GE 150 Astronomy

1. GE 150 Astronomy Week #1 January 14,16 2014

2. Science is not just… • A list of previously known facts about nature • A list of equations handed down from Ancient times • A set of laws that were discovered by Dead White Guys a long time ago and are kept from the general public

3. Science Is… • a continuing process that • seeks to understand the rules and laws of nature • uses systematic observations • uses mathematical models • experimentally tests ideas • subject to independent verification These are the components of the scientific method used to comprehend the universe: i.e. observe, theorize, predict, test and modify

4. Ascientific theoryis a collection of ideas that explain a phenomenon in a way that is consistent with laws, observations and experiments.

5. The word “theory” connotes “uncertainty” to laypersons, but this is incorrect usage for scientists. A scientific theory, such as the “Theory of Gravity,” or “Theory of Relativity” is a hypothesis that has been extensively tested and passed all tests (so far) It would be better if scientists said “body of knowledge known as...” instead of “theory of...” But they rarely do, so YOU must interpret!

6. Side Bar: What do we mean by a “Theory” • Not a “guess” but a way to explain and predict results and observations • Must always be tested and verified in light of new information • New observations and experimental results must be explained by existing theories or they need to be modified • The longer they hold up to testing the stronger the theory • All theories are refined over time: This is a strength of theories

7. Watch out! These words are commonly used in English but have a DIFFERENT meaning in science! • Theory • Model • Belief

8. Scientists sometimes say things like “We believe the Earth is round.” They should say, “evidence tells us” but often are lazy. When they say believe, in a scientific sense, they mean believebased on evidence. Who is to blame for muddled terminology? Scientists! Sometimes we’re terrible communicators!

9. What do Astronomers do? • Make observations using telescopes • Analyze data/results of observation • Create theories about what is seen and what might exist yet unseen • Create computer models that simulate what occurs in the Universe • Invent, design, and build instruments that let us see beyond the Earth! BUT, most astronomers do NOT spend much time looking through telescopes

10. How big is stuff? Scale of the Universe

11. The numbers in astronomy are so large (and small) that astronomers use scientific notation. 100 = 1 101 = 10 102 = 100 103 = 1000 5.3 x 103 = 5,300 104 = 10,000 8.9 x 104 = 89,000 and, for small numbers 10-1 = 0.1 10-2 = 0.01 2.1 x 10-2 = 0.021 10-3 = 0.001 6.6 x 10-3 = 0.0066

12. Astronomical distances and sizes are very, very, very, very large. So, astronomers use different units. • One “Astronomical Unit” (AU) average distance between Sun and Earth • 93,000,000 miles • 150,000,000 km • 1.5 x 108 km • Distance Light Travels in One Year is a “Light-year” (LY) • 9.46 x 1012 km • 63,000 AU or 6.3x 104 AU • 0.307 parsecs (pc)

13. 1025 1020 1015 1010 105 http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/

14. planet: a “large” body in orbit around a star • satellite (or moon): typically a smaller body orbiting a planet At the scale of the size of a planet or moon we describe things in terms of kilometers (km)

15. The Sun star: a huge ball of gas (mostly Hydrogen) held together by gravity and generating light through thermonuclear reactions

16. At the scale of the Solar System distances are described in terms of the Astronomical Unit or AU (ave. distance from Earth to the Sun).

17. Few 1000 Light-years – Range of most visible stars At the scale of the Milky Way distances within Galaxy are described in terms of Light-years

18. Getting to Know the Neighborhood • The Universe is “clumpy” – gravity tends to pull galaxies together in clusters of various sizes • Size Hierarchy: • Groups - few million ly • Clusters – 100s million ly • Super Clusters – billion ly • The Universe – 13.7 billion ly Central region of the Virgo Cluster

19. Thousands of km Astronomical Unit A few to about 1,000 Light-years 10,000 to 100,000 Light-years Millions of Light-years Billions of Light-years

20. 1 day – Speed more than 1000 km/hr 1 Year – Speed more than 100,000 km/hr Speed more than 70,000 km/hr 230 Million Years to orbit – Speed about 800,000 km/hr Within the Group 300,000 km/hr Speed of clusters increases with distance

21. 1025 1020 1015 1010 105 100 10-5 http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/ 10-10 10-15

22. The Small Stuff Matter & The 4 Fundamental Forces of Nature

23. Matter - Atoms Basic building block of nature 92 naturally occurring elements Currently 20-26 more can be manufactured

24. Structure of an Atom – Not to scale! New quantum view old “solar system” view

25. Four Fundamental Forces • Electromagnetism • Strong Nuclear Force • Weak Nuclear Force • Gravity

26. Fundamental Forces in Nature Graviton ignore

27. Fundamental Forces in Nature • Electromagnetic (EM) Force • Combination of Electricity and Magnetism • Moving charges can generate a magnetic field • Example: radio interference • Moving magnets generate electricity • Examples: car’s alternator, turbines at power plant • Force that holds atoms & molecules together • Force generates light (photons)

28. Fundamental Forces in Nature • Strong Nuclear Force • Holds protons & neutrons together in nucleus of an atom • 100 times stronger than the repulsion between 2 Protons! • Very short range – only works in an atom’s nucleus!

29. Fundamental Forces in Nature • Weak Nuclear Force • Force responsible for radioactive decay • i.e. responsible for changing one subatomic particle into another

30. Fundamental Forces in Nature • Gravitational Force • Force between massive bodies • Always attractive – no “repulsive” gravity • Weakest but the dominant force in the Universe

31. Basic Observations The Night Sky

32. What do you think? • Do the stars stay in the same position in the sky all day/night long? • Do we see the same stars all year round, every night?

33. What do you think? • What causes the stars move? • Do the stars actually move in the way they appear from Earth? • Is the daily motion of the Sun different from the stars?

34. Constellations 88 internationally recognized constellations by International Astronomical Union (IAU) Asterisms: popular patterns but are not “official” constellations Big Dipper Little Dipper The Teapot Summer Triangle The Sickle Constellations Vs Asterisms

35. Consider the dome of the sky over our heads…. inverted mixing bowl ….

36. Imagining a spinning Celestial Sphere surrounding Earth aids in thinking about the position and motion of the sky

38. The View from Space Celestial Coordinates • Longitude  Right Ascension • Latitude  Declination

39. Horizon Coordinates Altitude = High Azimuth = SE Nadir

40. Celestial Sphere Rotation Celestial Sphere Rotation Star B Star B 2 2 Star A Star A 1 2 2 1 North Star Celestial Sphere Celestial Sphere 3 3 1 1 4 4 3 3 Horizon Earth’s Equator 4 4 Celestial Sphere Rotation Celestial Sphere Rotation Figure 1 Figure 2 Where would we label the directions North, South, East, West on the horizon in Figure 2?