Chapters 21, 22, 23, 24
Just for fun a calculation question: There are approximately 100 billion galaxies in the observable Universe. If each of these galaxies has 10 billion stars similar to our Sun, and each of these stars has 1 planet suitable for life as we know it, how many habitable planets are there in observable Universe?
1 sextillion (1,000,000,000,000,000,000,000 or 1021) Chapter 1
About how many new stars are born in the Milky Way in one Earth year?
1-10 Chapter 21
About how many new stars are born in a starburst galaxy in one Earth year?
100 Chapter 21
Approximately how old is the Universe?
14 billion (14,000,000,000) years. Chapter 1: Currently, we think that the Universe is about 13.7 billion years old. The Sun formed about 4.5 billion years ago, and life appeared on Earth about 3.5 billion years ago. Anatomically modern humans first appeared in Africa about 200,000 years ago, and the written word is only about 4,000 years old. We've observed other galaxies for 1,000 years, but only known what they were for the last 100 years. We may have only been around for a blink of the Universe's history, but we've managed to figure out a great deal about it in that time.
What is the surface temperature of this star?
20,000 K Chapter 15: The surface temperature and colour are related, regardless of the other properties of the star. A bluish white colour corresponds to a 20,000 K star.
A star is exactly one parsec from the Earth. It is measured at some point during the year to be 1 arcsecond away from a very distant (i.e., fixed) star. If we kept monitoring the position of this star for the rest of the year, which of the following positions could we never see it in?
3 arcseconds from the fixed star Chapter 15
What is the earliest time from which we have evidence for life on Earth?
3.85 billion years ago Chapter 24
What was the approximate temperature of the Universe when the CMBR was emitted?
3000 K Chapter 22: Probably fooled some of you on this one. The blackbody curve of the CMB that we see corresponds to a temperature of 3 K. However, this curve is greatly redshifted, since space has expanded so much between us and the CMB. This makes the CMB seem much cooler than the Universe was when it was emitted, which was about 3000 K. Since the temperature of the CMB decreased by a factor 1000 over the past 13.6 billion years, the wavelength of the CMB was increased by a factor 1000 since the CMB was formed, i.e. if the typical CMB wavelength today is 1 millimeter, then it was 1 millimeter/1000 = 1 micrometer when the CMB was formed!
What is a quasar?
A "quasi-stellar radio source", a powerful accretion disk around a supermassive black hole. Chapter 21: Quasars are the extremely hot, very bright region of gas and dust around a supermassive black hole. As the material spirals in, it heats up, producing some of the brightest light in the known universe. These sources were initially found with radio telescopes, therefore the designation "radio source" in the name.
Which of the following is most likely to produce an elliptical galaxy?
A dense protogalactic cloud with almost no angular momentum. Chapter 21: Dense protogalactic clouds are better at getting rid of heat, so that the stars can form much more quickly. This eats up all of the available gas, so no disk forms. Sparse ones will leave a lot of gas around to form a disk. An excess of angular momentum will flatten the galaxy into a disk-like shape.
What is a stromatolite?
A kind of rock Chapter 24
Which of the following is not a possible orbit in the context of Kepler's First Law? a) A planet moves in an ellipse with the Sun at one focus. b) A planet moves in a circle with the Sun at the centre. c) A planet moves in an ellipse with the Sun at the centre. d) All are possible.
A planet moves in an ellipse with the Sun at the centre. Chapter 3: A planet moving in an ellipse would have the Sun at one focus of the ellipse.
Watt is a What? Oops, sorry... I meant to ask "What is a Watt?" a) A unit of energy. b) A unit of power. c) A unit of kinetic energy. d) That was a terrible joke.
A unit of power. Chapter 5: A watt is a Joule (a unit of energy) per second (a unit of time). Such a unit describes what we call power. Written out in terms of meters, kilograms and seconds, this works out to 1 W = 1 (kg * m2 / s3). a) and c) have units of Joules, and d) is obviously incorrect. It was an awesome joke.
Why must you cool an extreme infrared space-based telescope down to observe faint objects?
A warm telescope will emit its own infrared spectrum. Chapter 6: A warm object emits blackbody radiation. For a spaceborne telescope, this blackbody curve peaks near the extreme infrared, meaning the detector will pick up a lot of photons coming from the body of the telescope. This is very bad. If the telescope is cooled down, it will not emit as many photons in the energy range it is meant to detect, which means less background noise in the spectra and images.
About where is our solar system located within the Milky Way Galaxy?
About two-thirds of the way from the center of the galaxy to the outskirts of the galactic disk. Chapter 1: We are one of 100 billion or so stars in the Milky Way galaxy, orbiting around the galactic center at about 220 kilometres per second. At the galactic center lies a black hole that weighs as much as about 4 million suns!
A particle of light (a photon) hits an electron. All of the photon's energy is turned into kinetic energy in the electron, and no photons are left after the collision. What light/matter interaction has taken place?
