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# ls1 - AST 3722C summary for lecture on tuesday january 8...

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AST 3722C summary for lecture on tuesday january 8, class #1. warning: this is not supposed to be a substitute for reading the textbook. Textbook Chapter 5: What astronomers do is measure I -- photon flux. I is a function of a lot of things: wavelength direction time polarization I = I(lambda, Omega, t, P) So in this class you're going to learn about how we measure this function. We must infer everything physical about the Universe just from interpreting the samples of this function that we get. And we often don't get to sample across a very large range of parameter space. But you could imagine a hypothetical situation where you sample the whole cel. sphere at every wvln in very short intervals of time with very good spatial resolution. This is not possible techn. Yet but we can approach some interesting things, e.g.: LSST Pan-STARRS are 2 projects that will soon go online to sample the sky at visible wavelengths to a faint magnitude at few-day intervals at good spatial res at 4 wavelengths. Textbook Chapter 7: recall the celestial sphere from AST 2002. The cel sph spins around earth, though that's just a model -- Earth is spinning. Stars are more or less fixed on the acrylic. Planets, Sun, Moon for the most part move with the acrylic too but not entirely. We'll get to more on all of this later. spherical trig terms: great circle - shortest distance between 2 points on the sphere. a great circle has to enclose the center of sphere. small circle - a circle on the sphere that doesn't enclose the center of the sphere spherical angle - 2 great circles intersect. spherical triangle - 3 great circles intersect. note that I didn't clearly make this distinction in class but: in a spherical triangle, you have 3 "sides" and 3 angles. those angles are indeed spherical angles -- and you can measure or calculate the numerical value of the angle between the 2 "sides" that are making each angle. the sides are represented by angles too -- the relevant

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