Lecture 2

1. Lecture 2 ASTR 111 – Section 002 Introductory Astronomy: Solar System Dr. Weigel

2. http://www.astro.ljmu.ac.uk/courses/phys134/magcol.html

3. Reading for this week • The reading for this week is Chapter 1 (all) and Chapter 2 (sections 2.1-2.2 only) • The quiz will cover this reading and the topics covered in this week’s lectures • The quiz will be available on BlackBoard at 10:15 am … noon today.

4. A note on lecture notes

5. Outline • Angular Measurements Review • Accuracy, Precision, and Bias • The Scientific Method • Astronomical Distances • Ancient Astronomy

6. Angular Measurements Result

7. B A • What is the angular distance between points A and B on this slide (In degrees and arcminutes). Answer depends on where you are sitting. To get arcminutes, take angle in degrees and multiply by 60. • Predict what will happen if you made your measurement in two different parts of the room. Relative to the middle of the room: (1) as you move to the front of the room, angular distance should increase (2) as you move to the walls, angular distance should decrease.

8. B A • Do you think there will be a relationship between a person’s height and the angle they measure? A shorter person will have smaller fingers -> larger angular measurements. A shorter person will have shorter arms -> smaller angular measurements. (Try to simulate this with your hand and arm!) Based on this, the answer is that we don’t expect them to have different angular measurements.

9. B A • Next week you sit in the same chair but weigh 30pounds less. Will your (angular) measurements change? • If you used the width of your hand or the width of your finger to measure, you would expect the angular distance you measured to increase (skinnier hand and finger). • If you used the distance between your knuckles on your finger, you would not expect a change in your measurement (if you lose weight, the distance between your knuckles is not expected to change because your bone size should not change).

10. http://antwrp.gsfc.nasa.gov/apod/ap071025.html

11. Outline • Angular Measurements • Accuracy, Precision, and Bias • The Scientific Method • Astronomical Distances • Ancient Astronomy

12. Precision, Accuracy, and Bias • Whenever you take measurements, you should account for them • Fundamental terms that you must understand when interpreting measurements • Not covered in your book

13. Accuracy vs. Precision Target is red Shots are black

14. Accuracy vs. Precision Target is red Shots are black High precision Low accuracy High precision High accuracy

15. Accuracy vs Precision Mnemonic: You’ll get an A for Accuracy

16. Bias Target is red • The left target shows bias – the measurements were made with high precision, but the were consistently “off” in the same direction. Shots are black

17. Summary • Accuracy – all measurements or values are clustered around the true value (you’ll get an A for accuracy, because you are on the true value) • Precision – all measurements are clustered but are not centered on true value • Bias – measurements are not centered on true value Center of red dot is true value No bias

18. Group work (~ 4 minutes) • Draw a diagram like the ones on the previous slide that show • Low precision and high bias • High accuracy and very low precision • On a piece of paper, write down • Possible causes of low accuracy – be specific! (Don’t say “human error”) • Possible causes of bias – be specific! associated with your angular measurements

19. Question 1.

20. Question 1. Impossible to have both High accuracy and very low precision. But you can have moderate accuracy and moderate precision

21. Question 2. • Low accuracy because of moving hand and difficulty in lining up dots exactly • Low precision because you are using scale that increments in degrees • Bias could happen if your hand (or everyone’s hand in group) was exceptionally large. Then everyone would measure angle to be smaller than it really is.

22. Group work (~ 3 minutes) • Which diagram best represents the statement: “Preliminary polling results indicated that Obama won Virginia by a landslide because the preliminary poll results were all from Northern Virginia”. B D A C

23. Group work (~ 3 minutes) • Which diagram best represents the statement: “Preliminary polling results indicated that Obama won Virginia by a landslide because the preliminary poll results were all from Northern Virginia”. B D A C

24. Outline • Angular Measurements • Accuracy, Precision, and Bias • The Scientific Method • Astronomical Distances • Ancient Astronomy

25. The Scientific Method

26. What is Science? • A set of facts • Something that professional scientists do • The underlying Truth about the Universe • The collection of data and formation of a hypothesis • None of the above

27. What is Science?1) A set of facts? • We are constantly making new discoveries and collecting new data • Technology and experiments are changing • Old Theories are replaced by new Theories • Scientific ``Facts''

28. What is Science?2) A thing that professional scientists do? • What is a scientist? • Do you need a PhD? • Amateur Scientists play an important role in discovery • Being scientific DOES NOT required a Union Card

29. What is Science?3) The underlying Truth about the Universe? Capitalization, too much? Suspect a Scientist should be.

30. What is Science?4) The collection of data and formation of a hypothesis • No, but getting closer

31. What is Science?5) The collection of data and formation of a hypothesis • None of the above

32. What is Science? • A system of knowledge covering general truths or the operation of general laws especially as obtained and tested through the scientific method http://www.merriam-webster.com/dictionary/science

33. The Scientific Methodthe process • characterization of existing data • formulation of a hypothesis • formulation of a predictive test • experimental testing, (important: error elimination and characterization) • report and peer review • validate or revise hypothesis

34. Cat Scientist http://shakespearessister.blogspot.com/2009/08/cat-experiments.html

35. Comment on reddit.com • Ask a Question -Is what i'm seeing my reflection or another cat? • Do Background Research - Go to other mirror to determine what true reflection looks like • Construct a Hypothesis - The other cat is my reflection. • Test Your Hypothesis by Doing an Experiment - move myself. see if reflection duplicates my motions as in the mirror. • Analyze Your Data and Draw a Conclusion - I am seeing another cat • Communicate Your Results - have my master post on reddit http://www.reddit.com/r/science/comments/9e1vh/olivia_the_cat_doublechecks_if_similar_cat_beyond/

36. Important • Science is a process • Humans have concluded that this is the best process by which to explain observations

37. Outline • Angular Measurements • Accuracy, Precision, and Bias • The Scientific Method • Astronomical Distances • Ancient Astronomy

38. Parallax

39. Parallax

40. Parallax 10 20 30 40 50 60 70 80 90

41. Parallax • When the apparent position of an object (numbers on speedometer) changes because of the change in position of the observer (driver’s seat to passenger’s seat).

42. Another example http://www.astro.ljmu.ac.uk/courses/phys134/magcol.html

43. The Parsec

44. Astronomical distances are never measured in Car hours, dotsecs, and Moon Units • Car Hour (ch) • the distance a car can travel in one hour at a speed of about 60 miles/hour. How far is Baltimore? About an hour. • Car Year (cy) • the distance a car can travel in one year at a speed of about 60 miles/hour • dotsec (ds) • the distance at which the two dots on the screen subtend an angle of 1 arcsec • Moon Unit (MU) • One Moon Unit is the average distance between Earth and the Moon A time A distance

45. Astronomical distances are often measured in astronomical units, parsecs, or light-years • Light Year (ly) • One ly is the distance light can travel in one year at a speed of about 3 x 105 km/s or 186,000 miles/s • Parsec (pc) • the distance at which 1 AU subtends an angle of 1 arcsec or the distance from which Earth would appear to be one arcsecond from the Sun • Astronomical Unit (AU) • One AU is the average distance between Earth and the Sun • 1.496 X 108 km or 92.96 million miles

46. Earth Sun Observer’s view of Sun and Earth from outer planet

47. Gods-eye view - Looking down on Sun and Earth Observer’s view “

48. Gods-eye view Observer’s view

50. Group Problem • Form groups of exactly 4 • Optimal configuration is two students in one row and two students in another row No Yes