Flashcards in Chapter 3 - The System Sun-Earth Deck (35):
What is the sun primarily made of?
75% hydrogen, 23% helium and 2% other elements.
What is the definition of luminosity?
It is defined as the total radiation of sun radiated into solid angle omega = 4pi.
What order of magnitude is the luminosity of the sun? (in terms of Watt)
What is the solar constant SC?
The solar constant is the absorbed power per unit area in the space outside the earth atmosphere by an ideal absorber under normal incidence.
What is the value of the solar constant averaged over one year?
What is the relationship between the solar constant and the luminosity?
SC = 1/(4 π r_se^2) * L
SC = solar constant
r_se = radius sun-earth
L = luminosity
What order of magnitude is the Sun's mass? (in terms of kg)
(2* ) 10^30
What is the annual weight loss of the Sun?
Approx 10^17 kg, so about 10^-13 of total sun mass.
How is the Stefan-Boltzmann law defined?
Radiated power of body is:
P_em = e * A * sigma * T^4
e: emissivity (0
Calculate the effective temperature of the Sun surface.
L = 3.82 * 10^26 W
R_sun = 7*10^8 m
P_em = L = 4 π R_sun^2 * sigma * T_eff^4
=> T_eff = 5780K
What is the overall reaction of the energy production in the sun?
4p -> 4He + 2e+ + 2v_e + 26.73MeV
e+ : positron
What are the two major fusion reactions in stars? How much do they contribute in our star?
1) Direct p-p drain (mostly everything, 98% ish)
2) CNO-cycle (1.6%)
Describe the direct p-p drain fusion reaction that occurs in the sun.
Fusion of protons to deuterons:
p + p -> d + e+ + v_e
Fusion of deutrons with additional protons:
d + p -> 3He + gamma + 5.49 MeV
Then there are several tertiary reactions. Two of them are:
3He + 3He -> 4He + 2p + 12.86 MeV (86%)
3He + p -> 4He + e+ + v_e + 18.77 MeV (2*10^-5 %)
Describe the CNO-cycle, also known as the Bethe-Woizsäcker cycle.
Formation of 4He from p catalyzed by heavy elements CNO:
12C + p -> 13N + gamma (unstable, quickly:)
13N -> 13C + e+ + v_e
13C + p -> 14N + gamma
14N + p -> 15O + gamma (unstable, quickly:)
15O -> 15N + e+ + v_e
15N + p -> 12C + 4He
What does the relative importance of the p-p drain and CNO-cycle depend upon?
The core temperature. If our sun was a little hotter, the CNO-cycle would play a more dominant part before becoming the dominant process at even higher temperatures.
Derive the shell model of the sun as an ideal gas.
Which picture of the energy production does the shell model give us?
That 90% is produced in the core, within a radius of 0.25 R_sun.
What is the temperature of the core, according to the shell model? What about the density?
About 15 million K. Density of about 100 g / cm^3, which is about 70 times the average density.
How is energy liberated in the core transported through the radiation zone? How far does the radiation zone stretch?
By gamma radiation. It stretches to about 0.7 R_sun.
How is the energy transported beyond the radiation zone, and what is this zone called? How far does it stretch?
After 0.7 R_sun, the energy is transported by thermal convection up till the surface. This is called the convection zone.
Where does the visible radiation emitted by the sun come from? How does the temperature change in this zone?
The very thin photosphere (about 200 km). It decreases (from 8000K to 4500 K).
How is the photosphere structured? Draw a picture, and give typical values of size.
By convection rolls (granules). See slides.
Which zone follows the photosphere? How thick is this zone? What does it consist of?
The chromosphere follows the photosphere. It is approximately 10 000 km thick. It consists of hot particles having enough energy to leave the photosphere.
What follows outside the chromosphere? What does it consist of? What is the temperature here, and how thick is it?
The corona. Consists of very hot particles. Temperature ofa bout 1 million K and a thickness of 1 million km.
What are solar winds?
Solar winds are particles with sufficient energy to leave the gravitational pull of the sun.
Name some dynamic activities on the sun.
Eruptions, protuberances, flares, sun spots.
What are flares?
Flares are short eruptions that lasts from some minutes to hours. Very energetic.
What are sun spots?
(badly explained in notes, check some other source)
What is the radius of the earth?
6.4 * 10^6 m.
What is the equation for the incident power P from the sun?
P = (1-R) * π * R_earth^2 * SC,
where R is the reflectivity, and SC is the solar constant.
What is the albedo, and what does it depend on?
The albedo is the reflectivity of earth. It depends on things such as clouds, water, snow, vegetation, desserts. The values are quite different, for example water at equator (normal incidence) contributes R = 0.05 while in the Northern hemisphere it can be as much as 0.25. Clouds and snow have values that range from 0.2-0.7.
If we treat the Earth as a black body with emissivity e = 1, what is the equilibrium temperature of the earth?
(1-R) * π * R_earth^2 * SC = 4πR_earth^2 * sigma * T_E^4
T_E = -19C. This is obviously false, because the green house effect is not accounted for. (average temperature is +15C).
How do we measure the integrated absorption due to atmospheric molecules depending on the length of path through the atmosphere?
By air mass, AM. AM0 is outside the atmosphere, AM1 is at the equator, AM1.5 is at Munich etc.
How much does the energy flux of the inside of the earth contribute to the temperature?
Almost nothing, ≈ 0.02%.