Astronomy & Cosmology - Polls and Homework
When and how were most of the helium nuclei in the universe created?
3 minutes after the Big Bang, via nuclear fusion. During the first second after the Big Bang, photon collisions formed protons and antiprotons as well as electrons and positrons. The matter and anti-matter annihilated, but there was a bit of extra matter, and this remained as the universe cooled. About three minutes after the Big Bang, the temperature became cool enough for deuterium to form and then fuse into helium nuclei. A few hundred thousand years later, the universe became cool enough for those helium nuclei to capture electrons and become neutral atoms. Although a lot of helium has formed in nuclear fusion in stars, 10 times more helium was created in the first three minutes after the Big Bang.
Hubble's Law is v=Hd where H=22 km/s per million light years. A galaxy named Bon Jovi is moving away from us at 110 km/s. How far away is that galaxy?
5 million light years
If the Sun suddenly collapsed into a Black Hole without changing its mass, the Earth would
Continue in its usual orbit, with darkness beginning 8 minutes later
T or F: In the Hertzsprung-Russell diagram of Figure 18.14, stars at the upper left have low surface temperature and high luminosity.
False. Stars at the upper left have high surface temperature and high luminosity. The temperature axis of the H-R diagram is reversed from a typical graph, with surface temperature decreasing towards the right.
T or F: An object in orbit is weightless because it is moving too quickly to be affected by gravity.
False. Any freely falling object will experience weightlessness. Objects in orbit are continuously falling towards the central object but have enough sideways velocity to stay in orbit rather than falling straight down. Gravity's effects are independent of an object's speed.
T or F: Figure 22.3 shows that the supergiant star Xi Cygni is shaped like a crescent moon instead of a sphere.
False. As the figure caption explains, Xi Cygni is so big that only a small piece of it is shown in the figure; that piece happens to look a bit like a crescent. Like all stars, Xi Cygni is nearly spherical.
T or F: Like white dwarfs and neutron stars, black holes get smaller in size as their mass increases.
False. Black holes satisfy the normal expectation of more massive objects being larger, as can be seen from the formula R_S=2GM/c^2 , where M is the mass of the black hole), where a larger mass corresponds to a larger Schwarzschild radius.
T or F: The autumnal equinox occurs about March 21 and features nearly 12-hour nights everywhere on Earth.
False. Everywhere on Earth has roughly 12 hours of daylight and 12 hours of night at the vernal equinox (March 21) and the autumnal equinox (September 21).
T or F: Most of the volume of the interstellar medium is filled with H II regions containing ionized hydrogen.
False. H II regions (pronounced "H two regions") contain ionized hydrogen and are an important component of the interstellar medium, but they occupy a very small fraction of its volume.
T or F: The inflationary universe model predicts that the universe contracted by a factor of 10^50 shortly after the Big Bang; this successfully explains why the cosmic microwave background radiation is so uniform and why our universe is at critical density.
False. Inflation predicts that the universe expanded by a factor of 10^50 rather than contracting. The rest of the statement is accurate.
T or F: Conservation of angular momentum causes a figure skater who is spinning and then brings their arms inwards to spin more slowly.
False. It's the opposite - as the figure skater becomes smaller, their spin must increase to conserve angular momentum, which is the product of their mass, size, and rotational speed.
T or F: A black hole is an object so dense that only X-rays can escape from it.
False. No type of light can escape from a black hole. X-rays are sometimes used to detect black holes, but they are leaving from accretion disks that lie outside the black hole's event horizon, so they are not escaping from the black hole itself.
T or F: Table 18.2 tells us that there is no way to measure a star's diameter unless it is part of a binary system.
False. One of the methods listed in the table only works for binary systems, but measuring how long it takes for the Moon's edge to fully eclipse the star works for single stars.
T or F: Refracting telescopes use mirrors to focus the incoming light.
False. Refracting telescopes use lenses to focus the light; reflecting telescopes use mirrors to focus the light.
T or F: Our best current candidate for the dark matter is a Weakly Interacting Massive Particle. Millions of these particles would pass through you each second without interacting with the regular matter in your body.
True. It's very strange to think of particles being able to pass through us without interacting with the atoms in our bodies, but we already know that this happens with neutrinos. The incredibly low interaction rate with WIMPs appears to explain why we haven't detected them yet in laboratory experiments.
Figure 17.5 shows that the strongest hydrogen absorption lines are found in stars of spectral type A.
True.
T or F: At the center of the Milky Way galaxy is a dark central object found to have a mass of over 4 million solar masses compressed within a region the size of Mercury's orbit. Characterizing this region and showing that the density is so high that it appears to be a supermassive black hole led to Andrea Ghez and Reinhard Genzel sharing half of the 2020 Nobel Prize in Physics.
True.
T or F: Because distances are difficult to measure, as of 100 years ago, galaxies like M31 were thought to be spiral-shaped nebulae within the Milky Way galaxy.
True.
T or F: Some quasars are able to generate more luminosity than an entire galaxy despite not being significantly larger than our solar system.
True.
T or F: Star formation begins when gravity causes the core of a molecular cloud to collapse, leading its density to increase by a factor of 10^20.
True.
T or F: The cosmological principle implies that the universe looks roughly the same at all locations (homogeneity) and in all directions (isotropy).
True.
T or F: The interstellar medium (ISM) refers to gas and dust between stars, including giant clouds called nebulae and dense clouds where new stars are forming.
True.
T or F: The method called "spectroscopic parallax" can be used when a star's spectral and luminosity classes are known from its spectrum. Spectroscopic parallax refers to reading that star's luminosity off the H-R diagram and then comparing that with its apparent brightness to determine its distance.
True.
T or F: The size and rotational speed of the disk of hot gas in the center of the galaxy M87 implies that it surrounds a black hole of at least 3.5 billion solar masses.
True.
T or F: In Astronomy, parallax refers to the amount that a star's position in the sky shifts versus more distant background stars as the Earth moves through its orbit.
True. (sometimes referred to as trigonometric parallax.)
T or F: Dark matter comprises 90% of the total mass of our Milky Way galaxy but no more than 50% of the mass in the thin disk near the Sun's location.
True. At least half of the mass within a few hundred light years of the Sun appears to be from the luminous stars and gas, but in the outer halo of our galaxy it's primarily dark matter.
T or F: A helium nucleus has slightly less mass than four hydrogen nuclei combined.
True. Energy is released when hydrogen fuses into helium precisely because the final helium nucleus has slightly less mass than four hydrogen nuclei combined. Mass has been turned into energy.
T or F: As shown in Figure 20.11, dust absorbs visible light from stars but shines brightly with its own infrared light.
True. Figure 20.11 shows in the left panel that dust absorbs visible light from stars. The right panel of Figure 20.11 shows that the same regions that are dark on the left are now bright, because they emit significant infrared light due to blackbody emission from the dust grains.
T or F: In general relativity, the downward acceleration of an object due to Earth's gravity is caused by the way that Earth's mass curves spacetime.
True. Figure 24.8 attempts to depict this; Earth causes the local space to curve in a 4th dimension (time), causing objects like us (analogous to the ant) to fall towards the center of the Earth.
T or F: A blue galaxy must have formed new stars in the last 100 million years before its light was emitted.
