Icarus Planet The orbit of HD 80606b The small circles represent 1 hour intervals The four positions are separated by 19 hours It gets really hot 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 stars It 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 Magnitude Copyright 2009 Pearson Education Inc How do our lifetimes compare to the age of the universe The Cosmic Calendar A scale on which we compress the history of the universe into 1 year Copyright 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 a grapefruit The Earth is the size of a tip of a ball point pen about 15 m away The distances between planets are huge compared to their sizes How far away are the stars On the same scale the stars are thousands of kilometers away How big is the Milky Way Galaxy It would take more than 3000 years to count the stars in the Milky Way Galaxy at a rate of one per second The Milky Way 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 the universe On a cosmic calendar that compresses the history of the universe into 1 year human civilization is just a few seconds old and a human lifetime is a fraction of a second Copyright 2009 Pearson Education Inc 1 3 Spaceship Earth Our goals for learning How is Earth moving in our solar system How is our solar system moving in the Milky Way Galaxy How do galaxies move within the universe Are we ever sitting still 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 at surprisingly fast speeds Earth rotates around its axis 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 5 pointing to Polaris and rotates in the same direction it orbits counterclockwise as viewed from above the North Pole Copyright 2009 Pearson Education Inc Our Sun moves randomly relative to the other stars in 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 rotation reveals one of the greatest mysteries in astronomy Most of Milky Way s light comes from disk and bulge but most of the mass is in its halo Copyright 2009 Pearson Education Inc 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 Copyright 2009 Pearson Education Inc Edwin Hubble Copyright 2009 Pearson Education Inc Vesto Slipher Copyright 2009 Pearson Education Inc My measurements Copyright 2009 Pearson Education Inc Hubble discovered that all galaxies outside our Local Group are moving away from us the more distant the galaxy the faster it is racing 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 hr Earth orbits Sun 100 000 km hr Solar system moves among stars 70 000 km hr Milky Way rotates 800 000 km hr Milky Way moves in Local Group Universe expands Copyright 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 the Sun at a distance of 1 AU 150 million km How is our solar system moving in the Milky Way Galaxy Stars in the Local Neighborhood move randomly relative to one another and orbit the center of the Milky Way in about 230 million years Copyright 2009 Pearson Education Inc What have we learned How do galaxies move within the universe All galaxies beyond the Local Group are moving away from us with expansion of the universe the more distant they are the faster they re moving Are we ever sitting still No Copyright 2009 Pearson Education Inc Chapter 2 Discovering the Universe for Yourself Copyright 2009 Pearson Education Inc 2 1 Patterns in the Night Sky Our goals for learning What does the universe look like from Earth Why do stars rise and set Why do the constellations we see depend on latitude and time of year Copyright 2009 Pearson Education Inc What does the universe look like from Earth With the naked eye we can see more than 2000 stars as well as the Milky Way Copyright 2009 Pearson Education Inc Constellations A constellation is a region of the sky 88 constellations fill the entire sky Copyright 2009 Pearson Education Inc Thought Question The 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 Question The 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 The Celestial Sphere Stars at different distances all appear to lie on the celestial sphere The ecliptic is the Sun s apparent path through the celestial sphere Copyright 2009 Pearson Education Inc The Celestial Sphere The 88 official constellations cover the celestial sphere Copyright 2009 Pearson Education Inc The Milky Way A band of light that makes a circle around the celestial sphere What is it Our view into the plane of our galaxy Copyright 2009 Pearson Education Inc The Milky Way Copyright 2009 Pearson Education Inc The Local Sky An object s altitude above horizon and direction along horizon specify its location in your local sky Copyright 2009 Pearson Education Inc The Local Sky Zenith The point directly overhead Horizon All points 90 away from zenith
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