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5/10/2015 (c) Vicki Drake, SMC 1 EARTH-SUN RELATIONS Rotation, Revolution, Seasons.

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Presentation on theme: "5/10/2015 (c) Vicki Drake, SMC 1 EARTH-SUN RELATIONS Rotation, Revolution, Seasons."— Presentation transcript:

1 5/10/2015 (c) Vicki Drake, SMC 1 EARTH-SUN RELATIONS Rotation, Revolution, Seasons

2 5/10/2015 (c) Vicki Drake, SMC 2 EARTH’S ROTATION The Earth rotates on its axis The Earth rotates on its axis One complete rotation (360 0 ) takes approximately 24 hours One complete rotation (360 0 ) takes approximately 24 hours Rotation is from West to EastRotation is from West to East Sun appears to ‘rise’ in East and ‘set’ in West Sun appears to ‘rise’ in East and ‘set’ in West Rotation speed is variableRotation speed is variable Fastest at the equator Fastest at the equator

3 5/10/2015 (c) Vicki Drake, SMC 3 EARTH’S REVOLUTION ABOUT THE SUN The Earth revolves about the Sun The Earth revolves about the Sun One complete revolution takes daysOne complete revolution takes days 365 days, 5 hours, 48 minutes, 36 seconds 365 days, 5 hours, 48 minutes, 36 seconds Approximately 365 ¼ Earth days Approximately 365 ¼ Earth days The Earth’s revolution is slightly elliptical, not circular The Earth’s revolution is slightly elliptical, not circular Direction of revolution is counter- clockwise from an outer space perspectiveDirection of revolution is counter- clockwise from an outer space perspective

4 5/10/2015 (c) Vicki Drake, SMC 4 AXIS TILT AND REVOLUTION Earth moves in a constant plane – Plane of the Ecliptic – in its revolution about the Sun Earth moves in a constant plane – Plane of the Ecliptic – in its revolution about the Sun All the planets (and even the sun) are moving in the Plane of the EclipticAll the planets (and even the sun) are moving in the Plane of the Ecliptic Earth’s axis is tilted about from perpendicular to Plane of Ecliptic Earth’s axis is tilted about from perpendicular to Plane of Ecliptic Earth’s tilt has two characteristics: Earth’s tilt has two characteristics: Angle of inclinationAngle of inclination ParallelismParallelism

5 5/10/2015 (c) Vicki Drake, SMC 5 ANGLE OF INCLINATION AND PARALLELISM The angle of inclination, the tilt of 23½ degrees, is a constant. The angle of inclination, the tilt of 23½ degrees, is a constant. The angle does not change throughout the entire revolutionThe angle does not change throughout the entire revolution Parallelism means the axis is always pointed in the same direction Parallelism means the axis is always pointed in the same direction The axis does not point in different directions as the Earth moves in its orbitThe axis does not point in different directions as the Earth moves in its orbit

6 5/10/2015 (c) Vicki Drake, SMC 6 EARTH’S ELLIPTICAL REVOLUTION The Earth, in its elliptical revolution, has an average distance of approximately 93,000,000 miles from the Sun The Earth, in its elliptical revolution, has an average distance of approximately 93,000,000 miles from the Sun At two points in the revolution, the distance varies At two points in the revolution, the distance varies Perihelion: Earth is closest to Sun, ~91.5 million milesPerihelion: Earth is closest to Sun, ~91.5 million miles Aphelion: Earth is farthest from Sun, ~95.5 million milesAphelion: Earth is farthest from Sun, ~95.5 million miles

7 5/10/2015 (c) Vicki Drake, SMC 7 PERIHELION AND APHELION 91,500,000 miles 95,500,000 miles

8 5/10/2015 (c) Vicki Drake, SMC 8 PERHELION AND APHELION - DATES Perihelion occurs on, or about, January 3 Perihelion occurs on, or about, January 3 Northern Hemisphere WinterNorthern Hemisphere Winter Aphelion occurs on, or about, July 4 Aphelion occurs on, or about, July 4 Northern Hemisphere SummerNorthern Hemisphere Summer

9 5/10/2015 (c) Vicki Drake, SMC 9 PERIHELION At Perihelion, the Earth’s orbit is the closest to the Sun. At Perihelion, the Earth’s orbit is the closest to the Sun. The Northern Hemisphere is ‘tilted away’ from the sun, receiving less solar radiation, with shorter daylight hours. The Northern Hemisphere is ‘tilted away’ from the sun, receiving less solar radiation, with shorter daylight hours. This is the Winter period for the Northern Hemisphere. This is the Winter period for the Northern Hemisphere.

