1. Contact Information Mike Skrutskie – mfs4n - 924-4328 Room 262 – Astronomy Building – Office Hours: Monday 1:30 – 2:30 Thursday 10:30 – 12:00 Room 262 Astronomy (my office) if those don't work contact me for arrangements Course TA – Kim Sokal - krs9tb Room 267 Astronomy Building By appointment

2. How Do You Make Sense of it All?

3. Astronomy: A Search for Organization? Stars.... Galaxies....

4. Astronomy: A Search for Organization?

5. Our Galaxy (the Milky Way) in Perspective: How do we fit in? Galaxies, collections of billions of stars assembled and bound by gravity, are a primary unit of Universal structure. Any random deep view of the night sky shows a universe peppered with galaxies – each containing hundreds of billions of stars.

6. Our Galaxy (the Milky Way) in Perspective: How do we fit in? Imagine we are able to travel to a point billions of light years away and look back toward our galaxy... Us?

7. Our Galaxy (the Milky Way) in Perspective: How do we fit in? Associated WWW Link The Stars Near Our Sun A distant galaxy similar to our Milky Way Our sun (a star) resides out toward the edge of a thin and flat collection of 100 billion stars – the Milky Way Galaxy

8. Our Galaxy (the Milky Way) in Perspective: How do we fit in? Associated WWW Link The Stars Near Our Sun

9. Our Galaxy (the Milky Way) in Perspective: How do we fit in? The Sun is embedded in the Milky Way (far from the center).  We have a myopic perspective.  The Milky Way is thin and flat, yet we see a lumpy diffuse band across the sky because of our proximity.

10. Our Galaxy (the Milky Way) in Perspective: How do we fit in? The Sun is embedded in the Milky Way (far from the center).  We have a myopic perspective.  The Milky Way is thin and flat, yet we see a lumpy diffuse band across the sky because of our proximity.

11. Our Galaxy (the Milky Way) in Perspective: How do we fit in? The Sun is embedded in the Milky Way (far from the center).  We have a myopic perspective.  The Milky Way is thin and flat, yet we see a lumpy diffuse band across the sky because of our proximity. Aitoff Projection

12. Our Galaxy (the Milky Way) in Perspective: How do we fit in? Infrared light penetrates dust better than visible light.  An infrared view of the Milky Way reveals the real Galaxy.

13. Astronomy: A Search for Structure? Hierarchical structure in the Universe leads to an extended mailing address..... Earth The Solar System (in capital letters) The Milky Way Galaxy The Local Group The Local Supercluster The Universe Implicit in understanding this structure is knowing how far away things actually are.... not an easy task!

14. Understanding Structure: Divining Depth

16. Still, we are focusing on phenomenology....

17. Astronomy: A Search for Origins!!! Where did all the structure and organization come from? How did it emerge over time? What were the starting conditions? What physical processes were important?  We wish to explain, not just observe.

18. Astronomy: A Search for Origins!!! Where did all the structure and organization come from? How did it emerge over time? What physics/physical processes were important? Hydrogen + Helium + Gravity ⇨ Stars, Galaxies, and Humans given about 14 billion years.

19. A Five-Minute History of the Universe The “Big Bang” brings matter, space and time into existence.  It happened 13.7 billion years ago. » - a number now known to better than 1 percent!now known  The early Universe contained only uniformly distributed Hydrogen and Helium.only Almost immediately gravity begins to form stars and galaxies.  Stars “process” Hydrogen and Helium into heavier elements like Iron, Calcium, and Oxygen. After 9 billion years of cosmic recycling (4.6 billion years ago) our Sun forms from the “ashes” for previous generations of stars.  At the same time system of planets form from debris left in orbit around the Sun. Life originates quickly on Earth.  but only becomes “complex” ½ billion years ago. Lecture outline: A Brief Brief History of the Universe

