Daytime Observing: Sun, Noon, South

1. Daytime Observing: Sun, Noon, South

2. 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

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

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

5. Look North in Westerville

6. Look North on Hawai’i

7. Pete at the Pole

8. You’re stranded on a desert island. You locate the pole star. It is 17 degrees above the northern horizon. What is your latitude? • 73 degrees south • 17 degrees north • Depends on the time of the day • Depends on the time in the year

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

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

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

12. 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.

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

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

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

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

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

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

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

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

21. 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

22. 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”

23. 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

24. Angles and Size

25. 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

26. 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”

27. Activity: Angles • See also iSkylab Manual, Moon Option