Patterns in the Sky & Constellations

1. Patterns in the Sky & Constellations

2. WebAssign, etc. • Course Homepage: http://faculty.otterbein.edu/UTrittmann/IS2403-02/index.htm • Username: first initial plus last name, no space • Uwe Trittmann  utrittmann • HW #1 due Friday 8pm

3. Review Sun’s Shadow and Position • Tangent = ratio of 2 sides of triangle • Sun is never overhead in Westerville

4. What is Astronomy? • The science dealing with all the celestial bodies in the Universe • Cosmology is the branch of astronomy that deals with the cosmos, or Universe as a whole • The medieval list of the Liberal Arts: grammar, rhetoric, logic (trivium); arithmetic, music, geometry and astronomy (quadrivium) • Is an “exact science” for ~5000 yrs • Most rapid advancements in astronomy have occurred during the Renaissance and the 20th century • Success has been a result of development and exploitation of the scientific method

5. Astronomy and Culture • Astronomy had and has an enormous influence on human culture and the way we organize our lives • For example: • The year is the rotation period of the Earth around the Sun • The year is subdivided into months, the period of the Moon around the Earth • The weeks seven days are named after the seven bodies in the solar system known in antiquity: Sunday, Monday, Saturday (obv.), Tuesday=Mardi, Wednesday = Mercredi, Thursday=Jeudi, Friday=Vendredi

6. Our vantage point: Earth

8. Basic Observations in Astronomy • We see (on clear days!): • A very bright disk that is up about 12 hours. It comes up in a specific direction, rises higher until it reaches a maximal altitude in a second direction, then sinks lower until disappearing in a direction opposite of the direction where is came up • A less bright object that changes its appearance and is also up for a (different) duration of 12 hours. Same rise/set pattern as very bright object. • When the very bright disk is not visible, we see many tiny specs of light of different brightness and color

9. Basic Observations in Astronomy • We see further: • The tiny specs move across the sky as the hours go by. One group moves across the sky in 12 hours. Same rise/set pattern as bright object. • The position of the specs wrt other specs is fixed, but they move wrt to the ground • Careful observation reveals a handful of exceptions from this rule: • some bright specs move slowly wrt to the other fixed specs, and also are visible 12 hours. Same rise/set pattern as bright object. • One spec sits at the center of this motion and does not move

10. Conventions • These patterns repeat every day, let’s name them • Sun • East, South, West • Moon • Daytime + Nighttime = Day (needs to be revisited later!) • Planets • Polaris, the North Star

11. More names, now that we’ve seen Observer Coordinates • Horizon – the plane you stand on • Zenith– the point right above you • Meridian – the line from North to Zenith to south

12. Hypothesis • During a day, it looks like all “lights in the sky” travel around us, like the are fixed to an (invisible) sphere that turns around us. • Call it The Celestial Sphere

13. Further Observation • If we move to a new observing place on Earth, the pattern remains the same (bright light rises & sets, etc.), but: • Position of North Star changes • Maximal altitude of Sun, special stars changes

14. Conclusion: Earth’s coordinates projected onto Sky The Celestial Sphere • An imaginary sphere surrounding the earth, on which we picture the stars attached • Axis through earth’s north and south pole goes through celestial north and south pole • Earth’s equator  Celestial equator

15. Celestial Coordinates Earth:latitude, longitude Sky: • declination (dec) [from equator,+/-90°] • right ascension (RA) [from vernal equinox, 0-24h; 6h=90°] Examples: • Westerville, OH 40.1°N, 88°W • Betelgeuse (α Orionis) dec = 7° 24’RA = 5h 52m

16. Confusing! Let’s go with Patterns in the Sky! • We can group specs of light together to form triangles, squares, etc. • This allows us to find them the next night and follow their motion • Talk to other observers, and give them names: Bear, Bull, Lion, Hunter, Queen, etc.  The Constellations

17. Constellations of Stars About 5000 stars visible with naked eye About 3500 of them from the northern hemisphere Stars that appear to be close are grouped together into constellations since antiquity Officially 88 constellations (with strict boundaries for classification of objects) Names range from mythological (Perseus, Cassiopeia) to technical (Air Pump, Compass)

18. Constellation 1: Orion Orion as seen at night Orion as imagined by men

19. Orion “from the side” Stars in a constellation are not connected in any real way; they aren’t even close together!

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

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

22. 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!

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

24. 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

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

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

27. Look North in Westerville

28. Look North on Hawai’i

29. Pete at the Pole

30. 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

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

32. 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!)

33. 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!)

34. 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