Term
| What does our Milky Way galaxy look like? |
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Definition
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Term
| • What kind of galaxy is our Milky Way? |
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Definition
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Term
| • What aspects of the Milky Way's appearance tell us where we are in it? |
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Definition
| The star count in each direction, distribution of globular clusters |
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Term
| • How do we tell how big the Milky Way is? |
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Definition
| Main sequence star clusters |
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Term
| • What are the structural components of our galaxy? |
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Definition
| Disk, bulge, visible halo, dark halo, galactic center |
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Term
| • What are the ingredients for ongoing star formation? |
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Definition
| Stellar dust and hot, low density gas |
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Term
| • Where is the ongoing star formation in the Milky Way? |
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Definition
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Term
| • How do stars & gas recycle in the Milky Way? |
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Definition
| Ongoing star formation in gravitationally collapsing, fragmenting gas clouds; gas shoved around by supernovae and stellar winds |
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Term
| • What are orbits of stars like in the disk, bulge and halo of our galaxy? |
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Definition
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Term
| • How do the ages of galactic and globular clusters compare? |
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Definition
| Globular clusters have more stars and are much older than less dense galactic clusters |
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Term
| • How do the stars in the disk differ from those in the spheroidal components (bulge and halo)? |
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Definition
| Middle aged stars versus old stars |
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Term
| • Where are the globular clusters in our Milky Way galaxy? |
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Definition
| The disk, bulge, and halo |
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Term
| • How old are the globular clusters in our galaxy? |
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Definition
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Term
| • What color are spiral bulges compared to spiral disks and what does that tell us about ongoing star formation? |
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Definition
| Blue to yellow and the stars are metal rich in the disk to metal poor in the bulge |
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Term
| • How old is the bulge of our galaxy relative to the disk of our galaxy? |
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Definition
| The disk is full of younger, middle aged stars versus the older stars and globular clusters. |
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Term
| • How do we weigh spiral galaxies? |
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Definition
| Count stars and gas directly; 90% of total mass in dark matter |
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Term
| • How long does it take our solar system to go around our galaxy once? |
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Definition
| 240 million years roughly |
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Term
| • How do we know dark matter exists in our spiral galaxies? |
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Definition
| We can only detect it through its gravity |
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Term
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Definition
| Dark matter is about 25% of the universe; more is unknown about it than is known. |
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Term
| • What are the two kinds of spiral arms? |
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Definition
| Density waves and material arms |
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Term
| • Why are density wave spiral arms so narrow? |
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Definition
| Short lifetime of massive, luminous stars |
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Term
| • What are the major types of galaxies? How are they structured? |
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Definition
| Spirals, Ellipticals, Irregulars |
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Term
| • What kind of galaxies is most numerous? |
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Definition
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Term
| • Where is the dark matter in spiral galaxies (relative to visible matter)? |
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Definition
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Term
| • How much mass is there in dark matter in galaxies compared to normal matter? |
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Definition
| It’s about 90% of the mass of the galaxy |
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Term
| • How do we determine the distances to galaxies? |
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Definition
| Hubble Constant; a star’s red shift |
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Term
| • What are two ways that elliptical galaxies can be formed? |
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Definition
| 2 spiral galaxies collide and transform; when a more massive galaxy merges with a lesser massive, the effects are smaller and the massive galaxy can maintain its shape. |
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Term
| • When two spiral galaxies collide, do any stars collide? Does their gas interact? |
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Definition
| No the probability is almost 0; the gas however will interact gravitationally and trigger possible star formation |
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Term
| • How do we weigh elliptical galaxies? |
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Definition
| Central stellar velocities, not much central dark matter. |
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Term
| • Why is the gas in elliptical galaxies so hot? |
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Definition
| Lots of dark matter in outer parts |
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Term
| • What types of galaxies have the most star formation? |
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Definition
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Term
| • What types of galaxies have the least star formation? |
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Definition
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Term
| • Why do galaxies gather in clusters? |
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Definition
| Galaxies gravitate towards one another |
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Term
| • If the Universe is expanding, how can galaxies cluster? |
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Definition
| The gravity of a galaxy cluster is stronger than the expansion of the universe. |
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Term
