The Equator bisects the sphere of the Earth. It is therefore called a great circle
 
 
 

Geography as a Field of Learning

Geography is a generalized discipline that has the face of planet Earth as its focus.  It derives from the Greek roots geos = Earth; graphia = descrption that is  “earth description,”  Geography con be viewed as the areal differentiation of Earth’s surface.

The fundamental questions of geographic inquiry are: a) “Why is What Where?” and b) “So What?”

Geography’s basic characteristics are as follows: It looks at how things differ from place to place; It has no peculiar body of facts or objects it can call wholly its own; It is a very broad field of inquiry and “borrows” its objects of study from related disciplines; It is both a physical science and a social science because it combines characteristics of both and can be conceptualized as bridging the gap between the two; and It is interested in interrelationships, that is, examining how various factors (both physical and cultural) interrelate.

Geography has two main branches, Physical Geography and Cultural Geography: Physical Geography—also known as environmental geography, it looks at those Earth elements that are natural in origin; and Cultural Geography—also known as human geography, looks at elements of human endeavor.

The Major Environmental Spheres

The Earth can be viewed as a complex system composed of four basic subsystems that includes the solid, gaseous, liquid and biotic parts of the Earth’s surface all of which are interrelated  they are:
The Lithosphere—the solid, inorganic portion of Earth; it comprises the rocks of Earth’s crust and the mineral matter that overlies the solid bedrock; (litho is Greek for “stone”).
TheAtmosphere—the gaseous envelope of air that surrounds Earth (atmo is Greek for “air”).
The Hydrosphere—water in all its forms, with the oceans making up the majority of it (hydro is Greek for “water”).
The Biosphere—all the living organisms of Earth (bio is Greek for “life”).
 

The Solar System
The Origin of the Solar System: The Nebular Hypothesis of Solar System Formation
Several consecutive steps towards the formation of our Solar System: (1) a vast and diffuse nebula of gas and dust. (2) Slowly, gravitational forces cause the nebula to contract and heat up. (3) Eventually it becomes a rotating disk surrounding the protostar that will become the Sun. (4) Small rocky bodies develop in the inner reaches of the solar system, and these collide with each other to create larger asteroid-sized bodies called planetesimals. (5) Larger planetesimals accrete smaller planetesimals, leading to the formation of the nine major planets and the asteroid belt.

The geographer’s concern with spatial relationships properly begins with the relative location of Earth in the universe. Solar system—system of nine planets (and moons, comets, asteroids, meteors) revolving around the Sun; Earth is third.  The Sun—medium-sized star and makes up more than 99 percent of the solar system’s mass. The Sun is one of perhaps 100,000,000,000 stars in the Milky Way Galaxy, which is one of at least a billion galaxies in the universe.

Earth’s planetary orbit lies in nearly the same plane as all the other planets, except that of Pluto’s, which is somewhat askew. Earth, like all the planets, revolves from west to east. Earth, like the Sun and most of the other planets, rotates from west to east on its own axis.
 
 

The Earth

The Size and Shape of Earth: the frame of reference determines whether one looks at Earth as being large or small. The Earth is an oblate spheroid rather than a true sphere, though the variation from true sphericity is exceedingly minute, and so for most purposes it can properly be considered a sphere: Greek scholars as early as six centuries B.C. began believing Earth was a sphere, with several making independent calculations of its circumference that were all close to reality. Earth shape is affected by two main facts: (1) It bulges in midriff, because of pliability of Earth’s lithosphere; (2)  It has topographical irregularities. In context of Earth’s full dimensions, these variations are minute.

The Geographic Grid:The location of point X can be described as 2B or as B2; the location of Y is 3D or D3.
A system of accurate location is necessary to pinpoint with mathematical precision the position of any spot on Earth’s surface. The grid system is the simplest technique, using a network of intersecting lines. The Graticule—the grid system for mapping Earth that uses a network of parallels and meridians (lines of latitude and longitude). Four Earth features provide the set of reference points essential to establish the graticule as an accurate locational system: the North Pole, the South Pole, the rotation axis, and the equatorial plane (an imaginary plane passing through Earth halfway between the poles and perpendicular to rotation axis).

The Equator—the imaginary midline of Earth, where the plane of the equator intersects Earth’s surface. Is the parallel of 0° latitude.

