exam 1 study guide

# exam 1 study guide - Introduction 16:05 In astronomy temp...

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Introduction 16:05 In astronomy, temp is like motion low temp = limited motion, high = increased motion Kelvin (k) for temp 0k means no motion K = 273 + Celsius Distance = speed-of-light x time Speed of light = 186,000 mi/sec or 3 x 10^5 km/sec We see the light that left millions of years ago bc although speed-of-light is fast, it does take time to reach us Astronomical unit (AU) = distance from earth to sun Solar mass = mass relative to mass of sun 1 solar mass = 1.99 x 10^30 kg Assumptions: There exists an objective, knowable Universe that is the same for everyone. The same physical laws apply throughout the Universe. The same physical laws are equally valid at different times in the Universe. Occam’s Razor : When you have two competing explanations that make exactly the same predictions, the simpler one is the better No experiment or observations can measure a value with perfect accuracy. So, all measurements have a value and an associated uncertainty. Knowing the measurement uncertainty can be critical to whether you can reject or accept your hypothesis.

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Chapter 2 16:05 What Causes the Seasons? Earth’s tilt = 23.5 degrees Seasons are caused by the tilt of the Earth’s axis, which causes the sun’s path through out sky and the intensity of sunlight to vary over the course of each year Earth rotates, not sun Horizon – boundary between earth and sky Zenith – point directly overhead Meridian – imaginary half-circle stretching from horizon due south, through the zenith, to horizon due north (N to S) Sun reaches zenith only in tropics SEE PICTURE ON PAGE 20 Key point: seasons occur because of combo of earth’s axis tilt and its orbit around sun. If earth did not have an axis tilt, we would not have seasons (bc different sides tipped toward sun at different times this way) Solstice = when a hemisphere is tipped most directly towards sun Summer (June), winter (December) Equinox = when hemisphere changes from being toward sun to away from sun (fall, September) and when away from sun to toward sun (spring, March) Day of these are first days of seasons Opposite for southern hemisphere At equator, most direct sunlight on equinoxes and least direct on solstices At higher latitudes, seasons are more extreme, with most extreme at poles (sun above horizon for 6 months and below for 6 months) Why do constellations depend on time of year?
Chapter 2 16:05 Constellation = region of the sky with well-defined borders; familiar patterns of stars help us locate these constellations Constellations make up celestial sphere surrounding earth. It is a useful illusion bc it allows us to map the sky as seen from earth North/south celestial pole = point directly over poles Celestial equator = projection of earth’s equator around celestial sphere Ecliptic = yearly path of Sun around celestial sphere (annual path with respect to constellations, not daily path through local sky) Earth’s west-to-east rotation causes everything on celestial sphere to appear to move around us

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