Absorption Chapter 5: In absorption events, the photon is completely swallowed up by matter. It can be converted into kinetic energy (where an object speeds up or starts to jiggle), or electromagnetic potential energy (when an electron absorbs a photon, then moves further away from a nucleus to a higher energy orbit). If only part of the energy was absorbed, and the rest left in the form of a photon, this would be a scattering event. If the photon bounced off of the electron and came back, it would be reflection. If the electron was moving, then slowed down to make a photon, it would be emission (emission is the opposite of absorption). If the photon passed right by the electron, we would say it was transmitted.
An atom is missing an electron in one of its electron energy levels, and another electron moves in to fill the space. Which transition would emit the most energetic photon?
An electron drops in energy from the 4th energy level to the lowest (first) energy level. Chapter 5: If the electron drops in energy, that energy has to go somewhere. You can't create or destroy energy; you can only change its form. In this case, the lost energy becomes a photon. The more energy the electron loses, the more energy the photon has. The most energy is lost when the electron takes the biggest step down, so the answer is a). If the electron gains energy, that energy has to come from somewhere. It can only do this if it absorbs a photon.
Kepler's Third Law relates the following characteristics of a planet:
Average distance and period. Chapter 3: Kepler's Third Law states that the cube of the average distance of a planet is related to the square of its orbital period. As an equation, a3 = p2 where a is in Astronomical Units (the distance from the Sun to the Earth) and p is in Earth years.
How has Jupiter helped protect life on Earth (i.e. Why is Jupiter Earth's big brother)?
By gravitationally beating up many of the objects that may have collided with us Chapter 24
What is the main benefit of using CCD cameras over standard film cameras?
CCDs detect a higher fraction of photons. Chapter 6: CCDs have a much better efficiency than film or your eyes. This means that, for a given number of incident photons, you will detect many more with a CCD than the other methods. The more signal, the shorter your exposures need to be to get the same results, which is very desirable.
Which of the following describes our Universe, in terms of expansion? a) recollapsing b) critical c) coasting d) accelerating
Chapter 23: We live in an accelerating Universe. This was discovered in 1998 by comparing the apparent brightness of white dwarf supernovae with their redshifts.
If the Universe were infinite and fairly evenly distributed with stars, but didn't have a Big Bang at the beginning (i.e. it was a "static universe"), what would the night sky look like?
Completely bright Chapter 22: If there were an infinite number of stars, and we could see for an infinite distance, there would be a star at every position in the night sky (actually, if you are good at doing math that involves infinities, you can prove that there would be an infinite number of stars at every position in the night sky!). This would mean that every single part of the sky would actually glow infinitely bright, because every shell around us would have roughly the same brightness, and summing up the constant brightness of infinitely many shells would give an infinite sum! This makes no sense, of course, and people like to argue that it would not be infinitely bright, but rather as bright as the surface of a typical star (which of course still contradicts the darkness of the night sky). However, if you think about this conundrum a little further you figure out that in an infinite static universe there should be no stars. Stars use up high energy fuel (hydrogen) to finally over trillions or maybe quadrillions of years convert it into low energy ash (iron). You need hydrogen injection in the first place (from the Big Bang) to have a universe filled with stars. An infinite static universe should at best be filled with cold iron balls and not produce any radiation.
Which of the following lists the components of the Universe from most massive (or energetic, remember E = mc2) to least massive?
Dark energy, dark matter, regular matter Chapter 22: Currently we think that 73% of all matter/energy in the Universe is dark energy, 23% is dark matter, and 4% is regular matter. We can't directly detect a whopping 96% of the Universe right now, and didn't even know it existed until a few decades ago!
What life-bearing environment on Earth is most similar to where there might be life on the ice-bound Jovian moon Europa?
Deep-sea vents Chapter 24
When is/was gravitational contraction an important energy generation mechanism for the Sun?
During the contraction of the solar nebula. Chapter 14: Fusion hadn't started yet, and the heating of the solar nebula relied on gravitational contraction
Which of the following most accurately describes the overall nuclear process that powers our sun? a) Five protons collide to produce an alpha particle, three electrons, three neutrinos and radiative energy. b) An alpha particle is split into four protons, two electrons and neutrinos, and radiative energy. c) Four protons combine to create an alpha particle, two electrons and neutrinos, and radiative energy. d) Two heavy helium nuclei combine to create a single alpha particle, two electrons and neutrinos, and radiative energy.
Four protons combine to create an alpha particle, two electrons and neutrinos, and radiative energy. Chapter 14: Proposal a) would not even be possible in principle since five nucleons (here: protons) in the initial stage cannot leave only four nucleons (here: two protons and two neutrons in the alpha particle) in the final stage. Same for d), which starts out with eight nucleons. Proposal b) does not work because four protons contain more energy than an alpha particle.
What spectral type describes our Sun? a) K b) F c) O d) G
G Chapter 15: More specifically, our Sun is a G2V star... main sequence luminosity class, spectral type G2 (spectral types are further divided by number [G0, G1...G9]).
Which of the following places the eras in order of ascending time (or descending temperature)?
