1. Chapter 15 Place and Time Sections 15.1-15.6

2. Copyright © Houghton Mifflin Company. All rights reserved.15 | 2 Place & Time In Physical Science events occur at different places and at different times. Another way to say it – events are separated by space and time. Our five senses make it possible to know about objects and their positions relative to one another. Time is a bit more evasive – we relate time to changes we observe in our environment. Intro

3. Copyright © Houghton Mifflin Company. All rights reserved.15 | 3 One Dimensional Location Location requires a reference system with one or more dimensions. A one-dimensional system is shown below. A straight line  (+)infinity to (-)infinity Origin and units of length must be indicated. Examples include temperature scales, left/right, above SL/below SL, profit/loss. Section 15.1

4. Copyright © Houghton Mifflin Company. All rights reserved.15 | 4 Cartesian Coordinates A two-dimensional system is one in which two lines are drawn perpendicular with an origin assigned at the point of intersection. Horizontal line = x-axis Vertical line = y-axis The system we commonly use is the Cartesian coordinate system, named after the French philosopher/mathematician René Descartes (1596-1650). Section 15.1

5. Copyright © Houghton Mifflin Company. All rights reserved.15 | 5 Cartesian Coordinates – Two Dimensional x number gives the distance from the y-axis. y number gives the distance from the x-axis. Many cities are laid out in a Cartesian pattern with streets running N-S & E-W. We want to be able to determine locations on earth and in space. Section 15.1

6. Copyright © Houghton Mifflin Company. All rights reserved.15 | 6 Latitude and Longitude Location on earth is established by means of a coordinate system – latitude & longitude Since the earth turns on axis, we can use the geographic poles as north-south reference points. Geographic poles – the imaginary points on the surface of the earth where the earth’s axis projects from the sphere Equator – an imaginary line circling the earth’s surface half way between the N & S poles –The equator is a “great circle” – a circle on the surface of earth in a plane that passes through the center. Section 15.2

7. Copyright © Houghton Mifflin Company. All rights reserved.15 | 7 The Equator Copyright © Bobby H. Bammel. All rights reserved. Section 15.2

8. Copyright © Houghton Mifflin Company. All rights reserved.15 | 8 Latitude Latitude - the angular measurement in degrees north and south of the equator The latitude angle is measured from the center of the earth relative to the equator. Lines of equal latitude are circles drawn on the surface and parallel to the equator. Section 15.2

9. Copyright © Houghton Mifflin Company. All rights reserved.15 | 9 Latitude Lines of latitude are also called parallels – –There are an infinite number of parallels between 0 o and 90 o N or S (of equator) Going from the Equator  poles these parallels represent a series of complete circles of which the equator is the largest and they become progressively smaller going North and South Only the equator is a “great circle.” All of the other parallels are “small circles,” with the North & South poles being points. Section 15.2

10. Copyright © Houghton Mifflin Company. All rights reserved.15 | 10 Longitude Longitude - imaginary lines drawn on the surface of the earth running from N to S poles and perpendicular to the equator Lines of longitude are also called meridians. Meridians are half circles that are portions of “great circles.” An infinite number of lines can be drawn as meridians. Section 15.2

11. Copyright © Houghton Mifflin Company. All rights reserved.15 | 11 Longitude Longitude is the angular measurement, in degrees, east or west of the reference meridian, the Prime Meridian (0 o ) at Greenwich, England. –A large optical telescope was located there. Maximum value of 180 o E or W Section 15.2

12. Greenwich Observatory © Ron Hann All Rights Reserved Copyright © Houghton Mifflin Company. All rights reserved.15 | 12

13. Copyright © Houghton Mifflin Company. All rights reserved.15 | 13 Diagram Showing Latitude and Longitude of Washington, D.C. Section 15.2

14. Copyright © Houghton Mifflin Company. All rights reserved.15 | 14 Great Circle Distance The shortest surface distance between any two points on earth is the great circle distance. The Earth is not flat!!! A great circle is any circle on the surface of a sphere whose center is the center of the sphere. Nautical mile (n mi) – one minute of arc of a great circle 1n mi = 1.15 mi 60 nautical miles = 1 o Section 15.2