True. For a galaxy to appear blue, it must have a lot of O and B main sequence stars, and those stars have main sequence lifetimes of 1-30 million years. So there must have been significant formation of new stars in the past 100 million years.
T or F: Rainbows result from a natural spectrometer composed of raindrops.
True. Isaac Newton designed the first human-made spectrometer, using a pinhole and a prism. But nature has been doing this ever since the first rainfall; light traveling from air into water refracts (bends), and this splits the various colors of light, which then reflect off the back of the raindrops and head towards our eyes.
T or F: Every chemical element exhibits a different set of spectral lines.
True. It depends upon the specific set of electron energy levels that the element has. A more detailed statement would point out that every different ionization state of every chemical element has its own set of spectral lines i.e., ionized oxygen has different spectral lines than neutral oxygen.
When it is summer in Australia, it is
Winter in New Jersey
Why do virtually all of the galaxies in the Universe appear to be moving away from us?
basically all galaxies are moving away from all other galaxies
Desirable qualities for a modern large telescope site on Earth's surface:
1. Clean airflow for good "seeing". 2. No light pollution from nearby cities. 3.High altitude to reduce water vapor. 4. Most nights are cloudless.
Four fundamental forces of nature:
1. Gravity 2. Electromagnetism 3. The weak nuclear force 4. The strong nuclear force We know that all of them except gravity were unified into a single force at very high temperature shortly after the Big Bang; attempts to unify gravity with the others have led to string theory but not yet to a clear success.
The phases of the Moon are caused by the following:
1. How much of the side facing Earth is illuminated by the Sun. 2. The Moon's orbit around Earth.
What are ways to detect exoplanets?
1. Measure Doppler shifts of a star as the star and exoplanet both orbit their common center-of-mass. 2. Look for periodic dimming in a star's light curve as the exoplanet crosses in front of it. 3. Image the exoplanet directly in the infrared while subtracting the light from the host star.
Kepler's Laws:
1. Objects orbiting the Sun trace out ellipses with the Sun at one focus. 2. A planet's orbit sweeps out equal areas in equal intervals of time. 3. For an object orbiting the Sun, the square of its orbital period in years equals the cube of the semi-major axis of its orbit measured in AU.
Light:
1. can be referred to as electromagnetic radiation. 2. in empty space, light always moves at a fixed speed. 3. light waves can move in a vacuum. 4. interacts with matter in the form of particles of energy called photons. 5. sometimes act like a particle, called a photon, instead of a wave.
The sidereal day is shorter than the solar day by roughly 4 minutes for the following reasons:
1. it is defined versus the stars, and the stars rise 4 minutes earlier each solar day. 2. Earth's orbit around the Sun causes one extra rotation per year versus the stars.
Interstellar dust affects visible starlight in the following ways:
1. makes it redder 2. scatters some of it 3. absorbs some of it 4. reflects some of it Interstellar dust scatters some of the visible starlight, and some of that scattered light is reflected back in the direction it came from. Interstellar dust absorbs some of the visible starlight, and it absorbs blue light more than red light, making the starlight that passes through the dust appear redder than it was originally.
As the first person known to have observed the skies with a telescope, Galileo's important discoveries included:
1. that Jupiter has moons, which showed that Earth was not a special planet. 2. that our Moon has geological features like Earth, again making Earth less special. 3. the phases of Venus, which had been predicted by the Copernican model. 4. the band of light across the sky called the Milky Way was comprised of many individual stars.
Table 17.1 shows that the following statements are true:
1. the Sun's surface temperature is twice as hot as that of Betelgeuse 2. orange stars always have cooler surface temperatures than blue stars. There is a direct correspondence between a star's color and its surface (but not core) temperature. Size is determined by surface temperature or color only for main sequence stars, but not for white dwarfs or red giants.
Compared to a photon with wavelength 800 nm, how much energy does a photon with wavelength 400 nm have?
2 times as much. The formula for photon energy is E = hf where h is Planck's constant and f is frequency. We also know that the speed of light is given by c=lambda*f This means that wavelength (lambda) and frequency are inversely proportional. So the 400nm photon has half the wavelength but twice the frequency of the 800nm photon and hence it has twice the energy.
An object moving towards Earth at half the speed of light shines an orange laser (wavelength of 600 nm) at us. What wavelength (in nm) do we see the light at?
300 nm.
Roughly how long after the Big Bang did the universe become transparent to light for the first time?
380,000 years (i.e., roughly 400,000 years) after the Big Bang, the universe cooled enough for neutral atoms to form. All of the free electrons combined with protons and helium nuclei to form hydrogen and helium atoms. While the free electrons scattered light of all energies, neutral atoms only absorb a few specific energies, so the universe changed from opaque to transparent. The resulting Cosmic Microwave Background radiation was discovered in 1964 by Penzias and Wilson. All of this occurred before the end of the cosmic "Dark Ages", which were a time when no stars were yet present but the Cosmic Microwave Background radiation was already visible.
Speed of light is
3x10^5 km/s.
Approximately, what is the highest frequency at which you can wave your hand: 0.2 Hz, 1 Hz, 4 Hz, or 40 Hz?
4 Hz.
40 degrees north latitude goes right through New Jersey.How high is Polaris in the sky as viewed from New Jersey?
40 degrees above the horizon (50 degrees from the zenith)
In order to stay fit, you take a 20-pound barbell with you on an interstellar journey to a planet with the same mass as Earth but twice Earth's radius. How many pounds would that barbell weigh on the planet's surface?
5 pounds. 20 pounds = G M(Earth) M(barbell)/ R^2(Earth). The barbell's weight on the new planet will be given by F = G M(Earth) M(barbell)/ (2 R^2(Earth) ) which is four times smaller, or 5 pounds.
Which of the following statements describe dark matter in the Milky Way galaxy? (Check all that apply) A. It is 95% of the Galaxy's mass B. It is found in a spherical "halo" extending far beyond the luminous parts of the galaxy C. It emits electromagnetic radiation as a blackbody D. It has no gravitational effect on the visible stars or gas
A and B. Additionally, the dark matter does not appear to emit any electromagnetic radiation (hence the description of being "dark"). And the presence of dark matter is inferred by the ability of its gravity to explain how stars could orbit the center of the Milky Way so quickly without having escape velocity and leaving our galaxy.
Which of the following statements about quasars are accurate? (Check all that apply) A. They can outshine the galaxy that surrounds them by a factor of 100 or more. B. They are typically found in the halos of galaxies, far from their centers. C. They cannot easily be distinguished from stars by taking a picture. D. About half of their spectra show blueshifts.
A and C. In astronomical images, quasars look just like stars, and we cannot easily see their surrounding galaxies. But when we look closely enough with the Hubble Space Telescope, quasars are always found in the centers of dimmer surrounding galaxies. All of their spectra show redshifts. QSO stands for quasi-stellar object.
Which of the following statements are true about the hot and cold spots in the Cosmic Microwave Background radiation shown in Figure 29.20? (Check all that apply) A. They match the angular size predicted for hot and cold spots in a universe whose density matches critical density. B. They match the angular size predicted for hot and cold spots in a universe whose density exceeds critical density. C. They match the angular size predicted for hot and cold spots in a universe whose density is less than critical density. D. They reveal fluctuations in density in the early universe, where the densest regions eventually collapsed into galaxies and galaxy clusters.
