Chapter_1_notes - GEOG 101 Chapter 1 – Earth-Sun...

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Unformatted text preview: GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ Geography Geography • • • • • More than just memorizing place names! Space is to Geography as Time is to History Geo – the earth Geo Graphos – to write about Graphos Geography means “to write about the earth” ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Geography Geography • Can be divided into three areas of study: – Physical Geography – the science of life the environments, from local to global scales environments, – Human Geography – the study of how the humans interrelate with their environment humans – Geographical Techniques – remote sensing, remote geographic information systems, air photo interpretation, cartography interpretation, ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Physical Geography Physical • Can be divided into four realms: – The Atmosphere – gaseous layer surrounding gaseous the earth the – The Hydrosphere – water in solid, liquid, and water gaseous forms gaseous – The Lithosphere – the solid earth The – The Biosphere – life, in all its varied forms ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ 1 GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ ___________________________________ Chapter 1 Chapter Earth-Sun Relationships Originally, the earth was flat and at the center of the universe…or so we thought. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Early Round Earth Proponents Early • Pythagoras in 540 B.C. • Aristotle in 350 B.C. • Eratosthenes – Egypt, 230 B.C. Eratosthenes • Posidonius – Egypt, 80 B.C. Posidonius ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ More Recent Proofs of a Round Earth More • Magellan (1519-1522 A.D.) – Proved the earth is a solid, curved figure ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ • Proof the Earth is a Sphere – Navigation – Astronomy – Lunar Eclipses – Satellites – Space Flight 2 GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ …But, the Earth is NOT a sphere! …But, • Jean Richer (1671) – Sent by Louis XIV from Paris to Cayenne, French Guiana – Prized pendulum clock lost 2½ minutes a day – Gravity (Newton, 1686) is the force which draws mass to the center of the Earth – Thus, the Earth’s radius is larger at Cayenne than at Paris – Which implies that the Earth is an ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Oblate Ellipsoid North/South (Polar) Diameter: 12,714 km East/West (Equatorial) Diameter: 12,756 km ___________________________________ …However, the Earth is at the center of the universe…right? center • Ptolemy – Geocentric “Earth-centered” Universe “Earth• Copernicus (1543) – Postulated the Heliocentric “Sun-centered” Universe with planets and stars “Sunorbiting the Sun in circular orbits – No Proof Given • Johannes Kepler (1609) – Laws of Planetary Motion – First Law – Planets (only) orbit the sun in elliptical, not circular, orbits – Second Law – A line connecting the Earth and Sun sweeps out equal areas in equal time periods – Third Law – Does not pertain to us here • (Period of revolution)2 ∝ (distance from the sun)3 ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Planetary Motions Planetary • Revolution – movement of the Earth about the Sun • Rotation – movement of the Earth about its axis – A rotating sphere implies there are North and South North Poles (intersection of the Earth’s axis with the surface) ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ • Viewed from above the North Pole, the Earth revolves around the Sun counter-clockwise counterand rotates on its axis in a counter-clockwise countermanner. The same is true for the moon. 3 GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ Planetary Motions Planetary ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Locating Places on the Earth Locating • Latitude – measure of the north-south dimension northSince we have an axis of rotation, we can measure one dimension relative to that axis ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ • North and South Poles – locations where the North axis of rotation intersects the earth’s surface • Equator – a line around the earth’s surface that is Equator equidistant from the two poles Thus, the equator divides the earth into two hemispheres. hemispheres Any such line is called a Great Circle. Any Great • A Nautical Mile – one minute of arc length at the Nautical equator – thus, the earth’s circumference is 21,600 nmi ___________________________________ North Pole = 90oN South Pole = 90oS Equator = 0o ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Latitude: 0o to 90o North or South ___________________________________ 4 GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ Locating Places on the Earth Locating • Latitude All lines of latitude are parallel; hence they are also called parallels parallels Only the equator is a Great Circle; all other parallels are Small Circles Small ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Locating Places on the Earth Locating • Longitude – measure of the east-west dimension eastNo “natural” starting point – by convention, the astronomical observatory in Greenwich, England is used ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ • Prime Meridian – 0o of longitude – passes Prime through the Greenwich Observatory • Longitude – east or west of the Prime Meridian • Unlike lines of latitude, ALL lines of longitude ALL converge at the poles; hence, a longitude line is one-half of a Great Circle one• Opposite the Prime Meridian is 180o longitude – also called the International Date Line International ___________________________________ Longitude: East or West 0o to 180o ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ 5 GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ Latitude Latitude Longitude ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ …Back to Kepler and his and 1st Law ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ • Kepler’s 1st Law – All planets (only) Kepler’s Law All revolve about the sun in elliptical orbits elliptical • Therefore, the earth sometimes is closer to Therefore, the sun and sometimes it is farther away the • On average, the earth is about 150 million On kilometers from the sun kilometers • Nearest – 147 million km – Perihelion – Jan 4 Perihelion • Farthest – 152 million km – Aphelion – July 4 Aphelion 6 GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ ___________________________________ ___________________________________ BUT, THE ELLIPTICAL NATURE OF THE EARTH’S ORBIT IS NOT THE REASON NOT THE WHY WE