Lecture 2: Discovering the Universe for Yourself: The Basics of Astronomy

1. Slide: Welcome:, but I'm still not Prof. Rebecca Martin. I just have her slides which are the same as those of Prof. Stephen Lepp---who I also am not. I'm Prof. David Jeffery. Just call me David---one, two, three, "David". I'll be substituting for Prof. Lepp who is unavailable this week for lectures---but he's still running the course via Canvas.
2. Slide: What does the universe look like from the Earth:
   1. Wikipedia: Naked eye: In astronomy: "Theoretically, in a typical dark sky, the dark adapted human eye would see the about 5,600 stars brighter than +6m (fiducial human limit) while in perfect dark sky conditions about 45,000 stars brighter than +8m (maybe extreme human limit) might be visible." (Slightly edited.) These numbers are NOT for all at once.
   2. File: Galaxies file: milky_way_death_valley.html.
3. Slide: Constellations:
   1. File: Sky map files: sky_map_all_sky.html. All the official IAU 88 constellations which tile the whole sky without overlap. The constellation stars are just relatively random groupings of stars on a patch of the sky in which someone---with a lot of imagination---once decided looked like something or maybe not even that when giving a name.
4. Slide: Thought Question: The brightest stars in a constellation:
5. Slide: Thought Question:: Answer.
   1. Nix.
6. Slide: The Celestial Sphere I:
   1. The celestial sphere is an imaginary sphere centered on the Earth on which we project all astronomical objects for location purposes.
7. Slide: The Celestial Sphere II: Rotation of.
   1. The celestial sphere rotates on the celestial axis once per sidereal day = 86164.0905 s = 1 day - 4 m + 4.0905 s (on average) which is a bit shorter than the solar day = current mean value 86400.002 s which varies down by ∼ -18.1 s and up by 29.9 s (see Wikipedia: Solar time: Apparent solar time).
8. Slide: The Celestial Sphere III: The north celestial pole (NCP).
   1. Nix.
9. Slide: The Celestial Sphere IV: The south celestial pole (SCP).
   1. Nix.
10. Slide: The Celestial Sphere V: The celestial equator.
    1. Nix.
11. Slide: The Celestial Sphere VI : The ecliptic.
    1. In astronomy, apparent means as seen from the Earth.
    2. The Earth orbits the Sun relative to the observable universe---and this we consider an absolute rotation. But geometricallly, you can take either to orbit the other and we do use both points of view as convenient.
    3. File: Celestial Sphere file: celestial_sphere_videos.html.
12. Slide: The Milky Way I:
    1. File: Sky map files: sky_map_all_sky.html. The all-sky sky map shows the Milky Way as a band on the celestial sphere.
13. Slide: The Milky Way II:
    1. File: Galaxies file: milky_way_local.html.
    2. File: Galaxies file: milky_way_map.html.
14. Slide: The Milky Way III:
    1. Nix.
15. Slide: The Local Sky I: zenith.
    1. nadir.
16. Slide: The Local Sky II: The horizon.
    1. Nix.
17. Slide: The Local Sky III: The meridian.
    1. Nix.
18. Slide: The Local Sky IV: altitude and azimuth.
    1. Nix.
19. Slide: Question: The meridian is:
    1. Nix.
20. Slide: Question Answer: The great circle that runs from that passes through due north, zenith, due south, and nadir.
    1. Nix.
21. Slide: Question: All of the following are points on your local sky. Which one does not move on the celestial sphere in the course of a day?
