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

04/18/2304/18/23 (c) Vicki Drake, SMC(c) Vicki Drake, SMC 11

EARTH-SUN EARTH-SUN RELATIONSRELATIONS

Rotation, Revolution, SeasonsRotation, Revolution, Seasons


EARTH’S ROTATIONEARTH’S ROTATION The Earth rotates on The Earth rotates on

its axisits axis One complete rotation One complete rotation

(360(36000) takes ) takes approximately 24 approximately 24 hourshours• Rotation is from West to Rotation is from West to

EastEast Sun appears to ‘rise’ in Sun appears to ‘rise’ in

East and ‘set’ in WestEast and ‘set’ in West

• Rotation speed is Rotation speed is variablevariable

Fastest at the equator Fastest at the equator


EARTH’S REVOLUTION ABOUT EARTH’S REVOLUTION ABOUT THE SUNTHE SUN

The Earth revolves about the SunThe Earth revolves about the Sun• One complete revolution takes 365.2422 One complete revolution takes 365.2422

days days 365 days, 5 hours, 48 minutes, 36 seconds365 days, 5 hours, 48 minutes, 36 seconds ApproximatelyApproximately 365 ¼ Earth days 365 ¼ Earth days

The Earth’s revolution is slightly The Earth’s revolution is slightly elliptical, not circularelliptical, not circular• Direction of revolution is counter-Direction of revolution is counter-

clockwise from an outer space clockwise from an outer space perspectiveperspective


AXIS TILT AND REVOLUTIONAXIS TILT AND REVOLUTION Earth moves in a constant Earth moves in a constant

plane – plane – Plane of the EclipticPlane of the Ecliptic – in its revolution about the – in its revolution about the SunSun• All the planets (and even All the planets (and even

the sun) are moving in the the sun) are moving in the Plane of the EclipticPlane of the Ecliptic

Earth’s axis is tilted about Earth’s axis is tilted about 23.523.500 from perpendicular from perpendicular to Plane of Eclipticto Plane of Ecliptic

Earth’s tilt has two Earth’s tilt has two characteristics:characteristics:• Angle of inclinationAngle of inclination• ParallelismParallelism


ANGLE OF INCLINATION AND ANGLE OF INCLINATION AND PARALLELISMPARALLELISM

The angle of The angle of inclinationinclination, the tilt , the tilt of 23½ degrees, is of 23½ degrees, is a constant.a constant.• The angle does not The angle does not

change throughout change throughout the entire revolution the entire revolution

ParallelismParallelism means means the axis is always the axis is always pointed in the pointed in the same directionsame direction• The axis does not The axis does not

point in different point in different directions as the directions as the Earth moves in its Earth moves in its orbitorbit


EARTH’S ELLIPTICAL EARTH’S ELLIPTICAL REVOLUTIONREVOLUTION

The Earth, in its elliptical revolution, The Earth, in its elliptical revolution, has an average distance of has an average distance of approximately 93,000,000 miles approximately 93,000,000 miles from the Sunfrom the Sun

At two points in the revolution, the At two points in the revolution, the distance variesdistance varies• Perihelion: Earth is closest to Sun, Perihelion: Earth is closest to Sun,

~91.5 million miles~91.5 million miles• Aphelion: Earth is farthest from Sun, Aphelion: Earth is farthest from Sun,

~95.5 million miles~95.5 million miles


PERIHELION AND APHELIONPERIHELION AND APHELION

91,500,000 miles

95,500,000 miles


PERHELION AND APHELION - PERHELION AND APHELION - DATESDATES

Perihelion occurs on, or about, Perihelion occurs on, or about, January 3January 3• Northern Hemisphere WinterNorthern Hemisphere Winter

Aphelion occurs on, or about, July 4Aphelion occurs on, or about, July 4• Northern Hemisphere SummerNorthern Hemisphere Summer


PERIHELIONPERIHELION

At Perihelion, the Earth’s orbit is the At Perihelion, the Earth’s orbit is the closest to the Sun .closest to the Sun .

The Northern Hemisphere is ‘tilted The Northern Hemisphere is ‘tilted away’ from the sun, receiving less away’ from the sun, receiving less solar radiation, with shorter daylight solar radiation, with shorter daylight hours.hours.

This is the Winter period for the This is the Winter period for the Northern Hemisphere.Northern Hemisphere.


PERIHELIONPERIHELION


APHELIONAPHELION

At Aphelion, the Earth’s orbit is At Aphelion, the Earth’s orbit is furthest away from the Sun.furthest away from the Sun.

