Chapter 1A Modern View of the Universe1.1 Scale of the UniverseDistancesEarth to Moon 1 Light SecondEarth to Sun 500 Light Seconds = 8 Light Minutes Solar System ½ Light DayTo Prox. Centauri 4.3 Light YearsAndromeda- Nearest galaxy- 2.5 million LY away; 100,000 LY in size- Will eventually merge with the Milky Wayo Send sun shooting off into another placeObservable Universe- Speed of light is finite (300,000 km/s)- Universe in only 14 billion years old = can only see a distance of 14 billion light years into the universe - How many Galaxies in Observable universe?o 100 billion galaxieso How many stars?100 billion in each galaxy, so 1022 stars in observable universeMore stars than grains of sand on all beaches on EarthRecapDistances- Moon 1 Light Second- Sun 8 Light minutes (1 AU)- Proxima Centauri 4 Light Years- Andromeda 2.5 Million Light YearsSizes- Sun 5 light seconds- Solar System ½ light day- Milky Way 1 Million light years- Observable Universe 14 Billion Light YearsSun is only of 1022 stars in observable universe1.2 History of the UniverseHow did we come to be?- Big Bang 14 billion years agoo Hubble expansion – evidence – universe is constantly expanding- Structureo In 1st billion years little there – no galaxies, stars, planetso Just H and He created in big bangWhere do the other elements come from?- 13 Billion years ago some of the H and He started to clump into starso 1st generation made of pure H and He- Nuclear Fusiono At center of star, fusing H and He into heavier elements: H and He  carbon  oxygen  Iron- Stars = Recycling Plantso Star dies and spews matter into universe, including elements H, He, C, O, Fe, etc. (more produced in deaths of massive starts)o Matter mixes with other matter floating in universe > new cloud of dust and gas >new generations of starsOur Universe- 10 billion years ago galaxy formed- 4.5 billion years planets formedo Sun = star born in cloud of gas and dust By product = star and rotating disk, planets born out of this diskRecap- Big bang – 14 billion yearso Milky way = 10 billion years Sun and solar system = 4.5 billion- Stars must die so that we can live1.3 Spaceship EarthHow is Earth moving through Space?1. Rotation2. Orbit3. Solar system moves in Galaxya. Orbits around center of galaxy (28K Light Year Orbit) every 230 million years4. Galaxy through universea. Hubble Expansioni. Local group galaxies move towards each other, other local groups move away from each otherTest QuestionsDistances - An astronomer discovers an object at a distance of 28 million light years from the Earth. Based on the distance, which of the following is this object most likely to be?a. A new planet in our solar system b. Star in Milky wayc. Artificial satellite orbiting Earth d. A galaxy- The spacecraft Voyage 1 is now at a distance of about 100 AU from the Erath. It is…a. Closer than the Sunb. Farther than Sun but not as far as Proxima Centauric. Father than Prox. Cent. But not as far as Andromeda Galaxyd. Father than Andromeda GalaxyAges- How long after the Universe began did our solar system form?a. 4.5 billion years b. 9.5 billion c. 14 billion d. 26,000 yearsStars- Number of stars in a typical galaxy is roughly?a. 1,000 b. 1 million c. 1 billion d. 100 billionHow the elements formed- The Carbon contained within this sheet of paper was produceda. When the universe was very hot during big bangb. Inside stars before formation of Earthc. Inside sun around time of earth’s formationd. Inside the EarthObservable Universe- Short answer. Be able to explain itChapter 2Discovering the Universe for Yourself2.1 Patterns in the Night SkyMovement of Stars- Rise in east, set in westo Move together in a fixed pattern- Celestial Sphereo Stars appear to lie on same “imaginary sphere” regardless of distanceso 88 constellations Each cover a region of the skyo Zodiac constellations Lie on the elliptical plane of the Sun- Stars near North Celestial pole are circumpolar, they never seto Stars near S. Celestial pole are never seen by usLocal Sky- Zenith: point directly overhead- Horizon: boundary between Earth and skyo all points 90 degrees from the Zenith- Meridian: Line from North horizon to South horizon, passing through Zenith- Altitude: Object’s location above horizon (in degrees)o Azimuth is degrees clockwise from due North- Direction: Location along horizon (E, SW, etc.)Constellations depend on latitude- Zenith determines what part of the sky you seeo Polaris = north In Charlottesville Polaris is about 38 degrees above the horizon (Latitude is 38 degrees N)o Latitudes which constellations are hidden below the horizon- Constellations seen depend on the time of yearRecapWhat does universe look like from Earth?- Each position in sky belongs to one of 88 constellationso 12 zodiacs along path of sun- Specify position of an object in the local sky by altitude above the horizon and its direction along the horizonWhy do starts rise and set?- Because of Earth’s rotation- Which stars rise and set in local sky depends on the location of the Earth2.2: Reasons for the SeasonsEarth’s Axis Tilt- Points to North Celestial pole throughout the year at 23.5 degreeso Tilt effects amount of sunlight in local sky Seasons depend on the effect of axis tilt on directness of sunlight?- Direct sunlighto Sun position in the sky is different in each season High is summer, lower in winter- Axis tilt changes slightly over timeo Wobbles over about 26,000 yearso Polaris won’t always be the North StarProgression of Seasons- For Special Pointso Summer Solstice Most direct sunlight (June 21) Highest path- NE to NWo Winter Solstice Least direct sunlight (Dec. 21) Lowest path- SE to SWo Spring (vernal) Equinox and Fall (autumnal) Equinox Rises precisely in E and sets precisely in W- Seasonal changes at more severe at higher latitudeso Near north pole Dark ½ of the year, light the other halfRecapWhat causes seasons?- Tilt of Earth’s axis causes sunlight to hit different parts of the Earth more directly during Summer and less directly during winterHow do we mark the progressions of the seasons?- The summer and winter solstices is when the Northern Hemisphere gets its most/least direct sunlight- Spring and Fall Equinoxes are when both hemispheres get the same amount of light2.3 The MoonWhy do we see phases of the moon?- Consequences of moon’s orbit around Eartho 29.5 days = Lunar phases- Motionso 3