A and D. The hot and cold spots in the CMB represent minute fluctuations in temperature, only one part in 100,000 different from uniformity. They imply equally minute variations in density in the early universe, but those ever-so-slightly denser regions expanded slower than their surroundings and eventually became so much denser than the rest that they were able to collapse into galaxies and galaxy clusters. The typical angular size of the spots matches that predicted for a universe at critical density to 1% precision.
Which of the following methods can be used to estimate the amount of dark matter in a galaxy cluster? (Check all that apply) A. Measure the velocities that galaxies in the cluster are moving at B. Use the Very Large Telescope on Cerro Paranal to study the Magellanic Clouds. C. Use arcs produced by gravitational lensing to create a map of all the mass in the cluster D. Use X-ray observations to infer the temperature of the gas between galaxies in the cluster
A, C, D. Galaxy velocities, gravitational lensing, and X-ray observations all enable us to infer the amount of mass that the cluster has. All of these methods indicate that dark matter is present between the galaxies as while as within them and that it provides roughly 90% of the mass of each galaxy cluster.
Which photon has the most energy? A.A green photon from a laser pointer (λ = 550 nm = 5.5 ×10-7m) B. A yellow photon from the Sun (λ=580nm = 5.8×10-7m) C.An infrared photon from a remote control (λ = 940 nm = 9.4 ×10-7m) D.A radio photon from an iClicker (λ = 0.33 m)
A. A green photon from a laser pointer (λ = 550 nm = 5.5 ×10-7m) E = hf ; λf = c so E = hc/λ
Which of the following conditions are even extremophiles unable to tolerate? A. hydrothermal vents at 300 degrees Celsius B. 1000 times atmospheric pressure at the bottom of ocean trenches C. water ten times as salty as seawater D. pH values near 0 or 13 E. temperatures as low as -25 degrees Celsius
A. hydrothermal vents at 300 degrees Celsius. Amazingly, life has been found in all of these conditions except for 300 degrees Celsius, which is well above the boiling temperature of water. The textbook describes that the heat record for extremophiles is 122 degrees Celsius and that life has been found in all of the other listed conditions.
Which of the following is not expanding in the expanding Universe? A. the size of individual galaxies B. the space between galaxies C. the distance between galaxies D. the wavelength of photons traveling through the Universe
A. the size of individual galaxies
If the Sun formed from a molecular cloud with lots of other stars at the same time, why isn't the solar system part of a star cluster today?
All of the stars formed with different velocities and have moved away
Which of the following are powered by central supermassive black holes? (Check all that apply) A. Type II supernovae B. active galactic nuclei C. quasars D. the Orion nebula
B and C. Quasars are the most luminous type of active galactic nucleus, and both are powered by central supermassive black holes, which are not found anywhere outside the centers of galaxies.
Which of the following happen shortly after a massive star creates iron in its core? (check all that apply) A. iron fuses into heavier elements like lead B. iron refuses to fuse, leading to a lack of pressure to counter gravity C. the core collapses into a stable white dwarf that will slowly cool over billions of years D. the core collapses into a neutron star E. the sudden influence of neutron degeneracy pressure causes an outward shock wave that, combined with energy from neutrinos, blows the outer layers of the star apart in a Type II supernova explosion
B, D, and E. Iron does not fuse, which removes the outward pressure in the core, allowing gravity to force a collapse. There is enough gravity to overcome electron degeneracy pressure and collapse to much denser conditions than a white dwarf, so dense that protons and electrons combine to form neutrons and neutrinos. The resulting neutron star has the density of an atomic nucleus, packing roughly 2 solar masses of material into a sphere with a radius of 20 km. The resulting neutron degeneracy pressure resists further compression and generates an outward-going shockwave whose energy combines with that of the neutrinos to blow apart the outer layers of the star in a Type II supernova.
The Fermi paradox refers to the idea that extraterrestrial life is common in our galaxy even though we have not seen evidence for it. Which of the following offer plausible solutions? (Check all that apply) A. The building blocks of organic molecules, including carbon, nitrogen, and oxygen, are not found outside our solar system. B. Technological civilizations are not (yet) common. C. Technological civilizations choose not to broadcast their presence in ways that we can detect. D. Technological civilizations do not last long before self-destructing.
B,C, and D. The Fermi paradox is resolved if, even though life is common in our galaxy, technological civilizations are hard to find because they haven't evolved widely or don't last long or are good at hiding their presence from us. While carbon, nitrogen, and oxygen are indeed necessary for life as we know it, they are produced by nuclear fusion in stars and are widely available throughout our galaxy and universe.
If you were to look at our solar system in 15 billion years, what would you see? A. the Sun, still on the main sequence B. a white dwarf C. a neutron star D. a black hole
B. a white dwarf
What are Red Giants? A. stars that fuse hydrogen into helium in the core B. stars that fuse hydrogen into helium in a shell around the core C. stars that break apart helium by fission in the core D. objects that are not massive enough to start fusing hydrogen in the core
B. stars that fuse hydrogen into helium in a shell around the core.
Which of the following is true about the Sun? A. the Sun has the highest luminosity of all the stars we can see B. the Sun has the highest apparent brightness of all the stars we can see C. both A and B D. neither A nor B
B. the Sun has the highest apparent brightness of all the stars we can see
An interferometer is a set of multiple telescopes set far apart whose light is then combined. The biggest advantage of this is
Better angular resolution, as you'd get from a single telescope spanning the separation of the telescopes
Which of the following is NOT an advantage that the Hubble Space Telescope (HST) has over ground based telescopes? A. HST is above the atmosphere so it can take sharper images B. HST can observe ultraviolet and infrared wavelengths that don't reach the ground C. HST has a larger diameter than all ground-based optical telescopes D. HST is less affected by light emitted or scattered by the atmosphere
C. HST has a larger diameter than all ground-based optical telescopes
Rank the following in terms of when they initially formed, starting with the earliest to form. A. galaxies, deuterium nuclei, protons, hydrogen atoms B. deuterium nuclei, protons, hydrogen atoms, galaxies C. protons, deuterium nuclei, hydrogen atoms, galaxies D. hydrogen atoms, protons, deuterium nuclei, galaxies
C. protons, deuterium nuclei, hydrogen atoms, galaxies
What is our best current model for the nature of most of the dark matter?
Cold dark matter. A small fraction of the dark matter could consist of regular matter (protons, neutrons, and electrons) in the form of white dwarfs, brown dwarfs, and black holes, but the low observed incidence of gravitational lensing by MACHOs (MAssive Compact Halo Objects) implies that the majority of the dark matter in our galaxy must not be in the form of regular matter. The large-scale structure observed in the galaxy distribution favors the cold dark matter model over that of hot dark matter, where cold dark matter particles move slowly but hot dark matter particles would move more quickly.
In our universe today, dark energy provides 70% of the critical density and matter provides the other 30% of critical density. Which of the models depicted in Figure 29.9 best describes our universe?
Curve 4 corresponds to our universe, where the matter's gravity caused the expansion to decelerate after the Big Bang, but dark energy recently caused the universe's expansion to switch to acceleration. We expect the acceleration to continue indefinitely.