The Northern Hemisphere is ‘tilted The Northern Hemisphere is ‘tilted toward’ the Sun, resulting in more toward’ the Sun, resulting in more solar radiation, and longer daylight solar radiation, and longer daylight hours.hours.

This is the Northern Hemisphere This is the Northern Hemisphere Summer period.Summer period.


APHELIONAPHELION

Changes in Axis Orientation, Tilt Changes in Axis Orientation, Tilt and Revolutionand Revolution

Orientation of Earth’s axis changes during a Orientation of Earth’s axis changes during a 23,000-year cycle called 23,000-year cycle called precessionprecession

The Earth’s degree of tilt (The Earth’s degree of tilt (obliquityobliquity) changes ) changes through a 41,000-year cycle – ranging between through a 41,000-year cycle – ranging between 22.5 and 24 degrees22.5 and 24 degrees

Earth’s orbit (revolution) about the Sun changes Earth’s orbit (revolution) about the Sun changes from nearly circular to elliptical and back every from nearly circular to elliptical and back every 100,000 years – this process is called 100,000 years – this process is called eccentricityeccentricity

Milankovitch TheoryMilankovitch Theory: these changes can be linked : these changes can be linked to long-term climate changes based on latitudinal to long-term climate changes based on latitudinal differences in insolation (incoming solar radiation)differences in insolation (incoming solar radiation)



CIRCLE OF ILLUMINATIONCIRCLE OF ILLUMINATION During rotation, at any given time, half of the Earth is During rotation, at any given time, half of the Earth is

receiving solar radiation – daylightreceiving solar radiation – daylight The other half of the Earth is in darkness – nightThe other half of the Earth is in darkness – night The ‘line’ separating day from night is the The ‘line’ separating day from night is the Circle of Circle of

IlluminationIllumination The image below illustrates the Circle of Illumination The image below illustrates the Circle of Illumination

without the tilt of the axiswithout the tilt of the axis


INSOLATION AND LATITUDESINSOLATION AND LATITUDES

Insolation:Insolation: solar radiation received by solar radiation received by the Earth (the Earth (inincoming coming solsolar radiar radiation)ation)

SeasonsSeasons: Variations of insolation due to : Variations of insolation due to spherical surface of Earthspherical surface of Earth

Some latitudes receive more insolation: Some latitudes receive more insolation: • Angle of incidenceAngle of incidence• Duration Duration


INSOLATION AND LATITUDESINSOLATION AND LATITUDES Only one latitude, at any Only one latitude, at any

time during Earth’s time during Earth’s revolution, receives revolution, receives insolation at right angles at insolation at right angles at noonnoon• The subsolar point on the The subsolar point on the

EarthEarth• Zenith Angle for SunZenith Angle for Sun

Intensity of insolation Intensity of insolation measured by using Sun’s measured by using Sun’s zenith anglezenith angle• Sun’s angle above horizon Sun’s angle above horizon

at local noonat local noon The angle at which Sun’s The angle at which Sun’s

rays strike Earth’s surface rays strike Earth’s surface determines amount of determines amount of insolationinsolation• More direct angle = More direct angle =

greater insolationgreater insolation

Subsolar point


LATITUDES and SUN RELATIONSLATITUDES and SUN RELATIONS The following three latitudes are important because of their significance The following three latitudes are important because of their significance

to seasons on the Earthto seasons on the Earth• On certain days of the year (Equinoxes and Solstices), the Sun’s Zenith Angle, at On certain days of the year (Equinoxes and Solstices), the Sun’s Zenith Angle, at

local noon, will be 90local noon, will be 9000 above one of these latitudes above one of these latitudes EquatorEquator:: 0 000

• an imaginary line on the Earth's surface equidistant from the North Pole and South Pole 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 Hemisphere 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) 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 Equatorthe Sun’s location, at local noon is directly over the Equator

Tropic of Capricorn:Tropic of Capricorn: 23½ 23½00 South South• One day per year (Winter Solstice: December 21, 22) the Sun’s location, at local noon, is in One day per year (Winter Solstice: December 21, 22) the Sun’s location, at local noon, is in

the Capricorn constellationthe Capricorn constellation Tropic of CancerTropic of Cancer:: 23½ 23½00 North North

• One day per year (Summer Solstice: June 21,22) the sun’s location, at local noon, is in the One day per year (Summer Solstice: June 21,22) the sun’s location, at local noon, is in the Cancer constellationCancer constellation

