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Astronomy Chapter 1 notes

by: Lisa Render

Astronomy Chapter 1 notes PHYS 1350

Marketplace > University of Nebraska at Omaha > Physics > PHYS 1350 > Astronomy Chapter 1 notes
Lisa Render
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About this Document

Chapter 1, sections 1-3
Principles of Astronomy
Charles St Lucas
Class Notes




Popular in Principles of Astronomy

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This 6 page Class Notes was uploaded by Lisa Render on Wednesday September 28, 2016. The Class Notes belongs to PHYS 1350 at University of Nebraska at Omaha taught by Charles St Lucas in Fall 2016. Since its upload, it has received 8 views. For similar materials see Principles of Astronomy in Physics at University of Nebraska at Omaha.


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Date Created: 09/28/16
1.1 Our View of the Modern Universe Monday, August 22, 2016 12:57 PM What is our place in the universe? • A grand tour of the heavens ○ To survey the universe and the methods astronomersuse to study it ○ To see the measuring units used by real astronomers ○ To assess the scientific method and show how pseudoscience fails scientific tests ○ To boldly go where no class go before • The Universe ○ Some astronomersbelieve that the universe is about 14 billion years old (Maya) ○ The universe is so vast that we are actually receiving light and radio signals from the past ○ Light from the sun takes about 8 minutes ○ Light from the moontakes about 1 second ○ Light travels at a finite speed • A sense of time ○ (diagram) • Scientific Notation ○ Scientists deal with very large and very small numbers ○ Need a way to deal with all the ZEROs ○ A number between 1 and 10 times an integer power of 10 ○ 300 = 3.0 X 10 2 ○ 3,000= 3.0 X 10 3 8 ○ 300,000,000= 3.0 X 10 ○ .003 = 0.003 3.0 X 10-3 • The Metric System ○ Meters (39.37 inches) instead of feet (m) ○ Kilo means thousand ○ Mega means million ○ Milli means 1/1000(thousandth) ○ Centi means 1/100(hundreth) ○ Kilmeter is 1000 metersor about 5/8 ○ (units of measurement) ○ ○ • Definition: light-year ○ The distance light can travel in 1 year = 10 trillion kilometers(6 trillion miles)  =186,000miles per second  X 60 seconds per minute  X 60 minutes per hour  X 24 hours per day  X 365.25 days per year • What This Means ○ When we are looking at distant objects in space, we are really looking back in time ○ The further the object is from us, the further back in time we are actually seeing (lookback time) Distance = velocity x time The Scale of the Universe • Our Place in the Universe • We live on the third planet orbiting a small, disregarded yellow star in the Orion Arm of a medium sized Galaxy called the Milky Way • In a million years we might be merging with Andromeda Star • A large, glowing ball of gas that generates heat and light through nuclear fusion in its core (our sun is a star) ○ Nuclear fusion = generating energy through atoms bouncing off of each other ○ Hydrogen and helium nuclear reactions going off constantly ○ Atmosphereprotects us from the radiation of the sun  Space suits protect us from frying or freezing (sun and lack thereof) Planet • A moderatelylarge object that orbits a star • A moderatelylarge object that orbits a star • It shines by reflected light ○ Does not give off light on its own • Planets may be rocky, icy, or gaseous in composition Moon (or satellite) • An object that orbits a planet • (is Pluto a planet?) ○ Pluto is a minor planet ○ (more like a big asteroid) ○ Pluto doesn’t orbit a planet so it's not a moonbut it does orbit a star Asteroid • A relativelysmall and rocky object that orbits a star • (is Pluto an asteroid?) ○ It's a really big asteroid Comet • A relativelysmall and icy object that orbits a star • Icy crust of hydrogen when exposed to the sun, the hydrogen turns to gas ○ Dust and plasma tails ○ Coma of escaping gas Solar (Star) System • A star and all the material has, including its planets and moons • (Statistically, with the idea that each star has a solar system with planets (rarely would it not), it isn't that far out to assume that there is life outside of our solar system) Nebula • An interstellar cloud of gas and/or dust • Not all are star/planet forming--someare the death of such • (Hydrogen is the most abundant element in the universe) Galaxy • A great island of stars in space, all held together by gravity and orbiting a commoncenter • (what's inside a black hole) ○ Matter that is infinitely dense The Universe • The sum total of all matter and energy ○ That is everything within and between all galaxies • (multiverses,alternate universes, ripples in the fabric of time and space, black holes, time travel, etc.) • The Cosmic Web How did we come to be? 1. Big bang theory ○ The expansion of the universe began with the hot and dense Big Bang. ○ Regions of the universe have expanded with time ○ The universe continues to expand, but on smaller scars gravity has pulled mattertogether to make galaxies ○ The universe continues to expand much like baking bread rises ○ If the universe doesn’t go on forever, what is after that? 2. Galaxies as cosmic recyclingplants ○ The early universe contained only two chemical elements: hydrogen and helium ○ All other elements were made by stars and recycled from one stellar generation to the next within galaxies like our milky way 3. Life cyclesof stars ○ Many generations of stars have lived and died in the Milky Way 1. Stars are born in clouds of gas and dust, planets may form in surrounding disks 2. Stars shine with energy released by nuclear fusion, which ultimately manufactures all 2. Stars shine with energy released by nuclear fusion, which ultimately manufactures all elements heavier than hydrogen and helium 3. Massive stars explode when they die, scattering the elements they’veproduced into space ○ This cycle repeats 4. Earth and life ○ By the time our solar system was born, 4.5 million years ago How can we know what the universe was like in the past? • Light travels at a finite speed (300,000km/s) Destination Light travel time Moon 1 second • Sun 8 minutes Sirius 8 years Andromeda Galaxy 2.5 million years • Thus, we see objects as they were in the past ○ The farther away we look in distance, the further back we look in time ○ (if we travel faster than the speed of light then are we technically traveling back in time) • We have pictures of the Andromeda Galaxy, but it's from 2.5 million years ago--and we won't know what it looks like now for another 2.5 million years. • At great distances, we see objects as they were when the universe was much younger Why can't we see a galaxy 15 billion light-yearsaway? (assume the universe is 14 billion years old) A. No galaxies exist at such a great distance B. Galaxies may exist at that distance, but their light would be too faint for our telescopesto see C. Looking 15 billion light-years away means looking to a time before the universe existed What is our place in the universe? • Earth is part of the solar system, which is in the Milky Way Galaxy, which is a memberof the Local Group of galaxies in the Local Supercluster How did we cometo be? • The matter in our bodies came from the Big Bang, which produced • All other elements were constructed from H and He in stars and then recycled into new star systems,including our solar system How can we know what the universe was like in the past • When we look to great distances, we can 1.2 The Scale of the Universe Friday, August 26, 2016 1:25 PM Definition: light-year • The distance light can travel in 1 year • About 10 trillion kilometers(6 trillion miles) • =186,000miles per second • X 60 seconds per minute • X 60 minutes per hour • X 24 hours per day • X 365.25 days per year How big is the Earth compared to our solar system? • Reducing the sizer of the solar system by a factor of 10 billion, the sun is now the size of a large grapefruit (14 cm) ○ The earth would be the size of the tip of a ballpoint pen • On a 1 to 10 billion scale ○ Sun is the size of a large grapefruit (14 cm) ○ Earth is the size of a tip of a ballpoint pen ○ Earth is 15 meters away ○ The distance between planets are huge compared to their sizes How far away are the stars? • 1 to 10 billion scale ○ 590 meters to Pluto (just a few minutes to walk) ○ It would be the distance across the united states to walk to the nearest star How big is the Milky Way Galaxy • The milky way has about 100 billion stars • If the sun were the size of a grain of sand, the milky way would be the size of the sun • If the milky way were the size of a grapefruit, the sun would be bigger than anything in our solar system • 100,000light years across • Suppose you tried to count the more than 100 billion stars in our galaxy, at a rate of one per second, how long would it take you? ○ About 3 thousand years How big is the universe? • The milky way is one of about 100 billion galaxies • 14 billion light years in radius (28 billion light years in diameter) • 10 stars/galaxy x 10 galaxies = 10 stars • It has as many stars as grains of sand on all of earth (somewhatincomprehensible) How do our lifetimes compare to the age of the universe? • The cosmic calendar: a scale on which we compressthe history of the universe into 1 year ○ Human existence is about half an hour old. 1.3 Spaceship Earth Friday, August 26, 2016 1:37 PM How is earth moving through space • Contrary to our perception, we are not “sitting still.” • We are moving with the Earth in several ways, surprisingly fast speeds. • Earth rotates around its axis once everyday. • Earth orbits the Sun (revolves)once every year…at an average distance of 1 AU ≈ 150 million km. with Earth’s axis tilted by 23.5º (pointing to Polaris) and rotates in the same direction it orbits, counter-clockwiseas viewed from above the North Pole. How do galaxies move within the universe • Galaxies are carried along with the expansion of the universe. But how did Hubble figure out that the universe is expanding?


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