© 2010 Pearson Education, Inc. 1 Visited class web page? Got and READ Syllabus? Got Lecture-Tutorials? Got Mastering Astronomy account and intro assignment? Read the first chapter of Johnson? A foot print on the moon Check list

© 2010 Pearson Education, Inc. Our Place in the Universe “Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.” Douglas AdamsDouglas Adams, The Hitchhiker's Guide to the Galaxy English humorist & science fiction novelist ( )

© 2010 Pearson Education, Inc. Our Place in the Universe

© 2010 Pearson Education, Inc. What is our place in the universe?

© 2010 Pearson Education, Inc. A large, glowing ball of gas that generates heat and light through nuclear fusion Star

© 2010 Pearson Education, Inc. Planet A moderately large object that orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous in composition. MarsNeptune

© 2010 Pearson Education, Inc. Moon (or Satellite) An object that orbits a planet Ganymede (orbits Jupiter)

© 2010 Pearson Education, Inc. Asteroid A relatively small and rocky object that orbits a star

© 2010 Pearson Education, Inc. Comet A relatively small and icy object that orbits a star

© 2010 Pearson Education, Inc. Pluto A relatively small yellow dog from Disney. “If Pluto is a dog, then what’s Goofy?” Continuing…

© 2010 Pearson Education, Inc. Solar (Star) System A star and all the material that orbits it, including its planets and moons

© 2010 Pearson Education, Inc. Nebula An interstellar cloud of gas and/or dust

© 2010 Pearson Education, Inc. Galaxy A great island of stars in space, all held together by gravity and orbiting a common center M31, the great galaxy in Andromeda

© 2010 Pearson Education, Inc. Universe The sum total of all matter and energy; that is, everything within and between all galaxies

© 2010 Pearson Education, Inc. How did we come to be?

© 2010 Pearson Education, Inc. How can we know what the universe was like in the past? Light travels at a finite speed (300,000 km/s). Thus, we see objects as they were in the past: The farther away we look in distance, the further back we look in time. DestinationLight travel time Moon1 second Sun8 minutes Sirius8 years Andromeda Galaxy2.5 million years

© 2010 Pearson Education, Inc. Example: We see the Orion Nebula as it looked 1500 years ago.

© 2010 Pearson Education, Inc. Example: This photo shows the Andromeda Galaxy as it looked about 2 1/2 million years ago. Question: When will we be able to see what it looks like now?

© 2010 Pearson Education, Inc. Light-year The distance light can travel in 1 year About 10 trillion kilometers (6 trillion miles)

© 2010 Pearson Education, Inc. How far is a light-year?

© 2010 Pearson Education, Inc. How far is a light-year?

© 2010 Pearson Education, Inc. Can we see the entire universe?

© 2010 Pearson Education, Inc. 23 Navigating the Universe: Sizes and Scales “I don’t pretend to understand the Universe. It’s a great deal bigger than I am” - Thomas Carlyle ( )

© 2010 Pearson Education, Inc. 24 Scale models of the Universe Scale Sun as a grapefruit (1:10,000,000,000)

© 2010 Pearson Education, Inc. 25 Where are the planets? Mercury = grain of sand, 6 meters away (19 feet) Venus = ball point pen tip, 11 meters (36 feet) away Earth = tip of ball point pen, 15 meters (49 feet) away –Moon = 4 cm away from Earth Mars = large grain of sand, 23 meters (75 feet) away Jupiter = marble, 78 meters (256 feet!) (R.I.P.)Pluto (R.I.P.) = head of a pin, 1/3 mile away On this scale, where is the nearest star?

© 2010 Pearson Education, Inc. 26 On this scale, the nearest stars would be a triple- star system formed by a cantaloupe, an apple and an orange, located a continent away. There is essentially nothing in between!!

© 2010 Pearson Education, Inc. 27 BIGNUMBERS LittleNUMBERS kilo- mega- (aka million) giga- (aka billion) tera- (aka trillion) centi- milli- Scale of the Universe

© 2010 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… The Earth rotates around its axis once every day.

© 2010 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 rotating in the same direction it orbits, counter- clockwise as viewed from above the North Pole.

© 2010 Pearson Education, Inc. Our Sun moves randomly relative to the other stars in the local Solar neighborhood… typical relative speeds of more than 70,000 km/hr but stars are so far away that we cannot easily notice their motion … And orbits the galaxy every 230 million years.

© 2010 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?

© 2010 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. We will revisit this topic again at the end of the course.

© 2010 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