The Great Circle—the largest circle that can be drawn on a sphere; it must pass through the center of the sphere; it represents the circumference and divides surface into two equal halves or hemispheres. The  Circle of Illumination—a great circle that divides Earth between a light half and a dark half.
 

Latitude: the distance measured north and south of the equator; it is an angular measurement, so is expressed in degrees, minutes, and seconds. The actual length of one degree of latitude varies according to where it is being measured on Earth, because of the polar flattening of Earth. Even with the variation each degree has a north–south length of about 111 kilometers (69 miles). The latitude  between 90°N and 90°S receives 12 hours of sunlight on March 20.

Parallel: an imaginary line that connects all points of the same latitude; because they are imaginary, they are unlimited in number. Seven parallels are particularly significant:
a) Equator, 0°; b) North Pole, 90° N; c) South Pole, 90° S; d) Tropic of Cancer, 23.5° N; e) Tropic of Capricorn, 23.5° S; f) Arctic Circle, 66.5° N; g) Antarctic Circle, 66.5° S

Longitude: the distance measured east and west on Earth’s surface.
Meridian: imaginary line of longitude extending from pole to pole (aligned in a north–south direction), crossing all parallels at right angles. (It’s not to be confused with its other definition, the sun’s highest point of the day.). Meridians are not parallel to each other, except where they cross at the equator, where they are also the furthest apart.  They close together northward and southward, converging at the poles. The Prime meridian—the meridian passing through the Royal Observatory at Greenwich, England. Longitude is measured from this meridian both east and west to a maximum of 180°.

Earth Movements

The functional relationship between Earth and the Sun is vital because life on Earth is dependent on solar energy. Two basic Earth movements are critical for continuously changing the geometric perspective between the two: (a) Earth’s daily rotation on its axis; and 2. Earth’s annual revolution around the Sun.

Earth’s Rotation on Its Axis: Earth rotates toward the east on its axis, with one complete rotation taking 24 hours. This eastward spin creates an illusion that the celestial bodies are rising in the east and setting in the west. Although the speed of rotation varies from place to place, it is constant in any given place, so humans do not experience a sense of motion. This rotation has several striking effects on the physical characteristics of Earth’s surface: a) There is an apparent deflection in the flow path of both air and water; called the Coriolis effect, it deflects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. b) Any point of the surface will pass through the increasing and decreasing gravitational pull of the Moon and the Sun. c) Most important of all, there is a diurnal (daily) alternation of light and darkness, which in turn influences local temperatures, humidity, and wind movements. The rotation of the Earth about its axis is partially responsible for  (a) tides. (c) the Coriolis effect. (d) jet lag. (e) day/night alternation

Earth’s Revolution around the Sun:  The Tropical year—the time it takes Earth to complete one revolution around the Sun; for practical purposes it can be simplified to 365.25 days. The Earth’s revolution is an ellipse, which varies the Earth–Sun distance:  The varying distance between Earth and the Sun is not an important determinant of seasonal temperature fluctuations.

Perihelion: the point in an orbit that takes a planet nearest to the Sun. The Earth’s elliptical orbit brings it closest to the Sun at perihelion, that is at 147,166,480 kilometers or 91,455,000 miles, on January 3. 

Aphelion: the point in an orbit that takes a planet furthest away from the Sun (for Earth, it is 152,171,500 kilometers or 94,555,000 miles, on July 4).

The Annual March of the Seasons

Plane of the ecliptic: is the imaginary plane that passes through the Sun and through every point of Earth’s orbit around the Sun. It is not perpendicular to Earth’s rotation axis, which allows for seasons to occur.
Inclination: is the  degree to which Earth’s rotation axis is tilted (about 23.5? away from the perpendicular).
Polarity: is also called parallelism; occurs because Earth’s axis always points toward Polaris, the North Star, no matter where Earth is in its orbit.
Insolation: is the incoming solar radiation. The angle at which the Sun’s rays strike Earth determines the amount of insolation reaching any given point on Earth. That angle is a result of the combined effect of rotation, revolution, inclination, and polarity.

Solstices
Solstice: ia one of two times during year in which the Sun’s perpendicular (vertical) rays hit the northernmost or southernmost latitudes (23.5°). On or about December 21 (called the winter solstice in Northern Hemisphere). On or about June 21 (called the summer solstice in Northern Hemisphere).

Tropic of Cancer: is the parallel of 23.5° north latitude, which marks the northernmost location reached by the vertical (perpendicular) rays of the Sun; occurs on or about June 21.

