ASTR 124: Introduction to Stars and Galaxies

1. ASTR 124: Introduction to Stars and Galaxies Instructor: Ryan Lynch

2. Contact Information • Office: 304 Stone Hall (National Radio Astronomy Observatory) • Office Hours: 2:00-3:00 pm, Mon. through Fri. • Email: rsl4v@virginia.edu • Phone: 434.244.6868

3. Important Information • No required textbook • Optional textbook is Foundations of Astronomy, 9th ed. by Michael Seeds • If you have not already done so you MUST buy the student response system clickers • Attendance is required on all exam days • If you know you will miss an exam you must make prior arrangements

4. List of Exam Days

5. Grading Scheme

6. 0 of 5 What building and room are you in? • Chemistry Auditorium • 107 Clark Hall • McCormick Observatory • 265 Astronomy Building

7. Concept Review • Some basic algebra may be needed • This includes solving an equation with one unknown or using logarithms • Metric System • Distance, mass, temperature… • I will assume that you are already familiar with these • I will review logarithms in class

8. Scientific Notation • We will use a good bit of scientific notation • Represents big and small numbers through powers of ten • 5 billion = 5,000,000,000 • This has 9 places after the 5 • In scientific notation, this is 5 x 109

9. Scientific Notation (cont.) • Also use it for small numbers • 0.000634 has 4 places before the 6 • Includes the zero before the decimal place • 0.000634 = 6.34 x 10-4 • Note negative sign in exponent

10. More Examples • What is 654,200,000,000 in scientific notation? • What is 0.05703 in scientific notation?

11. 0 of 5 What is 4.56 x 107 in normal notation? • 4,560,000,000 • 45,600,000 • 0.000000456 • None of the above

12. Concept Review (cont.) • Mass vs. Weight • Mass is a measure of how much matter • Weight is a measure of the force on an object • Mass cannot change unless matter is added or removed • Weight can change if gravity is stronger or weaker

13. Concept Review (cont.) • Vectors consist of both a number and direction • 30 miles a way is just a number • 30 miles West is a vector • Plain numbers are called scalars

14. Concept Review (cont.) • Velocity – change in position over some time • Velocity is a vector!! • Speed – scalar form of velocity…no direction! • Acceleration – change in velocity over time • Acceleration is a vector, too!!

15. Concept Review (cont.) • Forces • Forces are vectors • Can add and subtract • The sum of all forces on some body is called the Net Force

16. Forces (cont.) • Net forces cause acceleration • force equals mass times acceleration • Measured in Newtons (metric) or pounds (imperial)

17. Concept Review (cont.) • Gravity • Very important force • Newton’s law of gravity • Negative because it is always attractive • Decreases as the square of the distance

18. Gravity (cont.) • Everything feels gravity • Self-gravity is the gravitational force an object exerts on itself

19. Concept Review (cont.) • Energy • Non-directional (scalar) • Comes in different forms • The sum of all mass and energy in a system cannot change

20. Concept Review (cont.) • Atoms • Made up of a nucleus (protons and neutrons) surrounded by electrons • Protons have positive charge • Electrons have negative charge • Neutrons have no charge

21. Concept Review (cont.) • Atoms of different elements have different numbers of protons • Ions have too many or too few electrons • Have a charge; can be positive or negative • Ionized means to be an ion • Usually refers to having too few electrons, or positive charge

22. Recognizing and Correcting Misconceptions The Flat Earth Society

23. Misconceptions • One obstacle to learning is our own misconceptions • Sometimes we don’t even know we have them • Must learn to recognize them and why they are mistaken

24. The Flat Earth Society • The Flat Earth Society Home Page • This all seems rather silly to us, but it makes sense to some people • Let’s look at the “evidence”

25. The Flat Earth Society (cont.) • Obvious problems with “evidence” • Many, many experiments confirm no ether • Gravity keeps things on the Earth; pulls towards center, not towards South Pole

26. The Flat Earth Society (cont.) • More problems… • No gravitational charge; always attractive • Centrifugal force from going around the Sun is less than 1/10th of a pound • Grigori Eifimovich was the 19th century Russian, Rasputin, NOT Christopher Columbus

27. Overcoming Misconceptions • Some things we take for granted may not be obvious to others • Often because some one doesn’t/doesn’t want to know

28. The Method of Science • To counter our own misconceptions it is important to know how science works • Facts: Something that is easilyobserved to be true

29. The Method of Science (cont.) • Speculation: Ideas put forward to explain some phenomenon; may not be fully supported or may go beyond current knowledge, but shouldn’t violate things that are already known

30. The Methods of Science (cont.) • Hypothesis: An idea that explains some phenomenon that can be tested and is based on well developed ideas; an educated guess

31. The Methods of Science (cont.) • Theory: An explanation for some phenomenon that has been tested and is consistent with other accepted theories and supporting evidence • Only as good as the experiments that test it

32. The Methods of Science (cont.) • Law: Theories that are very well tested and almost universally accepted • Note that Einstein expanded Newton’s Laws, but did not invalidate them

33. The Methods of Science (cont.) • Science is constantly changing – old theories may be replaced with better ones as new information becomes available

34. Correcting Misconceptions • There are several checks you can do • Self-consistency – Are your ideas in conflict with one another? • General consistency – Are your ideas in conflict with the evidence, or with other good theories? • Common sense – Do your ideas give sensible results when you really think about them?

35. Correcting Misconceptions (cont.) • Of course, to recognize any problems you need knowledge about the subject • What is “common” for one person may not be common for another • Only comes with experience and study

36. Correcting Misconceptions (cont.) • One of the goals of this class is to make science and astronomy more common to you

37. The Scale of the Universe

38. 0 of 5 What best describes the Milky Way? • It is our home solar system • It is our home galaxy • It is our home universe • None of the above

39. The Universe and Everything In It… • Many people hold misconceptions about the terms in the last slide • The solar system is the collection of planets, comets, asteroids, and other small objects orbiting our sun • Astronomers have discovered dozens of other solar systems

40. The Universe and Everything In It… • A galaxy is a collection of stars, planets, dust, and many other forms of matter, held together by gravity • Our galaxy, the Milky Way, is one of many billions

41. The Universe and Everything In It… • The Universe is the whole of everything that we, as scientists, can see • The Universe may in fact be infinite in size

42. How Big is the Universe? • How far apart should we move the Earth and Sun? • How far away is Pluto?

43. How Big is the Universe? • How far away is center of galaxy? • How far away is nearest galaxy? • How far to the most distant objects we can see?

44. How Many Stars… • There are 6 billion people on Earth. How many times more stars are there in the galaxy? • How many stars in the whole universe?

45. 0 of 5 How many universes can we see from Earth? • 300 billion • 1022 • 1 • Infinite • 5

46. Extra Credit Question • Lets say that a star has a radius of 700,000 km, the galaxy is a sphere with a radius of 4 x 1017 km, and there are 300 x 109 stars in our galaxy. If we scaled the galaxy down to the size of the Earth, with a radius of 6,400 km, how big would a star be? What everyday objects are roughly this size? About how much distance separates the stars in this scale model, if they are distributed evenly? Given your answer, do you think it is likely that stars will every collide? Explain.