20. A Five-Minute History of the Universe The “Big Bang” brings matter, space and time into existence.  It happened 13.7 billion years ago. a number now known to better than 1 percent!  The early Universe contained only uniformly distributed Hydrogen and Helium. Almost immediately gravity begins to form stars and galaxies.gravity  Stars “process” Hydrogen and Helium into heavier elements like Iron, Calcium, and Oxygen. After 9 billion years of cosmic recycling (4.6 billion years ago) our Sun forms from the “ashes” for previous generations of stars.  At the same time system of planets form from debris left in orbit around the Sun. Life originates quickly on Earth.  but only becomes “complex” ½ billion years ago. Lecture outline: A Brief Brief History of the Universe

21. A Five-Minute History of the Universe The “Big Bang” brings matter, space and time into existence.  It happened 13.7 billion years ago. a number now known to better than 1 percent!  The early Universe contained only uniformly distributed Hydrogen and Helium. Almost immediately gravity begins to form stars and galaxies.  Stars “process” Hydrogen and Helium into heavier elements like Iron, Calcium, and Oxygen. After 9 billion years of cosmic recycling (4.6 billion years ago) our Sun forms from the “ashes” for previous generations of stars.  At the same time system of planets form from debris left in orbit around the Sun. Life originates quickly on Earth.  but only becomes “complex” ½ billion years ago.

22. A Five-Minute History of the Universe The “Big Bang” brings matter, space and time into existence.  It happened 13.7 billion years ago. a number now known to better than 1 percent!  The early Universe contained only uniformly distributed Hydrogen and Helium. Almost immediately gravity begins to form stars and galaxies.gravity  Stars “process” Hydrogen and Helium into heavier elements like Iron, Calcium, and Oxygen. After 9 billion years of cosmic recycling (4.6 billion years ago) our Sun forms from the “ashes” for previous generations of stars.  At the same time system of planets form from debris left in orbit around the Sun. Life originates quickly on Earth.  but only becomes “complex” ½ billion years ago. Lecture outline: A Brief Brief History of the Universe

23. A Five-Minute History of the Universe The “Big Bang” brings matter, space and time into existence.  It happened 13.7 billion years ago. a number now known to better than 1 percent!  The early Universe contained only uniformly distributed Hydrogen and Helium. Almost immediately gravity begins to form stars and galaxies.  Stars “process” Hydrogen and Helium into heavier elements like Iron, Calcium, and Oxygen. After 9 billion years of cosmic recycling (4.6 billion years ago) our Sun forms from the “ashes” for previous generations of stars.  At the same time system of planets form from debris left in orbit around the Sun. Life originates quickly on Earth.  but only becomes “complex” ½ billion years ago. Lecture outline: A Brief Brief History of the Universe

24. A Five-Minute History of the Universe The “Big Bang” brings matter, space and time into existence.  It happened 13.7 billion years ago. a number now known to better than 1 percent!  The early Universe contained only uniformly distributed Hydrogen and Helium. Almost immediately gravity begins to form stars and galaxies.  Stars “process” Hydrogen and Helium into heavier elements like Iron, Calcium, and Oxygen. After 9 billion years of cosmic recycling (4.6 billion years ago) our Sun forms from the “ashes” of previous generations of stars.  At the same time a system of planets form from debris left in orbit around the Sun. Life originates quickly on Earth.  but only becomes “complex” ½ billion years ago. Lecture outline: A Brief Brief History of the Universe

25. A Five-Minute History of the Universe The “Big Bang” brings matter, space and time into existence.  It happened 13.7 billion years ago. a number now known to better than 1 percent!  The early Universe contained only uniformly distributed Hydrogen and Helium. Almost immediately gravity begins to form stars and galaxies.  Stars “process” Hydrogen and Helium into heavier elements like Iron, Calcium, and Oxygen. After 9 billion years of cosmic recycling (4.6 billion years ago) our Sun forms from the “ashes” of previous generations of stars.  At the same time a system of planets form from debris left in orbit around the Sun. Life originates quickly on Earth.  but only becomes “complex” ½ billion years ago. Lecture outline: A Brief Brief History of the Universe Stars form Stars die

