EESC1150 Week 1 Notes
EESC1150 Week 1 Notes EESC1150
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This 7 page Class Notes was uploaded by Erin Bleck on Sunday July 17, 2016. The Class Notes belongs to EESC1150 at Boston College taught by Dr. Thomas Kuchar in Summer 2016. Since its upload, it has received 34 views. For similar materials see Astronomy in Earth and Environmental Sciences at Boston College.
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Date Created: 07/17/16
January 19, 2016 AstronomyNotes.com - Exams o Midterms are not cumulative 3 exams (drop the lowest grade) 50% of grade o Final is cumulative (May 11 at 9:00am) 25% of grade - Grade is based on a bell curve (average grade will be a B) o No extra credit o If there are any issues about grading (Canvas) let professor or TA know immediately - Science is o A continuing process that Seeks to understand the rules and laws of nature Uses systematic observations Uses mathematical models Experimentally tests ideas (predictions) o Subject to independent verification (more than one person needs to produce the same result) o Components of the scientific method used to comprehend the universe Observe Theorize Predict Test Modify - A scientific theory is a collection of ideas that explain a phenomenon in a way that is consistent with laws, observations, and experiments o Must Explain a wide variety of observations with a few simple principles Be supported by a large, compelling body of evidence Not have failed any crucial test of its validity o New observations and experimental results must be explained by existing theories or they need to be modified The longer they hold up to testing the stronger the theory All theories are refined over time: this is a strength of theories “Failure is not an option; it’s a requirement” - When scientists say “believe,” they mean they believe based on evidence - Idealized scientific method o Make observations o Ask a question o Suggest a hypothesis o Make a prediction o Perform a test: experiment or additional observation o Test does not support hypothesis; revise hypothesis or make a new one o Test does support hypothesis; make additional predictions and test them - What do astronomers do? o Make observations using telescopes o Analyze data/results of observation o Create theories about what is seen and what might exist yet unseen o Create computer models that simulate what occurs in the universe o Invent, design, and build instruments that let us see beyond the Earth o But most do not spend much time looking through telescopes - Gravity is a fact, a hypothesis, and a theory - Evolution is a fact, a hypothesis, and a theory - That the Earth is round has been known since 500 BC - The Moon’s phases are caused by the Sun’s light falling on different areas of the Moon as viewed from Earth - The time it takes the Moon to go around the Earth is about one month - The time it takes the Earth to go around the Sun is about one year - Seasons are caused by the Earth tilting toward (summer) or away (winter) from the Sun results in more direct sunlight - The speed of light in the vacuum of space is 186,000 miles per second - The time it takes light to travel from the Sun to the Earth is about 10 minutes (closer to 8 minutes) - The nearest star is the Sun (8 light minutes away) - The age of the universe is roughly 14 billion years - The age of the Earth is roughly 5 billion years - The universe is expanding - The universe will end by expanding forever Notes January 21, 2016 Scale of the Universe - The numbers in astronomy are so large (and small) that astronomers use scientific notation - Astronomical distances and sizes are very, very, very, very large. So astronomers use different units. o 1 AU = average distance between the Sun and the Earth 93 million miles 150 million kilometers o Distance light travels in one year = 1 ly 9.46 x 10^12 km 63,000 AU or 6.3 x 10^4 AU 0.307 parsecs (pc) - Although the light-year (ly) is a unit of distance, it’s value tells us something important besides distance o It’s how long ago the light left a star o So we are always seeing things as they were and not as they currently are The stars or galaxies may not currently exist or look like they do to us - Planet – a moderately large object that orbits a star; it shines by reflected light o May be rocky or gaseous in composition o Ex. Earth - Satellite (or moon) – typically a smaller body orbiting a planet o Ex. Earth’s Moon - Scale of a planet or moon – hundreds to thousands of km - Star – a huge ball of gas (mostly H) held together by gravity and generating light through thermonuclear reactions o Scale = thousands of km o Ex. Sun o Majority of mass of our solar system o Largest gravity of solar system - Solar (star) system = a star and all the material that orbits it, including its planets, moons, etc. o Scale = AU - Few 1000 ly = range of most visible stars o At the scale of the Milky Way distances within Galaxy are described in terms of ly o We don’t see many stars past 3000 ly - Sun’s orbit is 230 million years to travel around the Galaxy - Q: If we made a scale model of the solar system with the Sun as a grapefruit, the planets would be various small objects scattered at distances from feet to tens of yards. On the same scale, where would the next star (grapefruit) be? o Across the US o There is a lot of empty space - Getting to know the neighborhood o The sum total of all matter and energy; that is, everything within and between all galaxies o The Universe is “clumpy” – gravity tends to pull galaxies together in clusters of various sizes – from dozens to thousands o Scale = billions of ly - Thousands of km (planet) AU (solar system) 