10 5/10/2015 (c) Vicki Drake, SMC 10 PERIHELION

11 5/10/2015 (c) Vicki Drake, SMC 11 APHELION At Aphelion, the Earth’s orbit is furthest away from the Sun. At Aphelion, the Earth’s orbit is furthest away from the Sun. The Northern Hemisphere is ‘tilted toward’ the Sun, resulting in more solar radiation, and longer daylight hours. The Northern Hemisphere is ‘tilted toward’ the Sun, resulting in more solar radiation, and longer daylight hours. This is the Northern Hemisphere Summer period. This is the Northern Hemisphere Summer period.

12 5/10/2015 (c) Vicki Drake, SMC 12 APHELION

13 Changes in Axis Orientation, Tilt and Revolution Orientation of Earth’s axis changes during a 23,000-year cycle called precession Orientation of Earth’s axis changes during a 23,000-year cycle called precession The Earth’s degree of tilt (obliquity) changes through a 41,000-year cycle – ranging between 22.5 and 24 degrees The Earth’s degree of tilt (obliquity) changes through a 41,000-year cycle – ranging between 22.5 and 24 degrees Earth’s orbit (revolution) about the Sun changes from nearly circular to elliptical and back every 100,000 years – this process is called eccentricity Earth’s orbit (revolution) about the Sun changes from nearly circular to elliptical and back every 100,000 years – this process is called eccentricity Milankovitch Theory: these changes can be linked to long-term climate changes based on latitudinal differences in insolation (incoming solar radiation) Milankovitch Theory: these changes can be linked to long-term climate changes based on latitudinal differences in insolation (incoming solar radiation) 5/10/2015 (c) Vicki Drake, SMC 13

14 5/10/2015 (c) Vicki Drake, SMC 14 CIRCLE OF ILLUMINATION During rotation, at any given time, half of the Earth is receiving solar radiation – daylight During rotation, at any given time, half of the Earth is receiving solar radiation – daylight The other half of the Earth is in darkness – night The other half of the Earth is in darkness – night The ‘line’ separating day from night is the Circle of Illumination The ‘line’ separating day from night is the Circle of Illumination The image below illustrates the Circle of Illumination without the tilt of the axis The image below illustrates the Circle of Illumination without the tilt of the axis

15 5/10/2015 (c) Vicki Drake, SMC 15 INSOLATION AND LATITUDES Insolation: solar radiation received by the Earth (incoming solar radiation) Insolation: solar radiation received by the Earth (incoming solar radiation) Seasons: Variations of insolation due to spherical surface of Earth Seasons: Variations of insolation due to spherical surface of Earth Some latitudes receive more insolation: Some latitudes receive more insolation: Angle of incidenceAngle of incidence DurationDuration

16 5/10/2015 (c) Vicki Drake, SMC 16 INSOLATION AND LATITUDES Only one latitude, at any time during Earth’s revolution, receives insolation at right angles at noon Only one latitude, at any time during Earth’s revolution, receives insolation at right angles at noon The subsolar point on the EarthThe subsolar point on the Earth Zenith Angle for SunZenith Angle for Sun Intensity of insolation measured by using Sun’s zenith angle Intensity of insolation measured by using Sun’s zenith angle Sun’s angle above horizon at local noonSun’s angle above horizon at local noon The angle at which Sun’s rays strike Earth’s surface determines amount of insolation The angle at which Sun’s rays strike Earth’s surface determines amount of insolation More direct angle = greater insolationMore direct angle = greater insolation Subsolar point

17 5/10/2015 (c) Vicki Drake, SMC 17 LATITUDES and SUN RELATIONS The following three latitudes are important because of their significance to seasons on the Earth The following three latitudes are important because of their significance to seasons on the Earth On certain days of the year (Equinoxes and Solstices), the Sun’s Zenith Angle, at local noon, will be 90 0 above one of these latitudesOn certain days of the year (Equinoxes and Solstices), the Sun’s Zenith Angle, at local noon, will be 90 0 above one of these latitudes Equator: 0 0 Equator: 0 0 an imaginary line on the Earth's surface equidistant from the North Pole and South Pole that divides the Earth into a Northern Hemisphere and a Southern Hemispherean imaginary line on the Earth's surface equidistant from the North Pole and South Pole that divides the Earth into a Northern Hemisphere and a Southern Hemisphere Two days per year (Autumnal Equinox: September 21,22 and Vernal Equinox: March 20) the Sun’s location, at local noon is directly over the EquatorTwo days per year (Autumnal Equinox: September 21,22 and Vernal Equinox: March 20) the Sun’s location, at local noon is directly over the Equator Tropic of Capricorn: 23½ 0 South Tropic of Capricorn: 23½ 0 South One day per year (Winter Solstice: December 21, 22) the Sun’s location, at local noon, is in the Capricorn constellationOne day per year (Winter Solstice: December 21, 22) the Sun’s location, at local noon, is in the Capricorn constellation Tropic of Cancer: 23½ 0 North Tropic of Cancer: 23½ 0 North One day per year (Summer Solstice: June 21,22) the sun’s location, at local noon, is in the Cancer constellationOne day per year (Summer Solstice: June 21,22) the sun’s location, at local noon, is in the Cancer constellation Arctic Circle: 66½ 0 North Arctic Circle: 66½ 0 North marking the southern limit of the area where the sun does not rise on the Northern Hemisphere winter solstice (December 21) or set on the summer solstice (June 21)marking the southern limit of the area where the sun does not rise on the Northern Hemisphere winter solstice (December 21) or set on the summer solstice (June 21) Antarctic Circle: 66½ 0 South Antarctic Circle: 66½ 0 South marks the northern limit of the area where the Sun does not set on the Southern Hemisphere summer solstice (December 21) or rise on the winter solstice (June 21)marks the northern limit of the area where the Sun does not set on the Southern Hemisphere summer solstice (December 21) or rise on the winter solstice (June 21)

