Lecture 4

1. Lecture 4 ASTR 111 – Section 002

2. Note • I’ll post all slides after class

3. Terms While you are waiting for class to start, try to define these terms • Apogee/Perigee • Subtend • Parsec, light-year, AU • Parallax • Solar and Sidereal time • Small angle formula

4. Terms While you are waiting for class to start, try to define these terms • Ecliptic • Zenith • Tropic of Cancer, Capricorn, Artic and Antarctic Circle • Equinox, Solstice • Zodiac • Accuracy, Precision, and Bias

5. Tuesday September 15th • Class is canceled. • Quiz is still due at 9 am on the 15th. • I will be available via email.

6. First Exam • On 9/29 • Based on lecture notes, problems worked in lecture, and quizzes. • Approximately 50 questions • In the Testing and Tutoring Center (using Blackboard system) • Typically 25 minutes to complete

7. Outline • Quiz Discussion • Rotation – review generally • The Seasons – review generally • The Moon in its orbit • Math review

8. Quiz (“homework”) Discussion

9. Bias Many types. Two common ones are: • Measurement bias or just “bias” • Selection bias

10. Measurement Bias True value (measured using good instrument) Bias – measurements are not centered on true value. (Usually due to mis-calibration of an instrument.)

11. Measurement Bias True value (measured using tape measure) 9 ft 10 ft 11 ft Bias – measurements are not centered on true value. (Usually due to mis-calibration of an instrument.)

12. Questions • Most of the lectures were very clear but the quarter exercise on thursday was a little unclear and confusing to me. • I was a little confused on Thursday's about Accuracy Vs. Precision. I understand what they mean, but when we were in groups and answering the questions I was a little confused. When we had to draw low precision and high bias I got confused. • Astronomical distance. The concept is a little hard to grasp and the numbers are so large which only aides confusion. • The most unclear pat of the lecture on Thursday was the concept of angular seperation. • Apogee and Perigee in means of degrees • Occasionally you misunderstand a question that a student asks and answer with a completely unrelated explanation. I can usually identify what you thought the question was and what you're explaining but I feel like most students are often confused. • When we discussed bias in terms of practical examples as opposed to the bullseye. • Accuracy Bias and Precision • I felt that the most unclear part of Lecture 2 was the measurement of Parallax. I understand the overall concept but not how to measure it. • I would say that the most confusing part was the group question, where we had to measure our distance from the board using the "hand rule." • The most unclear part of the lecture was what we as students are required to do outside of class. As in are the tests and quizzes based mostly off the lectures, or research we do in the textbook outside of class?

13. Questions • The few slides having to do with measurement (e.g., car hours, etc.) --- what was a little unclear was how it related back to astronomy. • explanation of angular measurement • The most unclear part was the difference between bias and accuracy. • Parsec's and the bias portion of the lecture on thrusday. • Some of the questions on the group projects • how to solve the apogee vs perigee problems • The only hazy part of the lectures was on Thursday. You gave an example about parallax using a before and after picture, I wasn't sure if the second picture was taken further left or right. • The most unclear part of the lecture was the group exercise involving the lines being drawn. I understand the counterclockwise movement of the earth but I was unsure on whether both stars moved to the left or if only one of the stars did. • Learning how to calculate angular measurements. • Learning about angular distances and their equations, went a little to fast. • Some of the stuff about arc minutes and seconds maybe? • some of the vocabulary was not clearly defined (or defined too quickly), and it made some things confusing • For me, the most unclear part was the angles and arcminutes. I know how to calculate arcminutes, it's just that I don't really understand what it's purpose is. • Using your hand as a way to measure angles was a little bit unclear. • The most unclear part of the lectue on Thursday was the small angle formula • The most unclear part of the lecture on Tuesday was the instructors view on attendence. • I was unclear about parallax and on question 6 of the group work at the end of thursday's lecture. • Nearby stars and distant stars from earth in January and earth in July. • The explanation on how the hands were used to measure degrees was a bit fuzzy. 

14. “All of the students said something was not clear. Therefore the lecture was not clear to the average student.”

15. “All of the students said something was not clear. Therefore the lecture was not clear to the average student.” Wrong – the sample of responses he showed was bias; he did not show the responses That said “everything was clear”.