GUT, electroweak, particle, nucleosynthesis, nuclei, atoms. Chapter 22: See the handy diagram on p. 649.
Which of the following observations led to the idea of dark matter?
Galaxies were found to be more massive than their luminosities would suggest. Chapter 23: We could estimate the mass of stars and dust from the luminosity of the galaxy, but found that this mass alone couldn't explain the rotation characteristics of the galaxy. Thus, there must be something else there that is heavy, but not something we can see.
How did Johannes Kepler contribute to Astronomy?
He determined that planets move in ellipses with the Sun in one of the focal points, and proposed Kepler's Laws of Planetary Motion. Chapter 3: Kepler used Brahe's measurements to determine that planetary motion made sense if the planets were allowed to move around the Sun in ellipses.
What was Nicholas Copernicus' most notable contribution to modern day Astronomy?
He proposed a simplified heliocentric model of the solar system. Chapter 3: Copernicus realized that some of the complex problems in the geocentric (Earth centered) model would not occur in a sun-centered model. He still used circular orbits to describe the motions of the planets around the Sun, which caused his predictions to be inaccurate.
Ptolemy created an astronomical model that allowed for very accurate predictions of the positions of the stars and planets. Why is his model no longer favored today?
His model had the Earth as the center of the solar system. Chapter 3: After adding epicycles to the model, the retrograde motion was (somewhat) explained. However, his model fell out of favour when Copernicus, Brahe and Kepler came up with a better heliocentric (sun centered) model for the solar system.
What was the early Universe (about 15 minutes after the big bang) made of?
Hydrogen and helium, with very little heavier elements. Chapter 1: The young Universe was hot enough to make helium (and a little lithium) through nuclear fusion. However, it cooled off too quickly to make anything heavier. It was only when stars were formed that heavier elements could be made.
What is the Sun mostly made of?
Hydrogen and helium. Chapter 1: The Sun does produce heavier elements, but it is still mostly made of its fuel: H and He. It will start to run out of fuel in about 5 billion years, and will eventually become a red giant star before living out the end of its life as a white dwarf. We will discuss this later in the chapters on stellar astrophysics.
The early Universe contained a roughly uniform distribution of hydrogen and helium, with small pockets of higher density (see Fig. 21.2). Where would you expect galaxies to form?
In the regions of higher density Chapter 21: These dense regions exerted more gravitational force on the nearby gases, pulling them in to form protogalactic clouds.
How can inflation help explain the large-scale uniformity of the Universe today?
It allowed for thermal equilibration between objects that are no longer in the same observable Universe. Chapter 22: There is a problem with the Big Bang model if there was no inflation in the early Universe. If we look to the edge of our observable Universe in one direction, we see pretty much the same thing as we do if we look in the other direction. These two regions are too far apart from each other to have ever interacted. That is, they are not in each other's observable Universes. How did they know to look the same? Inflation answers this by saying that the early observable Universes of these regions (very, very early, like 10-36 s old) contained each other, but after inflation, they couldn't see each other anymore. They spent that first 10-36 s hanging out, bumping into each other, and making sure they were at roughly the same temperature and density before parting ways and never seeing each other again.
The Martian meteorite ALH84001 found in Antarctica was a source of excitement for what reason?
It contained evidence that life might have existed on Mars. Chapter 24
A camera flash appears to be bright white in colour. What does this tell you about the light that was emitted?
It contains a mixture of light from across the visible spectrum. Chapter 5: Objects that look black reflect very little visible light, so what we call black is actually an absence of visible light. Richly hued, colored objects reflect a specific wavelength of light very strongly, which is why we only see one color of light coming off of them. White objects reflect (or in this case, a white light source emits) a broad band of colours, and they all combine to give us white light. There is no such thing as a "white" photon.
Why do we call dark matter "dark"?
It does not seem to emit nor absorb electromagnetic radiation. Chapter 23: We cannot see non-baryonic dark matter, like WIMPS, because they don't interact with photons of any wavelength.
An X-ray source triples in luminosity over the course of a day. What can we conclude about the source?
It must be smaller than a light day across. Chapter 21: If the whole object is changing in luminosity simultaneously, it must be relatively small. If it were large (say 1 light year in diameter), the change in luminosity would be "smeared out" over a year, because we would see the near side getting brighter a year before the far side does.
Why is grass green? a) It absorbs green light and emits all other colors. b) It transmits green light and absorbs all other colors. c) It reflects green light and absorbs all other colors. d) It emits green light due to its surface heat.
It reflects green light and absorbs all other colours. Chapter 5: If a) were true, and grass emitted its own light, it would glow even if there was no sunlight illuminating it (things like glow sticks and light bulbs emit light, non-glowing objects only reflect light that you shine on them). If b) were true, grass would look green, but would also be transparent.
Why does the sun remain roughly the same size?
It tries to expand because of the heat and light it generates, which balances the contraction it feels due to gravity. Chapter 14: Gravitational equilibrium is the correct answer, but b) describes something completely different. Gravitational equilibrium occurs when the energy generated by the sun causes an expansion force that exactly cancels out the contraction force of gravity.