18 5/10/2015 (c) Vicki Drake, SMC 18 ZENITH ANGLE AND LATITUDES – WITHOUT TILT 66 1/2 0 N 23 1/2 0 N /2 0 S 66 1/2 0 S

19 5/10/2015 (c) Vicki Drake, SMC 19 SOLSTICES, EQUINOXES, AND LATITUDES: NORTHERN HEMISPHERE BIAS! Summer Solstice: Sun’s Zenith Angle of 90 0, at noon, is located at Tropic of Cancer, (23 ½ 0 ) North Summer Solstice: Sun’s Zenith Angle of 90 0, at noon, is located at Tropic of Cancer, (23 ½ 0 ) North On or about June 21, 22On or about June 21, 22 Winter Solstice: Sun’s Zenith Angle of 90 0, at noon, is located at Tropic of Capricorn, (23 ½ 0 ) South Winter Solstice: Sun’s Zenith Angle of 90 0, at noon, is located at Tropic of Capricorn, (23 ½ 0 ) South On or about December 21, 22On or about December 21, 22 Vernal Equinox and Autumnal Equinox: Sun’s Zenith Angle of 90 0, at noon, is located at the Equator, 0 0 Vernal Equinox and Autumnal Equinox: Sun’s Zenith Angle of 90 0, at noon, is located at the Equator, 0 0 On or about March 20 and September 21, 22 respectivelyOn or about March 20 and September 21, 22 respectively

20 5/10/2015 (c) Vicki Drake, SMC 20 SUMMER SOLSTICE Summer Solstice, June 21, 22 Summer Solstice, June 21, 22 Northern Hemisphere is tilted towards the Sun Northern Hemisphere is tilted towards the Sun Latitudes higher than North receive 24 hours of sunlight Latitudes higher than North receive 24 hours of sunlight Latitudes higher than South receive 24 hours of night Latitudes higher than South receive 24 hours of night Longest period of daylight for one day in year for Northern Hemisphere latitudes Longest period of daylight for one day in year for Northern Hemisphere latitudes First day of Summer: Northern HemisphereFirst day of Summer: Northern Hemisphere Vertical rays of Sun at noon

21 5/10/2015 (c) Vicki Drake, SMC 21 WINTER SOLSTICE Winter Solstice, December 22 Winter Solstice, December 22 Northern Hemisphere tilted away from the Sun Northern Hemisphere tilted away from the Sun Latitudes higher than North receive 24 hours of night Latitudes higher than North receive 24 hours of night Latitudes higher than South receive 24 hours of daylight Latitudes higher than South receive 24 hours of daylight Longest period of night for one day for Northern Hemisphere latitudes Longest period of night for one day for Northern Hemisphere latitudes First day of Winter: Northern HemisphereFirst day of Winter: Northern Hemisphere Vertical rays of sun at noon

22 5/10/2015 (c) Vicki Drake, SMC 22 EQUINOXES: VERNAL, AUTUMNAL Sun’s vertical rays at noon

23 5/10/2015 (c) Vicki Drake, SMC 23 VERNAL (SPRING) EQUINOX Vernal Equinox, March 20 Vernal Equinox, March 20 Zenith Angle of Sun at noon is 90 0 above Equator Zenith Angle of Sun at noon is 90 0 above Equator Day and night are of equal length at all locations on the Earth Day and night are of equal length at all locations on the Earth First day of Spring, Northern Hemisphere First day of Spring, Northern Hemisphere Calendar (including specific dates) and even monuments based on Vernal Equinox Calendar (including specific dates) and even monuments based on Vernal Equinox For example: the Council of Nice decreed in 325 A.D. that "Easter was to fall upon the first Sunday after the first full moon on or after the Vernal Equinox”For example: the Council of Nice decreed in 325 A.D. that "Easter was to fall upon the first Sunday after the first full moon on or after the Vernal Equinox” Julian and Gregorian CalendarJulian and Gregorian Calendar Early Egyptians built the Great Sphinx so that it points directly toward the rising Sun on the day of the Vernal Equinox.Early Egyptians built the Great Sphinx so that it points directly toward the rising Sun on the day of the Vernal Equinox.