15. Copyright © Houghton Mifflin Company. All rights reserved.15 | 15 Determining the Distance Between Two Places - Example Determine the number of nautical miles between place A (10 o S, 90 o W) and place B (70 o N, 90 o E) Notice that we are going over the North Pole to get there. How many degrees are between points A & B? 10 o + 90 o + 30 o = 130 o 60 n mi = 1 o 130 o x 60 n mi/1 o = 7800 n mi Section 15.2

16. Copyright © Houghton Mifflin Company. All rights reserved.15 | 16 Maps Generally maps are designed for some type of “navigation.” Since the earth is nearly a sphere (3-D) and most maps are flat (2-D) they are necessarily ‘projections.’ The places on a map are shown relative to each other, and the fundamental frame of reference is the lines of latitude and longitude. Most with “north” at the top Scales are provided to determine distance. Section 15.2

17. Copyright © Houghton Mifflin Company. All rights reserved.15 | 17 Time Time - the continuous forward flowing of events The continuous measurement of time requires the periodic movement of some object as a reference. The second has been adopted as the international unit of time. Vibration of the cesium-133 atom now provides the reference of a second – 9,192,631,770 cycles per second Section 15.3

18. Copyright © Houghton Mifflin Company. All rights reserved.15 | 18 Days Apparent Solar Day – the elapsed time between two successive crossings of the same meridian (line of longitude) by the sun (361 o ) Sidereal Day – the elapsed time between two successive crossings of the same meridian by a star other than the sun (360 o ) Section 15.3

19. Copyright © Houghton Mifflin Company. All rights reserved.15 | 19 Solar Day vs. Sidereal Day The earth must rotate through 360 o plus 0.985 o to complete one rotation w/ respect to the sun. The Solar Day is 4 min. longer than the Sidereal Day. Section 15.3

20. Copyright © Houghton Mifflin Company. All rights reserved.15 | 20 Days During one complete revolution (orbit) around the sun, the earth rotates (spins) 365.25 times but one complete revolution is only 360 o. Therefore during each full rotation the earth moves slightly less than 1 o of angular distance. 360 o /365.25 days = 0.985 o /day 360 o /24hr  15 o /hr  0.985 o /4 minutes Section 15.3

21. Copyright © Houghton Mifflin Company. All rights reserved.15 | 21 Time Measurement A 24-hour day begins at midnight and ends 24 hours later at midnight. Noon local solar time – when the sun is on the observer’s meridian Ante meridiem ( A.M. ) – the hours before noon Post meridiem ( P.M. ) – the hours after noon 12 o’clock should be stated as “12 noon” or “12 midnight.” In addition 12 midnight should have the dates “12 midnight, July 26-27.” Section 15.3

22. Copyright © Houghton Mifflin Company. All rights reserved.15 | 22 Standard Time Zones The earth is divided into 24 time zones, each containing approx. 15 o of longitude or 1 hour. (Remember that the earth rotates 15 o /hour!) The first time zone begins at the prime meridian and extends approximately 7.5 o both east and west. The centers of each time zone are multiples of 15 o. Section 15.3

23. Copyright © Houghton Mifflin Company. All rights reserved.15 | 23 Time Zones of the Conterminous United States Section 15.3

24. Copyright © Houghton Mifflin Company. All rights reserved.15 | 24 Losing and Gaining Time Traveling west you will “gain” time. As you cross into a new time zone, your watch will be 1 hour ahead of the new time zone. Example: Driving from eastern Kansas (at noon) into Colorado (now it is only 11 A.M.) Driving east you “lose” an hour. Therefore if you travel all the way around the earth going west, you will “gain” 24 hours. Section 15.3

25. Copyright © Houghton Mifflin Company. All rights reserved.15 | 25 International Date Line The International Date Line is located at the 180 o meridian – exactly opposite the Prime Meridian. When one crosses the IDL traveling west, the date is advanced into the next day. When one crosses the IDL traveling east, one day is subtracted from the present date. Section 15.3

26. Copyright © Houghton Mifflin Company. All rights reserved.15 | 26 Apparent North-South Movement of the Sun During a year the sun appears to change its overhead position from 23.5 o N to 23.5 o S. –23.5 o N is the farthest north and 23.5 o S is the farthest south that the vertical noon sun reaches. Tropic of Cancer – the parallel at 23.5 o N Tropic of Capricorn – the parallel at 23.5 o S As the Earth revolves around the sun, the noon sun is directly over different latitudes during the year because of the constant 23.5 o tilt of the Earth to the sun. Section 15.4