Which of the following has been found in meteorites that landed on Earth? A. DNA B. triglycerides C. proteins D. amino acids
D. Amino acids. They have been found in meteorites, as have fatty acids. Proteins, DNA, and triglycerides are more complex molecules and have not been found.
Which of the following did not form via the gravitational collapse and assembly of initial clumps in the early universe that were denser than the surrounding matter? A. galaxies B. galaxy clusters C. superclusters D. planets E. the Milky Way
D. planets
Which of the following represents less than 1% of the total energy density of our universe? A. dark energy B. dark matter C. hydrogen and helium gas between stars and galaxies D. stars and planets
D. stars and planets
Which of the following statements best describes our current knowledge of the expansion of the universe? A. the expansion has always been accelerating and will continue forever B. the expansion has always been decelerating, and collapse is imminent C. the expansion was accelerating, is now decelerating, and expansion will soon turn into collapse D. the expansion was decelerating, is now accelerating, and expansion will continue forever
D. the expansion was decelerating, is now accelerating, and expansion will continue forever
Pulsating variable stars:
Delta Cephei and RR Lyrae are specific stars that are pulsating variables; stars like them are referred to as Cepheids and RR Lyrae respectively. Polaris is a Cepheid-type variable.
Which of the following is not a feature of interstellar dust? A. Dust emits infrared light B. Dust scatters starlight C. Dust reddens starlight D. Dust reflects starlight E. Dust adds emission lines to the spectrum of background stars
E. Dust adds emission lines to the spectrum of background stars
The constellations in Table 2.1 of the textbook are offset from common astrological "signs" by almost one month. Why?
Earth's axis of rotation has precessed by 1/12 of a circle since the astrological signs were defined. The direction in which the Earth's axis of rotation points (from South to North) moves through a large circle on the sky every 26,000 years. Polaris won't be the North Star for much longer. Astrological signs were defined 2,000 years ago, so we're 1/13 of the way through the precession, and that shifts which constellation of the Zodiac the Sun is in at a given date by nearly a month.
What can be used in a spectrometer to disperse the light into a full spectrum of colors?
Either a prism or a grating can be used. The prism refracts (bends) different colors of light by different amounts, separating them. A diffraction grating uses diffraction for a different kind of bending, but the result is the same.
What shape are the orbits of planets in our solar system?
Elliptical with the Sun at one focus.
T or F: There is no way to observe galaxies as they existed 13 billion years ago.
False. Telescopes function as time machines. By looking at very distant galaxies, we can indeed see galaxies as they existed about 1 billion years after the Big Bang; these galaxies' light has spent the subsequent 13 billion years traveling to Earth.
T or F: In 1998, two groups of astronomers studying Type Ia supernovae reported evidence that the expansion of the universe is decelerating.
False. The 1998 discovery that the expansion of the universe is *accelerating* was initially controversial but became widely accepted within a few years. It was rewarded with the 2011 Nobel Prize in Physics. It revealed that most of the energy density of our universe is in the form of a mysterious substance called dark energy.
T or F: Only stars that have final masses greater than 1.4 times the mass of the Sun can become white dwarfs.
False. The Chandrasekhar limit is indeed 1.4 solar masses for the final mass of the star after it loses mass to create a planetary nebula. But it is only stars with final masses less than this value that can become white dwarfs; more massive stars end up as neutron stars or black holes after Type II supernova explosions.
T or F: According to Table 26.2, if you want to use a single distance estimation method to study galaxies at distances ranging from 10 to 1000 Mpc, you should use Redshifts. Hint: 1 Mpc = 3.26 million light-years.
False. The best technique would be Type Ia Supernovae, because Redshifts do not become useful until the distance is at least 300 million light-years, and here the lower end of the distance range corresponds to 30 million light-years. Type Ia Supernovae and Redshifts are both good distance estimators out to the outer end of the desired distance range.
T or F: Figure 17.2 shows that Polaris appears brighter in the night sky than Sirius.
False. The figure shows the rather strange magnitude scale, in which smaller (more negative) numbers correspond to brighter objects. Sirius is the brightest star in the night sky, at magnitude -2, whereas Polaris is brighter than most other stars at magnitude +2.
T or F: Figure 28.23 shows that, for stars observed to orbit the center of the Andromeda galaxy, the rotational velocity decreases at radii greater than 10,000 light-years.
False. The statement describes the Expected curve that shows predicted star velocities based on the gravity of the luminous matter but is not accurate for the Observed curve. The excess in velocity of the Observed curve compared to that expected from the luminous matter is our primary evidence for the presence of dark matter in galaxies.
T or F: Objects in spectral classes O,B, and A have masses too low to fuse protons and are referred to as brown dwarfs.
False. The statement is false but would be true if spectra types L, T, Y appeared instead. Brown dwarfs are too low in mass to fuse hydrogen nuclei (protons) into deuterium, but they are able to generate low amounts of heat by fusing the small amount of existing deuterium in their cores into helium.
T or F: The Local Group consists of 14 galaxies.
False. The textbook notes that the Local Group contains about 60 galaxies, and more dwarf galaxies of the Milky Way are still being discovered. There are 14 galaxies identified in Figure 28.14 as being part of the Milky Way's region within the Local Group.
T or F: There are 3600 arcseconds in 1 arcminute.
False. There are 60 arcseconds in 1 arcminute and 60 arcminutes in 1 degree. Multiply those together, and there are 3600 arcseconds in 1 degree.
False. White dwarfs with higher masses are bigger than white dwarfs with lower masses.
False. While objects with larger masses are usually bigger, the opposite is true for both white dwarfs and neutron stars. Higher mass gives gravity more power to compress them despite the pushback from degeneracy pressure, so higher mass white dwarfs are smaller.
Why does the narrow-band filter look like a mirror?
Filters only transmit certain wavelengths of light and reflect the rest
A planet has a mass of 1028 grams and a radius of 7,623 kilometers. What is its density in g/cm3?
For the given radius R, first change it from km to cm using R*(10^5cm/km). Then the volume is 4/3 π R^3 and the density is 10^28/volume = 5.4 g/cm^3.
Table 17.2 tells us that a star whose spectrum features strong lines of both sodium and ionized calcium along with many lines of ionized metals belongs to spectral type
G. Stars of spectral type G, like our Sun, have this particular combination of absorption lines in their spectra.
Compared to elliptical galaxies, spiral galaxies have more
Gas, dust, and young stars
Compare globular clusters, open clusters, and associations of stars.
Globular clusters are the oldest while associations are the youngest. Globular clusters have the most stars and are the most massive.
Use Hubble's Law to determine the recessional velocity in km/s that we expect to measure for a galaxy located at a distance of 10 million light-years.
In the units given in the textbook, Hubble's constant H has a value of 22 km/s per million light-years. The equation is v = Hd, so at a distance of 10 million light-years, we get a recessional velocity of v = (22 km/s/million light-years)*(10 million light-years) = 220 km/s
Based on Table 5.1, what kind of light do human beings emit the most of?
Infrared. Like all objects in the universe, human beings emit blackbody radiation. Because our skin temperature is roughly 373 Kelvin, our emission spectrum peaks in infrared light. This is why you can see humans when wearing night vision goggles, even in the dark. Human beings also absorb light - that's what makes the sunlight feel warm on our skin and can give us a sunburn.
Roughly how many times will Earth orbit the Sun during the time it takes the Sun (with its solar system) to orbit once around the center of the Milky Way?
It takes 225 million years for our solar system to make one orbit around the center of the Milky Way and exactly 1 year for Earth to orbit the Sun, so the answer is 225,000,000.
The element that an atom belongs to is identified by which of the following?
Its number of protons. The number of protons in the atom's nucleus determines the type of chemical element. The number of neutrons in the atom's nucleus determines which isotope of that element it represents. The number of electrons is compared to the number of protons to determine if an atom is neutral or ionized. All neutrons are identical to each other, so there is no such thing as type of neutrons (and the same statement applies to protons and electrons).
Which of the following is an exoplanet?
Kepler-62d is an exoplanet orbiting the star Kepler-62.
Two stars, named Larson and Johansson, have the same luminosity i.e., they both emit the same amount of light per second. If Larson is four times as far away from Earth as Johansson, how will Larson's brightness appear to us compared to Johansson's?
Larson will be 16 times dimmer. The Inverse Square Law tells us that the brightness of an object decreases by a factor of its distance squared. So for equally luminous objects, 4 times further means 16 times dimmer.
Newton's laws:
Laws of motion: 1. An object at rest or moving at constant velocity will remain that way unless acted upon by an outside force. 2. The acceleration of an object is proportional to and in the same direction as a force acting upon it. 3. The actions between two objects are equal in strength and opposite in direction. Law of gravity: 4. The gravitational force between objects with masses M1 and M2 and separation R is given by: F=G M1 M2 / R^2 .
The equation E=mc^2 means that
Mass can be converted into energy.
What type of gas occupies most of the volume of the interstellar medium?
Neutral hydrogen atoms.
Newton's reformulation of Kepler's third law was introduced in Section 3.3 (including Example 3.4). In section 18.2, this is applied to binary star systems. If the orbit of two stars relative to each other is an ellipse with a semi-major axis of 2 A.U., and it takes them 1 year to complete each orbit, what is the combined mass of the two stars in solar masses?
Newton's reformulation of Kepler's third law is D^3 = (M1+M2) P^2 where D is the semi-major axis of the relative orbit in A.U., the masses are given in solar masses, and the orbital period is given in years. We have 2^3 = (M1+M2) x 1^2 Solving for the sum of masses, we have (M1+M2)=2^3/1=8 solar masses .
If the Earth's axis were not tilted with respect to its orbital plane, how would the seasons compare to now?
No measurable seasons.
Why have so few exoplanets been detected that have masses and orbital periods like Earth?
None of the detection techniques are good at finding low-mass planets with long periods.
Our universe is 13.8 billion years old. Stars like the Sun spend about 11 billion years on the main sequence. The textbook notes that all globular clusters have main-sequence turnoffs at luminosities below the luminosity of the Sun. Given this information, what do you think is a typical age for globular clusters?
Nothing in our universe should be older than it, so the maximum possible answer is 13.8 billion years. The main sequence turnoffs being below a solar luminosity tell us that Sun-like stars in globular clusters have already left the main sequence, so the globular clusters must be more than 11 billion years old.
Spectral class of stars from highest to lowest surface temperature:
O B A F G K M (L T Y) <- Brown Dwarfs
The most massive main sequence stars are
O dwarfs. They are the most massive, but least common, stars along the main sequence. They are bigger than the Sun but much smaller than giant or supergiant stars. Red dwarfs, also known as M dwarfs, are the least massive and most common stars along the main sequence.
The Sun is stable in size due to hydrostatic equilibrium, which is defined as a balance between the forces
Pressure and gravity. Hydrostatic equilibrium refers to the balance between gravity, which tries to make the Sun collapse inwards, and pressure from collisions of its plasma particles, which pushes outwards.
What are found in a typical atomic nucleus?
Proton and neutron. Although a hydrogen nucleus consists only of a single proton, all other chemical elements have both protons and neutrons in their nuclei.
Parts of the electromagnetic spectrum in the correct order, from longest wavelength (lowest frequency) to shortest wavelength (highest frequency):
Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma-ray
What color is visible light that has a frequency of 4.3x10^14 Hz?
Red. Following example 5.1, we have λ = c/f λ = 3.00 × 10^8 m/s / 4.3x10^14 Hz = 7.0 × 10^(-7) m / (Hz * s) = 7.0 × 10^(-7) m 7.0x10-7 m * (109 nm/m)= 700 nm which is at the red end of the visible spectrum i.e., red light (violet is at the blue end i.e., 400 nm)
Rutgers receives 10% of the observing time on the Southern African Large Telescope (SALT), which has a roughly 10 meter diameter primary mirror. The Hubble Space Telescope (HST) has a primary mirror that is about 2.5 meters in diameter. Which telescope can collect more light, and by what factor?
SALT can collect 16 times more light. SALT's primary mirror has a diameter 4 times larger than HST's. Following Example 6.1 in the textbook, the collecting area is equal to π r^2 = π d^2/4 where r is radius and d is diameter of the primary mirror. So the area is proportional to the diameter squared, and SALT has 16 times more collecting area than HST.
In Hubble's galaxy classification scheme shown in Figure 26.6, the Milky Way would best be identified as
SBb. As a barred spiral galaxy, the Milky Way must have type SB. The textbook notes that the tightness of its spiral arms is intermediate between an "a" and a "c" classification, so the Milky Way is best classified as type SBb.
Which type of star has the longest main-sequence lifetime?
Spectral Type M have the longest main-sequence lifetimes; they will spend about 100 billion years fusing hydrogen before leaving the main sequence.
How old was the universe when the light from a galaxy that we observe to be at a redshift of 4 was emitted?
Table 29.1 shows that the universe was 11% of its current age at a redshift of 4. 0.11*13.8 billion years = 1.5 billion years.
Why was there a 3 second delay when Mission Control in Houston, TX was talking to the Apollo astronauts located on the Moon?
That's the time it takes light to travel from Earth to the Moon and back. Radio waves travel at the speed of light, and they had to travel from Earth to the Moon and back for the astronauts' response to be heard by Mission Control.
The modern view of our universe holds that
The Sun is at the center of the solar system, and the Earth and other planets rotate around it.
How long does it take light to travel from the nearest star to Earth, in seconds?
The Sun is the nearest star to Earth, located 150 million kilometers away. That's 150x10^6 km = 1.5x10^8 km. Light travels at a speed of 300,000 km/s = 3x10^5 km/s. The time it takes to travel somewhere at a constant speed equals the distance divided by the speed: time = distance/speed = 1.5x10^8 km / 3x10^5 km/s = 15x10^7 km / 3x10^5 km/s = 5 x 10^2 s = 500 s
In section 1.8 of the OpenStax Astronomy textbook (page 28), the authors write that "The typical atom is far emptier than the solar system out to Neptune." What do they mean by this?
The nucleus of an atom occupies a much smaller fraction of its volume than the fraction of our solar system's volume (out to Neptune's orbit) that is occupied by the Sun.
