ASTR HW 5

Which of the following statements about thermal radiation is always true? A hot object produces more total infrared emission than a cooler object. All the light emitted by hot object has higher energy than the light emitted by a cooler object. A hot object emits more radiation per unit surface area than a cool object. A cold object produces more total infrared and radio emission per unit surface area than a hot object.

A hot object emits more radiation per unit surface area than a cool object. This is part of the first law of thermal radiation (the Stefan-Boltzmann law)

In order for an atom to absorb a photon (a particle of light), the photon must have energy matching the difference in energy between energy levels in the atom. the atom must have lost all of its electrons. the photon must have enough energy to remove an electron from the atom. A or C B or C

A or C the photon must have energy matching the difference in energy between energy levels in the atom. the photon must have enough energy to remove an electron from the atom.

If you heat a gas so that collisions are continually bumping electrons to higher energy levels, when the electrons fall back to lower energy levels the gas produces an emission line spectrum. radio waves. thermal radiation. X-rays. an absorption line spectrum.

an emission line spectrum.

The ___________ of the Hubble Space Telescope is better for shorter (bluer) wavelengths of light than for longer (redder) wavelengths of light

angular resolution

The Very Large Array. What kinds of light are these telescopes designed to detect? radio waves X rays ultraviolet light infrared and visible light light with extremely short wavelengths

radio waves This is the Very Large Array in New Mexico; the many radio telescopes are used together for interferometry.

According to modern science, approximately how old is the Sun? 11,000 years 400 million years 4.5 billion years 25 million years

4.5 billion years

Rank the layers of the atmosphere based on the energy of the photons that are typically emitted there, from highest to lowest. Corona chromosphere photosphere

Corona chromosphere photosphere The energy of the emitted light rises with temperature, so the ranking for this question is the same as that of Part C. In fact, the photosphere emits primarily visible light, the chromosphere primarily ultraviolet light, and the corona primarily X rays. This is why astronomers study the corona with X-ray telescopes and the chromosphere with ultraviolet telescopes, while we observe the photosphere with visible-light telescopes.

Which of the following changes would cause the fusion rate in the Sun's core to increase? Check all that apply. An increase in the core temperature An increase in the core radius A decrease in the core temperature A decrease in the core radius

An increase in the core temperature & A decrease in the core radius An increase in the core temperature increases the fusion rate because the fusion rate is very sensitive to temperature. A decrease in the core radius causes the core to heat up and increase in density, which therefore leads to an increased fusion rate.

Each of the following describes an "Atom 1" and an "Atom 2." In which case are the two atoms different isotopes of the same element? Atom 1: nucleus with 4 protons and 5 neutrons, surrounded by 4 electrons; Atom 2: nucleus with 5 protons and 5 neutrons, surrounded by 4 electrons Atom 1: nucleus with 8 protons and 8 neutrons, surrounded by 8 electrons; Atom 2: nucleus with 8 protons and 8 neutrons, surrounded by 7 electrons Atom 1 : nucleus with 6 protons and 8 neutrons, surrounded by 6 electrons; Atom 2: nucleus with 7 protons and 8 neutrons, surrounded by 7 electrons Atom 1: nucleus with 7 protons and 8 neutrons, surrounded by 7 electrons; Atom 2: nucleus with 7 protons and 7 neutrons, surrounded by 7 electrons

Atom 1: nucleus with 7 protons and 8 neutrons, surrounded by 7 electrons; Atom 2: nucleus with 7 protons and 7 neutrons, surrounded by 7 electrons They are isotopes both atoms have the same atomic number but different atomic mass numbers.

The large research observations on Mauna Kea use giant __________.

reflecting telescopes

Following are the different layers of the Sun's atmosphere. Rank them based on the order in which a probe would encounter them when traveling from Earth to the Sun's surface, from first encountered to last. Corona chromosphere photosphere

Corona chromosphere photosphere

Rank the layers of the Sun's atmosphere based on their temperature, from highest to lowest Corona chromosphere photosphere

Corona chromosphere photosphere Scientists were quite surprised when they first learned that the temperature increases with altitude in the Sun's atmosphere, and even today the heating mechanism is not fully understood. However, we know that magnetic fields play an important role in transporting heat upward, making the chromosphere hotter than the photosphere and the corona hotter still.

