GEOG 1290 Section C Fall 2024 PDF

Section C. Earth Sun Geometry and The Seasons Introduction to Physical Geography GEOG 1290 Department of Environment and Geography University of Manitoba...

Section C. Earth Sun Geometry and The Seasons Introduction to Physical Geography GEOG 1290 Department of Environment and Geography University of Manitoba Lisa Ford and Janna Wilson © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  Copyright Lecture slides, course notes, and educational resources are copyright-protected and made available to you for your personal educational use and private study only. Unless stated otherwise, further copying and distribution of these materials is strictly prohibited. © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited. © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  C.1 The Four Seasons Learning Objectives Describe the nature of Earth’s orbit around the Sun, including revolution, rotation, & axial tilt, & explain the concept of angle of incidence & how it varies by latitude. Discuss the seasons with reference to the Equator, the Tropic of Cancer, the Tropic of Capricorn, & the shifting subsolar point. Describe how humans experience the Earth–Sun geometric relationship. © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  The Shape of the Earth Oblate Spheroid: near-perfect sphere Bulge at the Equator - Circumference = 40,075 km Flattened at the Poles - Circumference = 40,008 km © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  Angle of Incidence Curvature influences angle of incidence by latitude Low latitudes have higher angle of incidence (↑ intensity) High latitudes have lower angle of incidence (↓ intensity) Subsolar point Sun is directly overhead 90 degree angle Figure 4-21 Atmospheric obstruction of sunlight (Hess and Finch, 2022, p. 93). © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  Spatial reference points Equatorial plane (Equator) Parallel of 0 degrees latitude Rotation Axis North and South Poles Figure 1-10 Earth’s rotation axis (Hess and Finch, 2022, p. 19) Plane of the ecliptic: an imaginary plane that passes through the Sun and every point of Earth’s orbit Figure 1-22 Plane of the Ecliptic (Hess and Finch, 2022, p. 19) © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  Earth’s orbit around the sun Counterclockwise revolution Elliptical path around Sun Perihelion: closest point in One full revolution = 365.24 orbit days Aphelion: farthest point in orbit One rotation = 24 hours Seasons are not caused by distance from sun! Plane of the ecliptic Aphelion 152,100,000 km 147,300,000 km Perihelion J. Wilson, 2022 © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  A Hypothetical Scenario If the Earth’s axis were perpendicular to the plane of the ecliptic: the subsolar point would always be at the Equator The circle of Illumination would always run directly North-South BUT, that’s not what actually happens Figure 3.9 Geometric Relationship if the Earth’s Axis were perpendicular to the plane of the ecliptic (Arbogast et al. 2018, p. 55) © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  The Cause of the Seasons The seasons are caused by a combination of rotation, revolution, and tilt/inclination Earth’s tilt, known as polarity (or parallelism) the Earth’s axis points towards the North Star (Polaris) Axis is tilted 23.5° from the perpendicular to the plane of ecliptic Axis maintains alignment during orbit around the Sun Figure 1-23 Earth’s rotation axis (Hess and Finch, 2022, p. 19) © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  Migration of the Sub-Solar Point As a result of the combination of factors, the subsolar point migrates throughout the year between the Tropic of Cancer and the Tropic of Capricorn (23.5°N and 23.5° S) Figure 3.11 Range of Seasonal Subsolar Point (Arbogast et al., 2018, p. 55) © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  The Four Seasons Figure 1-24 The annual march of the seasons (Hess and Finch, 2022, p. 20) © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  June Solstice (around June 21) North Pole is oriented most directly toward the Sun Rays of Sun at noon strike perpendicular to the surface of the Tropic of Cancer (23.5° N of the equator) Sub-solar point Arctic circle: all points North of 66.5° north latitude experience 24 hours of light on this day (all points within 23.5 degrees of the North Pole) Figure 1-24b June Solstice (Hess and Finch, 2022, p. 20) © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited. September and/or March Equinox (AKA autumnal or vernal equinox) all latitudes experience 12 hours of day and 12 hours of night all latitudes are bisected evenly by the circle of illumination Sub-solar point Located at the Equator Figure 1-24c Equinox (Hess and Finch, 2022, p. 20) © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  December Solstice (around Dec 21) rays of the Sun at noon strike perpendicular to the surface of the Tropic of Capricorn (23.5° S) day lengths are longer in the Southern Hemisphere day length is equal at the equator Antarctic Circle – all points South of the parallel of 66.5° south latitude experience 24 hours of light Figure 1-24d December solstice (Hess and Finch, 2022, p. 20) © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  Solstices and Equinoxes June Solstice September December March Equinox Equinox Solstice Date ~June 22 ~Sept. 23 ~Dec. 22 ~March 20 23.5° N 0° 23.5° S 0° Declination of Tropic of Equator Tropic of Equator Subsolar Point Cancer Capricorn Hours of 24 hrs. N. Pole 12 hrs. 24 hrs. S. Pole 12 hrs. daylight 12 hrs. Equator everywhere 12 hrs. Equator everywhere 0 hrs. S. Pole 0 hrs. N. Pole Season N. H. Summer N. H. Fall N. H. Winter N. H. Spring S. H. Winter S. H. Spring S. H. Summer S. H. Fall © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  Global Time 24 time zones Each zone covers 15 of longitude (takes Earth 1 hour to rotate that distance) 24 hours for a full rotation of 360 360/24 hr = 15/1 hr Prime Meridian (Greenwich, England) Standard 0 for time zone system International Date Line 180 Meridian marks the start and end of each calendar day Asymmetrical zones are the result of politics © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  Canadian Time Zones Figure C.1.e Time Zones and Daylight Savings Time (Natural Research Council of Canada, 2022, retrieved from https://nrc.canada.ca/en/certifications-evaluations-standards/canadas-official-time/time-zones-daylight-saving-time © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  Earth-Sun Geometric Relationship Solar Noon the time of day when the sun reaches its highest point above the horizon Figure 3.14 a & b. The Celestial Dome 3.14a & b (Arbogast, 2018, p. 59) © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  People and the Seasons Many human activities and holidays mark seasonal events, (harvests, many religious festivals, etc.) Summer Spring Figure C.1.f Stonehenge, England Autumn Image by Howard Walsh https://pixabay.com/photos/stonehenge-travel-tourist-england- 4614639/ E Winter W S © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.  References Arbogast, A., Ford, L., & Dagesse, D. (2018). Discovering Physical Geography (1st Canadian ed). Wiley. McKnight, T. L., & Hess, D. (2008). Physical Geography: A Landscape Appreciation (9 th ed). Pearson. Hess, D., & Finch, R. (2022). McKnight’s Physical Geography, A Landscape Appreciation (13th edition). Pearson. © Lisa Ford & Janna Wilson, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited.