Here is some advice and responses to frequently asked questions about study guide emails.

(1)

As an object heats up, what two things happen to its spectral curve? Given a continuous radiation spectrum for an object of a certain temperature, be able to identify the spectrum of an object that is slightly warmer or cooler based on these principles. Be able to sketch a graph (intensity vs wavelength) of a warmer or cooler object given a spectral graph of an object with a certain temperature.

(2)

How do we use the information from question 1 to estimate the temperatures of stars? Why do objects appear more red, then more yellow, then more blue as they get hotter? From a graph of intensity vs wavelength, be able to identify which of two stars appears redder or bluer and which is giving off more blue or red light.

(3)

Another term for the kind of light (electromagnetic radiation) emitted by the sun and most other objects in nature, regardless of their temperature or composition, is "blackbody radiation". Why is it called "blackbody radiation"? Your book's chapter 5 or the web can help you answer this. (TQ)

(4)

Two of the most easily recognizable constellations that are up in the sky at this time of year are Taurus and Perseus. Find the following information about these two constellations:

• Approximate location in the evening sky this month, based on the star chart on page A-31 (rough altitude and azimuth),
• star chart (sketch of the pattern of the 6-8 brightest stars and connecting lines that make up the constellation),
• name of the two stars designated alpha and beta (usually the two brightest),
• 2-3 sentence summary of the mythology behind the constellation.

This is pretty easy to find on the web. A good place to go for mythology is http://www.emufarm.org/~cmbell/myth/myth.html, but remember to keep your summary fairly short so it is easy to remember the most important parts. A good place to go for simple star charts is http://www.dibonsmith.com/constel.htm. For star names and other information, try http://www.astro.wisc.edu/~dolan/constellations/. To find the approximate altitude and azimuth (azimuth means direction along the horizon, like northeast, south, west, etc), you should use the star chart as indicated, but you may also consult the Starry Night software that comes with your book (this is also installed on the computers in the Astronomy lab, which you can use if you finish early in lab) ***OR*** go outside and *FIND* them with your own two eyes on a clear night (all are easily visible this time of year). When you are done, go out at night and find the constellation and explain what you know to a friend or classmate. It's fun to do and easier to remember that way. (TQ)

(5)

Explain why the Sun appears red when near the horizon. Also, explain why the sky is blue.

(6)

Based on the reading Cargo Cult Science, briefly summarize the story of the Millikan oil drop experiment. Explain why the history of scientific research after Millikan's work is something scientists should be embarrassed about. (TQ)

(7)

According to Feynman in the reading Cargo Cult Science, what sort of actions should scientists take in order to have the utmost integrity and therefore confidence in the accuracy of the results? Briefly explain two examples. (TQ)

(8)

Prior to the 20th century, most scientists accepted the idea that the atom was a "plum pudding" of positive charge, seeded with electrons. Ernest Rutherford's famous gold foil experiment changed our view, however. We now know that the positive charge in an atom is confined to a very, very small space in the nucleus, while the electrons "orbit" the nucleus, making the entire atom mostly empty space.

Read the first couple of paragraphs of Rutherford's original 1911 paper describing his experiment or (easier to read) the Wikipedia entry on the experiment. Explain how Rutherford reached his conclusion by answering the following questions. If the plum pudding model were correct, what would Rutherford have seen? What did he actually observe and how did that lead to his conclusions? (TQ)

(9)

Given a simple energy level diagram (e.g. "E=0,5,7,13"), be able to answer questions like "List the energies that an electron in this atom can absorb from its position in the lowest energy level." or "List the energies that an electron in this atom can emit from its position in a certain energy level." or "What's the longest/shortest wavelength transition for an electron from its current energy level?"

(10)

Explain how we use the principles of atomic emission and absorption to deduce the composition of different elements in clouds of gas, stars, etc.

(11)

What are "forbidden" spectral lines, and why do we not see forbidden lines in typical laboratory spectra while we see them all the time in interstellar gas clouds? Specifically, why do forbidden lines only occur in very low density environments? The Wikipedia page on forbidden lines may help (but it might be tough to translate for you), and any page that talks about the mythical element "Nebulium" may also be helpful in tracking down this answer. (TQ)

(12)

Know the two rules associated with Doppler shift (redshift/blueshift and radial velocity proportional to shift) and be able to apply them to real examples of spectra. Know the difference between radial and transverse velocity. If I show you a "rest" spectrum and a couple of other comparison spectra, be able to state whether the comparison objects are moving toward or away from us and which one is moving faster.

(13)

If star A is 100 light years away and star B is 200 light years away (neither star moving relative to us), will the light from one star be shifted relative to the other (and if so, will the light be blueshifted or redshifted)? Explain your answer. What if star A is moving away from us at 100 meters/sec, and star B is moving away from us at 50 meters/sec? Will both stars appears shifted? One more than the other? Explain. (TQ)

(14)

What are the four main functions of a telescope we discussed in class? Briefly define each with a simple sentence, and then state how the aperture diameter of the telescope affects (or doesn't affect) each one.

(15)

Why do astronomers use instruments attached to telescopes to gather light instead of looking through an eyepiece with their eye?

(16)

What causes stellar images to appear blurred ("seeing") when we look at them through ground-based telescopes?

(17)

Why don't planets twinkle like stars do? Your book can help you with this, and so can the web. (TQ)

(18)

Briefly explain how adaptive optics works to correct for atmospheric seeing.

(19)

Given the resolution equation, explain why it is that even though radio telescopes have much larger aperture diameters than optical telescopes, the typical resolution achieved when observing with radio telescopes is very poor.

(20)

Explain qualitatively how interferometry works to improve the resolution of radio telescopes. Why is it harder to accomplish with optical telescopes?

(21)

State and briefly explain the equation we use to estimate the lifetime of the Sun (based on the total fuel available and the luminosity). Be able to describe a similar example, such as a car ("tank holds 20 gallons, fuel burns at a rate of 4 gallons/hr, how many hours does the fuel last?")

(22)

Why is chemical energy not accepted as a viable method for energy generation in the Sun?

(23)

Explain how we concluded that meteoritic impacts are likely not responsible for the Sun's heat. Why is shrinking also not likely to be responsible for the Sun's heat?

(24)

Explain why both high temperature and high density are needed in order for fusion reactions to take place.

(25)

How is the core of the Sun defined? What is the envelope of the Sun?

(26)

Explain where the energy comes from in fusion reactions.

(27)

What is the "solar neutrino problem"? Despite this inconsistency with theory, even at a time when the inconsistency was unresolved, most scientists still believed that nuclear fusion is the source of energy for the Sun's core. Explain why this theory wasn't abandoned, as the scientific method suggests it ideally should have been.

(28)

Explain what happens in the radiative zone of the Sun. Why is energy transported via radiation in the radiative zone?

(29)

Explain what happens in the convective zone of the Sun. Why is energy transported differently in the convective zone? Why does energy ultimately leave the Sun in the form of light/radiation?