syllabus & course expectations & course links
Astronomy
Picture of the Day the
latest astrophysics discoveries
what's up in the sky
this week
Skywatcher's
Diary for this month
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September 26 |
September 27 |
September 28 |
September 29 |
September 30 |
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CALCIUM (energy level diagram in green book) |
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jit due by 2
pm |
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(always done before class) |
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recommended: 26(1-4) the redshift/blueshift part: 26(5) |
make sure you can state Kepler's 3 laws (at least applied to planets, even though we will apply to binary stars) (no reading on dark energy till the weekend) |
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homework |
measure
the wavelength and the frequency of the waves (see doppler applet
below) as would be determined by an observer who is a) stationary with respect to the source b) in relative approach to the source (at speed = 0.5, classical) c) in relative recession from the source (at speed = 0.5, classical) please dont bring me only the answers, but show work on the paper (which you will hand in) |
find H in units of inverse years |
starting with just basic physics laws, attempt to derive Newton's version of Kepler's 3rd law make the assumption that we did in class, that the orbits are both circles; you should have to use 1) newton's gravity law 2) newton's 2nd law 3) the formula for centripetal acceleration (discovered by newton, who invented calculus to derive it) 4) the formula for speed in a circular orbit AND 5) the center of mass equation |
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and binary star sections 19(9,10) |
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September 19 |
September 20 |
September 21 |
September 22 |
September 23 |
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jit due
2 pm today |
(you can reference a picture in the book if you want or an object we encountered in a previous lab... which lab in particular might you have encountered some pictures of fluorescing things ) also, make a stab as to whether the fluorescence is excited by uv light or by KE (via a collision) [remember that these are the two methods we learned can initiate fluorescence yesterday] remember the secret decoding graph on page 434 of Universe: the one you used to convert spectral type to temperature for "your star"? look at it again, and notice that the hydrogen Balmer lines are strongest in 10,000 K stars and weaker in both cooler and hotter stars... why is this? you should be able to think of 2 different good reasons (not that are necessarily correct, just possibly correct)... come to class with these reasons written down on the same paper as above! (no reading required here) |
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(always done before class) |
chapter 31, pp 1010 - 1017 photocopy available in the astro box annotate your photocopy with questions, filled-in missing steps, comments, etc some of the physics will be new even for the people who have completed physics, but there will be even more new for people in physics now circle those parts, so we can address them in class |
once again, look for omissions, mistakes, etc. look for new physics read critically! |
& section 5(8) in Universe including box 5-5 (did you find prometheum in the periodic table? the other element discovered relatively late is nearby in the periodic table) |
(and you should) Walker 11(1) on torque first 3 pages of Walker 11(6) on angular momentum (you have to find your own Walker) |
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homework |
1)
estimate
of solar corona temperature brought to class (on paper, to hand in;
show work) today use the FeXIV line in the flash spectrum for your temperature estimate 2) look at the Helium energy level diagram in the green book a) what temperature would the helium have to be for the electron to absorb VISIBLE light? b) what temperature would the helium have to be for the electron to absorb ULTRAVIOLET llight? c) what temperature would the helium have to be for the electron to EMIT VISIBLE light? for interpreting the energy level diagram: energy is still plotted upwards, in units of electron volts the numbers on the lines that connect different levels are the corresponding wavelength of light in ANGSTROMS that will be emitted or absorbed (depending on which way the electron is going) 1 nm = 1 ANGSTROM (so visible light in angstroms is 4000 A - 7000 A) |
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Orion's Great Nebula & the Trifid Nebula are starbirth sites; note that red- fluorescing nebulas can only surround BLUE (uv-emitting stars) The Helix Nebula
& fluorescing H II regions in
the M51 galaxy help us trace the spiral arms and places of recent
stellar birth The Crab Nebula
& [these
two supernovas left behind neutron stars (stars made entirely of
neutrons that are about the size of durham)] the eclipsed sun shows a red fluorescing atmosphere (which reveals the flash spectrum ) A Perseid Aurora
& Comet tails
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due saturday (tomorrow) noon |
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some people did it in lab last thursday, but not everyone |
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September 12 |
Septmeber 13 |
September 14 |
September 15 |
September 16 |
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1) calculated temperature of your planet 2) actual "surface" temperature of your planet (what important energy sources were not considered in the above calculations?) |
jit
due at 2 pm |
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(always done before class) |
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(skip sections 5-6 and you can skip the boxes too) some questions: what are the two classes of solar system planets? what are some ways in which they differ? what is the basic manner in which we think planets formed? |
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find out what's going on on/in the planet Earth |
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2
of the following 3: 1) derive the first equation in box 19-1 (vT = 4.74 m p, except with units) 2) derive the "log" versison of the inverse square law: m - M = 5 log (d/10) start with the definition of flux 3) find the apparent magnitude of the alpha centauri star combination |
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(NY Times, requires registration) |
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September 5 |
September 6 |
September 7 |
September 8 |
September 9 |
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jit due by 2
pm (although all JITS are not mandatory, I hope everyone will try the first one) selected jit answers |
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(always done before class) |
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know how to derive the parallax-distance formula (hint: you can do it with either simple trig or simple circle geometry) |
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1) what solar-system planet would astronomers have preferred to live on to measure parallaxes effectively? 2) why is there a limit to the distance for which parallax is measureable? (and what is that limit?) 3) what was the advantage of having the satellite(s) Hipparcos in measuring parallaxes? 19(3) and box 19-3 know the 2 rules of magnitudes and study the messy math carefully |
| homework |
for
next monday: a) your star's name & the spectral/luminosity class listed in the Appendix b) determine your star's temperature (in K) c) determine the wavelength of max intensity for your star AND what color your star would look to humans d) its luminosity relative to the sun (from the absolute magnitude, using the formula given in class) show work! (your luminosity ratio should also match that given in the appendix 5 table) e) the radius of your star (relative to sun) [see box 19-4 and follow the procedure exactly] f) if we define the sun as fist-sized, what real life object (either bring one or have a classroom object identified) that approximately matches your star's size g) determine what fraction of your star's luminosity is emitted in the uv, in the visible, and in the ir (using the spectrum explorer applet) h) the distance to your star (based on its listed apparent and absolute magnitude); you should get close to the distance listed i) the flux (in W/m2) for your star using the distance derived in (g) |
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(launch the explorer; it requires java, so that must be enabled; 2 new windows should open in a minute or 2-- a useless one and one containing axes; on the latter, click on the "blackbody" button to add a blackbody, type in the temperature below the thermometer, and you'll find the %s in another new, tiny window that opens |
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(if clear) or asteroid parallax (if not clear) |
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bright young stars glow in the x-ray |
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