Astronomy Ch. 14 Study Set

Briefly describe the distinguishing features of each of the layers of the Sun shown in Figure 14.4.

Outside to inside: Solar wind, Corona, Chromosphere, Photosphere and Sunspots, Convection Zone, Radiation Zone, Core. Solar wind is the gas and particles ejected from the Sun. The corona is the loose atmosphere around the sun. The chromosphere is a more dense but less hot atmospheric region that has small spikes of gas jet up into it from the surface. The photosphere is the visible surface of the Sun, and the region where sunspots develop. Sun spots are cooler regions which have intense magnetic fields. Convection zone is where the energy from the core is brought upwards via convection (the rising of hotter gases and the falling of cooler gases.) The radiation zone is where energy travels to the convection zone from the core primarily via photons. The Core is where fusion happens.

What do we mean by solar activity? Describe some of the features of solar activity, including sunspots, solar prominences, solar flares, and coronal mass ejections.

Magnetic fields create features on the Sun's surface and atmosphere. Sunspots, solar flares, coronal mass ejections, and solar prominences are all examples of such phenomenon. Sunspots are bubbles of cooler gas that is separated from the rest of the hot gas on the Sun's surface by a magnetic field, this keeps them from mixing and heating up. Sun spots tend to appear in pairs, and are connected by a loop of magnetic field lines. A solar prominence occurs when gas gets stuck in this loop, causing a hug arc of plasma in the corona. Solar flares are thought to be caused when the magnetic field lines are so twisted they snap and try to reorganize themselves. Coronal mass ejections are when huge bubbles of charged particles from flares or other solar storms escape from the Sun. These can hit Earth's magnetosphere and cause a geomagnetic storm that damages electronics in orbit, disrupt power plants and interfere with radio communications.

What is the difference between nuclear fission and nuclear fusion? Which one is used in nuclear power plants? Which one does the Sun use?

Nuclear fusion and nuclear fission are two different types of energy-releasing reactions in which energy is released from high-powered atomic bonds between the particles within the nucleus. The main difference between these two processes is that fission is the splitting of an atom into two or more smaller ones while fusion is the fusing of two or more smaller atoms into a larger one. Nuclear fission is used for nuclear power plants. Nuclear fusion is used by the sun.

What is the overall nuclear fusion reaction in the sun?

Nuclear fusion is the source of all energy the Sun releases into space. If the fusion rate is varied, so would the Sun's energy output, and large variations in the Sun's luminosity would almost surely be lethal to life on Earth. Fortunately, the Sun fuses hydrogen at a steady rate, thanks to a natural feedback process that acts as a thermostat for the Sun's interior. Solar energy production remains steady because the rate of nuclear fusion is very sensitive to temperature. A slight increase in the Sun's core temp. would mean a much higher fusion rate.

How do magnetic fields keep sunspots cooler than the surrounding plasma? Explain.

They separate the sunspot's gas from the rest of the Sun's surface gas. This prevents them from mixing and heating the sunspot back to the average surface temperature.

Why does nuclear fusion require high temperatures and pressures ?

To bond together, two nuclei must be thrown together with great force. This is because every nucleus has a positive charge and the nuclei repel each other when they come close. If that resistance is overcome and the nuclei actually begin to impact each other, then it is possible for one proton in one nucleus to change to a neutron and bind or 'fuse' together with the other nucleus.

Describe the end result of the p-p cycle (proton-proton)?

4p -> He⁴ + Energy Energy =(2positrons+2photons+2neutrino)

Why has the sun gradually brightened with time?

Because nuclear reaction have decreased the weight of the core of the sun, increasing the pressure. The core of the sun contracts under its own pressure, and this pressure travel outwards, increasing the temperature of the sun. And as temperature increases, luminosity and the fusion rate increase.

What two forces are balanced in gravitational equilibrium? What does it mean for the Sun to be in energy balance?

Gravity and thermal pressure (the heat from fusion in the core causes pressure.) The Sun is not expanding or contracting because the energy from gravity pulling inward is equal to the gas pressure pushing outward. The energy is in equilibrium.