Tropic of Capricorn: is the parallel of 23.5° south latitude, which makes the southernmost location reached by the vertical (perpendicular) rays of the Sun; occurs on or about December 21.

Arctic Circle: is the parallel of 66.5° north latitude; experiences 24 hours of either light (circa June 21) or dark (circa December 21).

Antarctic Circle: is the parallel of 66.5° south latitude; experiences 24 hours of either light (circa December 21) or dark (circa June 21).

Equinoxes
Equinox: the time of year when the perpendicular rays of the Sun strike the equator, the circle of illumination just touches both poles, and the periods of daylight and darkness are each 12 hours long all over Earth. On or about March 20 (called vernal equinox in Northern Hemisphere). On or about September 22 (autumnal equinox in Northern Hemisphere).

The equinoxes represent the midpoints in the shifting of direct rays of the Sun between the Tropic of Cancer and the Tropic of Capricorn.

Changes in Daylight and Darkness: The period of daylight varies throughout the year, increasing everywhere north of the equator from the shortest day of the year on the December solstice until the longest day of the year of the June solstice. Then days begin to shorten again in Northern Hemisphere. (Southern Hemisphere experiences an opposite effect.) . Both day length and the angle at which the Sun’s rays strike Earth are principal determinants of the amount of insolation received at any particular latitude.  Tropic latitudes are always warm/hot because they always have high Sun angles and consistent days close to 12 hours long.  Polar regions are consistently cold because they always have low sun angles.

Telling Time
It was difficult to compare time at different localities when transportation was limited to foot, horse, or sailing vessel. Thus there were no standard times; each community set its own time by correcting its clocks to high noon (meridian, not to be confused with meridian of longitude).
If you are traveling west toward Seoul from San Francisco, when you cross the international date line at noon it becomes the next day
Standard Time: Use of local solar time created increasing problems with advent of telegraph and railroad; railroads stimulated development of a standardized time system. An 1884 international conference divided world into 24 standard time zones, each extending over 15° of longitude (also determined prime meridian). Universal Time Coordinated (UTC) — formerly Greenwich mean time (GMT); a standardized time system that uses the local solar time of Greenwich (prime) meridian as its standard. (1) In international waters, time zone boundaries are defined specifically and consistently; (2) Over land areas, however, zone boundaries vary, sometimes undergoing great manipulation for political and economic convenience.

The International Date Line: International Date Line—Along with prime meridian, provides the anchor for the framework of time zones. It is the line marking where new days begin and old days exit from surface of Earth.  Experiences a time difference of an entire day from one side of the line to the other. Generally, the line falls on the 180th meridian except where it meanders to ensure two island groupings aren’t split apart in their schedules (Aleutian Islands and South Pacific Islands). The extensive eastern displacement of the date line in the central Pacific is due to the widely scattered distribution of many of the islands of the country of Kiribati.

Daylight Saving Time: a practice by which clocks are set forward by an hour (or more) so as to extend daylight into the usual evening hours. Created originally in Germany to help conserve electricity for lighting. Became U.S. national policy, though Arizona, Hawaii, and part of Indiana exempt themselves under the Uniform Time Act. Now gaining international acceptance.

The Moon
The Moon actually affects the physical geography of Earth because of its gravitational pulls, which generate the ocean tides (covered more extensively in Chapter 9).  It is also of interest to physical geographers because its features help to understand several principles in this branch of study: (a)  Its lack of atmosphere provides a good example for showing the black sky that results when there is no atmosphere to scatter blue light (covered in Chapter 3). (b)  Its temperature extremes are indicative of what occurs in an airless environment. (At night it is colder than any place on Earth, while during the day it reaches temperatures slightly higher than that at which water boils at Earth’s sea level (covered in Chapter 4). (c) Its land surface has changed little in the last 3 billion to 4 billion years (apart from the formation of craters), which exemplifies what occurs when there is no running water to erode and deposit (covered in Chapter 16).

Polaris
The Polaris is a star in the constellation Ursa Minor.  It appears to be in a fixed position in the sky above the North Pole. Because of this, it is often referred to as the North Star or polestar. Its fixed, unmoving position has allowed the star to be used for celestial navigation here on Earth. Because of the shifting of the Earth’s axis over a 26,000 year cycle, Polaris’ relative position to the North Pole will shift through time.  When this happens, it will cease to serve as a navigational reference.