ASTRO 101

1. ASTRO 101 Principles of Astronomy

2. Instructor: Jerome A. Orosz (rhymes with “boris”)Contact: • Telephone: 594-7118 • E-mail: orosz@sciences.sdsu.edu • WWW: http://mintaka.sdsu.edu/faculty/orosz/web/ • Office: Physics 241, hours T TH 3:30-5:00

3. Text: “Discovering the Essential Universe, Fifth Edition”by Neil F. Comins

4. Course WWW Page http://mintaka.sdsu.edu/faculty/orosz/web/ast101_fall2012.html Note the underline: … ast101_fall2012.html … Also check out Nick Strobel’s Astronomy Notes: http://www.astronomynotes.com/

5. Exam 2: • N=120 (1 missing) • Average = 68.6 • low = 20, high = 96.5 • A 90%--100% • A- 85%--89% • B+ 80%--84% • B 75%--79% • B- 70%--74% • C+ 65%--69% • C 60%--64% • C- 50%--59% • D 40%--49% • F 0%--39%

6. Homework/Announcements • Homework due Tuesday, November 13: Question 4, Chapter 8 (Describe the three main layers of the Sun’s interior.)

7. Next:The Big One

8. The Big One • We know that rocks can fall from the sky. One can ask at least three questions:

9. The Big One • We know that rocks can fall from the sky. One can ask at least three questions: • How big can they get?

10. The Big One • We know that rocks can fall from the sky. One can ask at least three questions: • How big can they get? • How often does it happen?

11. The Big One • We know that rocks can fall from the sky. One can ask at least three questions: • How big can they get? • How often does it happen? • Does it matter?

12. Evidence from the Past • The Moon has suffered collisions with large bodies in its history. • The largest craters are a few hundred km across.

13. Evidence from the Past • The Moon has suffered collisions with large bodies in its history. • The largest craters are a few hundred km across. These require impacting bodies a few dozen km across.

14. Evidence from the Past • The Moon has suffered collisions with large bodies in its history. • In fact, small impacts are frequently observed.

15. Evidence from the Past • Mercury has also suffered from bombardment by large bodies in its history.

16. Evidence from the Past • The Moon and Mercury are covered with impact craters, which is evidence of a large number of collisions in the past.

17. Evidence from the Past • The Moon and Mercury are covered with impact craters, which is evidence of a large number of collisions in the past. • There is no reason to think that the Earth was not also bombarded.

18. Evidence from the Past • The Moon and Mercury are covered with impact craters, which is evidence of a large number of collisions in the past. • There is no reason to think that the Earth was not also bombarded. • However, surface features on the Earth are subject to weathering, so older features are sometimes hard to find.

19. Craters on Earth • It is possible to find impact craters on Earth. • Some are obvious, such as this one in Arizona.

20. Craters on Earth • It is possible to find impact craters on Earth. • Some are obvious, such as this one in Arizona. • The impacting body was about 50 meters across, and it fell about 50,000 years ago.

21. Craters on Earth • It is possible to find impact craters on Earth. • Some are not so obvious, like this one in Quebec. • It is 100 km across, and about 250 million years old. http://www.unb.ca/passc/ImpactDatabase/

22. Craters on Earth • Other craters are not at all obvious. • This one is near Decaturville, Missouri. It is about 6 km across and about 300 million years old. http://www.unb.ca/passc/ImpactDatabase/

23. Craters on Earth • There are more than a hundred documented impact sites on Earth. http://www.unb.ca/passc/ImpactDatabase/

24. What Happens When One Hits? • The falling body has energy of motion, where E = 0.5 x (mass) x (velocity)2. This energy of motion is converted (rapidly) into other forms of energy upon impact.

25. What Happens When One Hits? • The falling body has energy of motion, where E = 0.5 x (mass) x (velocity)2. This energy of motion is converted (rapidly) into other forms of energy upon impact. • For small objects, most of this energy can be dissipated in the upper atmosphere.

26. What Happens When One Hits? • The falling body has energy of motion, where E = 0.5 x (mass) x (velocity)2. This energy of motion is converted (rapidly) into other forms of energy upon impact. • For small objects, most of this energy can be dissipated in the upper atmosphere. • For larger objects, some of this energy will be released at the ground level.

27. Does it hurt? • The amount of damage depends on the mass of the impacting body and on its speed. • Bodies with diameters less than a few meters burn up in the atmosphere. • Bodies larger than a few dozen meters across usually hit the ground, leaving a crater roughly 10 times larger.

28. Does it hurt? • Bodies with diameters less than a few meters burn up in the atmosphere. • Bodies larger than a few dozen meters across usually hit the ground, leaving a crater roughly 10 times larger. • Bodies around 50 to 100 meters cause significant local damage (similar to a H bomb).

