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Introduction to the Sky

Introduction to the Sky. Capella. Sirius. Aldebaran. Orion. Pleiades. Comet Hale-Bopp. Orion. Mars. Rigel. Betelgeuse. “ Observation ” is not “ Looking ”. “ Observation ” is not “ Looking ”. "You see , Watson, but you do not observe ." --- Sherlock Holmes.

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Introduction to the Sky

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  1. Introduction to the Sky

  2. Capella Sirius Aldebaran Orion Pleiades Comet Hale-Bopp

  3. Orion Mars Rigel Betelgeuse

  4. “Observation” is not “Looking”

  5. “Observation” is not “Looking” "You see, Watson, but you do not observe." --- Sherlock Holmes

  6. “Observation” is not “Looking”Instead: • Study carefully, comprehensively • Remember/record • Try to make connections • Identify systematic features

  7. Motivations for Observing the Sky • Curiosity • Practical applications • Navigation • Time-keeping • Calendar-keeping • Fear, religious belief • E.g. Astrology

  8. Polynesian Navigation

  9. Sky worship/astrology Egyptian Pharoh Akhenaton and family communing with Sun God (ca. 1350 BC)

  10. Astronomical MeasurementsWithout Telescopes • Angles (quantitative) • Sky to Sky • Earth to Sky • Brightnesses (crude) • Colors, Shapes (crude) • Changes in above with time

  11. Isosceles triangle:

  12. Units of Angular Measure

  13. Naked Eye Instruments for Angular Measures 1580 AD 150 BC

  14. Naked Eye Instruments for Angular Measures Limiting accuracy ~ resolution of human eye ~ 1 minute of arc 1580 AD 150 BC

  15. "Hand-y" Angle Measuring (crude but useful for orientation)

  16. 10 degrees 5 degrees Ursa Major (The Big Dipper)

  17. The Magnitude System(a brightness ranking)

  18. Example: Range of magnitudes in Big Dipper

  19. Star Colors (prism-dispersed image)

  20. Puzzlah #9 If you go out at 9 PM on a clear night, turn to the south, and look up at the sky, you will see a certain group of bright stars. How will the location of those stars in the sky change if you come back at midnight or several weeks later? (A) The locations of stars in the sky are always the same (they never change). (B) The locations change during the night but are always the same at a given time of night. (C) The locations change during the night and also change at a given time of night from month to month.

  21. Puzzlah #9 If you go out at 9 PM on a clear night, turn to the south, and look up at the sky, you will see a certain group of bright stars. How will the location of those stars in the sky change if you come back at midnight or several weeks later? (A) The locations of stars in the sky are always the same (they never change). (B) The locations change during the night but are always the same at a given time of night. (C) The locations change during the night and also change at a given time of night from month to month.

  22. Puzzlah #10 During the day, the Sun moves from east to west across the sky. In which direction do the stars move after the Sun has set? (A) The stars are stationary; they don't move (B) West (C) East (D) North (E) South

  23. Puzzlah #10 During the day, the Sun moves from east to west across the sky. In which direction do the stars move after the Sun has set? (A) The stars are stationary; they don't move (B) West (C) East (D) North (E) South

  24. Main Actors in the Sky

  25. STARS Form background "reference frame" About 2000-5000 visible to naked eye over whole sky Patterns of bright stars seem "fixed", unchanging Move "in lockstep" from East to West and return to same position in sky after 23h56m Called the “diurnal motion”

  26. Positions of stars in night sky at given time change systematically during the year

  27. SUN Brightest object (by far!) Scattered sunlight masks stars during day Steady brightness Slow, eastward motion against stars, 1o per day Returns to same position after 365.25 days, or one year.

  28. Lunar Phases MOON Second brightest object in sky (but much fainter than sun) Faster eastward motion against stars, 13o per day Dramatic change in (illuminated) shape or "phase" during cycle Cycle takes 29.5 days to return to same phase. 12 cycles per year Our "month" is based on lunar cycles

  29. Daily motions of Moon are easy to track

  30. Planets 5 brighter starlike objects that move with respect to the stars. Mercury, Venus, Mars, Jupiter, Saturn Merc, Venus always near Sun. Others, up to 180oaway. Motion is slower than Sun, Moon. Generally eastward, but loops to west

  31. "Retrograde Loop" in Mars Motion Eastward

  32. Other Phenomena Visible to Naked Eye } • Meteors • Comets • Star clusters • Diffuse nebulae • Milky Way • External galaxies Transient

  33. Constellations • Constellations are the patterns formed by brighter stars on the sky • Patterns seem fixed (i.e. don't change over years) • Recognized for millenia, by all cultures • Associated with mythological figures, animals, instruments, etc

  34. Stick-Patterns

  35. Official Names

  36. "Classical" figures added

  37. Greek amphora, ca. 400 BC, showing Leo, Aquila, Hercules, etc

  38. Orion, Taurus, Lepus in a classical celestial atlas.

  39. Hevelius, Firmamentum (1690)

  40. Cellarius, HarmoniaMacrocosmica, 1661

  41. More modern constellations Bode, 1801

  42. "Asterism"

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