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.
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corona
chromosphere
photosphere
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The Sun's photosphere is __________
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the visible surface of the Sun
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The word corona, as in the Sun's corona, means _____.
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crown
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Rank the layers of the Sun's atmosphere based on their density, from highest to lowest.
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photosphere, chromosphere, corona
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As you go upward in altitude through Earth's atmosphere __________.
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the density steadily decreases
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Rank the layers of the Sun's atmosphere based on their temperature, from highest to lowest.
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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.
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We use visible-light telescopes to observe
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the photosphere
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We use ultraviolet telescopes to observe
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the chromosphere
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We use the X-ray telescopes to observe
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the corona.
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Rank the layers of the atmosphere based on the energy of the photons that are typically emitted there, from highest to lowest.
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corona
chromosphere
photosphere
The energy of the emitted light rises with temperature, 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
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When we observe the Sun with an X-ray telescope, we see the _____.
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corona
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The layer of the Sun's atmosphere that is best observed with an ultraviolet telescope is the _____.
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chromosphere
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The Sun's photosphere is __________.
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the visible surface of the Sun.
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Which of the following changes would cause the fusion rate in the Sun's core to increase?
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-increases in the core temperature
-a decrease in the core radius
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Fusion requires bringing two positively charged nuclei so close together that the strong nuclear force can hold them against the electromagnetic repulsion of their positive charges. What conditions make fusion possible?
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extremely high temperature and high density
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When the Sun's core contracts, the core temperature __________.
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increases
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An increase in the core temperature increases
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the fusion rate because the fusion rate is very sensitive to temperature.
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A decrease in the core radius causes the core
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to heat up and increase in density, which leads to an increased fusion rate.
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Which of the following must occur for a star's core to reach equilibrium after an initial change in fusion rate?
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-If the fusion rate initially increases, then the core expands.
-If the fusion rate initially decreases, then the core contracts.
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The core of a star is in equilibrium when its
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temperature, size, and rate of nuclear fusion all hold steady.
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Suppose you could somehow start nuclear fusion in a box that stayed the same size. Increasing the fusion rate would cause the temperature inside the box to __________.
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increase
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If you heat an inflated balloon, what happens to it?
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The gas particles inside it move faster, causing it to expand until it stabilizes at a new, larger size.
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The fusion rate is higher when particles combine together more frequently.
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Fusion is represented by two particles combining together and a flash of light, and the fusion rate is represented by the height of the bar graph.
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Increasing the fusion rate releases more energy into the core, which
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raises the temperature and increases the internal pressure, causing the core to expand.
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Decreasing the fusion rate means less energy is released,
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so the temperature and internal pressure would decrease.
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The solar thermostat keeps the fusion rate fairly steady in a star like the Sun because
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a temperature increase causes the core to expand while a temperature decrease causes the core to contract.
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What would happen if the fusion rate in the core of the Sun were increased but the core could not expand?
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The Sun's core would start to heat up, and the rate of fusion would increase even more.
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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.
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However, 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 increasing. There would be no equilibrium.
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Our current understanding of nuclear fusion in the Sun's core is based primarily on __________.
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applying the laws of physics to calculate what must be occurring inside the Sun
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Which of the following lists the Sun's layers in the correct order (staring from the Sun's center and going outward)?
Which of the following statements accurately describes how we can best study different layers of the Sun with telescopes either on the ground or in space?
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We observe the photosphere with visible-light telescopes, the chromosphere with ultraviolet-light telescopes, and the corona with X-ray telescopes.
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A neutrino :
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is a lightweight (almost massless) particle that is a by-product of nuclear reactions and radioactive decay.
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Neutrinos have the unusual property that they do not interact with light
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and therefore they do not respond to the electromagnetic forces that affect protons and electrons. Neutrinos can therefore stream outward from the center of the Sun nearly uninterrupted by collisions. We can detect them (by looking for their very rare collisions with other particles) on Earth with the help of gigantic underground detectors such as South Dakota's Homestake Mine and the Sudbury Neutrino Observatory in Canada.
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To understand the interplay of observations and models you must first be able to distinguish between things that we observe and things that we infer from models. Consider the following statements about the Sun. Classify each statement as an observation or as an inference based on the current, accepted model for the Sun.
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Observations:
-the photosphere emits mostly visible light
-the corona is hotter than the photosphere
-the sun emits neutrinos
-the photosphere is made mostly of hydrogen and helium
Inferences form a model:
-the convection zone is cooler than the radiation zone
-the core temperature is 10 million K
-the sun generates energy by fusing hydrogen into helium in its core
-the composition of the photosphere is the same as that of the gas cloud that gave birth to our solar system
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"The corona is hotter than the photosphere." Which of the following statements provides observational evidence for this claim?
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The corona primarily emits X rays while the photosphere primarily emits visible light.
In general, higher temperature gas emits higher energy light. The fact that the corona emits primarily in X rays therefore indicates that it consists of higher temperature gas than visible-light-emitting photosphere.
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Now consider the statements in Part A that are inferred from models. A solar model is used to calculate interior conditions based on certain "known" characteristics of the Sun, such the Sun's total mass. How do we know the Sun's mass?
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We can calculate it by applying Newton's version of Kepler's third law with Earth's orbital period (1 year) and Earth's average distance from the Sun (1 AU).