Which of the following statements is true for all binary star systems? A.The lower-mass star orbits the higher-mass star, and the higher-mass star is stationary. B. Both stars orbit their common center of mass C. A spectrum is required to resolve what looks like a single star into two sets of absorption lines that shift with time D. Two stars noticeably change their positions on the sky as they orbit
The only statement that applies to all binary star systems is that both stars orbit their common center of mass. If the higher-mass star is a lot higher in mass than the lower-mass star, it can look like the lower-mass star orbiting a stationary higher-mass star the way a planet seems to orbit the Sun. However, both objects are orbiting their common center of mass; the center of mass of our solar system is slightly outside the Sun, so the Sun's orbit is very small. The 3rd statement is only true for spectroscopic binaries, and the 4th statement is only true for visual binaries.
What causes the four seasons?
The seasons are caused by the 23.5 degree tilt of the Earth's axis versus the direction perpendicular to the ecliptic plane. In the Northern hemisphere, this makes daylight last longest and the Sun be closest to overhead on June 21 and the daylight last the shortest time with the Sun lowest in the sky on December 21. It takes some time for the atmosphere to warm up and cool down, so the seasons lag these dates by about a month. The Earth's distance from the Sun has a minimal effect on its surface temperatures; the Earth is actually closest to the Sun in January.
T or F: A modern astronomical system for gathering light typically consists of a telescope, an instrument, and a detector.
The telescope gathers and focuses light, the instrument selects the wavelength range of interest, and the detector records the picture. If the instrument is a spectrometer, it also disperses the light into many colors.
Following the example in section 21.4 of the textbook, calculate the transit depth that a distant observer in another star system would see when the Earth crosses in front of the Sun. Note that the Earth's radius is 6371 km, and the Sun's radius is 695,700 km.
The transit depth is the fractional drop in brightness when the planet passes in front of the star. The planet blocks a fraction of the star's disk given by the ratio of their circular areas, π R^2. π divides out of that ratio, giving us: (R_Earth/R_Sun)^2 = (6371/695700)^2 = 8.4x10^-5 = 0.000084. That is slightly too small to be detected easily with current Earth technology, but if the aliens are more advanced, they know that Earth is here.
What is based on an orbital or rotational period?
The year is based on Earth's orbit around the Sun; the month is based on the Moon's orbit around the Earth; the day is based on Earth's rotational period.
Astronomical objects are seen to rotate around the sky once per day. How fast are they moving, measured in degrees per hour?
There are 24 hours in a day, and 360 degrees in a circle. So the speed is 360 degrees / 24 hours = 15 degrees/hour.
Our Sun fuses 6x10^8 tons of hydrogen per second, which equates to 5.4x10^11 kg/s. Assuming that the Sun's mass of 2.0x10^30 kg is made entirely of hydrogen, and that all of this hydrogen will eventually fuse into helium, how long will the Sun be able to produce energy before using all of its fuel?
There are two steps to solving this question. The first is to figure out for how many seconds the Sun can fuse hydrogen before exhausting its fuel. The second converts that answer to years. Step one: 2.0x10^30 kg / (5.4x10^11 kg/s) = 3.7x10^18 s Step two: 3.7x10^18 s x (1 year/3.16x10^7 s) = 1.2x10^11 years. That's 120 billion years, which is a factor of 10 longer than we actually expect our sun to fuse hydrogen for, and the reason is that detailed calculations show that only 10% of the Sun's hydrogen will be used for fusion before it changes its energy source and becomes a red giant star.
How many days does it take for the Moon's position versus the stars to shift by 60 degrees?
There are two ways to compute this. The Moon shifts position by roughly 12 degrees per day, so the rough answer will be 60 degrees/ (12 degrees/day) = 5 days. You can also think of this as the Moon taking 27 days to complete a single circle around Earth versus the background stars; since a circle has 360 degrees, 60 degrees is 1/15 of the circle, or 27/5=5.4 days. Either answer is acceptable; they differ because the Moon actually moves roughly 13 degrees per day versus the background stars but 12 degrees per day versus the Sun's position.
In the H-R diagram of a star cluster, the main sequence turn-off is the leftmost/uppermost location where main sequence stars are present. Why are the bluer, more luminous main sequence stars missing?
They have already stopped fusing hydrogen in their cores and left the main sequence. Stars that are bluer (hotter surface temperatures) and more luminous have shorter main-sequence lifetimes and have already moved off the main sequence. The main-sequence turnoff is the point where the main sequence starts to be populated by stars that are still fusing hydrogen in their cores.
T or F: X-ray telescopes must be placed in space because X-rays are not transmitted by the Earth's atmosphere.
This is true. Most wavelengths of light, including X-rays, are blocked by Earth's atmosphere. So X-ray telescopes must be placed in space.
Calculate the expected parallax in arcseconds for a star located 32.6 light-years from the Sun.
To compute parallax in arcseconds, we need to know the star's distance in parsecs. Since 1 parsec = 3.26 light years, this star is at a distance of 10 parsecs. Using D = 1/p where p is the parallax in arcseconds and D is the distance in parsecs, we solve for p = 1/D = 1/10 = 0.1 arcseconds.
What type of eclipse is most commonly visible from a randomly chosen location on Earth?
Total lunar eclipse. While Appendix I shows that total solar and total lunar eclipses are visible from somewhere on Earth with roughly equal frequency, a total lunar eclipse can be viewed from the entire half of Earth experiencing night, whereas even a partial solar eclipse is visible from a very small part of Earth's surface. Hence from a randomly chosen location on Earth's surface, a total lunar eclipse is most commonly visible.
T or F: Brown dwarfs have masses between 1/100 and 1/12 the mass of the Sun but are similar in size to the planet Jupiter.
True. Objects in that mass range cannot fuse protons into helium but can temporarily fuse existing deuterium to generate a small amount of heat. They are all close in size to Jupiter despite having larger masses than planets.
T or F: The comet orbits in Figure 3.10 stand out compared to asteroid and planet orbits in having perihelion several times closer to the Sun than aphelion.
True. Perihelion is the closest point to the Sun in an object's orbit, and aphelion is its furthest point. So perihelion is always closer to the Sun than aphelion, but most orbits are nearly circular and the difference is small. For highly elliptical (i.e., highly eccentric) orbits like the comets have, perihelion is many times closer to the Sun than aphelion.
T or F: From the Earth's North Pole, the star Polaris can be seen at the zenith.
True. Polaris is often referred to as the "North Star" because it is found on the celestial sphere by following the direction of the Earth's axis of rotation upwards from the North Pole. So when one is at the North Pole, Polaris will be directly overhead at all times of the day and night.
T or F: Radiation and convection both play a key role in transporting energy produced by nuclear fusion from the Sun's core to its surface.
True. Radiation is the primary energy transport mechanism through most of the Sun, with convection taking over near the surface. Radiation refers to heat transfer via light; convection refers to heat transfer by the bulk motion of gas or plasma. The third form of heat transfer, conduction, is not important in the Sun.
T or F: In terms of the initial mass when stars first reach the main sequence, the dividing line between stars that will eventually become white dwarfs and those that will end up as neutron stars is roughly 10 solar masses.
True. Stars that have initial masses above 10 solar masses will eventually undergo Type II supernova explosions and form neutron stars, with extremely massive stars forming black holes instead. Stars with lower initial masses will have final masses (after emission of a planetary nebula) below 1.4 solar masses and will become white dwarfs.