Which of the following statements about electrons is not true? Within an atom, an electron can have only particular energies. Electrons have very little mass compared to protons or neutrons. Electrons orbit the nucleus rather like planets orbiting the Sun. An electron has a negative electrical charge. Electrons can jump between energy levels in an atom only if they receive or give up an amount of energy equal to the difference in energy between the energy levels.

Electrons orbit the nucleus rather like planets orbiting the Sun.

When the temperature of the Sun's core goes down, what happens next? Fusion reactions speed up; the core expands and cools. Fusion reactions slow down; the core expands and heats. Fusion reactions slow down; the core shrinks and heats. Fusion reactions speed up; the core shrinks and cools.

Fusion reactions slow down; the core shrinks and heats.

In which case will the woman see a rainbow of color interrupted by a few dark absorption lines?

Hot light source and thin cloud of cool gas The hot light source produces a continuous spectrum, but the cool gas absorbs light at specific wavelengths, so that she sees an absorption line spectrum.

Which of the following must occur for a star's core to reach equilibrium after an initial change in fusion rate? Check all that apply. If the fusion rate initially decreases, then the core expands. If the fusion rate initially increases, then the core expands. If the fusion rate initially decreases, then the core contracts. If the fusion rate initially increases, then the core contracts.

If the fusion rate initially increases, then the core expands. If the fusion rate initially decreases, then the core contracts. Increasing the fusion rate releases more energy into the core, which raises the temperature and increases the internal pressure, causing the core to expand. Decreasing the fusion rate means less energy is released, so the temperature and internal pressure decreases. As you can see in the interactive figure, the solar thermostat keeps the fusion rate fairly steady in a star like the Sun because a temperature increase causes the core to expand while a temperature decrease causes the core to contract.

One of the first steps is to choose what type of observation to make. Recall that three basic types of astronomical observation are imaging (taking a photograph of an object), spectroscopy (spreading an object's light into a spectrum), and timing (measuring how an object's light varies with time). ---Sort each of the astronomical questions below into the appropriate bin based on the type of observation you would need to perform to answer it.

Imaging= how large is the andromeda galaxy? =are stars in the Orion Nebula surrounded by dusty disks of gas? =what are the major surface features of mars? Spectroscopy= what is the temperature of Jupiter's atmosphere? =is the star Vega moving toward us or away from us? =what is the chemical composition of the Crab Nebula? Timing= does the star Mira vary in brightness? =is the x-ray emission from the galactic center steady or changing?

Different telescopes are optimized for observing different wavelengths of light, so another consideration in planning an observation is deciding what type of telescope to use.---Each of the following statements describes an astronomical measurement. Place each measurement into the appropriate bin based on the type of telescope you would use to make it.

Infrared Telescopes= determine the surface temperature of Venus. = study a dense cloud of cold gas in space. Visible Light Telescope= measure the brightness of a star that is similar to our Sun. = Obtain a spectrum of sunlight reflected by Mars. X-Ray Telescope= observe the hot (1-million K) gas in the Sun's corona. =look for high-energy radiation from a supernova. (Cool objects emit in the infrared. The Sun and similar stars emit mostly in the visible; reflected light from Mars is therefore also visible light. Very hot gas emits X rays, which have very high energy (with only gamma-ray photons having more energy for light)).

Which of the following statements is true of green grass? It absorbs red light and emits green light. It means the lawn is healthy. It absorbs red light and reflects green light. It transmits all colors of light except green.

It absorbs red light and reflects green light.

Which of the following is not an advantage of the Hubble Space Telescope over ground-based telescopes? It never has to close because of cloudy skies. It is closer to the stars. Stars do not twinkle when observed from space. It can observe infrared and ultraviolet light, as well as visible light.