Recall that Newton's version of Kepler's third law allows us to calculate the mass of any object if we know the orbital period and distance of a much smaller object that orbits it. This means we can use not only Earth's period and distance to calculate the Sun's mass but the period and distance of any planet or even of a spaceship that we put into solar orbit.
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A solar model is used to calculate the expected temperature and density at all depths within the Sun. These results are then used to calculate the expected fusion rate within the Sun. We have confidence that the model is correct because it agrees with the observed characteristics of the Sun. Which of the following observations can be used to check that we really do know the Sun's internal fusion rate?
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Observations of neutrinos coming from the Sun
Measurements of the Sun's total energy output into space
The Sun shines with energy generated by fusion, so the total rate at which the Sun emits energy into space must be equal to the rate at which it generates energy by fusion in the core. Neutrinos are a product of fusion reactions, so they provide direct evidence concerning fusion in the core.
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convection zone:
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A convection zone is a region in which energy is transported outward by convection, which means hot material will rise and cooler material will fall.
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chromosphere:
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A chromosphere is the layer of the Sun's atmosphere below the corona; most of the Sun's ultraviolet light is emitted from this region, in which the temperature is about 10,000 K.
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photosphere:
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A photosphere is the visible surface of the Sun, where the temperature averages just under 6,000 K.
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radiation zone:
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A radiation zone is a region of the interior of a star in which energy is transported primarily by radiative diffusion.
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core:
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A core is the central region of a star, in which nuclear fusion can occur.
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corona:
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A corona is the tenuous uppermost layer of the Sun's atmosphere; most of the Sun's X rays are emitted from this region, in which the temperature is about 1 million K.
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Nuclear fusion of hydrogen into helium occurs in the
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core
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Energy moves through the Sun's __________ by means of the rising of hot gas and falling of cooler gas.
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convection zone
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Nearly all the visible light we see from the Sun is emitted from the
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photosphere
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Most of the Sun's ultraviolet light is emitted from the narrow layer called the _________ where temperature increases with altitude.
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chromosphere
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We can see the Sun's ________ most easily during total solar eclipses.
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corona
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______ is the layer of the Sun between its core and convection zone.
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radiation zone
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The average number of sunspots on the Sun gradually rises and falls over time, making what we call the sunspot cycle.
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The following graph shows how the number of sunspots (equivalent to the percentage of the Sun's surface covered by sunspots) changes with time. The main peaks on the graph represent times of solar maximum and the main dips represent times of solar minimum.
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Sunspots are regions of intense magnetic fields, and other phenomena of "solar activity" — including solar flares and other types of solar storms — are also associated with intense magnetic fields.
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These phenomena of solar activity are therefore most common when sunspots are most numerous and least common when sunspots are rare.
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Listed following are events or phenomena that occur during either the part of the sunspot cycle known as solar minimum or the part known as solar maximum. Match these items to the correct part of the sunspot cycle.
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Solar maximum:
-occurs about 11 years after a solar maximum (on average)
-sunspots are most numerous on the Sun
-solar flares are most common
-orbiting satellites are most at risk
-auroras are most likely in Earth's skies
Solar minimum:
occurs about 5 to 6 years after a solar maximum (on average)
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X-ray images of the Sun generally show the
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corona
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Which of these layers of the Sun is coolest?
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photosphere
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Which of these groups of particles has the greatest mass?
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four individual protons
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Scientists estimate the central temperature of the Sun using
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mathematical models of the Sun.
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At the center of the Sun, fusion converts hydrogen into
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helium, energy, and neutrinos.
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Solar energy leaves the core of the Sun in the form of
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photons
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How does the number of neutrinos passing through your body at night compare with the number passing through your body during the day?
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about the same
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The total mass of the Sun is about 2×1030 kg, of which about 75 % was hydrogen when the Sun formed. However, only about 13 % of this hydrogen ever becomes available for fusion in the core. The rest remains in layers of the Sun where the temperature is too low for fusion.
Based on the given information, calculate the total mass of hydrogen available for fusion over the lifetime of the Sun.
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2x10^29 kg
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The total mass of the Sun is about 2×1030 kg, of which about 75 % was hydrogen when the Sun formed. However, only about 13 % of this hydrogen ever becomes available for fusion in the core. The rest remains in layers of the Sun where the temperature is too low for fusion.
Combine your results from part A and the fact that the Sun fuses about 600 billion kg of hydrogen each second to calculate how long the Sun's initial supply of hydrogen can last. Give your answer in both seconds and years.
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3x10^17 s
1z10^10 years
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The total mass of the Sun is about 2×1030 kg, of which about 75 % was hydrogen when the Sun formed. However, only about 13 % of this hydrogen ever becomes available for fusion in the core. The rest remains in layers of the Sun where the temperature is too low for fusion.
Given that our solar system is now about 4.6 billion years old, when will we need to start worrying about the Sun running out of hydrogen for fusion?
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6x10^9 years
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Sunspots appear darker than their surroundings because they
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are cooler than their surroundings.
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What causes the cycle of solar activity?
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changes in the organization of the Sun's magnetic field
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Which of these things poses the greatest hazard to communications satellites?
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particles from the Sun
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Which of the following years had the least sunspot activity?
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1987
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What is the approximate range in latitude over which sunspots appear?
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Sunspots appear over a range of 40-50∘N latitude to 40-50∘S latitude.
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According the figure, how do the positions of sunspots appear to change during one sunspot cycle? Do they get closer to or farther from the equator with time?
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Sunspots get closer to the equator during a sunspot cycle.
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