27. Copyright © Houghton Mifflin Company. All rights reserved.15 | 27 Diagrams of Sun's Position (Degrees Latitude) at Four Different Times of the Year Section 15.4

28. Copyright © Houghton Mifflin Company. All rights reserved.15 | 28 Daylight Due to the great distance from the sun, the light rays incident on earth’s surface are parallel. Therefore, one half of the earth’s surface will be illuminated (daylight) all the time and one half will be in darkness all the time. But the number of daylight hours at any place on earth depends on the latitude and the day of the year. Section 15.5

29. Copyright © Houghton Mifflin Company. All rights reserved.15 | 29 Earth’s Tilt As the earth revolves around the sun, its axis remains tilted 23.5 o from the vertical. This constant tilt of the earth with respect to the sun causes the earth’s seasons. As the earth revolves around the sun we also designate 4 particular days – Winter solstice, Vernal equinox, Summer solstice, and Autumnal equinox. Light/dark hours are always the same at the equator. Section 15.5

30. Copyright © Houghton Mifflin Company. All rights reserved.15 | 30 Vertical Noon Position of the Sun Winter Solstice – 23.5 o S = Tropic of Capricorn Vernal Equinox – 0 o = Equator Summer Solstice – 23.5 o N = Tropic of Cancer Autumnal Equinox – 0 o = Equator Solstice – “the Sun stands still” equinox – “equal night” Section 15.5

31. Copyright © Houghton Mifflin Company. All rights reserved.15 | 31 Approximate Duration of Daylight Hours for June 21 & December 21 Noon is the approximate midpoint of daylight hours. Midnight is the approximate midpoint of dark hours. Section 15.5

32. Copyright © Houghton Mifflin Company. All rights reserved.15 | 32 The Year When the earth makes one complete orbit around the sun, we call the elapsed time is one year. More precisely, we can actually define two different years. The Tropical Year & the Sidereal Year. Section 15.5

33. Copyright © Houghton Mifflin Company. All rights reserved.15 | 33 Two Different Years Tropical Year – the time interval from one vernal equinox to the next vernal equinox – 365.2422 mean solar days –The elapsed time between 1 northward crossing of the sun above the equator to the next northward crossing. Sidereal year – the time interval for earth to make one complete revolution around the Sun with respect to any particular star other than the sun – 365.2536 mean solar days –20 minutes longer than the tropical year Section 15.5

34. Copyright © Houghton Mifflin Company. All rights reserved.15 | 34 The Sun’s Overhead Position Never greater than 23.5 o latitude The sun’s position is always due south at 12 noon local solar time, for an observer in the conterminous U.S., which includes Kansas! Solstice – farthest point of the sun from the equator (“the sun stands still”) Summer Solstice – most northern position –Vertical noon sun at 23.5 o N Winter Solstice – most southern position –Vertical noon sun at 23.5 o S Section 15.5

35. Copyright © Houghton Mifflin Company. All rights reserved.15 | 35 The Sun’s Overhead Position Therefore the sun’s position overhead varies from 23.5 o north to 23.5 o south of the equator When it is directly over the equator, both the days and nights have 12 hours all over the world. Equinox – sun is directly over the equator Vernal Equinox – March 21 Autumnal Equinox – September 22 Section 15.5

36. Copyright © Houghton Mifflin Company. All rights reserved.15 | 36 Earth's Positions, Relative to the Sun and the Four Seasons Section 15.5

37. Copyright © Houghton Mifflin Company. All rights reserved.15 | 37 Seasons Seasons affect almost everyone. Many of our holidays were originally celebrated as a commemoration of a certain season of the year. –Easter – coming of spring –Halloween – beginning of winter –Thanksgiving – harvest –Christmas – sun beginning its “journey” north Original dates more-or-less set by the movement of the earth around the sun. Section 15.5

38. Copyright © Houghton Mifflin Company. All rights reserved.15 | 38 The Calendar The measurement of time requires the periodic movement of some object as a reference. Probably the first unit of measurement was the “day.” The periodic movement of the moon (29.5 solar days) was likely the next time reference. Today’s month is based on the moon. The Sumerians (3000 B.C.) divided the year into 12 lunar months of 30 days each. Section 15.5