HAVE SEASONS! WHY ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ The Reason We Have Seasons is that the The Earth’s Axis is Tilted with Respect to the Plane of the Ecliptic • The Plane of the Ecliptic is the imaginary The Plane is plane in which the Earth’s orbit lies. plane • As the Earth revolves about the sun, As imagine the center of the Earth and the ellipse that it would transcribe. ellipse • During the Earth’s revolution about the During sun, the center of the earth always always remains in the Plane of the Ecliptic ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ • The Earth’s Polar Axis is tilted at a constant Polar The is inclination (toward the star, Polaris). Polaris • The Earth’s Polar Angle is 66½° – that is, Polar The is that Plane of the Ecliptic the angle between the Plane and the Earth’s axis. and • Or, we can say that the Earth’s Axial Tilt is Axial Or, is 23½° – the angle from being perpendicular the to the Plane of the Ecliptic. Plane • Both representations are correct – just make Both just sure to keep the definitions straight! sure ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ 7 GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Northern Hemisphere Northern Hemisphere ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ But why does this Axial Tilt cause the Seasons? Seasons? • Since the Earth’s axis is always inclined at a Since Polar Angle of 66½° (a tilt angle of 23½°) and always pointed at the star, Polaris, Polaris during part of the year, the North Pole will be pointed toward the sun (South Pole pointed away from the sun) and during the other part of the year, the North Pole will be pointed away from the sun (South Pole pointed toward the sun). pointed ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ 8 GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ If the Earth were not tilted on its axis… If ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ If the Earth were not tilted on its axis… If • The sun’s rays would always be at an angle always be The of (90°-latitude) at noon during all times of of latitude) the year. the • Note that the Circle of Illumination Circle Note separates the Earth into a sunlit hemisphere separates and a dark hemisphere – hence the Circle of hence Illumination is a Great Circle! Illumination is Great ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ But since the Earth IS tilted on its axis… IS ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Note the Northern Hemisphere Bias! 9 GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ But since the Earth IS tilted on its axis… IS • Equinox – one of two times during the one year when the sun’s rays are directly overhead at the equator overhead – On March 21– which is called the 21– • Vernal Equinox in the Northern Hemisphere or the • Autumnal Equinox in the Southern Hemisphere Autumnal in ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ – And on September 23– which is called the 23– • Vernal Equinox in the Southern Hemisphere or the • Autumnal Equinox in the Northern Hemisphere Autumnal in ___________________________________ But since the Earth IS tilted on its axis… IS • Solstice – one of two times during the year one when the sun’s rays are directly overhead at a point farthest from the equator at – At 23½°N on June 21– which is called the 21– • Northern Hemisphere Summer Solstice or the • Southern Hemisphere Winter Solstice ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ – At 23½°S on December 22– called the 22– • Northern Hemisphere Winter Solstice or the • Southern Hemisphere Summer Solstice ___________________________________ • A Calendar Year is defined as 365 days Calendar • However, it actually takes 365 days, 5 hrs, However, 48 min, and 46 sec for the Earth to make a single revolution about the sun! This is called a Tropical Year. Tropical • Because a Calendar Year and a Tropical Because and Tropical Year are not equal, we have to add a day Year are every fourth year – called a Leap Year. called Leap • Leap Seconds are added occasionally are (usually at 11:59PM on December 31) since the Earth wobbles on its axis. wobbles on ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ 10 GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ Given that the Earth IS tilted on its axis… Given ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ June 21 December 22 ___________________________________ Given that the Earth IS tilted on its axis… • Tropics – latitudes where the sun’s rays are latitudes directly overhead at noon during a solstice. directly – In the Northern Hemisphere, we have the Tropic of Cancer located at 23½°N latitude Tropic – In the Southern Hemisphere, we have the Tropic of Capricorn located at 23½°S latitude Tropic ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Given that the Earth IS tilted on its axis… • Circles – latitudes where the sun’s rays are latitudes on the horizon at midnight during a solstice. on – In the Northern Hemisphere, we have the Arctic Circle located at 66½°N latitude Arctic – In the Southern Hemisphere, we have the Antarctic Circle located at 66½°S latitude Antarctic ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ • Areas poleward of a circle experience at Areas poleward of least one 24 hour day and one 24 hour night least • The poles experience six months of sunlight The and then six months of darkness! and 11 GEOG 101 Chapter 1 – Earth-Sun Relationships ___________________________________ Given that the Earth IS tilted on its axis… • The Equator always has 12 hours of sunlight The Equator has and 12 hours of darkness each day and – Why? Because both the Equator and the Circle of Equator Circle Illumination are Great Circles! Thus, ALL Great Great Circles bisect one another. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ • During an Equinox, there are 12 hours of During Equinox there sunlight and 12 hours of darkness everywhere! everywhere – Why? Because the Circle of Illumination bisects Circle every parallel during an equinox! ___________________________________ In Case You Were Wondering… In • Kepler’s Second Law of Planetary Motion Kepler’s Second – The line joining the planet to the Sun sweeps out equal areas in equal times as the planet travels around the ellipse. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Graphic courtesy of: http://csep10.phys.utk.edu/astr161/lect/history/kepler.html The Analemma The ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ From http://www.steveirvine.com/analemma.html From http://www.20thcenturyglobes.com/glossary.htm 12 ...
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