How did an ancient Egyptian "hour" compare to the one we use today?
It varied in length depending on the seasons, because the relative length of day and night changes during the seasons. Chapter 3: They broke up their days and nights into 12 sections, and since the amount of daylight changes with the seasons, so too did the length of the hour.
How did Eratosthenes determine the size of the Earth?
Measuring the distance between two cities and considering the position of the sun at noon on the summer solstice in both places. Chapter 3: None of the other methods would have worked: the positions of the stars and planets don't depend on the size of the Earth in a way that was measurable at the time, Google hadn't been invented yet and the eclipse method would require one to know the distance from the Earth to the Moon.
Kepler's Second Law tells us that a planet with an elliptical orbit will:
Move more slowly when it is further from the Sun. Chapter 3: Kepler's Second Law formally states that a planet will sweep out equal areas in equal times as it passes around the Sun (i.e. its "areal velocity" is constant). In order for it to do this, it needs to travel at a faster rate when its distance from the Sun is smaller.
A motorcycle and a car are driving side by side on a highway at night. The motorcycle's headlight is twice as bright as each car headlight, so that the total light coming from each vehicle is the same. You are standing far enough from the vehicles that the angular separation of the car's headlights is much lower than the angular resolution of your eye. Can you tell which vehicle is which?
No, each will appear as a point source of equally bright light. Chapter 6: If the angular separation was comparable to your angular resolution, you may see that one object has a peanut-shaped single light, while the other has a circular single light, in which case you could reason correctly that the car is the peanut-shaped one. However, if the angular separation is much lower than your angular resolution, you could not tell the difference.
What is the interstellar medium composed of?
Quite sparse gas and dust particles Chapter 16: Most of the disk of the galaxy is populated with sparse gas and dust. These are denser in regions of high star formation, like in the spiral arms.
Which of the following is not a valid reason for why a galaxy may contain only very few young stars?
Short-lived stars are not produced by starbursts. Chapter 21: Short-lived stars are produced by starbursts, but they burn out within ten to hundred million years. That's why elliptical galaxies tend to contain mostly old, long-lived stars these days.
Which effect makes emission lines from far away galaxies look redder than they should, and why?
The Doppler effect; the galaxies are receding from us, so their light looks redder. Chapter 5: Most galaxies are rapidly receding from us. Because of this, the light that they emit seems to be stretched out. This corresponds to a longer wavelength, which makes light shift towards the red side of the visible spectrum. How much it shifts depends upon the speed at which the galaxy is running away.
During the Dark Ages, a time when scientific thinking was rapidly regressing in Europe, where did the majority of scientific advancement take place?
The Middle East. Chapter 3: E.g. Baghdad, in what is now Iraq, became a centre of scientific achievement. They worked on developing the theories of the Greeks, and translating and preserving their texts.
Which of the following observations led to the idea of dark energy?
The Universe's expansion was too fast to be explained through known physics. Chapter 23: The Universe started expanding at the Big Bang, and we expect gravity to slow this expansion down with time. However it actually seems to be accelerating, which makes us think there has to be a uniformly distributed energy present that drives the Universe apart at increasing speed.
Why do we know that gravitational contraction cannot be the source of energy which powers the sun?
The amount of gravitational energy of the sun is too small to power the sun for billions of years. Chapter 14: The amount of gravitational potential energy of the sun could sustain its current power output (i.e. luminosity) only for 25 million years, see slide 8 in the 9th lecture.
What is a light year, and what does it describe?
The distance travelled by light in one Earth year; distance Chapter 1: A light year is defined as the distance travelled by a photon (a particle of light) in a year, if it travels through empty space. Light travels at about 300,000 kilometers per second through vacuum, so one light second would be 300,000 kilometers. The moon is about one and a quarter light seconds away, and the sun is 8 light minutes away. The nearest star, a red dwarf named Proxima Centauri, is about 4.2 light years away. PS: Just for information. A speed of 300,000 kilometers per second is a speed of 1.08 billion kilometers per hour (because if you travel 300,000 kilometers in 1 second, then you travel 300,000 (kilometers/second) x 3,600 seconds = 1.08 billion kilometers in 1 hour, since 1 hour has 3,600 seconds).
Why are distant galaxies often irregular in shape?
The early Universe was crowded, so regular galaxies collided to produce irregular ones more often. Chapter 21
Why do astronomers think our Universe started with a "big bang"?
The galaxies are getting further apart, so a long time ago they must have been very close together. Chapter 1: Far away galaxies are moving further away from us. This is because the space between distant galaxies is expanding. We know the rate of expansion, and it tells us that about 14 billion years ago, there was no distance between the galaxies.
What causes the "lobes" of radio signal seen around AGN galaxies?
The glow of intergalactic gas stimulated by the jets of an AGN. Chapter 21: The powerful magnetic fields in AGN allow them to fire out high energy particles at near the speed of light. As these particles escape the galaxy and encounter the intergalactic medium, they lose some of their energy to collisions, which produce radio photons.
