Chapter 1: Introduction to Earth McKnight s Physical Geography: A Landscape Appreciation, Tenth Edition, Hess
Introduction to Earth Geography as a Field of Learning Science and Geography The Environmental Spheres The Solar System The Size and Shape of Earth The Geographic Grid Earth-Sun Relations The Annual March of the Seasons Telling Time 2
Geography as a Field of Learning Definition Earth Description Geo = earth Many sciences branch from geography Physical versus cultural Why what is where and so what? 3
Science and Geography The Scientific Method Observe phenomena Formulate a hypothesis Design an experiment Predict the outcome of the experiment Conduct the experiment Draw conclusions Scientific proof 4
Science and Geography Measurement Systems Need measurement systems to quantify scientific processes SI versus English units Conversions 5
The Environmental Spheres Four primary spheres 1. atmosphere air around us Atmo = Air 2. lithosphere rock and soil, solid part of the earth Litho = Stone 3. hydrosphere water in all its forms Hydro water 4. biosphere all living things, plants, animals, bacteria, viruses Bio = Life 1 2 4 3 Interactions between the spheres No part exists independently of the others! 6
The Solar System Formation of the Solar System Formed 4.5 to 5 billion years ago 8 planets revolve around the Sun 4 terrestrial planets 4 gas giants Earth is the third planet Figure 1-4 7
The Solar System Figure 1-5 8
The Size and Shape of the Earth Earth s Physical Characteristics Oblate spheroid Approximate diameter 7900 miles Bulges at equator, flattened at poles Equatorial diameter ~ 7926 miles Polar diameter ~ 7900 miles Circumference of 24,900 miles 9
Eratosthenes Measured the circumference of the earth in 247 BCE His circumference 26,700 miles actual 24,900 miles Used simple geometry and trigonometry! 10
Maximum Relief Difference in elevation between highest and lowest points on earth Total difference is 65,233 feet Top of Mt. Everest 29,035 feet above sea level Bottom of Mariana Trench 36,198m feet below sea level If the earth were a basketball, Mt. Everest would be one of the little pimples on the surface! 11
The Geographic Grid Location on Earth Need an accurate location on Earth to describe geographic features Use Earth s rotation axis to base location on the surface North Pole and South Pole Plane of the Equator halfway between poles and perpendicular to Earth s surface Graticule - the grid system Figure 1-9 12
The Geographic Grid Great Circles Circles which bisect a sphere and pass through the sphere s center Identify the shortest distance between two points on a sphere great circle distance (arc) Airplane routes are Great Circles Circle of illumination - Division between daylight and darkness Small circles all others Figure 1-10 13
Example of Geographic Grid Each point of earth s surface has a unique intersection of the grid lines Uses a coordinates system with X and Y axis 14
The Geographic Grid Latitudes Parallels angle north or south of the equator ¼ of 360 degrees = 90 degrees From Equator to Pole 7 important latitudes:» Tropic of Cancer and Capricorn (23.5 N and S)» Equator (0 )» Poles (90 N and S)» Arctic and Antarctic Circles (66.5 N and S) Know these!! Figure 1-12 15
Tropics Latitude Zones Hot, wet climate Between Tropics of Cancer and Capricorn 23.5 N and 23.5 S, with Equator in the middle Mid-Latitudes Temperate climate Between Tropic of Cancer and Arctic Circle (N) Between Tropic of Capricorn and Antarctic Circle (S) Polar Cold, dry climate North of the Arctic Circle (N) and south of the Antarctic Circle (S) 16
The Geographic Grid Longitudes Meridians Prime Meridian (0 longitude) located at Greenwich, England Zero Degrees = Prime Meridian 180 Degrees = International Date Line ½ of 360 degree circle is 180 degrees Measures as angle east or west of the Prime Meridian Must include east or west with all longitude lines except 0 degrees (Prime Meridian) and 180 degrees (International Date Line) Figure 1-16 Converge at the poles Farthest apart at the equator
Longitude Standardized Prime Meridian = Zero degrees longitude Goes through Greenwich, England, a suburb of London Chosen by international conference in 1880s to standardize longitude and time worldwide due to train travel Height of the British Empire so met at Royal Observatory made it the starting point for longitude. 18
Format for geographic location Where is Los Angeles? Latitude, Longitude Los Angeles: 34 N, 118 W GPS reading will be more accurate, down to minutes and seconds! 19
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Graticule geographic grid system of latitude and longitude lines 21
