Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 15, Problem 27E
The escape velocity from any astronomical object can be calculated as
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Considering your answer to the above question, how does this timescale for the Sun's evaporation by the solar wind compare to the age of the
Universe?
O The solar wind evaporation time is much longer than the age of the Universe
O The solar wind evaporation time is much shorter than the age of the Universe.
O The solar wind evaporation time is close to the age of the Universe (ie, within a few billion years
Assume that the solar wind causes the Sun to lose mass at a rate of 2 x 10’ kg/s. If you assume the
wind is emitted a constant rate, estimate the time (in units of Gyr =Gigayears = 10° years) that it
will take the entire Sun to evaporate via its solar wind emission.
(Of course, the rate won't be constant throughout the lifetime of the Sun---this is just a rough
estimate to understand the timescale associated with this process.)
[Hint: you need to look up a number and do several unit conversions; this is a *rate* problem. Enter
your answer as an integer or decimal, NOT in scientific notation.]
a) At solar maximum sunspots might cover up to 0.4% of the total area of the Sun. If the sunspots have a temperature of 3800 K and the surrounding photosphere has a temperature of 6000 K, calculate the fractional change (as a percentage) in the luminosity due to the presence of the sunspots.
b) A star of the same stellar class as the Sun is observed regularly over many years, and a time series of its bolometric apparent magnitude is collected. What would be the signal in this time series which indicated that the star had a magnetic dynamo similar to the Sun? Briefly describe two or three possible sources of other signals which could confuse the interpretation of the data.
Chapter 15 Solutions
Astronomy
Ch. 15 - Describe the main differences between the...Ch. 15 - Describe how energy makes its way from the nuclear...Ch. 15 - Make a sketch of the Sun’s atmosphere showing the...Ch. 15 - Why do sunspots look dark?Ch. 15 - Which aspects of the Sun’s activity cycle have a...Ch. 15 - Summarize the evidence indicating that over...Ch. 15 - What it the Zeeman effect and what does it tell us...Ch. 15 - Explain how the theory of the Sun’s dynamo results...Ch. 15 - Compare and contrast the four different types of...Ch. 15 - What are the two sources of particles coming from...
Ch. 15 - How does activity on the Sun affect human...Ch. 15 - How does activity on the Sun affect natural...Ch. 15 - Table 15.1 indicates that the density of the Sun...Ch. 15 - Starting from the core of the Sun and going...Ch. 15 - Since the rotation period of the Sun can be...Ch. 15 - Suppose an (extremely hypothetical) elongated...Ch. 15 - The text explains that plages are found near...Ch. 15 - Why would a flare be observed in visible light,...Ch. 15 - How can the prominences, which are so big and...Ch. 15 - If you were concerned about space weather and...Ch. 15 - Suppose you live in northern Canada and an...Ch. 15 - The edge of the Sun doesn’t have to be absolutely...Ch. 15 - Show that the statement that 92% of the Sun’s...Ch. 15 - From Doppler shifts of the spectral lines in the...Ch. 15 - Assuming an average sunspot cycle of 11 years, how...Ch. 15 - This chapter gives the average sunspot cycle as 11...Ch. 15 - The escape velocity from any astronomical object...Ch. 15 - Suppose you observe a major solar flare while...Ch. 15 - Suppose an eruptive prominence rises at a speed of...Ch. 15 - From the information in Figure 15.21, estimate the...
