Astronomy Notes 2015 Preface o Varying views of answers to problems leads to confirmation bias when testing a theory don t just look for examples of how to prove it o When considering a plan think in detail about how it might go wrong The Earth Galaxy Distances o Diameter of Earth 12 756 km o Earth to moon distance 384 401 km 238 856 mi o Earth to Sun Distance 1 5x1013cm 1AU Astronomical Unit o Pluto average distance is 39 44 AU o Nearest Stars D 1 000 000 AU 17 ly light year 1ly 63 000 Au 1 pc parsec 3 26ly o Parsec pc distance from the sun to an object that has a parallax angle of 1 arcsec or 1 o The local group D 5Mpc o Clusters of Galaxies D 500Mpc o AU avg distance between the earth and sun Ch 1 Reading Notes Thinking like an Astronomer o Astronomy means finding patterns among the stars o Astronomers think of our place in the universe as both a location and time o Our solar system consists of 8 planets including dwarf planets like Pluto as well as asteroids and comets o The Sun is located about halfway out from the center of the Milky Way Galaxy o The Milky Way is part of a small collection of a few dozen galaxies called The Local Group o The Milky Way and Andromeda galaxies are true giants within the Local Group while most others are dwarf galaxies o The Local Group itself is part of a much larger collection of thousands of galaxies known as the Virgo Supercluster o Even relatively small distances in the universe are so vast that they are measured in light years ly the distance light travels in 1 year o The Universe began 13 8 billion years ago in an event known as the Big Bang The only chemical elements in the early universe were hydrogen and helium o In the core of a star less massive atoms like hydrogen combine to form more massive atoms eventually leading to atoms such as carbon o Sputnik was the first man made satellite o Astronomers collect info from many varieties of light from highest energy gamma rays and X rays through ultraviolet visible and infrared down to the lowest energy radio waves o The scientific method is a systematic way of testing new ideas or explanations o Hypothesis a testable explanation of the observation Can be falsified proven incorrect 2 o Any idea that is not testable that is not falsifiable must be accepted or rejected based on intuition alone so it is not scientific o As continuing tests support a hypothesis by failing to disprove it scientists come to accept the hypothesis as a theory o Scientists use the word theory to mean a carefully constructed proposition that takes into account ever piece of data as well as our entire understanding of how the world works o The Cosmological Principle is the testable assumption that the same physical laws that apply here and now also apply everywhere at all times The physical laws that act in laboratories also act in the centers of stars or in the heart of distant galaxies o Occam s Razor states that when we are faced with two hypotheses that we explain all the observations extremely well we should use the one that requires the fewest assumptions until we have the evidence to the contrary 3 Key Pieces o Graphs independent variable x axis y dependent variable should be y axis Chapter 2 Reading Notes Motions of the Earth and Moon The Celestial Sphere o Earth rotates at 1 670 km per hour o Earth rotates counter clockwise once every 24 hour period o As the rotation of the earth takes us from west to east objects in the sky appear to move from east to west this is called apparent daily motion o The sky relative to the earth is like a huge sphere with the earth at its center This imaginary image is called the celestial sphere 3 Each point on this sphere indicates a direction in space Directly above the north pole is the north celestial pole ncp Directly above earth s south pole is the south celestial pole SCP The ecliptic is the path of the sun in the sky throughout the year Directly above earth s equator is the celestial equator which divides the night sky into a northern and southern half Angles between the north and south poles with the celestial equator are 90 degrees The zenith is the point in the sky directly above you wherever you are You can find the horizon by standing up and pointing your right hand at the zenith and your left hand straight out from your side The imaginary line that comes down from the zenith is called the meridian Local noon occurs when the sun crosses the meridian at your location this is the highest point the sun will reach on any given day Local midnight occurs when the sun is exactly opposite from its position at local noon The View from the Poles o Objects visible from the north pole follow circular paths that always have the same altitude or angle above the horizon o Objects close to the zenith appear to follow small circles while objects near the horizon follow the largest circles o From the north pole you always see the same half of the celestial sphere 4 o The side not visible in the north is the only side visible by the south pole Stars also seem to move clockwise around the south celestial pole instead of counter clockwise like in the north The View Away from the Poles o Latitude measures how far north or south you are on the surface of the earth o As the north celestial pole remains fixed in the sky all the stars appear to move around that fixed point in a counter clockwise motion o Circumpolar Stars can always be seen above the horizon o Stars that are too far north or south along the celestial poles can only be seen for part of the day o The only place where you can see the entire sky over the course of 24 hours on earth is the equator o A star on the celestial equator rises due east and sets due west o Stars north of the celestial equator rise north of east and set o Stars south of the celestial equator rise south of east and set o Polaris the north star is nearly equal to the latitude of its north of west south of west observer Revolutions Around the Sun lead to Changes during the Year o Earth orbits the sun in a nearly circular path in the same direction that it spins about its axis clockwise as viewed above earth s north pole Because of this motion stars change throughout the year and seasons occur Earth Orbits the Sun o Earth s average distance from the sun is 1 5x108 km an Astronomical Unit AU 5 o Earth orbits fully around the sun once each year o As it …