What is the panspermia hypothesis?
The idea that life originated in outer space before landing on the surface of the Earth Chapter 24
Why do far away galaxies look young?
The light from far away galaxies was emitted a long time ago when they were young Chapter 1: As mentioned in the answer to question 1), light from the Sun takes 8 minutes to get to us. So when we look at the sun, we see it the way it was 8 minutes ago. Some galaxies can be as far away as 10 billion light years, so we could be seeing these galaxies as they were 10 billion years ago! That's why, when we look far away, we see many more young galaxies. We also see many more colliding galaxies, as the Universe was a pretty crowded place back then.
Why can't we see further away than about 14 billion light years?
The light has not yet had time to reach us. Chapter 1: We cannot see anything before the big bang, which happened 14 billion years ago. When we look this far away, we see the Universe as it was about 300,000 years after the big bang, in something called the Cosmic Microwave Background Radiation.
Why won't hydrogen fuse at low temperatures?
The protons need to undergo very energetic collisions to form helium, which happens much more often at high temperatures. Chapter 14: It takes a lot of energy to get hydrogen nuclei (protons) close enough to each other to form helium. However, once they do form helium, much more energy is released than was needed in the first place. The net reaction produces energy, but can only happen under energetic (hot) initial conditions.
What is the "Local Group"?
The set of nearby galaxies, spanning about 10 million light years. Chapter 1: Our galaxy is one of many in a galaxy group about 10 million light years across, known as the "Local Group". This group, in part, is one of many groups that compose the 100 million light year wide Virgo Supercluster.
Why do we use the motion of atomic hydrogen gas clouds to gauge the masses of distant spiral galaxies?
They can be found far from the galactic centre. Chapter 23: The rotation speed of a cloud or a star in a galaxy is related to the total mass contained within the orbit of that body. Therefore, to estimate the mass of an entire galaxy, you should look at the motion of something on its edge.
Astronomers define any element but hydrogen, helium and lithium as "metals". Under this definition, the Earth's crust is made mostly of "metallic" substances. Where did these come from originally?
They were formed by fusion processes in stars. Chapter 1: The big bang produced hydrogen and helium, which eventually collapsed to form early stars. These stars then created the heavy elements through fusion, and at the end of their lives exploded as supernovae, seeding the surrounding areas with 'metals'. Human beings contain a lot of carbon, oxygen and other 'metals', all of which was formed from hydrogen and helium in long dead stars.
Why do we think that the CMB came from the era of atoms?
This is when photons were first allowed to freely propagate. Chapter 22: Before the era of atoms, the Universe was densely populated with ions and electrons. These tend to absorb, emit and scatter photons, which would have prevented photons from making it to us unhindered. When the atoms formed, the number of free ions went way down, so photons were free to zip along freely through the Universe in every direction, eventually reaching us from all directions, about 13.6 billion light years away.
Assuming there was a spaceship that could travel at close to the speed of light, what relativistic shenanigans would interstellar astronauts have to deal with?
Time would pass differently for them than for people on planets. Chapter 24
A transparent material
Transmits light very well. Chapter 5: A transparent material like glass allows most photons of visible light through without affecting them (transmission). An opaque material blocks most of the light, either by reflection or absorption.
You wish to observe a galaxy like the Milky Way, but in its infancy. Where do you look?
Very far away. We get an image of galaxies as they were billions of years ago, and so can see many young galaxies. Chapter 21: The collapse of the initial gas distribution into protogalactic clouds happened around the same time throughout the Universe. That tells us that most of the galaxies we see today formed around the same time. Therefore, to look at young galaxies, we need to look very far away to the young Universe. However, answer d is wrong, because there was nothing special about our neighborhood in the universe with respect to galaxy formation.
What property of light determines its "colour"?
Wavelength Chapter 5: The wavelength of a photon determines what color you see. Since the wavelength and the frequency of light are related through the speed of the photon, and all light goes the same speed, the frequency could also tell you the color.
You are looking at a tungsten lamp, which emits a very smooth, continuous spectrum in the wavelengths you are looking in. Suddenly, a dense cloud of hydrogen passes between you and the lamp. How does the spectrum change?
You start to see hydrogen absorption lines. Chapter 5: The light emitted by the tungsten will be absorbed by the hydrogen (if it is at a wavelength corresponding to a hydrogen transition). Therefore you'll see dips in the spectrum at those wavelengths, as not much of that light is making it through. The photons that don't meet the hydrogen transmission requirements will just pass through.
Why would it be a bad idea to shake hands with the antimatter version of yourself?
You would both annihilate and convert to photons. Chapter 22: Matter + Anitmatter = Energy, in the form of photons. A whole lot of it. Nuclear fission of Uranium, the process that fuels nuclear reactors and weapons, converts about 0.1% of the mass of the nuclei into energy. Matter-Antimatter reactions convert 100% of the mass of the objects involved into energy.
