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Chapter 1
The Earth as a Rotating Planet
This chapter deals with the way solar radiation drives energy and matter flows in the
atmosphere and oceans and how these flows are linked to weather and climate. This
chapter introduces you to some basic ideas about the Earth, its rotation, and revolution.
 The Earth is shaped as an oblate ellipsoid because the Earth's rotation causes it to
bulge slightly at the equator.
 The Earth rotates in an eastward direction.
 The Earth's rotation has three important environmental effects:
1. It imposes a daily, or diurnal, cycle of daylight, air temperature, air humidity, and
air motion.
2. It produces the Coriolis effect which deflects the flow of fluids (air and water) to
the left in the southern hemisphere and to the right in the northern hemisphere.
3. Tides result from the moon’s gravitational pull on the side of the Earth closest to
the moon, creating a rise and fall of ocean water as the Earth rotates.
 The Geographic Grid provides a system for locating features on the Earth’s surface
using parallels of latitude and meridians of longitude.
 Latitude is the angular distance of a point north or south of the equator. It increases
from a minimum of 0° at the equator to a maximum of 90° at the north and the south
poles. Lines of latitude are parallel to each other and describe circles that decrease in
circumference away from the equator.
 Longitude is the angular distance of a point east or west of the prime meridian at
Greenwich, England. It increases to the west and the east away from the prime
meridian (0°) to a maximum of 180°. Lines of longitude are farthest apart at the
equator and converge at the poles. All circles described by meridians of longitude are
the same circumference.
 A map projection is a system for changing the curved/spherical geographic grid to a
flat grid.
 Map scale relates distance on a map to distance on the Earth’s surface.
 The polar projection produces a map with true shapes of small areas.
 The Mercator projection shows true compass direction on any straight line on the
map and is useful for showing the flow of winds and ocean currents as well as lines of
equal air temperature and pressure.
 The Goode projection is an equal area projection useful for depicting geographical
features that occupy surface areas.
 The standard time system is based on twenty four time zones that keep time
according to standard meridians that are spaced 15° apart and represent a time
difference of one hour.
 The international date line is located near 180° longitude. Crossing this line in a
westward direction requires the calendar to be advanced by one day.
 The Earth revolves counterclockwise around the sun every 365¼ days in an elliptical
orbit.
 The Earth is closest to the sun at perihelion (~ January 3) and farthest from the sun at
aphelion (~ July 4).
 The Earth’s axis of rotation is tilted 23½° away from the perpendicular and its north
pole always points towards Polaris (the north star).
 The axial tilt and the revolution of the Earth around the sun combine to produce the
progression of the seasons.
 At an equinox, everywhere on Earth experiences a 12-hour day and a 12-hour night.
 At a solstice, polar regions experience either a 24-hour day or a 24-hour night.
 The maximum solar radiation is received at the subsolar point which crosses the
equator twice in the course of a year as it moves between the Tropic of Cancer to the
Tropic of Capricorn.
 Two important facts about the Sun-Earth energy flow system are that:
1. half of the Earth is always receiving solar energy.
2. Not all places on the Earth’s surface receive the same amount of energy.