1,000 ly (stars) 10,000 to 100,000 ly (galaxy) millions of ly (nearest galaxies) billions of ly (universe) Matter and the 4 Fundamental Forces of Nature - Matter – atoms o Basic building block of nature o 94 naturally occurring elements o Currently another 24 can be manufactured Less stable (especially when created large) because big atoms don’t want to be bigger than a certain size - Structure of an atom o Nucleus – center of atom Protons = + Neutrons = neutral change o Electrons = - Circle the atom in an electron cloud (new quantum view) o Type of element determined by the number of protons o Hydrogen – 1 proton o Helium – 2 protons * H and He are the 2 most common elements in the universe o Weight determined by the total number of protons and neutrons (electrons are too small and contribute very little to the weight of the atom) o Isotope = an element with a different number of neutrons - 3 flavors of H o 1 p and 0 n = 99.98% of all H o 1 p and 1 n = Deuterium; 0.0184% of all H o 1 p and 2 n = Tritium; trace amounts - 4 Fundamental Forces o Electromagnetism o Strong nuclear force o Weak nuclear force o Gravity o These 4 forces organize matter either on the subatomic level or on the large scale of the universe o Each has a characteristic Relative strength Range Effect on a property of matter Carrier particle - Gravity o Effect = all masses attract each other o Range = infinite but weakens with distance o Carrier particle = gravitation (graviton) Hypothetical – no one has seen a gravitational particle (but the other 3 forces have particles why would gravity be different?) o Strength = 10^-36 the weakest - Electromagnetic o Effect = opposites attract, likes repel o Range = infinite but weakens with distance o Carrier particle = photon o Strength = 1 - Strong nuclear force o Effect = three colors combine to make neutral combinations (ignore!) o Range = about 10^-15 meters (distance between protons in atomic nucleus) The glue that holds the protons and neutrons in the nucleus together o Carrier particle = gluon o Strength = 10^2 the strongest - Weak nuclear force o Effect = massive particles decay to lower-mass particles o Range = about 10^-18 meters (1/1000 proton diameter) o Carrier particle = W and Z o Strength = 10^-7 - Electromagnetic (EM) force o Combination of electricity and magnetism because Moving charges can generate a magnetic field Ex. Simple electromagnet Moving magnets generate electric fields Ex. Car’s alternator, turbines at power plant o Force that holds atoms and molecules together Keeps electrons orbiting the nucleus Makes bonds strong - Strong nuclear force o Holds protons and neutrons together in nucleus of an atom o 100 times stronger than the repulsion between 2 protons! (this is good because like charges normally repel) Gets the protons to stay together Having neutrons helps to neutralize a bit of the repulsive energy o Very short range – only works within the nucleus of an atom - Weak nuclear force o Force responsible for radioactive decay i.e. responsible for changing one subatomic particle into another - Gravitational force o Force between massive bodies o Always attractive – no “repulsive” gravity o Weakest but the dominant force in the Universe The Night Sky - What do you think? o Do the stars stay in the same position in the sky all day/night long? o Do you see the same stars year-round? o What causes the stars to move? o Do the stars actually move in the way they appear from Earth? o Is the daily motion of the Sun different from the stars? - Consider the dome of the sky over our heads as an inverted mixing bowl - Horizon coordinates o Everything is based on the horizon o Horizon – the lower edge of the visible sky o 4 cardinal positions = N, S, E, W o Zenith – the point directly overhead o Nadir – the point opposite the zenith in the sky Where you’re standing o Meridian – line runs from the N through the zenith to the S Important because they used the meridian to tell them if it was morning or afternoon o Altitude – how far an object is above the horizon o Azimuth – angle along horizon starting from N (N, S, E, W, and all combinations) N = 0 degrees E = 90 S = 180 W = 270 - Constellations vs. Asterisms o Constellations Were meant to help people recognize certain locations in the sky It was easier to say a concrete something (ex. Leo) vs. saying a triangle 88 internationally recognized constellations by International Astronomical Union (IAU) o Asterisms Popular patterns but are not “official” constellations Ex. Big dipper, little dipper, the teapot, summer triangle, the sickle - Q: The brightest stars in a constellation o May actually be quite far away from each other o Stars lie at different distances despite looking like they are all about the same distance from Earth - Imagine a celestial sphere surrounding Earth aids in thinking about the position and motion of the sky o North celestial pole is directly above Earth’s N Pole o South celestial pole is directly above Earth’s S Pole o Celestial equator is a projection of Earth’s equator onto the sky - Coordinates on the Earth o Latitude – position N or S of the equator (horizontal) In astronomy = declination (positive or negative degrees) N = positive 0 to 90 S = negative 0 to 90 o Longitude – position E or W of prime meridian (0 at Greenwich, England) (vertical) In astronomy = right ascension (hours) Every hour is equal to 15 degrees longitude - Where you stand on Earth makes the perception of the stars moving in the sky different than another place on Earth o Wherever the N star is from your position, it can help you find the N of the horizon can then label S, E, and W
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