What is your "Address" in the Universe, in the correct order?
You, Earth, Solar System, Milky Way Galaxy, Local Group, Universe. Chapter 1: Of course, if you wanted to give a being from another galaxy your address, you'd need to find a different way to tell them. Odds are they don't speak English, and even if they did they probably wouldn't have the same names for the planets, stars and galaxies as we do. So when astronomers tried to convey the location of our solar system to anyone who may come across the Pioneer or Voyager spacecraft, they had to use diagrams and astronomical reference points that another civilization in the Milky Way Galaxy might recognize, see: http://en.wikipedia.org/wiki/Pioneer_plaque - Relative_position_of_the_Sun_to_the_center_of_the_Galaxy_and_14_pulsars
Suppose we made a rotation curve for the moons of Jupiter. Which of the following would best describe this plot?
a falling curve Chapter 23: Most of the mass in this system is located in Jupiter. Therefore, the rotation curve will resemble that of our solar system (Fig 23.1b, p. 669), where most of the mass is located in the Sun.
Which of the following is not an advantage of reflection (mirror) telescopes over refraction (lens) telescopes? a) Reflectors collect more light than a refractor of the same size. b) Reflector optics are easier to manufacture. c) Lenses on refractors must be held from the edges, and are very heavy. d) Lenses cause chromatic aberration of the images.
a) Reflectors collect more light than a refractor of the same size. Chapter 6: Reflectors and refractors collect the same amount of light per unit area. The problem with refractors is that they are tough to make, have to be very long (reflecting allows you to make the tube more compact and the light still travels a long distance) and they degrade much faster (glass warps over time). That is why the majority of scientific telescopes are reflectors. Chromatic aberration occurs because different colours of light refract different amounts through glass (this is why a prism works). This means that photons of different wavelengths will focus at different lengths, blurring the object by different amounts for each colour.
You look up into the sky one day and realize something that astronomers have somehow missed until now: a second sun, pretty much the same as our usual sun (i.e. about the same size and mass and age), but a fair bit further away. You decide to call it Sun 2, because you aren't feeling very creative today. Which one (Sun 1 or Sun 2) looks bigger? a) Sun 1 b) Sun 2 c) they look the same size d) can't tell
a) Sun 1 Chapter 15: A star that's the same size will appear bigger the closer it is to you. This is only true if the stars are close enough to you that they don't appear as point sources (they are larger in angle than your angular resolution). The sun is close enough that we can see its shape, and Sun 2 will be as well.
Which one (Sun 1 or Sun 2) looks brighter? a) Sun 1 b) Sun 2 c) they look equally bright d) can't tell
a) Sun 1 Chapter 15: For objects that are about the same luminosity, the closer one will appear brighter. The brightness is related to the inverse distance squared, so a star that's twice as close will appear four times brighter. This is true even for angularly unresolved stars.
Which of the following is false? a) When you listen to the radio, you are using your ear to detect radio waves. b) Humans cannot detect infrared radiation, as it is not in the visible spectrum. c) The sun is similar to a black body, so we can tell its temperature from its spectrum. d) Most of the positive charge in an atom is concentrated in a tiny atomic nucleus.
a) When you listen to the radio, you are using your ear to detect radio waves. Chapter 5: Your ear does not detect radio waves. Radio waves are electromagnetic waves with a very long wavelength, which we use to transmit information through the air. This information is then interpreted by your radio, and converted into sound waves (pressure waves that travel through air).
Which of the following would be a plausible way to observe a MACHO? a) monitor a distant star for lensing events b) look into the galactic halo for their visible light output c) spot them on the outskirts of distant galaxies d) none of the above
a) monitor a distant star for lensing events. Chapter 23: MACHOs are too dim to be seen from Earth, but when they pass in front of background stars, they can focus some of the light towards the Earth, acting as a gravitational lens. This causes the stars to appear brighter than usual for a little while.
Which of the following is not a requirement for life on Earth ? a) Energy b) Oxygen c) Liquid water d) A nutrient source
b) Oxygen Chapter 24
Which of the following phases of a material is the hottest? a) Liquid b) Plasma c) Solid d) Gas
b) Plasma Chapter 5: If kept at the same pressure, a solid material will normally melt into a liquid, then boil into a gas, then start having its electrons stripped away (making it a plasma) as its temperature increases. Some materials skip a step, however. Carbon dioxide (CO2) is called "dry ice" in its solid form (around -80ºC at normal pressures). When you heat it up, it skips the liquid stage altogether and becomes a gas. This is known as sublimation.
Which of the following best represents the ratio of dark matter to regular matter in the Milky Way, in terms of mass? a) 0.1:1 b) 1:1 c) 10:1 d) 100:1
c) 10:1 Chapter 23: This is our best estimate, which we find from rotational dynamics (e.g. from rotation curves for the Milky Way galaxy like the one on slide 13 of lecture 20). We can also find the location of the mass through rotational dynamics, and it appears to be located in a halo that extends far beyond the disk of the galaxy. The dark matter is in a spherical shape, because it does not radiate away energy or collide with other objects, and therefore cannot collapse into a disk like the regular matter in a spiral galaxy.
