ASTR 264 - Chapter 5 (HW 3)
Fill in the blanks: 1. Nuclear fusion of hydrogen into helium occurs in the ________. 2. Energy moves through the Sun's ________ by means of the rising of hot gas and falling of cooler gas. 3. Nearly all the visible light we see from the Sun is emitted from the ________. 4. Most of the Sun's ultraviolet light is emitted from the narrow layer called the ________ where temperature increases with altitude. 5. We can see the Sun's ________ most easily during total solar eclipses. 6. The ________ is the layer of the Sun between its core and convection zone.
1. Nuclear fusion of hydrogen into helium occurs in the CORE. 2. Energy moves through the Sun's CONVECTION ZONE by means of the rising of hot gas and falling of cooler gas. 3. Nearly all the visible light we see from the Sun is emitted from the PHOTOSPHERE. 4. Most of the Sun's ultraviolet light is emitted from the narrow layer called the CHROMOSPHERE where temperature increases with altitude. 5. We can see the Sun's CORONA most easily during total solar eclipses. 6. The RADIATION ZONE is the layer of the Sun between its core and convection zone.
What is the overall fusion reaction that converts mass into other forms of energy in the Sun's core?
4 hydrogen nuclei become 1 helium nucleus
If two objects are the same size but one object is 3 times hotter than the other object, the hotter object emits
81 times more energy.
Which of the following statements about thermal radiation is always true?
A hot object emits more total radiation per unit surface area than a cool object.
Most continuous spectra are examples of what we also call thermal radiation spectra. Why do we call them "thermal" spectra?
Because the peak wavelength of the spectrum depends on the temperature of the object producing the spectrum.
Most interstellar clouds are made mostly of hydrogen (because hydrogen is the most common element in the universe). Why are these clouds usually dominated by the color red?
Because the strongest visible emission lines from hydrogen are red.
Suppose we obtain a single, detailed (high-resolution) spectrum of a star located many light-years away. What can we learn about the star?
CAN LEARN surface temp speed toward or away from us chemical composition (surface) CANNOT LEARN mass size (diameter) interior temperature distance speed across our line of sight
Sort each item into the appropriate bin based on which type of spectrum it represents.
CONTINUOUS SPECTRUM a graph of this spectrum shows a smooth curve arises from relatively dense objects like light bulb filaments, rocks, and people the only one of the spectra below that does not give us information about chemical composition EMISSION LINE SPECTRUM a graph of this spectrum has upward spikes produced by thin or low-density clouds of gas ABSORPTION LINE SPECTRUM a graph of this spectrum is a curve with sharp, downward dips produced when starlight passes through a thin or low-density cloud of gas
Comte was proven wrong in his claim that we could never learn the composition of stars. What do we know today that Comte did not know when making his claim, and that makes it possible for us to learn the chemical compositions of stars?
Every chemical element produces a unique spectral fingerprint.
Rank the layers of the of the Sun's atmosphere 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. photosphere chromosphere corona
FIRST ENCOUNTERED corona chromosphere photosphere LAST ENCOUNTERED
Rank the layers of the sun based on their distance from the Sun's center, from greatest to least. convection zone radiation zone photosphere corona chromosphere core
GREATEST DISTANCE corona chromosphere photosphere convection zone radiation zone core LEAST DISTANCE
Rank the layers of the Sun based on their density, from highest to lowest. convection zone radiation zone photosphere corona chromosphere core
HIGHEST DENSITY core radiation zone convection zone photosphere chromosphere corona LOWEST DENSITY
Rank the layers of the Sun's atmosphere based on their density, from highest to lowest. photosphere chromosphere corona
HIGHEST DENSITY photosphere chromosphere corona LOWEST DENSITY
Rank the layers of the atmosphere based on the energy of the photons that are typically emitted there, from highest to lowest. photosphere chromosphere corona
HIGHEST ENERGY OF THE PHOTONS corona chromosphere photosphere LOWEST ENERGY OF THE PHOTONS
Rank the following layers of the Sun based on the pressure within them, from highest to lowest. convective zone photosphere core radiation zone
HIGHEST PRESSURE core radiation zone convective zone photosphere LOWEST PRESSURE
Rank the following layers of the Sun based on their temperature, from highest to lowest. convective zone photosphere core radiation zone
HIGHEST TEMP core radiation zone convective zone photosphere LOWEST TEMP
Rank the layers of the Sun's atmosphere based on their temperature, from highest to lowest. photosphere chromosphere corona
HIGHEST TEMP corona chromosphere photosphere
How does a natural "solar thermostat" keeps the core fusion rate steady in the Sun?