29. Does it hurt? • Bodies larger than a few dozen meters across usually hit the ground, leaving a crater roughly 10 times larger. • Bodies around 50 to 100 meters cause significant local damage (similar to a H bomb). • Bodies larger than 1km cause damage on a global scale.

30. Does it hurt? • It is believed that the impact of an asteroid 12 to 15 km in diameter caused the extinction of the dinosaurs.

31. What Happens When One Hits? • Check out the Solar Systems Collisions Page: http://janus.astro.umd.edu/astro/impact/ • Asteroid 2004 NM will come very close to us in 2029… • http://science.nasa.gov/science-news/science-at-nasa/2005/13may_2004mn4/

32. How Often? • The rate of impacts was higher in the early history of the solar system (e.g. about 4 billion years ago).

33. How Often? • The rate of impacts was higher in the early history of the solar system (e.g. about 4 billion years ago). • Eventually, most of the small bodies were used up, so the impact rate dropped.

34. How Often? • The rate of impacts was higher in the early history of the solar system (e.g. about 4 billion years ago). • Eventually, most of the small bodies were used up, so the impact rate dropped. • However, the present-day impact rate is NOT zero.

35. How Often? • However, the present-day impact rate is NOT zero. • The impact rate depends on how big the impacting body is. Smaller bodies are much more common than larger bodies.

36. How Often? • However, the present-day impact rate is NOT zero. • The impact rate depends on how big the impacting body is. Smaller bodies are much more common than larger bodies. • The impact rates are uncertain and are based on a small number of events “observed” in the past.

37. How Often • Every day: bodies a few meters across and smaller. These explode in the atmosphere.

38. How Often • Every day: bodies a few meters across and smaller. These explode in the atmosphere. • Once a year: bodies around 10 meters across. Most explode in the atmosphere, but a few make small craters.

39. How Often • Every day: bodies a few meters across and smaller. These explode in the atmosphere. • Once a year: bodies around 10 meters across. Most explode in the atmosphere, but a few make small craters. • Once a century: bodies a few 10s of meters across. Atomic bomb-like energies.

40. How Often? • A body with a diameter of about 40m hit Tunguska, Siberia in 1908. Trees were knocked down over an area 200 km across. http://www.unb.ca/passc/ImpactDatabase/

41. How Often • Once a year: bodies around 10 meters across. Most explode in the atmosphere, but a few make small craters. • Once a century: bodies a few 10s of meters across. Atomic bomb-like energies. • Every million years: bodies around 1 km across. Widespread damage.

42. How Often • Once a century: bodies a few 10s of meters across. Atomic bomb-like energies. • Every million years: bodies around 1 km across. Widespread damage. • Every 100 million years: bodies around 10 km across. Mass extinctions.

43. What To Do? • Early Warning and Prevention: • One can survey the sky for near-Earth asteroids. Currently only a small fraction of the entire population has been found. • Several surveys are underway, and more are planned. • The hope is to spot potentially dangerous objects well in advance of when they will hit. • http://www.cnn.com/2003/TECH/space/09/02/asteroid.reut/index.html • http://www.guardian.co.uk/space/article/0,14493,1660485,00.html • http://neo.jpl.nasa.gov/risks/

44. What To Do? • Early Warning and Prevention: • If an object on a collision course is spotted, can anything be done?

45. What To Do? • Early Warning and Prevention: • If an object on a collision course is spotted, can anything be done? • http://www.youtube.com/watch?v=iq6q2BrTino

46. What To Do? • Early Warning and Prevention: • If an object on a collision course is spotted, can anything be done? • Presently, not much alongs these lines can be done, but perhaps in the coming decades we will have the capability to divert small bodies using nuclear weapons or similar technologies. • http://blogs.sundaymercury.net/weirdscience/2012/08/bruce-willis-cant-save-us-from.html

47. What To Do? • Early Warning and Prevention: • If an object on a collision course is spotted, can anything be done? • Here is a technical description of a neat idea, known as the “gravitational tractor” • http://arxiv.org/abs/physics/0608157

48. Next: Chapter 8 The Sun: Our Extraordinary Ordinary Star

49. The Sun and the Stars • The Sun is the nearest example of a star. • Basic questions to ask: • What do stars look like on their surfaces? Look at the Sun since it is so close. • How do stars work on their insides? Look at both the Sun and the stars to get many examples. • What will happen to the Sun? Look at other stars that are in other stages of development.

50. The Sun • There are two broad areas of solar research: • The study of the overall structure of the Sun. • The study of its detailed surface features. • Think of the distinction of “climate” and “weather” on Earth: • Climate refers to global trends. • Weather refers to local conditions.