It is closer to the stars. Distance to the stars has absolutely nothing to do with it, as should be apparent if you consider the scale of the solar system and the distances to stars to scale (as discussed in Chapter 1).

Figure showing a laboratory spectrum on the top and four object spectra underneath. Consider the spectra of the four objects shown beneath the laboratory spectrum. Based on these spectra, what can you conclude about Object 1? It is a star with a thin upper atmosphere. It is a very hot object, with a temperature above 1 million K. It is composed mostly of hydrogen, helium, and iron. It is moving toward us. It is moving away from us.

It is moving toward us Notice that the lines in Object 1's spectrum are all to the right of those in the laboratory spectrum. You can tell that this indicates a redshift - which means the object is moving away - because red is on the right side of these spectra (and blue is on the left).

Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red color? It is much more massive than the Sun. Its surface is cooler than the surface of the Sun. It is much brighter than the Sun. It is moving away from us.

Its surface is cooler than the surface of the Sun. Red light has lower energy than yellow or white light, so the red color of Betelgeuse tells us that its peak thermal radiation comes at lower energy than the peak thermal radiation of the yellow/white Sun. A lower energy of peak radiation means a lower temperature.

Figure showing a laboratory spectrum on the top and four object spectra underneath. Now consider Object 2. What can you say about Object 2 in comparison to Object 1? Object 1 had a higher temperature than Object 2. Object 2 contains more hydrogen than Object 1. Object 2 is moving away from us faster than Object 1. Object 2 is moving toward us while Object 1 is moving away from us.

Object 2 is moving away from us faster than Object 1. Object 2's lines are shifted farther to the right than Object 1's, which means it has a greater redshift and is moving away faster.

Listed following are distinguishing characteristics and examples of reflecting and refracting telescopes. Match these to the appropriate category. Reflecting Telescopes: Refracting Telescopes: The world's largest is 1-meter in diameter, most commonly used by professional astronomers today, very large telescopes become "top- heavy", The Hubble Space Telescope, world's largest telescope, incoming light passes through glass

Reflecting Telescopes: most commonly used by professional astronomers today, The Hubble Space Telescope, world's largest telescope Refracting Telescopes: The world's largest is 1-meter in diameter, Galileo's telescopes, very large telescopes become "top- heavy", incoming light passes through glass

_____________ separate the various colors of light, allowing astronomers to determine stellar composition and many other stellar properties.

Spectrographs

Suppose that Star X and Star Y both have redshifts, but Star X has a larger redshift than Star Y. What can you conclude? Star X is moving away from us faster than Star Y. Star X is coming toward us faster than Star Y. Star X is moving away from us and Star Y is moving toward us. Star Y is moving away from us faster than Star X. Star X is hotter than Star Y.

Star X is moving away from us faster than Star Y. The redshifts mean that both stars are moving away from us, and a larger redshift means a faster speed.

How does the light-collecting area of an 8-meter telescope compare to that of a 2-meter telescope? The 8-meter telescope has 8 times the light-collecting area of the 2-meter telescope. The answer cannot be determined from the information given in the question. The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope. The 8-meter telescope has 4 times the light-collecting area of the 2-meter telescope.

The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope. The 8-meter telescope is 4 times larger in diameter, so its light collecting area is 42 = 16 times greater.

Which of the following statements is an inference from a model (rather than an observation)? The photosphere emits visible light. The photosphere is made out of mainly hydrogen and helium. The Sun's core is gradually turning hydrogen into helium. The Sun emits neutrinos. The corona is hotter than the photosphere.

The Sun's core is gradually turning hydrogen into helium.

What would happen if the fusion rate in the core of the Sun were increased but the core could not expand? The Sun's core would start to cool down and the rate of fusion would decrease. The Sun's core would reach a new equilibrium at a lower temperature. The Sun's core would reach a new equilibrium at a higher temperature. The Sun's core would start to heat up and the rate of fusion would increase even more.