-------------------------------------------------------------------------------------------------------------------------------------------------------------- Arctic CircleArctic Circle: 66½: 66½00 North North

• marking the southern limit of the area where the sun does not rise on the Northern 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)Hemisphere winter solstice (December 21) or set on the summer solstice (June 21)

Antarctic CircleAntarctic Circle: 66½: 66½00 South South• marks the northern limit of the area where the Sun does not set on the Southern 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) Hemisphere summer solstice (December 21) or rise on the winter solstice (June 21)


ZENITH ANGLE AND LATITUDES ZENITH ANGLE AND LATITUDES – WITHOUT TILT– WITHOUT TILT

66 1/20 N

23 1/20 N

00

23 1/20 S

66 1/20 S


SOLSTICES, EQUINOXES, AND LATITUDES: SOLSTICES, EQUINOXES, AND LATITUDES: NORTHERN HEMISPHERE BIAS!NORTHERN HEMISPHERE BIAS!

Summer Solstice: Summer Solstice: Sun’s Zenith Angle of Sun’s Zenith Angle of 909000, at noon, is located at Tropic of , at noon, is located at Tropic of Cancer, 23.5Cancer, 23.500 (23 ½ (23 ½00) North) North• On or about June 21, 22On or about June 21, 22

Winter Solstice:Winter Solstice: Sun’s Zenith Angle of 90 Sun’s Zenith Angle of 9000, , at noon, is located at Tropic of Capricorn, at noon, is located at Tropic of Capricorn, 23.523.50 0 (23 ½(23 ½00) South) South• On or about December 21, 22On or about December 21, 22

Vernal EquinoxVernal Equinox and and Autumnal Equinox: Autumnal Equinox: Sun’s Zenith Angle of 90Sun’s Zenith Angle of 9000, at noon, is , at noon, is located at the Equator, 0located at the Equator, 000

• On or about March 20 and September 21, 22 On or about March 20 and September 21, 22 respectivelyrespectively


SUMMER SOLSTICESUMMER SOLSTICE Summer Solstice, June Summer Solstice, June

21, 2221, 22 Northern Hemisphere is Northern Hemisphere is

tilted towards the Suntilted towards the Sun Latitudes higher than 66.5Latitudes higher than 66.500

North receive 24 hours of North receive 24 hours of sunlightsunlight

Latitudes higher than 66.5Latitudes higher than 66.50 0

South receive 24 hours of South receive 24 hours of nightnight

Longest period of daylight Longest period of daylight for one day in year for for one day in year for Northern Hemisphere Northern Hemisphere latitudeslatitudes• First day of Summer: First day of Summer:

Northern HemisphereNorthern Hemisphere

Vertical rays of Sun at noon


WINTER SOLSTICEWINTER SOLSTICE Winter Solstice, Winter Solstice,

December 22December 22 Northern Hemisphere tilted Northern Hemisphere tilted

away from the Sunaway from the Sun Latitudes higher than 66.5Latitudes higher than 66.500

North receive 24 hours of North receive 24 hours of nightnight

Latitudes higher than 66.5Latitudes higher than 66.500 South receive 24 hours of South receive 24 hours of daylightdaylight

Longest period of night for Longest period of night for one day for Northern one day for Northern Hemisphere latitudesHemisphere latitudes• First day of Winter: First day of Winter:

Northern HemisphereNorthern Hemisphere

Vertical rays of sun at noon


EQUINOXES: VERNAL, AUTUMNALEQUINOXES: VERNAL, AUTUMNAL

Sun’s vertical rays at noon


VERNAL (SPRING) EQUINOXVERNAL (SPRING) EQUINOX Vernal Equinox, March 20Vernal Equinox, March 20 Zenith Angle of Sun at noon is 90Zenith Angle of Sun at noon is 9000 above Equator above Equator Day and night are of equal length at all locations Day and night are of equal length at all locations

on the Earthon the Earth First day of Spring, Northern HemisphereFirst day of Spring, Northern Hemisphere Calendar (including specific dates) and even Calendar (including specific dates) and even

monuments based on Vernal Equinoxmonuments based on Vernal Equinox• For example: the Council of Nice decreed in 325 A.D. For example: the Council of Nice decreed in 325 A.D.

that "Easter was to fall upon the first Sunday after the that "Easter was to fall upon the first Sunday after the first full moon on or after the Vernal Equinox” 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 Early Egyptians built the Great Sphinx so that it points

directly toward the rising Sun on the day of the Vernal directly toward the rising Sun on the day of the Vernal Equinox.Equinox.


