Copyright © 2009 Pearson Education, Inc.Icarus PlanetThe orbit of HD 80606b. The small circles represent 1 hourintervals.The four positions are separated by 19 hours. It gets reallyhot! The temperature rises from 900deg to 2000deg F.http://blogs.discovermagazine.com/badastronomy/2009/01/28/weather-sizzles-on-a-planet-that-kisses-its-star/Copyright © 2009 Pearson Education, Inc.How big is the universe?• The Milky Way is one of about 100 billion galaxies.• 1011 stars/galaxy × 1011 galaxies = 1022 starsIt has as many stars as grains of (dry) sand on all Earth’s beaches.Copyright © 2009 Pearson Education, Inc.• Now let’s step through the universe in powers of 10:Zooming Out or Zooming In 26 Orders of MagnitudeCopyright © 2009 Pearson Education, Inc.How do our lifetimes compare to the ageof the universe?• The Cosmic Calendar: A scale on which we compress thehistory of the universe into 1 yearCopyright © 2009 Pearson Education, Inc.What have we learned?• How big is the Earth compared to our solar system?— On a scale of 1-to-10 billion, the Sun is about the size of agrapefruit. The Earth is the size of a tip of a ball point penabout 15 m away. The distances between planets are hugecompared to their sizes.• How far away are the stars?— On the same scale, the stars are thousands of kilometersaway.• How big is the Milky Way Galaxy?— It would take more than 3000 years to count the stars in theMilky Way Galaxy at a rate of one per second. The MilkyWay Galaxy is about 100,000 light-years across.Copyright © 2009 Pearson Education, Inc.What have we learned?• How big is the universe?— 100 billion galaxies in the observable universe— 14 billion light-years in radius— As many stars as grains of sand on Earth’s beaches• How do our lifetimes compare to the age of theuniverse?— On a cosmic calendar that compresses the history ofthe universe into 1 year, human civilization is just afew seconds old, and a human lifetime is a fraction ofa second.Copyright © 2009 Pearson Education, Inc.1.3 Spaceship Earth• How is Earth moving in our solar system?• How is our solar system moving in the MilkyWay Galaxy?• How do galaxies move within the universe?• Are we ever sitting still?Our goals for learning:Copyright © 2009 Pearson Education, Inc.How is Earth moving in our solar system?• Contrary to our perception, we are not “sitting still.”• We are moving with the Earth in several ways, and atsurprisingly fast speeds.Earth rotates around itsaxis once every day.Copyright © 2009 Pearson Education, Inc.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- clockwise as viewed from above the North Pole.Copyright © 2009 Pearson Education, Inc.Our Sun moves randomly relative to the other starsin the local solar neighborhood…• at typical relative speeds of more than 70,000 km/hr.• but stars are so far away that we cannot easily notice their motion.… and it orbits the galaxy every 230 million years.Copyright © 2009 Pearson Education, Inc.More detailed study of the Milky Way’s rotationreveals one of the greatest mysteries in astronomy…Most of Milky Way’slight comes from diskand bulge ……. but most of themass is in its haloCopyright © 2009 Pearson Education, Inc.How do galaxies move within the universe?Galaxies arecarried alongwith theexpansion ofthe universe.But how didHubble figureout that theuniverse isexpanding?Copyright © 2009 Pearson Education, Inc.Edwin HubbleCopyright © 2009 Pearson Education, Inc.Vesto SlipherCopyright © 2009 Pearson Education, Inc.MymeasurementsCopyright © 2009 Pearson Education, Inc.Hubble discovered that…• all galaxies outside our Local Group aremoving away from us.• the more distant the galaxy, the faster it isracing away.Conclusion: We live in an expanding universe.Copyright © 2009 Pearson Education, Inc.Are we ever sitting still?Earth rotates on axis: > 1,000 km/hrEarth orbits Sun: > 100,000 km/hrSolar system moves among stars: ~ 70,000 km/hrMilky Way rotates: ~ 800,000 km/hrMilky Way moves in Local GroupUniverseexpandsCopyright © 2009 Pearson Education, Inc.What have we learned?• How is Earth moving in our solar system?— It rotates on its axis once a day and orbits theSun at a distance of 1 AU = 150 million km.• How is our solar system moving in the MilkyWay Galaxy?— Stars in the Local Neighborhood moverandomly relative to one another and orbitthe center of the Milky Way in about 230million years.Copyright © 2009 Pearson Education, Inc.What have we learned?• How do galaxies move within the universe?— All galaxies beyond the Local Group aremoving away from us with expansion of theuniverse: the more distant they are, the fasterthey’re moving.• Are we ever sitting still?— No!Copyright © 2009 Pearson Education, Inc.Chapter 2Discovering the Universe for YourselfCopyright © 2009 Pearson Education, Inc.2.1 Patterns in the Night Sky• What does the universe look like fromEarth?• Why do stars rise and set?• Why do the constellations we see depend onlatitude and time of year?Our goals for learning:Copyright © 2009 Pearson Education, Inc.What does the universe look likefrom Earth?With the naked eye,we can see morethan 2000 stars aswell as the MilkyWay.Copyright © 2009 Pearson Education, Inc.ConstellationsA constellation is aregion of the sky.88 constellationsfill the entire sky.Copyright © 2009 Pearson Education, Inc.Thought QuestionThe brightest stars in a constellation…A. all belong to the same star cluster.B. all lie at about the same distance from Earth.C. may actually be quite far away from each other.Copyright © 2009 Pearson Education, Inc.Thought QuestionThe brightest stars in a constellation…A. all belong to the same star cluster.B. all lie at about the same distance from Earth.C. may actually be quite far away from eachother.Copyright © 2009 Pearson Education, Inc.The Celestial SphereStars at differentdistances all appear tolie on the celestialsphere.The ecliptic is theSun’s apparent paththrough the celestialsphere.Copyright © 2009 Pearson Education, Inc.The Celestial SphereThe 88 officialconstellationscover the celestialsphere.Copyright © 2009 Pearson Education, Inc.The Milky WayA band of light thatmakes a circlearound the celestialsphereWhat is it?Our view into theplane of our
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