The Sun's core would start to heat up and the rate of fusion would increase even more As you know from Part B, an increase in the fusion rate will cause the core to expand in a normal (or main-sequence) star like the Sun, and this expansion will restore core equilibrium. But if for some reason the core could not expand, the higher temperature would make the fusion rate increase even more, creating a positive feedback loop in which the fusion rate and temperature would keep getting higher and higher. (That is, there would be no equilibrium.) In fact, as you'll learn when you study stellar life cycles, this is essentially what will occur when the Sun is near the end of its life.

Consider an atom of gold in which the nucleus contains 79 protons and 118 neutrons. What is its atomic number and atomic mass number? The atomic number is 118, and the atomic mass number is 197. The atomic number is 79, and the atomic mass number is 197. The atomic number is 118, and the atomic mass number is 79. The atomic number is 79, and the atomic mass number is 118.

The atomic number is 79, and the atomic mass number is 197.

Suppose you see two stars: a blue star and a red star. Which of the following can you conclude about the two stars? Assume that no Doppler shifts are involved. (Hint: Think about the laws of thermal radiation.) The blue star has a hotter surface temperature than the red star. The red star has a hotter surface temperature than the blue star. The blue star is more massive than the red star. The red star is more massive than the blue star. The blue star is farther away than the red star.

The blue star has a hotter surface temperature than the red star.

Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space? The cloud is cool and very dense, so that you cannot see any objects that lie behind it. The cloud is cool and lies between you and a hot star. The cloud is extremely hot. The cloud is visible primarily because it reflects light from nearby stars.

The cloud is cool and lies between you and a hot star. Atoms or molecules in the cloud therefore absorb specific wavelengths of light from the hot star.

The visible spectrum of the Sun. This photo shows the visible light spectrum of the Sun. Why does it have all those dark lines on it? The dark lines are caused by Doppler shifts. The dark lines represent wavelengths of light at which atoms near the Sun's surface absorb radiation from the hotter solar interior. The dark lines are not real, but rather are artifacts of the photographic process used to record the spectrum. The dark lines come from sunspots on the Sun, which are dark in color.

The dark lines represent wavelengths of light at which atoms near the Sun's surface absorb radiation from the hotter solar interior. In other words, the Sun has an absorption line spectrum because its surface (photosphere) acts like a cooler cloud over the much hotter interior.

The diagram represents energy levels in a hydrogen atom. The labeled transitions (A through E) represent an electron moving between energy levels. Suppose that an electron in a hydrogen atom absorbs 10.2 eV of energy, so that it moves from level 1 to level 2. What typically happens next? The electron remains in level 2 until it absorbs an additional 10.2 eV of energy. The electron jumps to level 3 as soon as it absorbs any additional energy. The electron returns to level 1 by emitting an ultraviolet photon with 10.2 eV of energy. A different electron drops into level 1, since it is now unoccupied.

The electron returns to level 1 by emitting an ultraviolet photon with 10.2 eV of energy.

Which of the following best describes why we say that light is an electromagnetic wave? Which of the following best describes why we say that light is an electromagnetic wave? Light is produced only when massive fields of electric and magnetic energy collide with one another. The term electromagnetic wave arose for historical reasons, but we now know that light has nothing to do with either electricity or magnetism. Light can be produced only by electric or magnetic appliances. The passage of a light wave can cause electrically charged particles to move up and down.

The passage of a light wave can cause electrically charged particles to move up and down.

The angular separation of two stars is 0.1 arcseconds and you photograph them with a telescope that has an angular resolution of 1 arcsecond. What will you see? The photo will seem to show only one star rather than two. The stars will not show up at all in your photograph. The two stars will appear to be touching, looking rather like a small dumbbell. You will see two distinct stars in your photograph

The photo will seem to show only one star rather than two. Because the angular separation of the stars is smaller than the telescope's angular resolution, the light of the two stars will be blurred together to look like a single star.

If we observe one edge of a planet to be redshifted and the opposite edge to be blueshifted, what can we conclude about the planet? The planet is actually two bodies, one moving toward us, the other away from us. The planet is in the process of falling apart. The planet is in the process of formation. The planet is rotating.

The planet is rotating.

