Patterns in the Sky & Constellations

Transcription

1 Patterns in the Sky & Constellations

2 Daily Homework & Warm-Ups Before class (8am): answer warm-up questions online about reading for the day ls/warmupdb/astronomy_section_1 After Class: use WebAssign, an online homework system daily! Password & username: first initial plus last name all lowercase, e.g. utrittmann Course Homepage from my homepage

3 Some of Today s Warm-Up Answers What is a constellation? S. One: A constellation is a pattern formed by a collection of stars. Most often they are named after the shape they make up or a figure in Greek mythology. Why is the Celestial North Pole directly "above" the earth's (geographic) north pole? Thad Guy: The celestial north pole is an extension of the Earth's geographic north pole and therefore always lies directly above it.

4 Peer Instruction: How it works Peer instruction is learning by instructing your fellow students and being instructed by them The process involves 6 steps: Mini-lecture by course instructor Conceptual multiple-choice question is put up Flash-cards are used to poll the audience A few minutes of discussion between students Final answer via flash-cards The instructor explains the correct answer

5 Who was the first man on the Moon? Yuri Gagarin Buzz Aldrin Neil Armstrong John Glenn

6 Concept Questions Concept questions maybe easy to answer, but are not simple You need background knowledge to answer them They teach you how to use facts and knowledge to find the answer to a problem They test if you got the concept rather than just knowing facts

7 It is New Moon. In one week, what will the phase of the Moon be? New Moon First Quarter Moon Full Moon Last Quarter Moon

8 Why it works Carefully chosen questions It is easier to be convinced and to convince if the reasoning is sound and hence the answer correct How answers are revised in a typical question Right to right Wrong to right Right to wrong No 2 nd answer wrong to wrong

9 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 20 th century Success has been a result of development and exploitation of the scientific method

10 Why study Astronomy? Practical reasons: seasons, tides, navigation, space technology, satellite communication Idealistic reasons: cosmological questions ( Where do we come from? ), aesthetics, curiosity Two things fill the mind with ever new and increasing admiration and reverence, the more frequently and enduringly the reasoning mind is occupied with them: the star spangled sky over me and the moral law in me. (I. Kant)

11 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

12 Our vantage point: Earth

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14 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

15 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

16 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

17 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

18 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

19 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

20 Conclusion: Earth s coordinates 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 projected onto Sky

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

22 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

23 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)

24 Constellation 1: Orion Orion as seen at night Orion as imagined by men

25 Orion from the side Stars in a constellation are not connected in any real way; they aren t even close together!

26 the Hunter Constellation 1: Orion Bright Stars: D) Betelgeuze E) Rigel Deep Sky Object: i) Orion Nebula

27 Constellation: Gemini the Twins zodiacal sign Brightest Stars: I) Castor J=K) Pollux