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Daytime Observing: Sun, Noon, South

Daytime Observing: Sun, Noon, South. Starry Monday. On Monday, Science 237 7pm lecture “The Planets” 8pm rooftop observing Show up for either to get 2% credit. Sun Measurement - 01. We measured at 11:30 am on Jan 29, 2014 Length of the shadow of a meter stick was 1.72m

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Daytime Observing: Sun, Noon, South

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  1. Daytime Observing: Sun, Noon, South

  2. Starry Monday • On Monday, Science 237 • 7pm lecture “The Planets” • 8pm rooftop observing • Show up for either to get 2% credit

  3. Sun Measurement - 01 • We measured at 11:30 am on Jan 29, 2014 • Length of the shadow of a meter stick was 1.72m • Trigonometry: 30.2 degrees (sig figs!)

  4. Sun Measurement - 02 • We measured at 2:00 pm on Jan 29, 2014 • Length of the shadow of a meter stick was 1.69m • Trigonometry: 30.6 degrees (sig figs!)

  5. Is this good or bad or what? • Compare to expected value: • Westerville location 40° N latitude • Celestial equator 90° off of that • “that” being North AND 40° above horizon • Sun’s celestial (not observer!) coordinates on January 29: -18°, i.e. south of Celestial Equator (see YourSky) • So: 40° + 90 °+18 ° = 148° above N horizon = 32° above S horizon

  6. Define Noon • I.e. agree on the word “noon” meaning (being equivalent to) “time when the sun reaches the highest altitude in the observer’s sky” • Note that this time is • different when you are further east or west • the same when you are further north or south • Note that the sun culminates in the North in the southern hemisphere!

  7. Define South • Either opposite of direction to the North Star • Or: direction in which the sun culminates

  8. Why are Polaris and the Sun in opposite directions? • They are not exactly, because “the north direction” and “the south direction” do not exist • Their positions are related because • the direction of Polaris defines the rotation axis of the celestial sphere • The sun is somewhere on the sphere • From a “skewed” perspective everything on the sphere culminates on the meridian

  9. Reminder: Observer Coordinates • Horizon – the plane you stand on • Zenith– the point right above you • Meridian – the line from North to Zenith to south

  10. What you see depends on where you are! • Your local sky – your view depends on your location on earth

  11. Constellation 1: Orion “the Hunter” Bright Stars: D) Betelgeuze E) Rigel Deep Sky Object: i) Orion Nebula

  12. Constellation 2: Gemini “the Twins” zodiacal sign Brightest Stars: I) Castor J=K) Pollux

  13. Constellation 3: Taurus “the Bull” zodiacal sign Brightest Star: F) Aldebaran Deep Sky Object: iii) Plejades

  14. Constellation 4: Ursa Major Other name: Big Dipper Stars: B) Dubhe C) Merak Navigation: go 5 times the distance from Merak to Dubhe and you are at Polaris.

  15. Constellation 5: Ursa Minor Other name: LittleDipper α Ursa Minoris is Polaris [A], the pole star

  16. Constellation 6: Canis Major “Big Dog” Stars: H) Sirius (brightest fixed star)

  17. Constellation 7: Cancer “Crab” No bright Stars

  18. Constellation 8: Leo “the Lion” zodiacal sign Brightest Star: G) Regulus

  19. Constellation 9: Cassiopeia Greek mythological figure: mother of Andromeda the big “W” in the sky No bright stars

  20. Constellation 10: Pisces “the Fishes” Zodiacal sign No bright stars

  21. Constellation 11: Pegasus Greek mythological figure: the winged horse big rectangle in the sky No bright stars

  22. Constellation 12: Andromeda Greek mythological figure: Daughter of Queen Cassiopeia and King Cepheus rescued from Cetus by Perseus Deep Sky Object: Andromeda Galaxy

  23. Position: Angles vs. Distances • Locations in the sky are easy to measure: 2 angles • Distances from observer are hard (one length)  Together they give the location of an object in three-dimensional space

  24. Angles and Angular Size Angles measured in degrees full circle = 360; right angle = 90 1 = 60' (minutes of arc or arc minutes) 1' = 60" (seconds of arc or arc seconds) Typical angular sizes: Moon 0.5, Sun 0.5,Jupiter 20”, Betelgeuse (α Ori) 0.05”

  25. The Trouble with Angles Angular size of an object cannot tell us its actual size – depends on how far away it is Sun and Moon have very nearly the same angular size (30' = ½) when viewed from Earth

  26. Without Distances … • We do not know the size of an object • This makes it hard to figure out the “inner workings” of an object • We can’t picture the structure of the solar system, galaxy, cosmos

  27. The most important measurement in Astronomy: Distance! • The distances are astronomical! • The distance scales are very different • Solar system: light minutes • Stars: light years • Galaxies: 100,000 ly • Universe: billions of ly • Need different “yardsticks”

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