24 5/10/2015 (c) Vicki Drake, SMC 24 AUTUMNAL (FALL) EQUINOX Autumnal Equinox, September 22 Autumnal Equinox, September 22 Zenith Angle of Sun at noon is 90 0 above Equator Zenith Angle of Sun at noon is 90 0 above Equator Day and night are of equal length at all locations on the Earth Day and night are of equal length at all locations on the Earth First day of Fall, Northern Hemisphere First day of Fall, Northern Hemisphere

25 5/10/2015 (c) Vicki Drake, SMC 25 SEASONS AND EARTH’S REVOLUTION Direct Rays 23 1/2 0 N Direct Rays 23 1/2 0 S

26 5/10/2015 (c) Vicki Drake, SMC 26 CALENDARS AND SEASONS Julian Calendar : Julian Calendar : Introduced in 46 BCIntroduced in 46 BC A regular year of 365 days divided into 12 months, and a leap day is added to February every four years.A regular year of 365 days divided into 12 months, and a leap day is added to February every four years. The Julian year is, on average, days long. The Julian year is, on average, days long.

27 5/10/2015 (c) Vicki Drake, SMC 27 CALENDARS AND SEASONS Gregorian Calendar Gregorian Calendar Decreed in 1582 by Pope Gregory Decreed in 1582 by Pope Gregory Equinox and solstices almost two weeks early on Julian CalendarEquinox and solstices almost two weeks early on Julian Calendar Pope Gregory dropped 10 days from calendar to put equinoxes and solstices back on track.Pope Gregory dropped 10 days from calendar to put equinoxes and solstices back on track. October 4 followed by October 15 October 4 followed by October 15 Changes in Gregorian Calendar Changes in Gregorian Calendar Add extra day to month of February every four years: “Leap Year”Add extra day to month of February every four years: “Leap Year” Exception - only century years divisible by 400 become leap yearsException - only century years divisible by 400 become leap years

28 5/10/2015 (c) Vicki Drake, SMC 28 SEASONS Distance between Earth and Sun NOT a determinant of seasons Distance between Earth and Sun NOT a determinant of seasons Perihelion occurs during Northern Hemisphere winterPerihelion occurs during Northern Hemisphere winter Determinant # 1: Angle of Incidence of Sun’s rays striking Earth’s surface Determinant # 1: Angle of Incidence of Sun’s rays striking Earth’s surface Latitudes receiving more perpendicular rays receive more insolation for heatingLatitudes receiving more perpendicular rays receive more insolation for heating Determinant # 2: Length of daylight hours Determinant # 2: Length of daylight hours Longer daylight hours means more insolationLonger daylight hours means more insolation Determinant # 3: Angle of Incidence and length of daylight hours directly affected by tilt of Earth’s axis Determinant # 3: Angle of Incidence and length of daylight hours directly affected by tilt of Earth’s axis

29 5/10/2015 (c) Vicki Drake, SMC 29 ANGLE OF INCIDENCE - INSOLATION The more vertical the rays of Sun means a more concentrated amount of solar radiation for a location.

30 5/10/2015 (c) Vicki Drake, SMC 30 ANALEMMA – MAPPING THE SUN’S MOVEMENT An analemma traces the annual movement of the Sun on the sky. An analemma traces the annual movement of the Sun on the sky. It illustrates the positions of the Sun at the same time of day (at approximately 24 hour intervals) and from the same location on Earth on successive days through the calendar year.It illustrates the positions of the Sun at the same time of day (at approximately 24 hour intervals) and from the same location on Earth on successive days through the calendar year. This apparent shift of Sun’s position is due to the Earth’s orbit about the SunThis apparent shift of Sun’s position is due to the Earth’s orbit about the Sun An analemma appears as a ‘loopy’ figure eightAn analemma appears as a ‘loopy’ figure eight the highest point is Summer the highest point is Summer the lowest point, Winter the lowest point, Winter

31 5/10/2015 (c) Vicki Drake, SMC 31 ANALEMMA

32 5/10/2015 (c) Vicki Drake, SMC 32 ANALEMMA The Analemma has a calendar printed on it The Analemma has a calendar printed on it This calendar indicates which latitude (subsolar point) receives the Sun’s direct rays at noon (“Zenith Angle”) on any day of the year.This calendar indicates which latitude (subsolar point) receives the Sun’s direct rays at noon (“Zenith Angle”) on any day of the year. The most northern latitude is North The most northern latitude is North The most southern latitude is South The most southern latitude is South


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