T or F: In celestial coordinates, declination ranges from -90 degrees to +90 degrees.
True. The celestial coordinates identify locations on the celestial sphere just like latitude and longitude label Earth's surface. Right ascension is like longitude and ranges from 0 to 360 degrees; declination is like latitude and ranges from -90 to +90 degrees.
T or F: It is possible to perform astrophotography with a cell phone because the cellphone camera's detector uses similar technology to the Charge-Coupled Devices (CCDs) used as detectors on telescope instruments.
True. The cellphone camera detector is actually very similar to a CCD used for astronomy! You can perform astrophotography with a cell phone camera, but you need to set it for a long exposure and make sure it will be stable during that exposure.
T or F: When light nuclei join together into heavier ones, it is called nuclear fusion.
True. The complementary process of nuclear fission occurs when a heavy nucleus splits into lighter ones.
T or F: The equivalence principle of general relativity states that in a sealed laboratory there is no way to distinguish free fall in a gravitational field from being in zero gravity.
True. The equivalence principle also states that in a sealed laboratory there is no way to distinguish being on a spaceship accelerating in zero gravity from being in a gravitational field (e.g., sitting on the surface of the Earth).
T or F: To determine a star's luminosity from its apparent brightness, we also need to know its distance from us.
True. The greatest challenge in astronomy is our lack of depth perception. Apparent brightness is proportional to luminosity divided by the square of the star's distance. If we know two of those three quantities, we can determine the third.
T or F: The Moon's gravity causes high tides at the locations on Earth that are nearest and furthest from the Moon.
True. The locations on Earth that are nearest and furthest from the Moon experience high tides. This can be understood as the locations nearest the Moon experiencing the strongest gravity from the Moon, and the locations furthest from the Moon feeling the strongest centrifugal force as the Earth orbits the center-of-mass of the Earth-Moon system.
T or F: Our Sun produces energy when two protons combine to form a deuterium nucleus, emitting a neutrino and a positron. The deuterium nucleus then combines with another proton to form a helium-3 nucleus, emitting a gamma-ray photon. After the previous steps occur twice, two helium-3 nuclei combine to form a helium-4 nucleus, emitting two protons.
True. The proton-proton chain involves hydrogen nuclei (protons) fusing into deuterium, deuterium fusing into helium-3, and then helium-3 fusing into the final output of helium-4. The net reaction is that 4 protons fuse to create one helium-4 nucleus, along with 2 neutrinos, 2 positrons, and 2 gamma-ray photons.
T or F: A degenerate gas of electrons provides the outwards pressure that keeps white dwarfs from collapsing further due to gravity.
True. The term "degeneracy" refers to having a lot of identical particles. Degeneracy pressure is caused by the Pauli exclusion principle of quantum mechanics, which tells us that if you try to pack a bunch of identical particles (electrons) into high density, they will push back. (This happens even at absolute zero temperature when the classical gas pressure drops to zero; it's part of the weirdness of quantum mechanics.) White dwarfs are supported against gravitational collapse by a degenerate gas of electrons, and neutron stars are supported by a degenerate gas of neutrons.
T or F: Typical air at sea level on Earth is about 10 million trillion times denser than the average density of interstellar gas in the Milky Way.
True. The textbook notes that the average density of interstellar gas in our galaxy is about 1 atom per cm^3 and that the density in the air in a typical room on Earth is about 10^19 atoms per cm^3. So the air on Earth is denser by a factor of 10^19 = 10^(1 + 6 + 12) = 10 x 10^6 x 10^12 = 10 million trillion.
T or F: All main sequence stars create energy by fusing hydrogen to helium in their core.
True. There is a one-to-one correspondence between stars on the main sequence of the H-R diagram and stars that are fusing hydrogen nuclei (protons) into helium in their cores.
T or F: Galaxies, clusters, and superclusters formed from lumps of matter in the early universe that expanded more slowly than the surrounding space, eventually stopped expanding and collapsed, and slowly merged together to form larger and larger structures.
True. This is called gravitational instability; regions that were slightly more dense than average expanded more slowly and thereby became a lot denser than average, making their gravity strong enough to stop following the overall expansion of the universe and collapse into galaxies. Gravity caused nearby galaxies to assemble together into galaxy clusters. Superclusters are regions where gravity has caused multiple clusters to assemble together.
T or F: The Search for Extraterrestrial Intelligence (SETI) primarily looks for signals at radio wavelengths because they are inexpensive to produce, transmitted by planetary atmospheres, and not significantly absorbed by interstellar gas or dust.
True. Those are the three main reasons for thinking that extraterrestrial civilizations are likely to intentionally send signals using radio waves rather than other types of light.
T or F: The Cosmic Microwave Background radiation was discovered in the 1960's by Penzias & Wilson at Bell Labs in Holmdel, NJ and was later found by the COBE satellite to match blackbody radiation with a temperature of 2.73 K.
True. We measure temperature in Kelvin, and 2.73 K means 2.73 degrees above absolute zero. (One K is equal to one Celsius degree.)
Figure 28.27 shows that galaxies form and grow through a combination of the collapse of gas clouds and mergers with smaller galaxies.
True. While a galaxy is first formed in the collapse of a cloud of gas, these first galaxies are very small, and many of them will merge together to produce a large present-day galaxy like the Milky Way.
T or F: The Copernican principle states that Earth does not occupy a special location in the universe; this implies that life should exist elsewhere in the cosmos.
True.If Earth is not a special location, the odds of us being the only planet, solar system, or galaxy with life in it are extraordinarily low.
An object moving away from Earth at half the speed of light shines a green laser (wavelength of 500 nm) at us. What wavelength (in nm) do we see the light at?
Using the formula for the Doppler shift, Delta lambda / lambda = v/c, where c is the speed of light, we have Delta lambda / lambda = (0.5 c)/c Delta lambda = 0.5 x (lambda) = 0.5 x 500nm = 250 nm That's an increase to the emitted wavelength, since an object moving away from us will be redshifted, so the observed wavelength is 500 nm + 250 nm = 750 nm, which is red light.
What features of the distribution of galaxies occupies the most volume in the universe?
Voids. As the textbook notes, 90% of the galaxies are found in 10% of the volume; this includes the filaments that contain clusters and superclusters. The rest of the volume consists of voids, which are large regions with few to no galaxies. The filamentary structure is often referred to as the cosmic web, but no actual cosmic spiders are present.
Use the Drake Equation in Example 30.1 to calculate the number of civilizations in our galaxy. Assume that R=10/year, L=10,000 years, and that each of the five f factors is equal to 0.1. Clarification: f_e and n_e are the same, so you can use either version of the Drake Equation that appears.
We get 10/year x 0.1 x 0.1x 0.1 x 0.1 x 0.1 x 10,000 years. Even without a calculator, we can group the big numbers and the small numbers and get 10^5 x 10^-5 = 1. The units cancel, as they should, to give us a number of civilizations. These are all plausible values for which the true values could be larger or smaller, and this shows that the Drake Equation can end up predicting 1 intelligent civilization in our galaxy - presumably that's us - or many more than 1 or much less than 1 (in which case humans are a surprise). So although it is a useful framework, it doesn't really answer the question we're asking, because our knowledge of the input factors is too imprecise.