AUTUMNAL (FALL) EQUINOXAUTUMNAL (FALL) EQUINOX

Autumnal Equinox, September Autumnal Equinox, September 2222

Zenith Angle of Sun at noon is 90Zenith Angle of Sun at noon is 9000 above Equatorabove Equator

Day and night are of equal length at Day and night are of equal length at all locations on the Earthall locations on the Earth

First day of Fall, Northern First day of Fall, Northern HemisphereHemisphere


SEASONS AND EARTH’S REVOLUTIONSEASONS AND EARTH’S REVOLUTION

Direct Rays 23 1/20 N Direct Rays

23 1/20 S


CALENDARS AND SEASONSCALENDARS AND SEASONS

Julian CalendarJulian Calendar::• Introduced in 46 BCIntroduced in 46 BC• A regular year of 365 days divided into A regular year of 365 days divided into

12 months, and a leap day is added to 12 months, and a leap day is added to February every four years. February every four years.

The Julian year is, on average, 365.25 days The Julian year is, on average, 365.25 days long. long.


CALENDARS AND SEASONSCALENDARS AND SEASONS Gregorian CalendarGregorian Calendar Decreed in 1582 by Pope GregoryDecreed in 1582 by Pope Gregory

• Equinox and solstices almost two weeks early Equinox and solstices almost two weeks early on Julian Calendaron Julian Calendar

• Pope Gregory dropped 10 days from calendar Pope Gregory dropped 10 days from calendar to put equinoxes and solstices back on track.to put equinoxes and solstices back on track.

October 4 followed by October 15 October 4 followed by October 15 Changes in Gregorian CalendarChanges in Gregorian Calendar

• Add extra day to month of February every four Add extra day to month of February every four years: “Leap Year”years: “Leap Year”

• Exception - only century years divisible by 400 Exception - only century years divisible by 400 become leap yearsbecome leap years


SEASONSSEASONS Distance between Earth and SunDistance between Earth and Sun NOT NOT a a

determinant of seasonsdeterminant of seasons• Perihelion occurs during Northern Hemisphere winterPerihelion occurs during Northern Hemisphere winter

Determinant # 1Determinant # 1: Angle of Incidence of Sun’s : Angle of Incidence of Sun’s rays striking Earth’s surfacerays striking Earth’s surface• Latitudes receiving more perpendicular rays receive Latitudes receiving more perpendicular rays receive

more insolation for heatingmore insolation for heating

Determinant # 2Determinant # 2: Length of daylight hours: Length of daylight hours• Longer daylight hours means more insolationLonger daylight hours means more insolation

Determinant # 3Determinant # 3: Angle of Incidence and length : Angle of Incidence and length of daylight hours directly affected by tilt of of daylight hours directly affected by tilt of Earth’s axisEarth’s axis


ANGLE OF INCIDENCE - ANGLE OF INCIDENCE - INSOLATIONINSOLATION

The more vertical the rays of Sun means a more concentrated amount of solar radiation for a location.


ANALEMMA – MAPPING THE ANALEMMA – MAPPING THE SUN’S MOVEMENTSUN’S MOVEMENT

An analemma traces the annual An analemma traces the annual movement of the Sun on the sky.movement of the Sun on the sky.• It illustrates the positions of the Sun at the It illustrates the positions of the Sun at the

same time of day (at approximately 24 hour same time of day (at approximately 24 hour intervals) and from the same location on Earth intervals) and from the same location on Earth on successive days through the calendar year. on successive days through the calendar year.

• This apparent shift of Sun’s position is due to This apparent shift of Sun’s position is due to the Earth’s orbit about the Sunthe 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 Summerthe highest point is Summer the lowest point, Winterthe lowest point, Winter


ANALEMMAANALEMMA


ANALEMMAANALEMMA The Analemma has a The Analemma has a

calendar printed on itcalendar printed on it• This calendar indicates This calendar indicates

which latitude (subsolar which latitude (subsolar point) receives the Sun’s point) receives the Sun’s direct rays at noon direct rays at noon (“Zenith Angle”) on any (“Zenith Angle”) on any day of the year.day of the year.

The most northern The most northern latitude is 23.5latitude is 23.500 North North

The most southern The most southern latitude is 23.5latitude is 23.500 South South

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

Documents

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