Question One: Why Are There Sunspots on the Sun

Wednesday, November 10, 2004 Please come to the front of the room and take back your papers.

EASY DISCUSSION ACTIVITY Please take out a piece of paper and answer the following: what has been the most challenging topic for you in the chapters covered for the 2nd exam (Ch. 5, 8-13)? When you are done, put it on the wooden podium. Don’t forget your name and section number!

Do we have discussion on Nov. 24? YES! You should come to discussion on Nov. 24. I think you’ll find it worth your while… However, if you absolutely cannot attend, then you may make it up by completing the following before Thanksgiving break. Use the Internet to find information about the Cassini Mission that has recently arrived at Saturn (http://saturn.jpl.nasa.gov). In a one to two page paper (double spaced) answer/do the following: (1) When did Cassini arrive at Saturn? (2) What will Cassini do during its 4-year mission? (3) When and where will the Huygens probe land? What is its mission? (4) Check out the recent images, choose one, and describe it. Be very careful not to copy (plagiarize) from any source! Reference all final URLs. Please include a note telling me why you were not able to attend discussion. This should be handed in to me before the 24th. Late submissions will not be accepted.

How do high mass stars evolve? High mass stars move off of the main sequence fairly quickly. Like low mass stars, they contract when they can no longer fuse hydrogen nuclei into helium nuclei. They, too, begin to fuse helium nuclei into carbon nuclei. Instead of becoming a giant star, though, they usually become a supergiant star. Because these stars are so massive, the central part of the cores’ are hotter and under greater pressure, so they can fuse the carbon nuclei into neon nuclei. Once they fuse all of the carbon nuclei that they can into neon, the core becomes further compressed, and the neon nuclei are fused into oxygen. This process continues, fusing new elements all the way up to iron. It takes energy to fuse iron nuclei into something else, so energy can no longer be generated through the fusion process. The force due to gravity has nothing opposing it, and the core collapses. The cores of massive stars are greater than 1.4 solar masses. The force of gravity is so great that the outward push of the electrons will not stop the collapse. Electrons and protons are brought so close together that they combine, forming neutrons. The outer layers of the star collapse towards the dense, rigid core. These layers rebound and give off a lot of energy. Such an event is known as a supernova. The core is left behind; what form this core is in depends upon its mass. If the core has a mass less than 3 solar masses, then a neutron star is left behind. See below. If the core is greater than 3 solar masses, see below (BH).

Neutron Stars and Pulsars The cores of massive stars are greater than 1.4 solar masses. If the core has a mass less than 3 solar masses, then a neutron star is left behind. The core is “squished” until the neutrons are as close together as the gravity of the high mass star can push them. Instead of the outward push of fusion-generated energy counteracting the inward pull of gravity, the outward push of the neutrons counteracts the inward pull of gravity, so the core stops collapsing. If a neutron star is quickly spinning and has a strong magnetic field angled to the rotational axis, it may also be a pulsar. Why would it spin rapidly? Angular momentum would be conserved during the final collapse of the core, which leads to a fast spinning neutron star. Radio waves are produced by fast moving electrons in the strong magnetic field and are observable only when the magnetic pole is directed toward Earth. (Much like a lighthouse, the pulses are produced each rotation when the beam of radio waves crosses the observer's line of sight.)

Black Holes If the core is greater than 3 solar masses, nothing can stop it from collapsing. All of the mass collapses down to a single point called a singularity. The escape velocity is so high that nothing, not even light, can escape if it enters a certain area around the singularity. This area is defined by the event horizon. We call this object black hole.

Properties of light: Could you explain the relationship between wavelength and energy? When an electron falls to a lower energy level a photon is emitted. Are those photons of light a different color depending on the wavelength of the photon? What is the effect of distance, radius and temperature on luminosity of a star?

Transparent materials transmit light, and opaque materials absorb light, but I was wondering if you could clear up how a material absorbs light? Also don't materials absorb colors, like if something's red it absorbs every color but red, which it reflects, how does an object go about absorbing something? What happens?