26. A Five-Minute History of the Universe The “Big Bang” brings matter, space and time into existence.  It happened 13.7 billion years ago. a number now known to better than 1 percent!  The early Universe contained only uniformly distributed Hydrogen and Helium. Almost immediately gravity begins to form stars and galaxies.  Stars “process” Hydrogen and Helium into heavier elements like Iron, Calcium, and Oxygen. After 9 billion years of cosmic recycling (4.6 billion years ago) our Sun forms from the “ashes” of previous generations of stars.  At the same time a system of planets form from debris left in orbit around the Sun. Life originates quickly on Earth.  but only becomes “complex” ½ billion years ago. Lecture outline: A Brief Brief History of the Universe

28. A Five-Minute History of the Universe The “Big Bang” brings matter, space and time into existence.  It happened 13.7 billion years ago. a number now known to better than 1 percent!  The early Universe contained only uniformly distributed Hydrogen and Helium. Almost immediately gravity begins to form stars and galaxies.  Stars “process” Hydrogen and Helium into heavier elements like Iron, Calcium, and Oxygen. After 9 billion years of cosmic recycling (4.6 billion years ago) our Sun forms from the “ashes” for previous generations of stars.  At the same time system of planets form from debris left in orbit around the Sun. Life originates quickly on Earth.  but only becomes “complex” ½ billion years ago. Lecture outline: A Brief Brief History of the Universe

29. A Five-Minute History of the Universe The “Big Bang” brings matter, space and time into existence.  It happened 13.7 billion years ago. a number now known to better than 1 percent!  The early Universe contained only uniformly distributed Hydrogen and Helium. Almost immediately gravity begins to form stars and galaxies.  Stars “process” Hydrogen and Helium into heavier elements like Iron, Calcium, and Oxygen. After 9 billion years of cosmic recycling (4.6 billion years ago) our Sun forms from the “ashes” for previous generations of stars.  At the same time system of planets form from debris left in orbit around the Sun. Life originates quickly on Earth.  but only becomes “complex” ½ billion years ago. Lecture outline: A Brief Brief History of the Universe

30. A Five-Minute History of the Universe The “Big Bang” brings matter, space and time into existence.  It happened 13.7 billion years ago. a number now known to better than 1 percent!  The early Universe contained only uniformly distributed Hydrogen and Helium. Almost immediately gravity begins to form stars and galaxies.  Stars “process” Hydrogen and Helium into heavier elements like Iron, Calcium, and Oxygen. After 9 billion years of cosmic recycling (4.6 billion years ago) our Sun forms from the “ashes” for previous generations of stars.  At the same time system of planets form from debris left in orbit around the Sun. Life originates quickly on Earth.  but only becomes “complex” ½ billion years ago.

31. A Single-Year Perspective If this history could be compressed into a single year: The Universe starts on January 1... The Solar System forms in early-September

32. A Single-Year Perspective If this history could be compressed into a single year: The Universe starts on January 1... The Solar System forms in early-September Life on Earth originates in mid-September – - Life becomes complex in early-December UR L 3.4 billion year old stromatolite fossils 0.3 billion year old trilobyte

33. A Single-Year Perspective If this history could be compressed into a single year: The Universe starts on January 1... The Solar System forms in early-September Life originates in mid-September – - Life becomes complex in early-December Dinosaurs roamed the Earth for two weeks between December 10 and December 25 Humanity (intelligence?) arose at 10 p.m. on December 31 Recorded history began around 11:59:45 on December 31

34. Overcoming Human Biases Location, Wavelength, and Time to name a few Lecture Notes: Human Biases in Astronomy

35. Human Biases Time  A human lifetime is a blink of the eye relative to the timescale of cosmic events. - Going back to that cosmic year, a human lifetime is about 2 one- hundredths of a second.  Stars and galaxies change incredibly slowly by comparison.  Astronomers must reconstruct the workings of the Universe from this “snapshot” view. Lecture Notes: Lookback time