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- Given that the solar spectrum corresponds to a temperature of T- 5800K and peaks at a wavelength of à = 500 nm, use Wien's law to determine the wavelength (2') corresponding to the peak of the blackbody curve (a) in the core of the Sun, where the temperature is T' - 10'K, (b) in the solar convection zone (10° K), and (c) just below the solar photosphere (10* K). [Hint: AT - A'T' (why?)] What form (visible, infrared, X ray, etc.) does the radiation take in each case?arrow_forward2 of 7 Question A2 a) Calculate the mass loss rate of the Sun M due to the solar wind flow. Assume average properties of the solar wind of number density 6 protons cm³, and a flow speed of 450 km s-1. Express your answer in units of both kg per year, and solar masses per year. b) Suppose the solar wind flow is perfectly radial. Calculate the expected rate of change of solar rotation frequency dw at the present time, based on conservation of angular momen- tum. Give your answer in units of rad s-1 y-1 (i.e., radians per second per year) and also in terms of fractional change per year, i.e., 1 du. w dt' Use a current solar rotation period of P = 25.38 days to calculate the current angular frequency of rotation w. The moment of inertia of a uniform sphere is MR². You can assume that the radius of the Sun is approximately constant, and the change in its moment of inertia due to the solar wind is only due to the mass loss. Page 3 c) By observing the rotation period of stars similar to the…arrow_forwardAn image of the disk of the Sun shows a higher brightness at the centre compared to the edges. Explain with the aid of a sketch the reasons for this darkening at the limb of the solar disk. In images of the solar photosphere there are small regions of the solar disk, about 500 km across, which are about 2.5 times brighter that the surrounding photosphere. Assuming a temperature of 5800 K for the background photosphere, calculate the temperature of these photospheric bright points. One explanation for these bright points is that the density is lower in these regions. Explain briefly how that could produce the observed brightening.arrow_forward
- What was the minimum volumeVrequired to supply enough magneticenergy to fuel the flare? What was the minimum volume V required to supply enough magnetic energy to fuel the flare? If the volume V is spherical, what is its radius? Is this greater than or less than the typical radius r≈104km of a sunspot?arrow_forwardAssuming that (1) the solar luminosity has been constant since the Sun formed, and (2) the Sun was initially of uniform composition throughout, as described by Table 9.2, estimate how long it would take the Sun to convert all of its original hydrogen into helium. [Hint: Calculate the mass of hydrogen in the sun and then divide it by the rate of hydrogen fusion (PPT slide 47.)]arrow_forwardIf a sunspot has a temperature of 4200 K and the average solar photosphere has a temperature of 5780 K, how much more energy is emitted in 1 second from a square meter of the photosphere compared to a square meter of the sunspot? (Hint: Use the Stefan-Boltzmann law, Eq. 7-1.)arrow_forward
- Suppose an eruptive prominence rises at a speed of 150 km/s. If it does not change speed, how far from the photosphere will it extend after 3 hours? How does this distance compare with the diameter of Earth?arrow_forwardExplain why there is the low number of observed solar neutrinos?arrow_forwardWhy are measurements of the Sun's 10.7 cm radio emission used to monitor the state of the solar cycle? Choose allcorrect answers.A. It provides a repeatable, objective measurement of solar activityB. It serves as a good proxy for EUV emissionsC. It is measured from space, so it is not affected by cloudsD. It can be used to predict the occurrence of coronal mass ejectionsarrow_forward
- High energy cosmic rays from space hit the nitrogen in the atmosphereand convert it from nitrogen (N14) into carbon (C14). This produces a steadyconcentration of C14 in the atmosphere once the decay rate of the C14 back intoN14 matches the conversion rate from the cosmic ray flux (which is assumedto be constant for reasons you can ask me about if you want) a) What kind of radiation (what kind of particle) does the C14 emit when it decays? Tellme how you know?b) The concentration of C14 in plants (and animals) comes into equilibrium with the at-mosphere because living things use the ambient carbon to make their cellular structures.However, once a plant dies, it no longer consumes C14. The C14 starts to decay away—allowing us to calculate when the plant died because the C14/C12 ratio doesn’t match theatmosphere. If the half life of C14 is 5000 years, what is the age of a piece of charcoal froma site from the Clovis peoples of North America if the concentration of C14 is 15% of…arrow_forwarda.Calculate the mass loss rate of the Sun M˙ due to the solar wind flow. Assume averageproperties of the solar wind of number density 6 protons cm−3, and a flow speed of 450 kms−1. Express your answer in units of both kg per year, and solar masses per year. b.Suppose the solar wind flow is perfectly radial. Calculate the expected rate of change ofsolar rotation frequency dω/dt at the present time, based on conservation of angular momentum. Give your answer in units of rad s−1 y−1(i.e., radians per second per year) and alsoin terms of fractional change per year, i.e., 1/ωdω/dt .Use a current solar rotation period of P = 25.38 days to calculate the current angularfrequency of rotation ω. The moment of inertia of a uniform sphere is 2/5 MR2. You canassume that the radius of the Sun is approximately constant, and the change in its momentof inertia due to the solar wind is only due to the mass loss. c.By observing the rotation period of stars similar to the Sun, it is inferred that their…arrow_forwardThe figure below shows measurements of the solar wind magnetic field at 1 AU over a 24 hour period. Themeasurements are in GSM coordinates and include the vector components of the field as well as the correspondingangles (θ is the polar angle, which correspond to Bz, and φ is the azimuthal angle). Based on the figure, briefly describewhat event occurred between 13 and 14 UT.arrow_forward
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