Earth-Sun Relations Rotation of the Earth 24 hours for one rotation (360 degrees = circle) Circular motion at all latitudes but the poles Rotation is counterclockwise relative to the North Pole Rotates toward the EAST Reason sun rises in the east and sets in the west Converge at the poles Poles in light ½ year, darkness ½ year Diurnal transition from light to darkness Circle of Illumination division between light and darkness Tidal effects from the Moon and Sun 22
Rotates toward the east Makes one complete rotation every 24 hours Tilted at 23.degrees from perpendicular of the Axis of Rotation (orbital plane) Where is surface rotation speed fastest? Slowest? 23
Earth-Sun Relations Earth s Revolution around Sun Rotation vs. Revolution One revolution takes 365 ¼ days Elliptical orbit Aphelion farthest July 4 Perihelion closest January 3 Average distance 1 AU Astronomical Unit = 92,955,806 miles Round to 93 million miles Figure 1-19 Earth at perihelion during Northern Hemisphere winter; aphelion during Northern Hemisphere summer 24
Earth-Sun Relations Orbital Properties Plane of the Earth s orbit is the Plane of the Ecliptic Earth s axis tilted at 23.5 Plane of ecliptic is not parallel to equatorial plane Polarity of the Earth s axis» Parallelism (polarity) earth does not wobble on its axis» North Pole always points toward Polaris ( North Star ) Figure 1-20 25
The Annual March of the Seasons Three important conditions Declination of the Sun Where sun is shining 90 to surface direct sun Solar altitude (angle) Length of day Two solstices June solstice December solstice Two equinoxes March equinox September equinox Figure 1-22 26
The Annual March of the Seasons June solstice Occurs on approximately June 22 each year Sun is directly overhead at 23.5 N latitude Antarctic Circle in 24 hours of darkness Marks start of summer in Northern Hemisphere; winter in Southern Hemisphere Figure 1-22 27
The Annual March of the Seasons December solstice Occurs on approximately December 22 each year Sun is directly overhead at 23.5 S latitude Arctic Circle in 24 hours of darkness Marks start of winter in Northern Hemisphere; summer in Southern Hemisphere Figure 1-22 28
The Annual March of the Seasons Equinoxes Occur on approximately March 21 and September 21 each year Day length is 12 hours worldwide ( equinox ) Sun is directly overhead at the equator Figure 1-22 29
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The Annual March of the Seasons Day length Always 12 hours at the equator In the Northern Hemisphere, day length increases after March equinox Maximum day length during June solstice in Northern Hemisphere Opposite for Southern Hemisphere 31
The Annual March of the Seasons Significance of seasonal patterns Spread of solar rays over small and large areas Direct sun = smaller area, more concentrated Tropical latitudes consistently warmer High sun angle, always long days Polar latitudes consistently cooler Low sun angle, some days sun never rises Large seasonal variations in temperature in midlatitudes Many factors, lots of seasonal changes in sun angle, day length, and location of declination (direct sun) Winter declination of the sun is in opposite hemisphere 32
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Telling Time Three physical measures of time Tropical year - seasons Lunar month new moon Solar day noon to noon, sun at highest position in the sky Solar noon Sun casts the shortest shadow Pre-modern people used this for time, so all towns were different Ante-meridian (AM before noon ) Post-meridian (PM after noon ) Figure 1-23 35
Telling Time Current time system 24 time zones Greenwich Mean Time (GMT) is standard Controlling Meridian for each time zone Several countries have multiple time zones in their borders Time zone boundaries subject to local political and economic boundaries of different nations 180 meridian chosen as the International Date Line 36
Telling Time Time zones of the world Figure 1-24 37
Telling Time Time zones of the United States Figure 1-25 38
Telling Time Daylight-saving time Move clocks ahead by an hour during the summer months Originally done by Germans during WWII; now practiced by many nations Conserves lighting energy by providing an extra hour of daylight 39
Summary Geography is the study of the distribution of physical and cultural attributes of Earth Many sciences have branched off of geography The scientific method is important when doing scientific studies Earth has four primary spheres: the atmosphere, the lithosphere, the hydrosphere, and the atmosphere The solar system formed 5 billion years ago and consists of 8 planets 40
Summary Earth is an imperfect sphere A latitude and longitude grid help identify locations on Earth s surface Earth rotates on its axis in 24 hours Earth revolves around the Sun in 365 ¼ days Tilt of Earth s axis causes seasons Equinoxes and solstices help identify when a seasonal transition occurs 41
Summary Time zones were established to have a uniform global time system Daylight-saving time was devised to conserve energy by adding an hour of daylight 42