| • How are galaxy clusters structured and how do we know they contain dark matter? |
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Definition
| Pairs, groups, clusters, possible superclusters; measure the mass of the combined galaxies |
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Term
| • What component of galaxy clusters contains the most mass? |
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Definition
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Term
| • Why is the gas in galaxy clusters so hot? |
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Definition
| It emits X-rays, galaxies shed gas (galactic winds, stripping) |
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Term
| • How did the hot gas that permeates galaxy clusters get enriched with heavy elements? |
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Definition
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Term
| • What are the largest gravitational structures in the Universe? |
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Definition
| Filaments of galaxies formed 2 billion years after the Big Bang. |
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Term
| • What is the most important physical fact that allows us to determine how the Universe has evolved? |
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Definition
| The universe is expanding |
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Term
| • Why is the sky dark at night? What does this tell us about the Universe? |
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Definition
| Olber’s Paradox; It has finite age |
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Term
| • What kind of Universe do we live in? |
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Definition
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Term
| • When we look at the most distant galaxies, how old do they appear to be? |
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Definition
| The deeper we look into space, the further back in time we look |
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Term
| • How did our Universe form? |
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Definition
| Extrapolating expanding universe back in time, Big Bang |
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Term
| • What observational fact led to the prediction of a Big Bang? |
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Definition
| Cosmic Microwave Background |
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Term
| • What is the Hubble law? |
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Definition
| The dominant motion in the universe |
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Term
| • What does the Hubble Law tell us about the age of our Universe? |
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Definition
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Term
| • How old is our Universe? |
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Definition
| 15 billion years old roughly |
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Term
| • Are all galaxies moving away from us? |
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Definition
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Term
| • Is there a center to the expansion of the Universe? |
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Definition
| No center to expansion, expansion from every point |
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Term
| • How has the Big Bang model been tested? |
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Definition
| Cosmic Microwave Background Radiation |
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Term
| • What elements were predicted to be created in the early Universe? |
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Definition
| Deuterium, lithium, helium 3, helium |
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Term
| • What "standard candle" recently allowed astronomers to discover that the Universe is accelerating its expansion? |
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Definition
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Term
| • What is causing the expansion of the Universe to accelerate? |
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Definition
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Term
| • What provides most of the mass/energy content of the Universe? |
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Definition
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Term
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Definition
| Vacuum energy, breakdown of general realitvity |
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Term
| • How does the abundance of deuterium tell us about what dark matter is (or is not) made of? |
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Definition
| Not made of normal matter = stuff like us? |
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Term
| • How was the Big Bang radiation (Cosmic Microwave Background Radiation) created? |
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Definition
| By Arno Penzias and Robert Wilson by using a well-calibrated horn antenna. |
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Term
| • What is the current temperature of the Big Bang radiation? |
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Definition
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Term
| What was the temperature of matter and radiation at the time the Big Band radiation was emitted? |
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Definition
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Term
| • Why is the Big Bang radiation now 1000 times cooler than when emitted? |
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Definition
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Term
| • How does the Big Bang radiation allow us to measure absolute motion? |
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Definition
| Doppler shift with respect to CMBR |
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Term
| • Why was the Big Bang radiation predicted to be slightly lumpy? |
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Definition
| We’re lumpy, grown by gravity from smaller lumps; universe a bit lumpy at “re” combination |
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Term
| • What are some problems with the simplest form of the Big Bang and how has the Big Bang model been modified to take care of these problems? |
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Definition
| Why do opposite sides look the same if they haven’t had time to exchange even light? Why is the universe so flat? Solved by inflation; also negative pressure of vacuum drove exponential expansion |
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Term
| • Is there life elsewhere in the Universe? |
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Definition
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Term
| • How long does the Solar System take to orbit the galaxy? |
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Definition
| 240 million years roughly |
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Term
| • How long have humans been technological |
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Definition
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Term
| • How long has there been life on Earth? |
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Definition
| 3.9 billion years for microbial life |
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Term
| • Have we been visited by aliens? |
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Definition
| Unsure of visits, speculative and theoretical. |
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