Which of the following experiments is least likely to yield useful results? a) A sea-level visual imaging telescope. b) A space-based infrared imaging telescope. c) A sea-level X-ray imaging telescope. d) A mountaintop visual telescope.
c) A sea-level X-ray imaging telescope. Chapter 6: Visible light penetrates the atmosphere quite well, so a sea level or mountaintop imaging telescope would be fine. It's better to put it into space where there is no such thing as weather or daytime, but that's expensive. Infrared doesn't penetrate the Earth's atmosphere very well, so any infrared telescope would have to be elevated quite high (ideally into space). X-rays are awful at penetrating the atmosphere, so a sea-level based X-ray telescope would not work very well at all. In fact, the first astronomical X-ray observation had to wait until satellite technology allowed for a space-based observatory.
Which of the following is not a good reason to launch a telescope into space? a) It can detect X-ray radiation. b) There is no atmospheric interference. c) It is closer to the objects it is measuring. d) It is able to take data 24/7.
c) It is closer to the objects it is measuring. Chapter 6: Putting a telescope into space puts it a few hundred kilometers above the Earth. This distance is peanuts compared to even the distance of the nearest star (4 light years or 38,000,000,000,000 km)
Which of the following is not a concern when considering whether or not planets around other stars may be able to support life? a) The stability of the orbit b) The lifetime of the star c) The number of planets orbiting the star d) The mass of the star, and hence the size of its habitable zone
c) The number of planets orbiting the star Chapter 24
Which of the following stars is the hottest? a) Justin Bieber b) a K star c) an O star d) Megan Fox
c) an O star Chapter 15: An O star can have an average surface temperature of 30,000 K, while Justin Bieber and Megan Fox have average surface temperatures of about 306 K.
Which one (Sun 1 or Sun 2) is more luminous? a) Sun 1 b) Sun 2 c) they are about equally luminous d) can't tell
c) they are about equally luminous Chapter 15: If they have about the same size and mass and age, then they also have about the same amount of hydrogen and about the same core temperature and density. Therefore they should have about the same hydrogen fusion rate and about the same energy output
You find an ion of a rare isotope of the (hitherto undetected) element Unobtanium while on a family vacation to Pandora. The nucleus of this isotope has 215 protons and 285 neutrons, and it has 213 electrons surrounding it. Which of the following are the correct atomic number, weight and charge (in that order)? a) 215, 500, -2 b) 500, 215, -2 c) 500, 215, +2 d) 215, 500, +2
d) 215, 500, +2 Chapter 5: The atomic number is simply the number of protons (here, 215), and the atomic weight is the number of protons plus the number of neutrons (215 + 285 = 500). The charge will be +1 for every proton, -1 for every electron, so the charge is 215-213=+2. Actually, a question of exactly this form won't be included in an exam, since it involves calculations (albeit extremely simple calculations).
If you have a spectrometer attached to your telescope, and are not capable of direct imaging, which of the following experiments can you not perform? a) Determine the radial speed of a star. b) Determine the colour of a star. c) Determine the rotational speed of a star. d) Determine the size of a galaxy.
d) Determine the size of a galaxy. Chapter 6: The radial speed of the star is found from an offset of the emission line positions from where you find them in a non-moving source. The colour can be found by looking at the blackbody continuum of the spectrum. The rotational speed can be found as it is described in the last question. However, since you only get a graph of intensity versus wavelength out of a spectroscopic measurement, you cannot measure the physical size of an object like a galaxy.
If you have a camera (but not a spectrometer) hooked up to your telescope, which of the following experiments can you not perform? a) Measure the period of a variable star (how long it takes to brighten and dim) b) Determine the colour of a star c) Measure the brightness of a star d) Find out how fast a star is rotating
d) Find out how fast a star is rotating Chapter 6: Measuring the period of a variable star is as easy as taking a long series of pictures, finding the brightness in the star of each, and making a graph of brightness versus time (what astronomers call a "light curve"). The colour can be pinned down by looking at the star through two or more filters and comparing its brightness in each. The rotation speed normally requires you to take the spectrum of the star, and look at how much the emission lines are broadened by the star's rotation (the light is redshifted from the part of the star that's spinning away from you, and blue shifted from the part of the light that's spinning towards you, making the line a lot broader).
Which of the following would allow you to estimate the total mass of a galactic cluster? a) the velocities of individual galaxies within the cluster b) the temperature of the intra-cluster medium c) gravitational lensing of background galaxies d) all of the above
d) all of the above Chapter 23: You can use Newtonian mechanics to find the mass through a), kinetic theory to find it through b), and general relativity to find it through c). All of these point to a large amount of mass in clusters being dark matter.