An image showing two stars. An image showing one star. The first telescopic photo shows what appears to be a single star. The second photo shows the same object, now revealed to be two distinct stars. What is the difference between the two photos? The second photo was taken by two telescopes rather than one. The second photo was taken with a telescope that has greater light-collecting area. The second photo has better (smaller) angular resolution than the first photo. The second photo comes from a radio telescope while the first photo comes from a visible-light photo.

The second photo has better (smaller) angular resolution than the first photo. Better angular resolution means we can see (resolve) the two individual sources that are blurred together in the first photo.

Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm). A particular star's spectrum shows the same hydrogen line at a wavelength of 486.0 nm. What can we conclude? The star is moving away from us. The star is moving toward us. The star is getting hotter. The star is getting colder.

The star is moving toward us. The wavelength is shifted from 486.1 to 486.0 nm, which means a shift to a shorter wavelength. A shorter wavelength means a shift to the blue end of the spectrum (a blueshift) so that the object is moving toward us.

Studying a spectrum from a star can tell us a lot. All of the following statements are true except one. Which statement is not true? We can identify chemical elements present in the star by recognizing patterns of spectral lines that correspond to particular chemicals. The total amount of light in the spectrum tells us the star's radius. Shifts in the wavelengths of spectral lines compared to the wavelengths of those same lines measured in a laboratory on Earth can tell us the star's speed toward or away from us. The peak of the star's thermal emission tells us its temperature: hotter stars peak at shorter (bluer) wavelengths.

The total amount of light in the spectrum tells us the star's radius. We cannot measure radius from a spectrum without additional information.

Which of the following is always true about images captured with X-ray telescopes? They are always very pretty. They always are made with adaptive optics. They show us light with extremely long wavelengths compared to the wavelengths of visible light. They always have very high angular resolution. They are always shown with colors that are not the true colors of the objects that were photographed.

They are always shown with colors that are not the true colors of the objects that were photographed. "True colors" make sense only for visible light, not X rays.

Suppose you watch a leaf bobbing up and down as ripples pass it by in a pond. You notice that it does two full up and down bobs each second. Which statement is true of the ripples on the pond? They have a frequency of 2 hertz. They have a frequency of 4 hertz. They have a wavelength of two cycles per second. We can calculate the wavelength of the ripples from their frequency.

They have a frequency of 2 hertz - Remember that hertz are units meaning "cycles per second."

Suppose you decide to make a graph of intensity against wavelength for the spectrum shown here. Which of the following shows what the graph will look like?

Upside down spike wavelength graph Notice that the downward spikes on the graph occur at wavelengths corresponding to the dark lines in the spectrum.

Which of the following correctly describes how the process of gravitational contraction can make a star hot? Gravitational contraction involves the generation of heat by chemical reactions, much like the burning of coal. When a star contracts in size, gravitational potential energy is converted to thermal energy. Gravitational contraction involves nuclear fusion, which generates a lot of heat. Heat is generated when gravity contracts, because gravity is an inverse square law force.

When a star contracts in size, gravitational potential energy is converted to thermal energy.

The Chandra X-ray Observatory must operate in space because: X rays do not penetrate Earth's atmosphere. X-ray telescopes require the use of grazing incidence mirrors. It was built by NASA. X rays are too dangerous to be allowed on the ground.

X rays do not penetrate Earth's atmosphere. To detect X rays, the observatory must be above Earth's atmosphere.

Which of the following statements about X rays and radio waves is not true? X rays travel through space faster than radio waves. X rays have higher frequency than radio waves. X rays and radio waves are both forms of light, or electromagnetic radiation. X rays have shorter wavelengths than radio waves.

X rays travel through space faster than radio waves.

This Figure showing blackbody curves for several stars and a human. This figure shows idealized thermal radiation spectra from several stars and a human. Based on this graph, at about what wavelength does a 15,000 K star emit its most intense light? about 20 nanometers about 100 nanometers About 100,000 nanometers about 1,000 nanometers

about 100 nanometers The blue curve represents the 15,000 K star and it peaks close to 102 = 100 nm on the wavelength axis.