Briefly describe how gravitational contraction generates energy. When was it important in the Sun's history? Explain.

It was important to get the Sun's core to start fusion. It generates energy by converting gravitational potential energy into thermal energy (i.e. heat.)

Why does the energy produced by fusion in the solar core take so long to reach the solar surface? Describe the processes by which energy generated by fusion makes its way to the Sun's surface.

Most of the Sun's energy starts in the core. It then takes hundreds of thousands of years for the energy exit as has to travel a long way to the surface. The energy goes from the core to the radiation zone as photons. The photons bounce around until they reach the top of the radiation zone when the temperature cools and the plasma can absorb the photons. The energy then works it way up through the convection zone. In the convection zone, the hotter gases drift up until the energy can escape to the photosphere or surface of the Sun.

What are the neutrinos? What was the solar neutrino problem, and why do we think it has now been solved?

Neutrinos are sub-atomic particles that can pass through most matter without interacting. Early attempts to detect them only turned up a third of the amount required by predictions based on models of the Suns core. We discovered there are three types of neutrinos and that early detectors only picked up one.

State the Sun's luminosity, mass, radius, and average surface temperature, and put the numbers into a perspective that makes them meaningful.

Radius: about 700,000 km (about 110 times the radius of the Earth, 10 times the average radius of Jupiter.) Mass: 2*10^30 kg (about 300,000 earths) Luminosity: 3.8 * 10^26 watts (1 second's worth of this amount of power would be enough to meet current energy demands for the next 500,000 years) Composition: 70% H, 28% He, 2% heavier elements Surface Temperature: 5800K(average) Core Temperature: 15 million K

Why are the chromosphere and corona best viewed with ultraviolet and x-ray telescopes, respectively? Briefly explain how we think the chromosphere and corona are heated.

The density in them is so low that we can't see the gas with visible light, except during a total eclipse. We can observe them using x-ray and ultraviolet telescopes though. This is due to the high temperatures. The heating of the corona and chromosphere is believed to be caused by the convection of gas, this convection shakes the magnetic field lines and energy is carried up them into the solar atmosphere where the energy is released as heat.

Describe the leading model for explaining the sunspot cycle. Does the sunspot cycle influence Earth's climate? Explain?

The field lines (which are strengthened by convection) get contorted by the Sun's rotation, which is faster at the equator. They cause more sunspots and other activity as they contort and then they eventually reset and solar activity becomes rarer. It is debated whether or not solar activity affects the climate, there are some patterns but it is unclear how great the effect is.

Describe the appearance and temperature of the Sun's photosphere. Why does the surface look mottled? How are sunspots different from the surrounding photosphere?

The photosphere appears to have a mottled or grainy texture. This is due to the presence of convection cells called granules which transport plasma up to the visible portion of the photosphere. The plasma is hottest at the center of the cell where it is rising and coolest at the periphery where it is descending. The photosphere is generally taken to have an effective temperature of 5800 degrees Kelvin. Sunspots are areas of the photosphere which have intense magnetic field activity which serve to reduce/disrupt the convection from lower in the sun thus lowering the temperature of the immediately surrounding plasma. This cooler material ( 4000-4,500 degrees K) appears dark as contrasted against the hotter material of the photosphere.

What is the sunspot cycle? Why is it sometimes described as an 11-year cycle and a 22-year cycle? Are there long term changes in solar activity?

The sunspot cycle is a cycle in which the average number of sunspots per year gradually rises and falls, 11 years between maximums and minimums (22 per cycle.) There have been times when there are almost no sunspots, indicating that the long term changes can possibly be very drastic.

Explain how mathematical models allow us to predict conditions inside the Sun. How can we be confident that the models are on the right track?

We can use mathematical models involving the known laws of physics to imagine what the Sun is like internally. We can then compare the results of the model's internal conditions, like temperature, pressure, and density, to the results/data of real world experiments, things like surface temperature, radius, luminosity, age, etc, and then we know whether the model is correct or not by how well the predict results match the real world results.