Midterm Flashcards
What is the Doppler effect?
The Doppler effect is caused by the motion of a light source either toward or away from an observer. When a light source moves toward or away from an observer, the observed wavelength is shifted from the emitted wavelength by an amount proportional to the speed of the object. Motion toward the observer results in a blue shift (shift to shorter wavelengths). Motion away from the observer results in a red shift (shift to longer wavelengths).
How much larger is the Sun than the Earth in diameter? In volume?
100× larger than that of the Earth. Thus, the volume of the Sun is about 10^6× (one million times) larger than that of the Earth
i.e. if the Sun were hollow it would take 10^6 Earth-sized objects to fill it.
What is hydrostatic equilibrium?
Hydrostatic equilibrium is a balance between the outward gas pressure in the Sun and the inward pull of gravity. The Sun supports its own weight by its outward gas pressure, so that it is neither contracting nor expanding.
What are the central and surface temperatures of the Sun?
The central temperature of the Sun is about 1.6 × 10^7 K and the temperature in the photosphere is about 5800 K.
What are the two most abundant elements in the Sun?
Hydrogen and helium are the two most abundant elements in the Sun (as well as in the universe as a whole).
What is the physical state of the material in the Sun?
Below the photosphere of the Sun, the hydrogen and helium in the Sun are in an ionized state, i.e. the electrons move freely rather than being bound to a particular nucleus.
What is the energy source of the Sun? Describe the physical process that releases energy. Discuss where this process occurs in the Sun and why it occurs there.
The Sun produces energy by the thermonuclear fusion of hydrogen to helium in its core. Through a series of reactions, four hydrogen nuclei are fused to produce one helium nucleus plus energy. The combined mass of the four hydrogen nuclei is slightly more than that of the resulting helium nucleus. The lost mass is converted to an equivalent amount of energy according to the relation E = mc2.
Nuclear fusion occurs only in the core of the Sun, since it is only there that the temperature is sufficiently high (T > 10^7 K). High temperature is required for nuclear fusion, since nuclei must collide at high speed in order to overcome their electrical repulsion.
About how much longer will the Sun’s present nuclear energy reserve last?
The Sun’s present hydrogen energy reserve will last for another 5 × 10^9 years (5 billion).
What mechanisms transport energy in the Sun? Describe each process. Where is each mechanism important?
Energy is transported in the Sun by both radiation and convection. In radiation, photons random walk outward in the Sun, carrying energy outward. In convection, hot gas rises and cool gas sinks, also carrying energy outward. Radiation is important through most of the solar interior, except for the outer 30% of the solar radius just below the photosphere, where convection is most important.
What is the evidence that convection occurs in the Sun?
The observation of granulation in the Sun’s photosphere provides direct evidence of convection. The bright areas in the granulation pattern are the tops of rising columns of hotter gas. The dark areas are sinking columns of cooler gas.
List the layers of the solar atmosphere, in order of increasing distance from the Sun. Discuss the temperature variation in the solar atmosphere.
layers: photosphere, chromosphere, transition zone, corona
The temperature is about 5800 K in the photosphere, drops slightly going outward into the chromosphere, and then begins to rise sharply in the transition zone. The temperature reaches over 10^6 K in the corona.
What is a spicule?
a jet of hot gas shooting upward found in the chromosphere
What is a prominence?
a looping region of hot gas, supported by magnetic field, that extends into the corona
What is a flare?
a violent outburst of radiation and particles from a small area in the solar atmosphere
Describe the properties of a sunspot.
Sunspots are regions in the photosphere that are somewhat cooler than the surrounding area and thus emit less light. They are regions of strong magnetic field, which inhibits heat flow. Sunspots tend to be found in groups of at least two. They last for about two months.
How often does a sunspot maximum occur?
A sunspot maximum occurs once every eleven years (11 yr).
What is the solar wind? What effect does it have on Earth?
The solar wind is a stream of charged particles, mostly protons and electrons, escaping from the solar corona. Solar wind particles that become trapped by the Earth’s magnetic field cause aurora. At periods of high solar activity, the resulting changes in the Earth’s ionosphere can affect radio communications on Earth. In extreme cases, power distribution systems on Earth have shorted out as a result of changes in the ionosphere brought about by interaction with the solar wind.
What is the underlying cause of the solar cycle?
The cycle of solar activity is a result of interaction between the Sun’s magnetic field and its rotation.
What is a neutrino?
A neutrino is a very low mass particle that interacts very weakly with other matter.
What produces neutrinos in the Sun? What happens to the neutrinos next? Why are astrophysicists interested in detecting neutrinos from the Sun?
Neutrinos are produced by nuclear reactions in the Sun, such as the fusion of two protons to form a deuterium nucleus. Neutrinos that are created in the Sun escape immediately. Thus, the solar neutrinos that we detect on Earth give us a direct measure of the nuclear reaction rate deep in the core of the Sun.
What is a “neutrino telescope”? Where are these located and why?
Neutrino telescopes use large amounts of matter—often large water tanks—which capture a very small fraction of the total number of neutrinos that pass through. Neutrino telescopes are located deep underground, to shield out other subatomic particles that, unlike neutrinos, cannot pass directly through the Earth.
What was the “solar neutrino problem”? What is the solution to this problem?
The solar neutrino problem was the finding that the number of neutrinos observed from the Sun by early neutrino detectors was was about one third the number that had been predicted by the standard solar model. The solution to this problem is the finding that neutrinos oscillate between three different types as they travel through space between the Sun and the Earth. Since only one type of neutrino was detected by early neutrino detectors, these experiments to measure the number of solar neutrinos being received found about one third of the number that was originally predicted. Later generation neutrino detectors detect all types of neutrinos and confirm the predictions of the standard solar model.
What is the definition of stellar parallax?
Stellar parallax is 1/2 of the annual shift in the apparent position of a nearby star, relative to more distant stars, due to the orbital motion of the Earth about the Sun.
What baseline is used in determining the parallax of a star and what is the length of this baseline?
The diameter of the Earth’s orbit is used as the baseline, which thus has a length of 2 AU.