The Hubble Space Telescope obtains higher-resolution images than most ground-based telescopes because it is: larger. closer to the stars. above Earth's atmosphere.

above Earth's atmosphere.

Most of the Sun's ultraviolet light is emitted from the narrow layer called the ______ where temperature increases with altitude.

chromosphere

Energy moves through the sun's _____ by means of the rising of hot gas and falling of cooler gas.

convection zone

Nuclear fusion of hydrogen into helium occurs in the _____.

core

we can see the sun's ______ most easily during total solar eclipses

corona

If our eyes were sensitive only to X rays, the world would appear __________. If our eyes were sensitive only to X rays, the world would appear __________. gray, black, and white like a medical X ray brighter than normal because X rays carry more energy than visible light photons dark because X-ray light does not reach Earth's surface green, yellow, and orange, because those are the colors of X rays

dark because X-ray light does not reach Earth's surface Because X rays from the Sun do not reach Earth's surface, eyes that were sensitive only to X rays would have nothing to see.

How do we know how old the Sun is? from Newton's version of Kepler's third law and the orbits of the planets from its speed and distance from us from ages of solar system meteorites, based on radioactive elements from calculating its fuel supply and how fast it is using it up

from ages of solar system meteorites, based on radioactive elements

What two physical processes balance each other to create the condition known as gravitational equilibrium in stars? the strong force and the electromagnetic force gravitational force and surface tension gravitational force and outward pressure the strong force and the weak force

gravitational force and outward pressure

Without telescopes or other aid, we can look up and see the Moon in the night sky because it glows through radioactive decay. reflects visible light. emits thermal radiation. emits visible light. reflects infrared light.

reflects visible light.

In which case will the woman see a just a spectrum that is almost entirely black except for few bright emission lines?

hot, glowing cloud of hydrogen gas The hot cloud emits light only at specific wavelengths, producing an emission line spectrum.

If you had only one telescope and wanted to take both visible-light and ultraviolet pictures of stars, where should you locate your telescope? on Earth's surface on a tall mountain in an airplane in space

in space While visible light can be observed from the ground, ultraviolet light can be easily observed only from space. Indeed, the capability of observing ultraviolet light is a major advantage of the Hubble Space Telescope over larger ground-based telescopes.

The Chandra X-ray observatory focuses x-rays with ___________ mirrors. grazing

incidence

The twin 10-m Keck telescopes can work together to obtain better angular resolution through a technique known as ________.

interferometry

Galileo's telescope designs using lenses were examples of ____________.

refracting telescopes

A 10-meter telescope has a larger ___________ than a 4-meter telescope.

light-collecting area

A gas heated to millions of degrees would emit mostly radio waves. an equal amount of all wavelengths of light. mostly X-rays. mostly ultraviolet light. no light, because it is too hot.

mostly X-rays.

The source of energy that keeps the Sun shining today is _________. chemical reactions (fire) nuclear fission gravitational contraction nuclear fusion

nuclear fusion

Which of these layers of the Sun is coolest? core radiation zone photosphere

photosphere

nearly all the visible light we see from the Sun is emitted from the ______

photosphere

Rank the layers of the Sun's atmosphere based on their density, from highest to lowest. Corona chromosphere photosphere

photosphere chromosphere corona As your answer correctly indicates, the density of the Sun's atmosphere decreases with altitude above the photosphere.

Assume the woman in the figure uses her prism to look at a spectrum of light coming from the object(s) shown. In which case will she see a continuous rainbow of thermal radiation?

prism to hot light source A hot light source produces a continuous spectrum (of thermal radiation)

The ______ is the layer of the Sun between its core and convection zone

radiation zone

Which of the following is not a good reason to place observatories on remote mountain tops? to reduce light distortion to be able to observe at radio wavelengths to reduce light absorption to reduce light pollution

to be able to observe at radio wavelengths

Which of the following forms of light can be observed with telescopes at sea level? Select all that apply. Select all that apply. X rays ultraviolet light visible light infrared light radio waves

visible light radio waves