37. Human Biases Time  A human lifetime is a blink of the eye relative to the timescale of cosmic events. - Going back to that cosmic year, a human lifetime is about 2 one- hundredths of a second.  Stars and galaxies change incredibly slowly by comparison.  Astronomers must reconstruct the workings of the Universe from this “snapshot” view. The Astronomer's task is similar to asking an alien anthropologist to reconstruct the intricacies of human relationships and politics from a snapshot of the events happening on Earth at one instant. Lecture Notes: Lookback time

38. Human Biases Time  A human lifetime is a blink of the eye relative to the timescale of cosmic events.  Astronomers must reconstruct the workings of the Universe from this “snapshot” view. This task is similar to reconstructing the intricacies of human relationships and politics from a snapshot of the events happening on Earth at one instant. Astronomers have two powerful tools to address this shortcoming  Light travels “slowly”. A stale view of the universe permits Astronomers to look back in time.look back Lecture Notes: Lookback time

39. “Lookback” Time Light takes time to get from one place to another.  Light travels at a speed of 300,000 km/s The travel time is instantaneous for most everyday experience where distances are small. Travel time becomes important for more distant objects Light takes just over a second to get to the Moon (400,000 kilometers away). In a year light traverses a distance of a light-year.

40. “Lookback” Time We get a “stale” view of the Universe, seeing more distant object as they were in the more distant past. – We see the Sun as it was 8.3 minutes ago because the light took 8.3 minutes to traverse the distance from the Sun to the Earth (150 million kilometers). For extremely distant objects, billions of light-years, the light takes billions of years to get here, bringing a view that is billions of years out of date.

41. “Lookback” Time We see the Sun as it was 8.3 minutes ago because the light took 8.3 minutes to traverse the distance from the Sun to the Earth (150 million kilometers). For extremely distant objects, billions of light years, the light takes billions of years to get here, bringing a view that is billions of years out of date.  We see the distant universe as it was in the distant past.

42. Human Biases Time  A human lifetime is a blink of the eye relative to the timescale of cosmic events.  Astronomers must reconstruct the workings of the Universe from this “snapshot” view. This task is similar to reconstructing the intricacies of human relationships and politics from a snapshot of the events happening on Earth at one instant. Astronomers have two powerful tools to address this shortcoming  Light travels “slowly”. A stale view of the universe permits Astronomers to look back in time.look back  Computer simulation can permit scientist to watch events play out over millions or billions of years. Insert the laws of physics and turn the crank... Lecture Notes: Lookback time

43. Real Simulation Collision between Galaxies Formation of Structure in the Universe Some computer animations:

44. Real Simulation Collision between Galaxies Formation of Structure in the Universe Some computer animations: Tour the Millenium Simulation

45. Human Biases Location

46. Human Biases Location

47. Human Biases Location

48. Human Biases Location  High density of matter compared with intergalactic space. 10 19 atoms per cubic centimeter in air. 1 atom per cubic “stadium” in intergalactic space.  High temperature compared with intergalactic space 300 Kelvins room temperature vs. 3 Kelvins elsewhere.  Dominance by elements other than hydrogen and helium.

49. Human Biases Location

50. Human Biases Wavelength

51. Human Biases Wavelength  The universe looks quite different when we look outside the tiny slice of the spectrum accessible to the human eye.

54. Human Biases Wavelength

55. Human Biases Comprehending large numbers  It's easy to visualize 5, 10, or even 100 things. What's the difference between a million, a billion, or a trillion (from a visualization standpoint)? How do we make large numbers conceptually meaningful?

56. Human Biases Comprehending large numbers  It's easy to visualize 5, 10, or even 100 things. What's the difference between a million, a billion, or a trillion (from a visualization standpoint)??? How do we make large numbers conceptually meaningful?  The mass of the Sun is 2,000,000,000,000,000,000,000,000,000,000 kg  Using scientific notation makes the above number manageable, but not necessarily comprehensible. = 2 x 10 30 kg

57. Human Biases Scale models can put these numbers in a relative context.

58. Human Biases Scale models can put these numbers in a relative context. NO!