    1. Nix.
22. Slide: Question Answer:
    1. Nix.
23. Slide: We measure the sky using angles I:
    1. Nix.
24. Slide: We measure the sky using angles II:
    1. Nix.
25. Slide: Angular Measurements: degree, arcminute ('), arcsecond ('').
    1. Nix.
26. Slide: Angular Size:
    1. Nix.
27. Slide: Thought Question:
    1. Nix.
28. Slide: Thought Question Answer:
    1. Nix.
29. Slide: Why do stars rise and set:
    1. Nix.
30. Slide: Our view from the Earth I: circumpolar stars always above the horizon.
    1. Nix.
31. Slide: Our view from the Earth II: circumpolar stars always below the horizon.
    1. Nix.
32. Slide: Our view from the Earth III: Rising and setting stars, etc.
    1. Nix.
33. Slide: Thought Question: What is the arrow pointing to in the sky?
    1. Nix.
34. Slide: Though Question Answer: The NCP (if star trails run clockwise) or the SCP (if star trails run counterclockwise). But only the NCP is an allowed answer.
    1. Delicate Arch, Arches National Park, Utah.
35. Slide: Review: Coordinates on the Earth: geographic coordinates: (i.e., latitude and longitude).
    1. Nix.
36. Slide: The sky varies with latitude, but not with longitude: Well yes and yes and no. Certainly, the sky you see varies with longitude and time of day.
    1. Nix.
37. Slide: Altitude of the NCP and the SCP:
    1. File: Celestial sphere file: declination_altitude.html.
38. Slide: Thought Question:
    1. Nix.
39. Slide: Thought Question Answer:
    1. Nix.
40. Slide: The sky varies as the Earth orbits the Sun:
    1. zodiac.
    2. zodiac constellations.
41. Slide: Summary: Why do the constellations we see depend on latitude and time of year:
    1. Nix.
42. Slide: Thought Question: The reason for the seasons:
    1. Nix.
43. Slide: Thought Question Answer: The reason for the seasons:
    1. Nix.
44. Slide: What causes the seasons:
    1. File: Earth file: earth_seasons_animation.html.html.
45. Slide: The Sun's altitude also changes with the seasons: This is a funny image since the Sun at solar noon should be aligned with gnomon (i.e., blade) London sundial aside from small variations due to small variations of ≤ 30 s in the solar day (see Wikipedia: Day: Apparent and mean solar day).
    1. Nix.
46. Slide: How do we mark the progression of the seasons:
    1. Nix.
47. Slide: summer solstice:
    1. Nix.
48. Slide: winter solstice:
    1. Nix.
49. Slide: vernal equinox:
    1. Nix.
50. Slide: fall equinox:
    1. Nix.
51. Slide: We can recognized the solstices and equinoxes by the Sun's path across the sky: Note that on equinox days two great circles (celestial equator where the Sun is on an equinox and horizon) intersect, and so day and night are equally long (12 hours) everywhere on Earth---except sort at the Earth's poles which are at perpetual sunrise / sunset.
    1. Nix.
52. Slide: Seasonal changes are more extreme at high latitudes:
    1. Nix.
53. Slide: How does the orientiation of the Earth's axis change with time? The axial precession.
    1. File: Celestial sphere file: axial_precession_animation.html.
       
54. Slide: Phases of the Moon I: Full Moon:
    1. Nix.
55. Slide: Phases of the Moon II: Phase diagram:
    1. File: Moon file: moon_lunar_phases_animation.html.
56. Slide: Phases of the Moon III: Phase diagram with rising times:
    1. Nix.
57. Slide: Phases of the Moon IV: Phase diagram with rising and setting times:
    1. Nix.
58. Slide: What causes eclipses?
    1. Nix.
59. Slide: Lunar Eclipses: Which are solar eclipses seen on the Moon.
    1. Nix.
60. Slide: Solar Eclipses I:
    1. Nix.
61. Slide: Solar Eclipses II: total solar eclipses.
    1. Nix.
62. Slide: Solar Eclipses III: total solar eclipse, totality, photosphere, solar corona, diamond ring effect.
    1. Nix.
63. Slide: Why don't we have an eclipse at every new and full moon?
    1. File: Eclipse file: eclipse_season.html.
64. Slide: solar eclipse paths:
    1. Nix.
65. Slide: Question: Lunar eclipses do not occur every lunar month because:
    1. Nix.
66. Slide: Question Answer:
    1. Nix.
67. Slide: Summary: Two conditions must be met to have an eclipse:
    1. Nix.