Page 97 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 2 Solar Energy to Earth and the Seasons 61
concepts review
KEy LEarning
■ Distinguish between galaxies, stars, and planets, and locate Earth.
Our Solar System—the Sun and eight planets—is located on a remote, trailing edge of the Milky Way Galaxy, a flat- tened, disk-shaped collection estimated to contain up to 300 billion stars. Gravity, the mutual attracting force exerted by all objects upon all other objects in proportion to their mass, is an organizing force in the Universe. The planetesimal hypothesis describes the formation of solar systems as a process in which stars (like our Sun) condense from nebular dust and gas, with planetesimals and then protoplanets forming in orbits around these central masses.
Milky Way Galaxy (p. 44) gravity (p. 45)
planetesimal hypothesis (p. 45)
1. Describe the Sun’s status among stars in the Milky Way Galaxy. Describe the Sun’s location, size, and relationship to its planets.
2. IfyouhaveseentheMilkyWayatnight,brieflyde- scribe it. Use specifics from the text in your description.
3. Compare the locations of the eight planets of the Solar System.
■ Summarize the origin, formation, and development of Earth, and reconstruct Earth’s annual orbit about the Sun.
The Solar System, planets, and Earth began to condense from a nebular cloud of dust, gas, debris, and icy comets ap- proximately 4.6 billion years ago. Distances in space are so vast that the speed of light (about 300000 km·s−1, which is about 9.5 trillion km per year) is used to express distance.
In its orbit, Earth is at perihelion (its closest position to the Sun) during our Northern Hemisphere winter (January 3 at 147255000 km). It is at aphelion (its farthest position from the Sun) during our Northern Hemisphere summer (July 4 at 147255000 km). Earth’s average distance from the Sun is approximately 8 minutes and 20 seconds in terms of light speed.
speed of light (p. 45) perihelion (p. 45) aphelion (p. 45)
4. Briefly describe Earth’s origin as part of the Solar System.
5. How far is Earth from the Sun in terms of light speed? In terms of kilometres?
6. Briefly describe the relationship among these enti- ties: Universe, Milky Way Galaxy, Solar System, Sun, Earth, and Moon.
7. Diagram in a simple sketch Earth’s orbit about the Sun. How much does it vary during the course of a year?
■ Describe the Sun’s operation, and explain the characteristics of the solar wind and the electromagnetic spectrum of radiant energy.
The fusion process—hydrogen nuclei forced together under tremendous temperature and pressure in the
Sun’s interior—generates incredible quantities of energy. Sunspots are magnetic disturbances on the solar surface; solar cycles are fairly regular, 11-year periods of sunspot activity. Solar energy in the form of charged particles of solar wind travels out in all directions from magnetic disturbances and solar storms. Solar wind is deflected by Earth’s magnetosphere, producing various effects in the upper atmosphere, including spectacular auroras, the northern and southern lights, which surge across the skies at higher latitudes. Another effect of the solar wind in the atmosphere is its possible influence on weather.
Radiant energy travels outward from the Sun in all directions, representing a portion of the total electromag- netic spectrum made up of different energy wavelengths. A wavelength is the distance between corresponding points on any two successive waves. Eventually, some of this radiant energy reaches Earth’s surface.
fusion (p. 45)
sunspots (p. 46)
solar wind (p. 46) magnetosphere (p. 47)
auroras (p. 47)
electromagnetic spectrum (p. 47) wavelength (p. 48)
8. How does the Sun produce such tremendous quanti- ties of energy?
9. What is the sunspot cycle? At what stage was the cycle in the year 2014?
10. Describe Earth’s magnetosphere and its effects on the solar wind and the electromagnetic spectrum.
11. Summarize the presently known effects of the solar wind relative to Earth’s environment.
12. Describe the various segments of the electromagnetic spectrum, from shortest to longest wavelength. What are the main wavelengths produced by the Sun? Which wavelengths does Earth radiate to space?
■ Illustrate the interception of solar energy and its uneven distribution at the top of the atmosphere.
Electromagnetic radiation from the Sun passes through Earth’s magnetic field to the top of the atmosphere—the thermopause, at approximately 500 km altitude. Incom- ing solar radiation is insolation, measured as energy delivered to a horizontal surface area over some unit of time. The solar constant is a general measure of insola- tion at the top of the atmosphere: The average insolation received at the thermopause when Earth is at its aver- age distance from the Sun is approximately 1372 W·m−2. The place receiving maximum insolation is the subsolar point, where solar rays are perpendicular to the Earth’s surface (radiating from directly overhead). All other lo- cations away from the subsolar point receive slanting rays and more diffuse energy.
thermopause (p. 49) insolation (p. 49) solar constant (p. 49) subsolar point (p. 49)