16. Selection bias Bias – measurements are not centered on true value Something not clear responses Everything clear responses Average response Selection Bias – Average of selected measurements are not centered on true value

17. Outline • Quiz Discussion • Rotation – review generally • The Seasons – review generally • The Moon in its orbit • Math Review – converting units and scientific notation

18. View of classroom from above Someone in back of room (distant object) Stage Student Instructor

19. Sidereal Time = star time Solar Time = sun time At 1, line points at sun and distant star Line 1 goes through sun and distant star

20. At 2, 24 sidereal hours since 1, line is now pointing at distant star only • Sidereal Time = star time • Solar Time = sun time Line 1 goes through sun and distant star At 1, line points at sun and distant star Line 1 goes through sun and distant star

21. At 2, 24 sidereal hours since 1, line is now pointing at distant star only • Sidereal Time = star time • Solar Time = sun time • Which is longer? • Sidereal day • Solar day At 1, line points at sun and distant star At 3, 24 solar hours since 1, line points at sun only

22. At 2, 24 sidereal hours since 1, line is now pointing at distant star only • Sidereal Time = star time • Solar Time = sun time • Which is longer? • Sidereal day • Solar day by ~ 4 min. At 1, line points at sun and distant star At 3, 24 solar hours since 1, line points at sun only

23. Where is Cygnus 24 solar hours later? • West • East • Vertical • West • East • Vertical

24. Where is Cygnus 24 solar hours later? • West • East • Vertical (Over the Pacific Ocean) A solar day is longer than a sidereal day. After sidereal day Cygnus is overhead. To get to a solar day, continue rotating for 4 minutes.

25. The two black lines represent poles stuck into the ground vertically (or along zenith) that extend out into space. Draw these lines and Earth after 24 solar hours have elapsed Cygnus

26. After 24 sidereal hours, pole is not quite aligned with sun The two black lines represent poles stuck into the ground vertically (or along zenith) that extend out into space. After 24 sidereal hours, pole is aligned with Cygnus again Cygnus

27. After 24 solar hours, pole is aligned with sun again The two black lines represent poles stuck into the ground vertically (or along zenith) that extend out into space. Draw these lines and Earth after 24 solar hours have elapsed After 24 solar hours, pole has already passed Cygnus Cygnus

28. Outline • Quiz Discussion • Rotation – review generally • The Seasons – review generally • The Moon in its orbit • Math Review – converting units and scientific notation

29. What causes the seasons? • Distance of the sun from earth • Tilt of Earth with respect to the ecliptic • Both 1. & 2. • None of the above • Primarily 2., but with a small contribution from 1.

31. That’s a Lie!

32. What causes the seasons? • Tilt of Earth with respect to the ecliptic which causes • Change in length of time sun is visible • Change in height of sun in sky • Change in distance to sun from observer in northern and southern hemispheres (true, but does not cause seasons!)

35. From http://www.dslreports.com/forum/remark,16822681 • Uses color saturation http://en.wikipedia.org/wiki/Saturation_(color_theory) The Moon in its orbit

37. Eventually we want to be able to explain …

38. A simple model • Moon executes circular orbit • Moon orbit is in Earth’s ecliptic plane

40. What is wrong with this picture?

41. Looking down on North Pole Can you “see” white ball if you are at Equator?

42. Looking down on North Pole NO! You would need to see through Earth! Can you “see” white ball if you are at Equator?

43. Looking down on North Pole If you walk around along the equator, where will you be able to see the white ball?

44. Looking down on North Pole NO! Can you “see” white ball if you are at Equator? NO! You would need to see through Earth!

45. Looking down on North Pole Can you “see” white ball if you are at Equator? NO! You would need to see through Earth! NO!

46. Looking down on North Pole Yes! Can you “see” white ball if you are at Equator? NO! You would need to see through Earth! Yes!

47. Looking down on North Pole Closer to scale

48. Draw a diagram that explains when you will first be able to see the first quarter moon if you live on the equator. • Stated another way, at what time will you see the 1st quarter moon rise from Earth?

49. Sun is to the right. 1st quarter moon is first visible at noon.

50. Fill in the dark and light parts of the Moon for A-D (from this perspective) • From the perspective of someone on Earth what position of A-E best fits the Moon view in the lower-left-hand corner? • In the blank boxes below, sketch how the Moon would appear from Earth from the four Moon positions that you did not choose for Question 2. Label each box with a letter. A E Sun’s rays Earth D B C View of Moon from Earth at one of the positions (A-E) above.