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Chapter 3 Notes (ALL)

by: Larresa Kelpin

Chapter 3 Notes (ALL) GEOG 104

Marketplace > Kansas > Geography > GEOG 104 > Chapter 3 Notes ALL
Larresa Kelpin
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These are notes on all the assignment material for Chapter 3.
Principles of Physical Geography
Johnson, William
Class Notes
Geography 104, university of kansas, Johnson




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This 7 page Class Notes was uploaded by Larresa Kelpin on Friday January 29, 2016. The Class Notes belongs to GEOG 104 at Kansas taught by Johnson, William in Summer 2015. Since its upload, it has received 27 views. For similar materials see Principles of Physical Geography in Geography at Kansas.


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Date Created: 01/29/16
CHAPTER 3| EARTH-SUN GEOMETRY AND THE SEASONS “<” = less than Learning Objectives 1. Understand the Earth’s position in space. 2. Describe the nature of Earth’s axial tilt and orbit around the Sun. 3. Discuss the concept of the subsolar point and its seasonal movement. 4. Explain why the Equator, Tropic of Cancer, and Tropic of Capricorn are important features associated with Earth-Sun geometry. 5. Explain the concept of Sun angle and how it varies both by latitude and seasonally. 6. Understand how we sense the Earth-Sun geometric relationship. 7. Demonstrate understanding of Earth-Sun relationships by accurately predicting outcomes based on variable tilt scenarios. OUR PLACE IN SPACE § Big Bang theory – the theory that the Universe originated about 14 billion years ago when all matter and energy erupted from a singular mass of extremely high density and temperature. - The primary evidences for this theory are: 1. The most distant star clusters are moving away from us at greater speeds than those that are relatively close 2. The amount of cosmic microwave background radiation is remarkably uniform through the Universe, which implies that it represents the leftover energy from an early period of rapid expansion. § The largest clearly definable unit within the Universe is a galaxy. - The Universe has approx. 50 billion galaxies, with each containing billions of stars. § We live in the Milky Way galaxy, with approx. 400 billion stars. - The MW is a spiral galaxy, consisting of a bright central region w/ a high density of stars and a flat circular region containing most of the other stars. - Younger, brighter stars form in long spiral arms that extend out from the galactic center, which is where our solar system lies. 1 CHAPTER 3| EARTH-SUN GEOMETRY AND THE SEASONS “<” = less than § There are eight official planets that orbit the Sun, the center of our solar system, with Pluto now considered a dwarf planet. Earth is the third planet from the sun. The Shape of Earth § Although Earth appears to be a perfect sphere, it bulges slightly at the Equator and is flattened somewhat at the poles to form an oblate spheroid. - The circumference of Earth measured at the Equator is 40,075 km (24,902 mi), while the circumference measured at the poles is slightly less: 40,009 km (24,860 mi). - The bulge is caused mainly by the centrifugal force of Earth’s rotation and by differences in density of the Larresa Kelpin 1/29/2016 12:41 PM Earth’s crust and gravitational field. Comment [1]: This is similar to the sideways push you feel when rounding a curve quickly § The shape is an important factor to consider regarding the in a car. Earth-Sun relationship. Earth presents a curved surface to the Sun’s rays, so the intensity of solar radiation received varies by latitude. - This difference is a reflection of the Sun angle, or the angle at which the Sun’s rays strike Earth’s surface. ∗ In general, the Sun angle is relatively high at low latitudes and becomes progressively less toward the poles. 2 CHAPTER 3| EARTH-SUN GEOMETRY AND THE SEASONS “<” = less than § In the above figure, you can see that lower latitudes receive intense solar radiation because the Sun angle is high (between 75º and 90º). The point where the Sun’s rays are perpendicular (Sun angle = 90º) and most intense is known as the subsolar point. In contrast, high latitudes receive less intense radiation because the Sun’s rays hit Larresa Kelpin 1/29/2016 12:40 PM at much < 90º. Comment [2]: The location of the subsolar point changes throughout the year. - This curvature has a corresponding effect on incoming solar radiation, which greatly contributes to geographic patterns on Earth such as atmospheric circulation and the global distribution of climate, vegetation and soils. Earth’s Orbit Around the Sun § Earth revolves in a counterclockwise direction relative to a view above the N Pole on a flat (imaginary) plane referred to as the plane of the ecliptic. § It takes about 365 days (365.24 days, exactly) for the Earth to make one full revolution. In comparison, Pluto require 248 Earth years to complete one orbit. - The Leap Year was added in order to correct the uneven length of time it takes for Earth to complete its orbit. § As Earth orbits, it follows an elliptical path, shown above. The Earth is at its closest to the Sun at perihelion 3 CHAPTER 3| EARTH-SUN GEOMETRY AND THE SEASONS “<” = less than (Jan. 3) and the farthest away from the Sun at aphelion (July 4). - We might assume that we would be experiencing summer when we are closer to the Sun, but in the Northern Hemisphere, we are experiencing winter. This is