Why does nuclear fusion of hydrogen into helium release energy?
a helium nucleus is lighter than 4 hydrogen nuclei, and the difference in mass is converted to energy by E = mc^2
What is the likely result of the merger of two large spiral galaxies?
an elliptical galaxy
Compared to galaxies today, galaxies in the early universe were
bluer and more massive. The most distant galaxies that we can observe are being seen as they existed in the first few billion years after the Big Bang. Galaxies at that stage were bluer, smaller, less massive, and clumpier than present-day galaxies.
What happens when a high mass star has fused to iron in its core?
core fusion stops because no nuclear reactions of iron can produce energy
If our universe contained luminous matter and dark matter but no dark energy, we would expect its expansion to currently be
decelerating. The gravity from matter causes the expansion of the universe to decelerate i.e., slow down. If our universe were dense enough, the expansion could eventually stop and reverse as a contraction, but that would happen in the distant future. An empty universe without matter would be expanding at a constant rate, and a universe with significant dark energy would have its expansion accelerating.
The majority of the gas in molecular clouds is in the form of
diatomic molecular hydrogen. The gas in molecular clouds is primarily molecular (hence the name). Since hydrogen is the most abundant element in the universe, it should not be surprising that molecular hydrogen, which is diatomic i.e., H2, is the majority of the gas in molecular clouds.
The surface at the edge of a black hole where the escape velocity is equal to the speed of light is called the
event horizon.
According to the textbook, when a small galaxy like the Sagittarrius dwarf galaxy collides with and disappears into a large galaxy like the Milky Way, this is called
galactic cannibalism. It occurs when a small galaxy is swallowed up by a larger one, as this question describes. A starburst might ensue if at least one of the galaxies has a large amount of gas that can be compressed to form new stars. A merger describes the collision of galaxies that have roughly equal size.
What powers the energy release of a quasar?
gravitational energy from material falling into a black hole
Stars that have just left the main sequence are fusing
hydrogen in shells surrounding their cores. Stars leave the main sequence when enough helium builds up in their core to cause hydrogen fusion to cease in that region, but hydrogen fusion continues in a spherical shell around the core. This causes the core to contract and heat and the outer layers of the star to expand; it becomes a red giant. Eventually, the core gets hot enough to fuse helium, which marks the end of the red giant phase.
Where in the Milky Way would you be most likely to find O and B main sequence stars?
in the thin disk. O and B stars have short main sequence lifetimes, so they will only be found in regions with young stars. Nearly all of the recently formed stars in our galaxy are found in the thin disk. O and B main sequence stars are usually found in the spiral arms, which are part of the thin disk.
Where in the Milky Way galaxy is our solar system located?
in the thin disk. We are located in the thin disk 26,000 light years from the center of the Milky Way, which places us roughly halfway between the center and the outer edge of the disk.
Most of the light emitted by stars is in the optical (visible) part of the spectrum. If we wanted to observe the starlight from the very first galaxies, at what wavelength should we observe?
infrared light
F=GM1M2/R^2 means that the gravitational force between two objects is
inversely proportional to the square of their separation.
An atom that has lost an electron is referred to as
ionized. Atoms are naturally found in their "ground state" with the electrons in the lowest possible energy levels. They have no net electrical charge because they have the same number of protons and electrons, so they are neutral. If an electron gains energy via a collision with another atom or by absorbing a photon and moves to a higher energy level, the atom is now in an excited state. If an electron gains so much energy that it can leave the atom entirely, the atom is now ionized and has a positive net charge.
The Large and Small Magellanic Clouds shown in Figure 26.9 are classified as
irregulars.
What happens to a white dwarf if it accretes material from a binary companion and reaches the white dwarf limit of 1.4 M_Sun?
it explodes as a white dwarf (Type Ia) supernova
A star is observed to have an absorption line spectrum. What does that mean?
it is absorbing light at certain wavelengths, corresponding to the various atomic elements in the star's atmosphere
Suppose you met an alien, whom you could see glowing in the dark with your own eyes. What could you say about its skin temperature?
it is hotter than human skin temperature
How does the energy generated by nuclear fusion leave the Sun's core?
it is mostly carried away by photons
Hydrogen gas at rest emits a spectral line at λ = 656 nm. We observe the same line in a distant star and measure its wavelength to be λ = 670 nm. What can we conclude about the star?
it is moving away from us
Hydrogen gas at rest emits a spectral line at λ = 656 nm. We observe the same line in a distant star and measure its wavelength to be λ = 656 nm. What can we conclude about the star?
it is not moving away from us or toward us
Figure 18.15 shows that the most common type of stars is
main sequence stars.
Dark matter is best described as a scientific ______ .
model
Compared to the Sun, the red supergiant Betelgeuse is
more massive, larger, cooler at the surface but hotter at the core, more luminous, denser, and younger than the Sun.
Edwin Hubble showed that distant galaxies are ____________ us, with their ___________ proportional to their _____________
moving away from; speed; distance
Figure 20.4 shows that cool interstellar gas can be detected in the spectrum of a background star via the presence of
narrow absorption lines. The spectrum of a star has relatively broad absorption lines. After that spectrum passes through an interstellar cloud, gas in that cloud causes additional narrow absorption lines to appear in the spectrum. The absorption lines from a star are broad because its surface is hot; the absorption lines from the interstellar gas are narrow because it is cool. While the final spectrum contains both broad and narrrow absorption lines, it is the presence of narrow absorption lines that allow us to detect cool interstellar gas.
What powers the Sun's tremendous luminosity?
nuclear fusion of hydrogen into helium
A constellation is
one of 88 regions that divide up the celestial sphere. Constellations are regions of the celestial sphere named after groupings of stars that appear near to each other on the sky. Those groups of stars are not generally close to each in three dimensions. Rather, their small separation on the sky creates the impression that they are physically near each other because we lack depth perception when looking into outer space.
Material near the center of the Sun is so hot that it forms a
plasma. The Sun is composed almost entirely of hydrogen and helium, which are usually gases except at extremely cold temperatures. However, the temperature in the central regions of the Sun is so hot that all electrons are stripped from hydrogen and helium, leaving a new state of matter where there are only positively charged nuclei and negatively charged electrons, without any neutral particles. This is called a plasma.
While a molecular cloud core is collapsing but before nuclear fusion begins, the object is called a
protostar. Once nuclear fusion begins, a star is born!
Radio jets are produced by
quasars or active galactic nuclei when energetic particles are ejected perpendicular to the accretion disk surrounding a supermassive black hole.
You observe a nearby star. When should you observe it again to see the largest shift in angular position?
six months later.
The Earth is closest to the Sun in January. So...
the Earth moves fastest around the Sun in January
During the night, objects in the sky are seen to move from East to West because
the Earth rotates about its axis from West to East. The apparent rotation of the Sun, Moon, planets, and stars around the sky at the rate of once per day is caused by the Earth spinning once per day.
Various objects listed in order from smallest to largest:
the solar system; the Milky Way; the Local Group
What is likely to happen when two galaxies of similar mass collide?
their shapes will be distorted by the mutual gravity
Cosmic Distance Ladder from first (nearest) step to last (furthest):
trigonometric parallax, RR Lyrae, spectroscopic parallax via the H-R diagram, Cepheids