Stellar Evolution: What exactly is a brown dwarf? Why are Brown Dwarfs on the line between planets and stars? Why is a brown dwarf not considered a star? If it is a failed star, how does it remains lit? What is the difference between thermal pressure and degeneracy pressure? Why isn’t the degeneracy pressure depend on temperature? What does the book mean by "hydrogen shell"? More specifically, what is a shell in astronomy terms? What is the difference between burning hydrogen in the core and burning it in the shell? Why is it that low mass stars, when they burn off shells, only burn hydrogen and helium, when the high mass stars burn hydrogen and then many other elements? (Note: shells are not being burned off. Fusion is occurring in a shell(s).) To add onto that - how many shells are burnt off in regards to both the low mass star and the high mass star? Do high- mass stars have more shells because they have more elements for fusion and do we need to know the different elements high-mass stars use for fusion for the exam? What type of effect does iron play on a star? Positive or Negative? Explain. Which kinds of stars have supernovas? In the stages that cause a star to be a giant, I don't understand how the star gets bigger (larger radius) after it has lost mass. I do not understand why the shell expands as the core shrinks. The star has exhausted the energy in the core, and I understand that the outer layers heat up but I don't understand how this leads to such a drastic change in size. Why do white dwarfs turn a white color after cooling and falling off the main sequence? How do you determine the difference in the rate of fusion when comparing different stars, meaning how much more higher is one star from the other? I would like to know why the larger a star is the shorter its lifetime is. I do not quite understand the reasoning behind it, it seems like larger stars should live longer since they should have more energy to give off. Please clarify the nuclear fusion within the sun with regard to the proton-proton chain. I understand the high-mass stars use the CNO process because they can burn more elements because of the properties associated with their size, but in the book it said that it releases as much energy as the proton-proton chain. I guess my question is why do don’t both types of stars use one particular energy method, and why does it equate to the same amount of energy no matter what process the stars uses? I know that we have gone over the proton-proton chain before in class but I am still not certain how these two terms go together. How do supergiants use energy as opposed to Main-sequence stars? What are the key differences between what happens in the cores of high- mass stars and the cores of low-mass stars through the different stages of their lifetimes?

Please explain the concept of helium capture in simple terms. What exactly is the "helium flash" and what does it do? Why is there a helium burst when a star goes from fusing hydrogen for fuel to fusing helium for fuel? (Note: there is no such thing as a He burst; it is a flash.) I don't understand sun shine at all. What is it exactly? How does it work? Why is it important? After the supernova explosion of high mass stars, can some of the elements released, other than the ones that are necessary for life, help create other stars?

HR Diagram: Can you explain luminosity classes? Where are brown dwarfs located on the H-R diagram? How does mass correlate with the H-R diagram? I don't understand the relationship between luminosity and mass on the main sequence. I understand that as the mass increases so will the luminosity, but in what proportion? How can you tell the turnoff point of a star cluster? What is the purpose of having a main-sequence turn off point? How exactly do we measure the age of a star using the main-sequence turnoff? (Note – we don’t determine the age of a star, we determine the age of a cluster of stars.) I would like to go over the stages of a stars life with H-R diagrams, showing the life tracks.

What does OBAFGKM stand for?

Spectrum/lines: Can you explain absorption and emission lines in clouds? What exactly do photons and electrons do in relation to the emission line and absorption line? Can you re-explain how the relationship between energy levels in atoms and absorption lines? Why does a particular electron decide whether to emit or absorb a photon? If it has to do with the levels of energy, why does it choose to stay on the level it is or emit the photon? Does it have to do with the time frame in which more energy is absorbed? Why is it that stars have absorption spectra rather than emission spectra? I understand that looking through a cloud will show you the emission and absorption lines, depending from where you view the cloud, but I don't really understand what they tell us about the light source, or why the cloud absorbs those specific wavelengths of light.

Further explain how our atmosphere blocks out all the different types of harmful wavelengths of light from the sun, but others (atmospheres of distant planets) can’t do the same job. When dealing with energy levels for an electron in a hydrogen atom, sometimes an electron cannot be accepted or not reach the next energy level. (Note: it is the photon that might not be accepted; the electron is already part of the atom.) What causes this? Why might one specific atom not reach that next energy level while another does?

Doppler Shift: In chapter 5 the Doppler effect is explained. I do not understand what they mean by "our line of sight." How come the Doppler shift will only tell us the speed of an object moving away from us? Does that mean it is moving like from our left side to right side or from next to us to far away from us? How do we compute the amount of blue or red shift of an apparent moving object and does the shift depend more on the speed or the distance of the object? If an object is moving away from us will it always be redshifted or could it be blueshifted?

MISC: How is orbital resonance & tidal heating responsible for Io's hot interior? How are the magnetic fields located in the sun produced and what effect do they have on the sun? What is the difference between a solar prominence and a solar flare?

How do you explain clearly (without any difficulty and in your own words) how the transfer of mass between two stars in a close binary system actually happens? How did all of the atoms in everything around us become placed on Earth specifically? How do you determine the difference in the rate of fusion when comparing different stars, meaning how much higher is [the rate of fusion in] one star from the other? I read somewhere that quasars were the most powerful objects in the universe and just wanted to know how this conclusion was reached, what makes them more powerful than a supernova?