3 Units of the Introduction The “Obvious” ViewEarth’s Orbital MotionThe Motion of the MoonThe Measurement of DistanceScientific Theory and the Scientific Method
4 What is Astronomy and how do we use the celestial sphere to study space?
5 What is Astronomy? Astronomy: study of the universe Universe Totality of all space, time, matter and energySolar system, stars, galaxies, astrobiology, etcActual science (physical)observations, data, facts
6 What is Astronomy?Astrology: study of the movements and relative positions of celestial bodies and their supposed influence on human affairshoroscopes, lunatics….
7 THE BIGGEST STARS IN THE UNIVERSE VIDEO E.1 The “Obvious” ViewEarth is average – we don’t occupy any special place in the universeScales are very large: measure in light-years, the distance light travels in a year – about 10 trillion milesTHE BIGGEST STARS IN THE UNIVERSE VIDEO
8 Celestial Sphere Ancients used to think stars moved around Earth Stars’ apparent motion is due to Earth’s rotation on axisAxis intersection points:-North Celestial Pole-South Celestial Pole-Midway = Celestial Equator
9 Celestial Sphere-Stars seem to be on the inner surface of a sphere surrounding the Earth-They aren’t!!-Use two-dimensional spherical coordinates (similar to latitude and longitude) to locate sky objects
10 E.1 Celestial Coordinates Declination:degrees north or south of celestial equator (similar to latitude)Celestial Equator = 0° (0-90)Above CE = +X°; below CE = -X°
11 E.1 Celestial Coordinates Right ascension (RA):measured in hours, minutes, and seconds eastward from position of Sun at vernal equinox (similar to longitude; east-west)
12 E.1 Celestial Coordinates Right ascension:Starting Line (0) = line from North star to Sun on the vernal equinox (March 21)Maximum RA= 24 hrs
13 How does the Earth’s orbital motion cause changes on Earth?
14 Revolution vs. Rotation Revolution: time it takes to orbit around an objectEXAMPLEEarth year: 365 ¼ days around the sun (counterclockwise)Moon: ~27 1/3 days around Earth (cc)
15 Revolution vs. Rotation Rotation: time it takes to complete a turn on its own axisEXAMPLEEarth day: 24 hours (counterclockwise)Moon: ~27 1/3 days (cc)
16 Synchronous Rotation Rotation time = Revolution time Always see same side of the moon!
17 E.2 Earth’s Orbital Motion Solar day-Daily cycle, noon to noon, is diurnal motion24 hoursSidereal day –Time it takes the stars to be in the exact same location23 hrs 56 min“sidus”= star
18 E.2 Earth’s Orbital Motion Ecliptic is plane of Earth’s path around Sunat 23.5° to celestial equator
19 E.2 Earth’s Orbital Motion Northernmost point (above celestial equator) is summer solsticeSouthernmost is winter solsticePoints where path cross celestial equator are vernal and autumnal equinoxes
22 E.2 Earth’s Orbital Motion Summer solsticelongest amount of daylight of yearusually June 21first day of summerWinter solsticeshortest amount of daylight of yearusually Dec. 21 or 22first day of winter
23 E.2 Earth’s Orbital Motion Vernal equinoxequal amount of daylight and darkusually March 20 or 21first day of springAutumnal equinoxusually Septfirst day of fall
24 E.2 Earth’s Orbital Motion Seasons are caused by:Combination of day length and sunlight angle due to axis TILTNot distance from sunPerihelion- January 3Aphelion- July 4
25 E.2 Earth’s Orbital Motion Tropical year (Our calendar)Time from one vernal equinox to the nextFollows seasonsSidereal yearTime for Earth to orbit once around Sun, relative to fixed starsFollows constellationsIn 13,000 years July and August will still be summer, but Orion will be a summer constellation
26 Watch the changing seasons Notice it is harder to tell in Southern Hemi. Because not as much land
27 E.2 Earth’s Orbital Motion Precession: rotation of Earth’s axis itself; makes one complete circle in about 26,000 years (like a top)
28 Essential QuestionHow does the motion of the moon cause us to see different phases and different types of eclipses?animated GIF created by Antonio Cidadao
30 E.3 Motion of the MoonHalf of moon’s surface is ALWAYS illuminated by the sun!!!Wax-growRight edgeWane-shrinkLeft edge
31 Lunar Phases Motion of the Moon animated GIF created by Antonio Cidadao
32 E.3 Motion of the Moon Synodic month 29.5 days to go through whole cycle of phasesPhases -different amounts of sunlit portion being visible from EarthSidereal monthTime to make full 360° around Earth (orbital time)27.3 days
33 Moon Features Natural Satellite Gravity causes tides Maria Most obvious darkened areasCratersCircular, bowl shaped holesFormed by impacts long agoNo erosion forcesAtmosphere, water, wind
35 Motion of the Moon Eclipse: When the sun or moon is blocked to an observer on Earth for a short period of time (minutes or hours)Caused by shadows of Earth or MoonUmbra- darkest part of the shadowPenumbra- lightest part of the shadowLunar eclipse:Moon is blockedSolar eclipse:Sun is blocked
36 Motion of the Moon Lunar eclipse: Earth is between Moon and Sun Only occurs during full moon phase
37 When the Earth’s shadow covers the Moon, we have a lunar eclipse
39 3 types of Lunar Eclipses PenumbralPartialTotal
40 3 types of Lunar Eclipses Penumbral lunar eclipsethe Moon only passes through the penumbra of Earth’s shadow
41 3 types of Lunar Eclipses Partial lunar eclipsepart of the Moon passes through the umbra of Earth’s shadow
42 3 types of Lunar Eclipses Total lunar eclipsethe entire Moon passes through the umbra of Earth’s shadow (turns red)Total Lunar Eclipes Time Lapse Video*Next Total Lunar Eclipse not until April 15, 2014*
43 Why is the Moon red during an eclipse? Atmosphere filters some sunlight and allows it to reach the Moon’s surfaceBlue light is removedRemaining light is red or orangeBent or refracted so that a small fraction of it reaches the MoonExact appearance depends on dust and clouds in the Earth’s atmosphere
44 E.3 Motion of the Moon Solar eclipse: Moon is between Earth and Sun New Moon3 typesPartialTotalAnnular
58 Constellations and parallax How do astronomers identify stars, name stars and calculate their distances?
59 ConstellationsPatterns of stars in the sky that’s “relative” distance doesn’t changeMost visible in Northern Hemisphere named after mythological heroes and animals by Greek astrologersDifferent constellations visible at night during different times of year; appear to move from east to west during night88 total constellationsStill used to specify large areas of the sky
60 Locating a starEasiest way: specify constellation then rank in order of brightness using Greek alphabetAlpha (α)- Brightest starBeta (β)- Second brightestMethod can only be used with naked eye since limited number of letters
61 The “Obvious” ViewStars that appear close in the sky may not actually be close in space:
62 Earth’s Orbital Motion 12 constellations Sun moves through during the year are called the zodiac
63 The Measurement of Distance Triangulation: measure baseline and angles, can calculate distance
65 The Measurement of Distance Parallax: similar to triangulation, but look at apparent motion of object against distant background from two vantage pointsLarger parallax= closer the objectSmaller parallax= farther the object
67 Measuring with Parallax Ruler, tape, cardboard, scissorsCut out both pieces along dashed lineFold up arrows on dotted linesStick pushpin through both pieces and cardboardSelect a colored targetMake a perpendicular baseline taping ruler to desk
68 Measuring with Parallax Put EYE ARROW on one end of baselineLine up EYE ARROW, REFERENCE ARROW and REFERENCE POINT (corner)-gunsightPivot TARGET ARROW until it is aligned with EYE ARROW and TARGET OBJECT (scale piece should NOT move, only the pointer)Read “Angle to Target object” and put on worksheet as “Target Angle 1”Repeat previous steps from opposite side of the baseline and write down Angle in “Target angle 2”Complete calculations (Baseline=30 cm)
69 Scientific Theory and the Scientific Method What is a Scientific theory and how is it developed?
70 Scientific Theory and the Scientific Method Scientific theories:must be testablemust be continually testedshould be simpleshould be elegantScientific theories can be proven wrong, but they can never be proven right with 100% certainty
71 Scientific Theory and the Scientific Methods Observation leads to theory explaining itTheory leads to predictions consistent with previous observationsPredictions of new phenomena are observed. If the observations agree with the prediction, more predictions can be made. If not, a new theory can be made.
72 Summary of the Introduction Astronomy: study of the universeStars can be imagined to be on inside of celestial sphere; useful for describing locationPlane of Earth’s orbit around Sun is ecliptic; at 23.5° to celestial equatorAngle of Earth’s axis causes seasonsMoon shines by reflected light, has phasesSolar day ≠ sidereal day, due to Earth’s rotation around Sun
73 Summary of the Introduction Synodic month ≠ sidereal month, also due to Earth’s rotation around SunTropical year ≠ sidereal year, due to precession of Earth’s axisDistances can be measured through triangulation and parallaxEclipses of Sun and Moon occur due to alignment; only occur occasionally as orbits are not in same planeScientific method: observation, theory, prediction, observation, …