39. Copyright © Houghton Mifflin Company. All rights reserved.15 | 39 The Zodiac Zodiac – the central, circular section of the celestial sphere that is divided into 12 sections Each section of the zodiac is identified by a prominent group of stars called a constellation. –Ancient civilizations name constellations for the the figure the stars seemed to form. Due to the Earth’s annual revolution around the sun, the appearance of the 12 constellations change during the course of a year. –A particular time of the year is marked by the appearance of a particular constellation. Section 15.5

40. Copyright © Houghton Mifflin Company. All rights reserved.15 | 40 Signs of the Zodiac Section 15.5

41. Copyright © Houghton Mifflin Company. All rights reserved.15 | 41 The Roman Calendar The early Roman calendar consisted of only 10 months. January and February did not exist but were the period of waiting for spring to arrive. Later January and February were added. The Julian Calendar was adopted in 45 B.C. during the reign of Julius Caesar. Augustus Caesar took over the throne after his adopted father Julius died. Section 15.5

42. Copyright © Houghton Mifflin Company. All rights reserved.15 | 42 The Roman Calendar Pre-700 B.C.~700 B.C.425 B.CJanuary MarchMarchFebruary AprilAprilMarch MayMayApril JuneJuneMay QuintilisQuintilisJune SextilisSextilisQuintilis SeptemberSeptemberSextilis OctoberOctoberSeptember NovemberNovemberOctober DecemberDecemberNovember FebruaryDecember

43. Copyright © Houghton Mifflin Company. All rights reserved.15 | 43 The Roman Calendar The names “July” and “August” were put into use when Augustus Caesar ruled the empire in honor of Julius and Augustus. In addition one day was added to August so that it would be as long as July (taken away from February.) Julian calendar had 365 days, and during every year divisible by 4, an extra day was added, since it takes approx. 365.25 days for the earth to orbit the sun. Section 15.5

44. Copyright © Houghton Mifflin Company. All rights reserved.15 | 44 Gregorian Calendar The Julian calendar was fairly accurate and was used for over 1500 years. In 1582 Pope Gregory XIII realized that the Julian calendar was slightly inaccurate. –The Vernal Equinox was not falling on March 21. A discrepancy was found. To correct this the Pope decreed that 10 days would be skipped. 365.2422 not 365.25 = discrepancy Every 400 years 3 leap years would be skipped. This is the calendar we use today. Section 15.5

45. Copyright © Houghton Mifflin Company. All rights reserved.15 | 45 Gregorian Calendar The leap years to be skipped were the century years not evenly divisible by 400. For example, the year 1900 was not a leap year, but 2000 was. The corrections make the calendar accurate to 1 day in 3300 years.

46. Copyright © Houghton Mifflin Company. All rights reserved.15 | 46 Seven-Day Week Origin unknown Perhaps, ¼ of the lunar period, coinciding with the moon’s change in phase More likely due to the presence of seven visible celestial objects in the sky – sun, moon, Mars, Mercury, Jupiter, Venus, and Saturn Section 15.5

47. Copyright © Houghton Mifflin Company. All rights reserved.15 | 47 The Days of the Week Section 15.5

48. Copyright © Houghton Mifflin Company. All rights reserved.15 | 48 Our Calendric Designation Notice that we say “Sunday, April 7, 2003.” The “Sunday” position falls within a seven-day count that cycles endlessly. The “April 7” position falls within a 365- day cycle that also repeats endlessly. The “2003” position is one that does not repeat, but is unique. –Year is measured from an agreed-upon starting point – the birth of Christ. Section 15.5

49. Copyright © Houghton Mifflin Company. All rights reserved.15 | 49 Precession of Earth’s Axis When we spin a toy top, it starts to wobble after a few seconds Physicists call this wobble precession. Earth slowly precesses in a clockwise direction. The period of precession is 25,800 years. In other words, it takes 25,800 years for the axis to precess through 360 o. Section 15.6

50. Copyright © Houghton Mifflin Company. All rights reserved.15 | 50 Precession of a Top & Earth Section 15.6

51. Copyright © Houghton Mifflin Company. All rights reserved.15 | 51 Precession of Earth’s Axis As the earth precesses, Polaris will not longer be the “north star.” It will be Vega. Precession of earth’s axis does not have an influence on the seasons, because the inclination of the earth (with respect to the sun) will remain constant. However the earth’s precession will slowly change the stars that can be seen in each hemisphere and season. Section 15.6