them. With extensive research, I may change my direct opinion, however, with the tiny bit of research that I have done, I will agree with how the scientists and the NASA space center have classified these solar system bodies.
On a clear, dark night, the sky may appear to be "full" of stars. Does this appearance accurately reflect the way stars are distributed in space? Explain.
Yes, because when we look in any direction into the galactic plane, we see stars and interstellar clouds that make up the milky way in the night sky.
A planet in another solar system has a circular orbit and an axis tilt of 35 degrees. Would you expect this planet to have seasons? If so, would you expect them to be more extreme than the seasons on Earth? If not, why not?
Yes, this planet would have seasons, because of the tilt that the planet has. However, compared to Earth, this planet would have more extreme seasons because of the more extreme tilt (Earth's is 23.5 degrees). The pole would be closer to the sun creating a hotter, longer summer, and a colder, longer winter. Because of this, spring and fall would be shorter. These lengths of each season are opposite of what they are on Earth.
What would happen if the Sun suddenly became a black hole without changing its mass? (a) The black hole would quickly suck in Earth (b) Earth would gradually spiral into the black hole (c) Earth would remain in the same orbit
c: The Earth would remain in the same orbit -- This is because the mass is consistent, therefore, so would the orbit of the Earth. If mass is the same, so is the orbit.
Describe in one or two paragraphs how the Milky Way would look from the outside if you could watch it for the next 100 billion years. How would its appearance change over that time period?
• The biggest changes over 100 billion years would be that all of the blue and yellow stars would start going out, meaning that they would die off. Only the red dwarfs would be left, which would burn for something like a trillion years. So, the Milky Way would be red, and would not contain any other color of stars. The Milky Way would also have merged with the Andromeda Galaxy, with that merging finished by about 6 billion years from now, so it would merge pretty early in that 100 billion years. Towards the end of those 100 billion years, all of those red stars would mainly turn into white dwarfs, leaving the galaxy to be dominated by only white dwarf stars that become colder and dimmer overtime.