because our distance from the Sun does not cause seasons, the Earth’s axial tilt does. The Earth’s Rotation and Axial Tilt § As Earth revolves around the Sun, it also spins on its axis, an imaginary line that extends from pole to pole. - It takes Earth 24 hours to make a complete rotation. During this, one-half of the Earth is illuminated while the other is in shadow. This boundary is called the circle of illumination and is constantly moving across Earth’s surface as it rotates. § In association with Earth’s rotational cycle, humans established 24 time zones that span specific portions of the planet. The contiguous U.S. contains four zones, the 4 CHAPTER 3| EARTH-SUN GEOMETRY AND THE SEASONS “<” = less than Eastern, Central, Mountain, and Pacific Time zones. Each of these zones covers about 15º of longitude because it takes 1 hour for Earth to rotate that distance (360º/24 h = 15º/h). § The Prime Meridian was chosen as the standard for the entire time zone system at the 1884 International Prime Meridian Conference in Washington, D.C. The vast majority of countries on Earth uses this system, which is referred to as Universal Time Coordinated (UTC), although some (such as Saudi Arabia) adhere to their own time systems. - The beginning and end of each calendar day is the International Date Line, located at 180º longitude. § It is important to remember that the axis is not at a 90º Larresa Kelpin 1/29/2016 12:38 PM Comment [3]: When travelling west, the day relative angle to the place of the ecliptic. The Earth’s moves ahead. axis is tilted 23.5° from a line perpendicular to the plane. THE SEASONS § Without the axial tilt, we would have no seasons because all places on Earth would receive a consistent intensity of solar radiation as the Earth revolves around the Sun. § The axial tilt maintains a constant tilt angle and orientation as Earth travels around the Sun. - In the image below, we can see that the tilt did not change, nor did the orientation of the tilt. Instead, the position of Earth relative to the Sun changed as its orbit progressed. 5 CHAPTER 3| EARTH-SUN GEOMETRY AND THE SEASONS “<” = less than Solstice and Equinox § In the Northern Hemisphere, the first day of summer is sometime toward the end of June. Conversely, in the Southern Hemisphere, the first day of summer is toward the end of December. § The dates that mark seasons are approximately the same every year because they indicate key periods within the Earth-Sun geometrical relationship. § Remember, the subsolar point moves between 23.5°N and 23.5°S over the course of a year. - Early astronomers found it useful to mark the passage of the season by noting the date when the Sun’s rays are perpendicular to the Equator, to the Tropic of Cancer (23.5°N) and to the Tropic of Capricorn (23.5°S). § March 20-21: Spring Equinox (vernal equinox) - Represents the official beginning of spring in the N. Hemisphere and the official beginning of fall in the S. Hemisphere. - The subsolar point is located at the Equator and neither Hemisphere is tilted toward the Sun. § June 20-21: Summer Solstice - Represents the official beginning of summer in the N. Hemisphere and the official beginning of winter in the S. Hemisphere. - The subsolar point is located at the Tropic of Cancer (23.5°N). The N. Hemisphere is tilted toward the Sun, and the S. Hemisphere is tilted away from the Sun. § September 22-23: Fall Equinox (autumnal equinox) - Represents the official beginning of fall in the N. Hemisphere and the official beginning of spring in the S. Hemisphere. - The subsolar point is now once again at the Equator and neither Hemisphere is tilted toward the Sun. § December 21-22: Winter Solstice - Represents the official beginning of winter in the N. Hemisphere and the official beginning of summer in the S. Hemisphere. - The subsolar point is located at the Tropic of Capricorn (23.5°S). The S. Hemisphere is tilted toward the Sun, and the N. Hemisphere is tilted away from the Sun. 6 CHAPTER 3| EARTH-SUN GEOMETRY AND THE SEASONS “<” = less than HUMAN INTERACTIONS: HOW WE SEE EARTH-SUN GEOMETRY ON EARTH Day and Night § The sun rises in the east and then arcs across the sky to set in the west. - As the arc progresses throughout the day, the Sun reaches its highest position at solar noon. * Solar noon is not necessarily equivalent to standard clock time because the time of sunrise and sunset varies across a time zone due to the curvature of Earth. Seasonal Changes in Sun Position and Length of Day § In addition to the daily or diurnal cycle of day and night, which is related to the Earth’s rotation, we can also see a seasonal cycle in the Sun’s position in the sky, which depends on orbital progression. - In the N. Hemisphere, the sun is higher in the sky during the Summer Solstice and lower during the Winter Solstice. - In relation, the days are longest during the Summer Solstice and shortest during the Winter Solstice. - The opposite is true for the S. Hemisphere. The sun is higher in the sky during the Winter Solstice and lower during the Summer Solstice. - In relation, the days are longest during the Winter Solstice and shortest during the Summer Solstice. § You can see the combined daily and seasonal migrations of the Sun, with respect to the Earth’s surface, in a graphical way by examining the figure below. This diagram is called a celestial dome, a sphere that shows the Sun’s arc, relative to the Earth, in the sky. 7


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