1. Bellringer Name as many Modern constellations in the night sky as you are able.

2. Bellringer – List of Modern Constellations

3. TURN IN SAFETY CONTRACTS IF YOU HAVE THEM, PLEASE & THANK YOU

4. Chapter 1 Charting the Heavens

5. Units of Chapter 1 1.1 Our Place in Space 1.2 Scientific Theory and the Scientific Method 1.3 The “Obvious” View Angular Measure Celestial Coordinates 1.4 Earth’s Orbital Motion 1.5 Astronomical Timekeeping 1.6 The Motion of the Moon 1.7 The Measurement of Distance Measuring Distances with Geometry

6. Our Place in Space Earth is average—we don’t occupy any special place in the universe Universe: totality of all space, time, matter, and energy

7. Our Place in Space Astronomy: study of the universe Scales are very large: measure in light-years, the distance light travels in a year—about 10 trillion miles

8. Scientific Theory and the Scientific Method Developed by Aristole Scientific theories: Must be testable Must be continually tested Should be simple Should be elegant Scientific theories can be proven wrong, but they can never be proven right with 100% certainty.

9. Scientific Theory and the Scientific Method Observation leads to theory explaining it Theory leads to predictions consistent with previous observations Predictions of new phenomena are observed. If observations agree with prediction, more predictions can be made. I f not, a new theory can be made.

10. The “Obvious” View Simplest observation: ~3000 stars visible at any one time distributed randomly human brain tends to find patterns

11. The “Obvious” View Group stars – Constellations Figures having meaning to those doing the grouping Useful: Polaris, which is almost due north Not so useful: Astrology Makes predictions about individuals based on the star patterns at their birth Orion’s Belt

12. The “Obvious” View Stars that appear close in the sky may not actually be close in space

13. The “Obvious” View Celestial sphere: Spherical coordinates (similar to latitude and longitude) to locate sky objects Zenith – Point directly above your head

14. Angular Measurements Full circle contains 360° (degrees) Each degree contains 60′ (arc-minutes) Each arc-minute contains 60′′ (arc-seconds) 1/3600 th of a degree Angular size of an object depends on actual size and distance away

15. Angular Measurements Examples Fingernail on Index Finger = 1 arc second Thumbnail = 2 arc seconds 1 arc second = viewing a dime @ 2 kilometers 10 Degrees = your clenched fist Big Dipper = 20 degrees Pluto = 0.1 arc second Equivalent ping pong ball (40mm) @ 80 Km

16. Celestial Coordinates Declination: degrees north or south of celestial equator Right ascension: measured in hours, minutes, and seconds eastward from position of Sun at vernal equinox Vernal Equinox – position of sun at equator on or near 3/21 Annually

17. 1.4 Earth’s Orbital Motion Solar Day - noon to noon Sidereal Day – Earth’s true rotation period Time required to return to same orientation relative to distant stars 24 hr period – earth rotates 361 o Earth also moves in orbit ~ 1 o Solar Day is 4 Minutes longer than Sidereal Day

18. Earth’s Orbital Motion Seasonal changes to night sky are due to Earth’s motion around Sun

19. Earth’s Orbital Motion 12 constellations Sun moves through during the year are called the zodiac; path is ecliptic

20. Earth’s Orbital Motion Ecliptic is plane of Earth’s path around Sun; at 23.5° to celestial equator Northernmost point (above celestial equator) is summer solstice; southernmost is winter solstice; points where path cross celestial equator are vernal and autumnal equinoxes Combination of day length and sunlight angle gives seasons Time from one vernal equinox to next is tropical year

21. Earth’s Orbital Motion Precession: rotation of Earth’s axis itself; makes one complete circle in about 26,000 years

22. Earth’s Orbital Motion Time for Earth to orbit once around Sun, relative to fixed stars, is sidereal year Tropical year follows seasons; sidereal year follows constellations— In 13,000 years July and August will still be summer, but Orion will be a summer constellation

23. Astronomical Timekeeping Solar noon: when Sun is at its highest point for the day Drawbacks: length of solar day varies during year; noon is different at different locations

24. Astronomical Timekeeping Mean (average) solar day —what clocks measure Takes care of length variation 24 time zones around Earth Takes care of noon variation.

25. 1.5 Astronomical Timekeeping World time zones

26. Astronomical Timekeeping Lunar month- complete lunar cycle Doesn’t have whole number of solar days Tropical year doesn’t have whole number of months Current calendar have months close to lunar cycle & adjusted so there are 12 of them in a year

27. Astronomical Timekeeping Synodic Month – time from one New Moon to the next Sidereal Month – time taken for the moon to rotate exactly 360 o Sidereal month is 2 days shorter than Synodic Month

28. Astronomical Timekeeping Year doesn’t quite have a whole number of solar days in it—leap years take care of this Add extra day every 4 years Omit years that are multiples of 100 but not of 400 Omit years that are multiples of 1000 but not of 4000 This will work for 20,000 years.

29. Motion of the Moon Moon takes about 29.5 days to go through whole cycle of phases—synodic month Phases - due to different amounts of sunlit portion being visible from Earth Time to make full 360° around Earth, sidereal month, is about 2 days shorter

30. Motion of the Moon Eclipses occur when Earth, Moon, and Sun form a straight line

31. Motion of the Moon Lunar eclipse: Earth is between Moon and Sun Partial when only part of Moon is in shadow Total when it all is in shadow

32. 1.6 Motion of the Moon Solar eclipse: Moon is between Earth and Sun Partial when only part of Sun is blocked Total when it all is blocked Annular when Moon is too far from Earth for total

33. Motion of the Moon Eclipses don’t occur every month because Earth’s and Moon’s orbits are not in the same plane

34. Measurement of Distance Triangulation: Measure baseline and angles, can calculate distance Use of simple geometry & trigonometry to estimate distances

35. Measurement of Distance Parallax: Apparent motion of an object against distant background Similar to triangulation Try with your outstretched arm & thumb and an object in the room. Simply alternate closing eyes Apparent displacement is Parallax

36. Measurement of Distance Measuring that angle and the distance between the cities gives the radius Simple Geometry Earth’s radius: Eratosthenes completed 2300 years ago Noticed that when Sun was directly overhead in one city, it was at an angle in another

37. More Precisely Measuring Distances with Geometry Converting baselines and parallaxes into distances

38. More Precisely 1-3: Measuring Distances with Geometry Converting angular diameter and distance into size

39. Summary Astronomy: Study of the universe Scientific method: Observation, theory, prediction, observation, … Stars can be imagined to be on inside of celestial sphere; useful for describing location Plane of Earth’s orbit around Sun is ecliptic; at 23.5° to celestial equator Angle of Earth’s axis causes seasons Moon shines by reflected light, has phases

40. Summary of Chapter 1 Solar day ≠ sidereal day, due to Earth’s rotation around Sun Synodic month ≠ sidereal month, also due to Earth’s rotation around Sun Tropical year ≠ sidereal year, due to precession of Earth’s axis Eclipses of Sun and Moon occur due to alignment; only occur occasionally as orbits are not in same plane Distances can be measured through triangulation and parallax