If the Sun's core were a bit hotter, the fusion rate would increase. This would produce more energy, which would cause the core to expand slightly and cool. The cooling would cause the fusion rate to slow back down until the Sun was back to the original size and temperature and fusion occurred at the original rate.
Incandescent light bulbs emit thermal radiation because their filaments are heated to about 2500 Kelvin. LED light bulbs emit only at particular visible wavelengths. Why do incandescent bulbs require more energy to shine with the same amount of visible light as LED bulbs?
Incandescent bulbs emit most of their energy as infrared light.
Imagine being on the Moon and looking at the thermal radiation spectrum of Earth. How would it compare to the spectra shown on the graph in the video?
It would be very similar to the spectrum of the human.
The "extraordinary" part of Comte's claim was his statement that we could never learn the composition of stars. Which of the following best summarizes the key lesson we should learn from the fact that his claim was ultimately proven wrong?
The advance of science and technology may someday provide ways to answer questions that seem unanswerable today.
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.
The blue star has a hotter surface temperature than the red star.
If one object has a large redshift and another object has a small redshift, what can we conclude about these two objects?
The one with the large redshift is moving away from us faster than the one with the small redshift.
Consider a planet orbiting another star that is very similar to our Sun. Assume the planet is about the size of Earth and has an Earth-like orbit around its star. Which of the following statements are true about the light coming from the star and planet?
The planet emits virtually all its light as infrared light, The star's spectrum peaks in visible light, and The star emits much more total light than the planet
From laboratory measurements, we know that a particular spectral line formed by hydrogen appears at a wavelength of 486.1 nanometers (nm). The spectrum of a particular star shows the same hydrogen line appearing at a wavelength of 485.9 nm. What can we conclude?
The star is moving toward us.
If we observe one edge of a star to be redshifted and the opposite edge to be blueshifted, what can we conclude about the star?
The star is rotating.
We can learn a lot about the properties of a star by studying its spectrum. All of the following statements are true except one. Which one?
The total amount of light in the spectrum tells us the star's radius.
If a distant galaxy has a substantial redshift (as viewed from our galaxy), then anyone living in that galaxy would see a substantial redshift in a spectrum of the Milky Way Galaxy.
This statement makes sense. The redshift means that we see the galaxy moving away from us, so observers in that galaxy must also see us moving away from them—which means they see us redshifted as well.
T/F: Lines of a particular element appear at the same wavelength in both emission and absorption line spectra.
True
For an object producing a thermal spectrum, a higher temperature causes the spectrum to have ___________.
a peak intensity located at shorter wavelength
Recall that one of the laws of thermal radiation states that a higher-temperature object emits photons with higher average energy (Wien's law). This law is illustrated by the fact that for a higher temperature object, the graph peaks at __________.
a shorter wavelength
What type of visible light spectrum does the Sun produce?
an absorption line spectrum
The absorption line spectrum shows what we see when we look at a hot light source (such as a star or light bulb) directly behind a cooler cloud of gas. Suppose instead that we are looking at the gas cloud but the light source is off to the side instead of directly behind it. In that case, the spectrum would __________.
be an emission line spectrum
In which of the following layer(s) of the Sun does nuclear fusion occur?
core
Thermal radiation gets its name because __________.
its spectrum depends on the temperature of the object emitting it
The neon "OPEN" sign appears reddish-orange because __________.
neon atoms emit many more yellow and red photons than blue and violet photons
Which of the following layers of the Sun can be seen with some type of telescope? Consider all forms of light, but do not consider neutrinos or other particles.
photosphere, chromosphere, and corona
Thermal radiation is defined as _________.
radiation with a spectrum whose shape depends only on the temperature of the emitting object
Compared to a cold object, a hotter object of the same size emits most of its light at __________ wavelengths and emits _____ light overall.
shorter, more
When we refer to the solar thermostat, we are referring to the idea that __________.
the Sun's core temperature naturally stays stable
The energy balance that contributes to the solar thermostat is a balance between __________.
the energy released in the core by fusion and the energy radiated from the Sun's surface into space