How did Tycho Brahe contribute to the field of Astronomy? a) He recruited Kepler as his assistant for analyzing his observational data. b) He determined that comets and novae occur much further away than the moon. c) He took extremely detailed and accurate measurements of the positions of heavenly bodies. d) all of the above.
d) all of the above. Chapter 3: Brahe observed distant objects and used the method of parallax to compare their distance to that of the Moon. He also created a large collection of measurements that Kepler would later use to formulate his laws of motion. And he recruited Kepler.
How did Galileo contribute to modern Astronomy? a) He refined the telescope for use as a scientific instrument. b) He discovered the largest 4 moons around Jupiter. c) He showed that Venus actually rotated around the Sun, not the Earth. d) all of the above.
d) all of the above. Chapter 3: Galileo greatly improved the power and precision of the telescope, allowing him to see the four large moons of Jupiter (now known as the Galilean moons). This was a serious blow to the idea that every celestial body rotated around the Earth. As well, he observed phases of Venus, which only made sense if both were considered to be rotating around the Sun.
Han Solo tells you that the Millenium Falcon can do the Kessel Run in less than twelve parsecs. What does this mean? a) His ship can complete the Kessel Run in a very short amount of time b) His ship can complete the Kessel Run in a very short distance c) George Lucas needs to take an astronomy class d) b) and c)
d) b) and c) Chapter 15: Twelve parsecs is a measure of distance equal to about 40 or so light years. Bragging about being able to finish a space route in 12 pc is like bragging about finishing a marathon in one kilometre. Of course, the star wars fans have corrected Lucas' mistake after the fact: http://starwars.wikia.com/wiki/Kessel_Run If you are a star wars fan (like me), please refrain from sending me hate mail.
You observe a star through two colour filters, and determine that it has a bluish white colour, like that of a B star. What does this tell you about the star's luminosity? a) it is about 103 to 104 times as luminous as the sun b) it is about 105 times as luminous as the sun c) it is about 0.01 to 0.1 times as luminous as the sun d) cannot tell
d) cannot tell Chapter 15: B stars can come in different luminosity classes (dwarfs, main sequence stars, giants, etc.), and will have different luminosities accordingly.
Which of the following would be a plausible way to observe a WIMP? a) monitor a distant star for lensing events b) look into the galactic halo for their visible light output c) spot them on the outskirts of distant galaxies d) none of the above
d) none of the above Chapter 23: WIMPs cannot be detected by normal astronomical means, as they don't interact with photons. Instead we have to look for them in particle physics labs, e.g. by looking for rare spontaneous recoils of atomic nuclei due to a hit by a WIMP. Or we have to look for them in collisions at the Large Hadron Collider, where WIMPs would lead to a "missing energy" signal by carrying away some of the collision energy without being seen.
What type of electromagnetic radiation does the majority of SETI use? a) gamma b) ultraviolet c) microwave d) radio
d) radio Chapter 24
You are a WIMP. Now, before you go filing complaints to the University administration about me insulting you, please remember that a WIMP is a Weakly Interacting Charged Particle. Which of the following pairs of forces don't you feel?
electromagnetic and strong Chapter 22: Anything with mass must feel the gravitational force, and WIMPs must have mass if they're going to explain why the visible part of galaxies appears to be too light. Because WIMPs are eletrically neutral they can't feel the electromagnetic force (if they could, they'd be able to interact with photons, as photons carry the electromagnetic force). If WIMPs felt the strong force, we'd be able to observe their interaction with atomic nuclei, which we don't. If WIMPs didn't feel the weak force, there would be no known process for creating them in the numbers that they must exist in now.
An optometrist finds that the focal plane of your eye does not coincide with your retina when you look at objects that are far away from you. What problem would you notice with your eyesight?
everything you see is blurry. Chapter 6: The focal plane is the distance from a lens in which all of the light rays will form a clear image of their source. If the focal plane does not coincide with the retina, a blurry image will result, as light rays from many parts of the object will end up on the same spot on the retina. When the retina is in the focal plane, each point on the object will be resolved to a point on the retina.
You are 1 AU from a neutron star. Which force do you feel the most?
gravity Chapter 22: At large distances, gravity is the strongest force as long as everything else is electrically neutral (and neutrons are neutral). However, at short distances, it is the weakest. Consider dropping a bowling ball off of a skyscraper. Gravity has hundreds of feet to accelerate it. Then, when it hits the ground, its electrons and the ground's electrons say "no way, man", and push away from each other, stopping the ball within centimetres. Gravity dominated at long distances to attract the ball to the ground, then electromagnetism took over and stopped it away when it got too close.
What does the apparent magnitude of a star tell you about that star?
how bright it looks Chapter 15: Apparent magnitude is how bright a star looks from the Earth. It is related to how luminous the star actually is, and how far it is from the Earth. However, you can't determine either of these characteristics if you only know the apparent magnitude.
You observe a single point of light, and see that its spectrum changes between redshifted and blueshifted over the course of a couple weeks, while the brightness remains the same. What kind of binary system would this indicate?
spectroscopic binary Chapter 15: A visual binary would appear as two points of light, while an eclipsing binary would get peridically dimmer and brighter.
