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AS101 Midterm Review

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Wilfrid Laurier University
Patrick Mc Graw

Lecture 11 2/11/2013 12:24:00 PM MIDTERM REVIEW: Time limit: 1 hour 50 questions, MC covers chapter 1-3, but a little bit less on chapter 1, more on chapter 1. Bring a calculator, but only a couple of questions require actual calculations. Formulas and exact numbers you need will be given—you just need to know how to use them. Some questions ask you to remember some of the basics, others ask you to apply what you know in some of the ways we’ve practiced. Chapter 1 Highlights:  An overview of our current understanding of the universe.  You should be able to: o Describe what structures are bigger than what other structures (example, solar system is part of the milky way galaxy, galaxies are part of clusters, etc.) o Describe the approximate relative sized of things (example: is Jupiter a million times bigger across than earth, or is it more like 10 times?)  Units: o Know what the following mean: astronomical units, light year. o Understand how to write a number in scientific notation.  Know how to convert units: for example, if 1 au = 1.5x10^8 km, then how many km is 5 au?  Know very approximately the sized of things, enough to be able to pick them out on a multiple choice list Chapter 1 summary:  We live on a planet, orbiting a star, forming part of a solar system, inside a galaxy, which is part of a cluster and supercluster. Superclusters form even bigger structures like walls, filaments, voids, etc.  Scientific notation: o Make it easier to write and compare very large or very small numbers. o Based on powers of 10 o So 3,000,000 = 3 x 10^6 o The exponent tells you how many places the first digit is from the decimal point.  Astronomical unit (au) o Defines as the average distance between the earth and the sun, o Mostly used for distances inside the solar system  Light year: o The distance light travels in a year. o Mostly used for distances between stars or bigger objects like galaxies. o If something is for example 4000 light years away, that means we see it as it was 4000 years ago.  Large planet (Jupiter) is about 10 times as big across as earth.  Sun is about 10 times as big across as Jupiter, so that makes it about 100 times as big across as earth.  Nearest other star: 4.3 ly away.  Miky way galaxies: about 80,000 ly across, contains about 100 billion star.  Nearest other galaxies: 1-2 million ly away  Farthest visible objects:  Around 12 billion ly away. The visible part of the universe includes around 100 bullion galaxies.  In our solar system, earth is a smallish planet, but not the smallest.  The un is a medium sized star—some are smaller but some are bigger.  The milky way is fairly large compared to most, but not the largest. And it is part of bigger structures: clusters, superclusters, etc. Chapter 2 Highlights:  Locating things in the sky: o Constellations and asterisms o Angular distances. o The celestial sphere.  The main cycles of the sky: o Daily: rising and setting, circles around celestial pole. o Yearly: seasons, suns apparent motion around the ecliptic, solstices, equinoxes, etc. o Monthly: moon phases o Eclipses.  Naming of stars  Declination and right ascension (for describing positions on the celestial sphere)  Changing your point of view (how does the sky look from different places on the earth?)  Angular sixe (depends on both actual size and distance away from the observer)  Precession. Chapter 2 Summary:  Constellations: o 88 regions in the sky, with well defined boundaries. Every star is in one constellation. Examples: ursal major, orion, Taurus…  Asterisms: o Patters or visible groups of stars. o Example: the big dipper, the winter circle. o They may include starts from more that one constellations.  Note: stars with the same constellation or asterism appear close to each other, but they might actually be at very different distances.  Zenith: o The point directly overhead.  Horizon: o Is 90˚ away from the zenith.  Meridian: o A north-south line passing through the zenith.  Celestial north (south) pole: o The point on the celestial sphere directly above the north (south) pole of the earth.  Celestial equator: o A circle on the celestial sphere directly above the earths equator.  Defined in elation to a particular observer: o Zenith o Horizon o Meridian  Daily cycles: o The basic idea:  Because the earth rotates every 24 hours, the celestial sphere appears to us to be rotating in the opposite direction, i.e. east to west.  Whatever your latitude is, that is also the angular distance of the celestial pole above the horizon.  The seasons: o Basic idea:  The earths axis is tilted sot that for part of the year, the northern hemisphere points toward the sun and gets more direct sunlight.  When the NH is pointing toward the sun and having summer, the SH is pointing away and having winter. So it’s the middle of summer in Argentina right now.  Two effects combine to make summer warmer: more hours of daylight, and sun hits at a more direct angle.  The warts changing distance from the sun makes almost no difference—its all about the tilt.  Seasons and the ecliptic: o Ecliptic:  Th apparent path of the sun across the celestial sphere during a year. o (the sun appears to over eastward compared to the stars, due to earths motion around the sun) o for this reason, some of the constellations visible at a given time of night (say midnight) will change during the year. (except that circumpolar constellations are visible all night, all year.)  Moon phases: o The moons orbit a
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