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Topic 4 Motions of the Earth, Moon, and Sun

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Presentation on theme: "Topic 4 Motions of the Earth, Moon, and Sun"— Presentation transcript:

1 Topic 4 Motions of the Earth, Moon, and Sun

2 Apparent Motions of Celestial Objects

3 Celestial sphere – imaginary dome above an observers head on which all celestial objects appear
Celestial objects – objects outside of the earth’s atmosphere that can be seen in the sky Zenith – highest point on celestial sphere, directly above observer’s head Apparent motion – the motion an object appears to have, but which isn’t real

4 Daily Apparent Motion Daily apparent motions caused by the rotation of the Earth Paths of objects form circles, or parts of circles called arcs Sun, moon, stars, etc. Some stars make circles around Polaris in one day, others make arcs Daily motions occur at a rate of 15o/hour

5 Star trails from New Mexico

6 How long did it take to make this photograph?





11 Apparent Motion of Planets
Daily apparent motion of the other planets is similar to that of the stars Apparent motion of the planets over the long term is different Planets change position relative to the stars around them Planets moving in their own orbits around the sun Stars will always stay in the same location relative to other stars Big dipper always looks the same

12 Apparent Motion of the Moon
Moon rises in the east and sets in the west Location changes in relation to the background stars

13 Apparent Motion of the Sun
Solar noon—when sun reaches highest point in sky for day Changes for a given location throughout the year Height depends on time of year and latitude Earth is tilted on its axis 23 ½ Degrees Different parts of the earth pointed toward sun at different times of year

14 Apparent Motion of the Sun
Solar Noon In Northern Hemisphere Highest in summer Lowest in winter In between spring and autumn Never reaches zenith or directly overhead

15 Apparent Motion of the Sun
Solar Noon Only locations that ever see sun directly overhead are between 23 ½ degrees North and 23 ½ degrees south latitudes Only locations ever pointed directly at sun Equator on March 21 and September 23 23 ½o North (Tropic of Cancer) on June 21 23 ½ o South (Tropic of Capricorn) on Dec. 21

16 Apparent path of sun changes throughout year
In Northern Hemisphere Sun always passes through southern sky Longest path occurs on June 21(summer solstice) Sun rises and sets furthest North Shortest path occurs on December 21 (winter solstice) Sun rises and sets furthest South Mid-length paths occur on March 21 and September 23 (equinoxes) Sun rises due east and sets due west


18 Models of Celestial Motions

19 Geocentric Model Stated that celestial objects revolved around Earth
Earth is stationary Could not explain motions of planets Adapted to have planets move in epicycles, or smaller circles as the revolved around Earth

20 Heliocentric Model Stated that the Earth rotated on an axis and moved around the sun, along with the other planets Also did not explain motions of the planets until elliptical orbits were proposed

21 Actual Earth Motions

22 Rotation Earth rotates on an imaginary axis
Rotates from west to east Rotates at an angle of 23 ½o from the plane of its orbit

23 Rotation Evidence for rotation Foucault Pendulum
If a large pendulum swings freely, its swing will appear to change at a rate of 15o/hour Actually Earth is rotating underneath it

24 Rotation Foucault Pendulum

25 Rotation Evidence for rotation Coriolis Effect
Objects are deflected from a straight path as they are projected up or down the Earth Deflected to the right in the Northern Hemisphere Deflected to the left in the Southern Hemisphere

26 Revolution Earth revolves around the sun
Revolves in an elliptical orbit with the sun at one foci Revolves at a rate of about 1o/day

27 Revolution Evidence for revolution Seasons
Earth moves so that different parts of its surface receive longer periods of sunlight at different times of the year

28 Revolution Evidence for revolution Constellations
Groups of stars that form patterns in the sky Help people landmark, or tell locations, in the sky Different constellations can be seen from a given location on the Earth at different times of the year

29 Revolution Evidence for revolution Apparent diameter of the sun
Changes throughout the year due to the elliptical orbit of the Earth Sun appears larger when Earth is at its perihelion Sun appears smaller when Earth is at its aphelion

30 Earth Motions and Time

31 Local time – time based on the rotation of the Earth
Same for all locations on a meridian Shown by the position of the sun in the sky (solar time)

32 Solar day – solar noon one day to solar noon the next day
Length varies throughout the year due to the changing speed of the Earth in its orbit throughout the year Mean solar day – average length of a solar day Used to tell time Broken into 24 hours

33 Time zones Earth broken into 24 time zones
Each is 15o wide All locations in a time zone keep the same time Time corresponds to the meridian in the middle of the time zone

34 Actual Motions of the Earth’s Moon

35 Moon revolves around the Earth
Takes 27.3 days Plane of moon’s orbit is tilted 5o compared to the plane of Earth’s orbit around the sun

36 Moon Phases Half of the moon always lit by the sun
As the moon revolves around the Earth, the amount of the lit portion that can be observed on Earth varies Called phases


38 1

39 New Moon

40 1 2

41 New Crescent

42 1 2 3

43 1st Quarter

44 1 2 4 3

45 New Gibbous

46 1 5 2 4 3

47 Full Moon

48 6 1 5 2 4 3

49 Old Gibbous

50 7 6 1 5 2 4 3

51 3rd Quarter

52 7 8 6 1 5 2 4 3

53 Old Crescent

54 7 8 6 1 5 2 4 3

55 Moon Phases Full moon  Full moon takes 29 ½ days
Earth moves in its orbit as the moon travels around the Earth When the moon makes one full revolution around the Earth it is not seen on Earth as being in the same phase due to the Earth’s change in position Moon must go further to be seen in the same phase again


57 Full Moon

58 27 1/3 days

59 New Gibbous

60 29 1/2 days

61 Full Moon

62 Tides Caused by the gravitational attraction between the Earth, moon, and sun Mostly the Earth and moon

63 Tides High Tide Occurs on side of Earth closest to the moon
Moon pulling on the water Also occurs on the opposite side of the Earth Earth is being pulled away from this side – leaves water Ocean water being pulled toward moon Earth getting pulled toward moon Moon High Tides

64 Tides High Tide Different locations on Earth experience high tide as the Earth rotate through the areas of higher water High tides at a given location occur a little more than 12 hours apart

65 Tides Low Tide Occurs on sides to right angles of high tides
Water pulled away from these locations Low Tides Moon

66 Tides Affect of the Sun on Tides
Sun doesn’t cause the tides, but can make them more extreme or more moderate Spring tides - Highest high tides and lowest low tides Occur when the sun, Earth and moon are all in a line New moon or full moon phases

67 Spring Tides Really low, low tides NewMoon Full Moon
Really high, high tides NewMoon Full Moon

68 Tides Affect of the Sun Neap Tides - Lower high tides and higher low tides Occur when the sun and moon are at right angles to each other 1st and 3rd quarters

69 3rd Quarter Neap Tides high, low tides low, high tides 1st Quarter

70 Eclipses Eclipses occur when one celestial object ends up in the shadow of another Solar Eclipse – when the sun is blocked by the moon, causing a shadow to be seen on the Earth New moon phase Seen on a very small portion of the Earth’s surface

71 Area of Partial Eclipse
Solar Eclipse Area of Total Eclipse Area of Partial Eclipse NewMoon

72 Eclipses Lunar Eclipse – when the moon passes into the shadow of the Earth Full moon phase Seen by all people on the darkened side of the Earth

73 All of darkened side of Earth can see eclipse
Lunar Eclipse All of darkened side of Earth can see eclipse Full Moon

74 Eclipses Eclipses do not occur during every phase cycle because the orbit of the moon is tilted 5o with the plane of the Earth’s orbit

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