2. Radiation Electromagnetic radiation consists of waves of electrical and magnetic disturbances. Tools of Astronomy It includes visible light, infrared and ultraviolet radiation, radio waves, microwaves, X rays, and gamma rays.

3. Radiation Electromagnetic radiation travels at the same speed and is classified by: Tools of Astronomy –Wavelengths—the distance between peaks on a wave. –Frequency—the number of waves or oscillations occurring per second.

4. Satellites, Probes, and Space-Based Astronomy Human Spaceflight Tools of Astronomy –Exploring the short term effects of space has been accomplished with the space shuttle program, which began in 1981. –Since habitation and research began in 2000, a multi-country space station called the International Space Station has been used to study the long-term effects of life in space.

5. Reaching for the Moon The Lunar Surface The Moon –The albedo of the Moon, the amount of sunlight that its surface reflects, is only about 0.07 (7 percent) contrasted with Earth’s average of 0.31 (31 percent). –Because the Moon has no atmosphere, surface temperatures can range from 400 K (127°C) in sunlight to 100 K (–173°C) where it is dark. –There is no erosion on the Moon—except for surface creep and wear caused by recent impacts—because it has no atmosphere or flowing water. –Craters on the Moon are preserved until one impact covers another.

6. –ecliptic –summer solstice –winter solstice –autumnal equinox –vernal equinox Objectives Identify the relative positions and motions of Earth, the Sun, and the Moon. Describe the phases of the Moon. Explain eclipses of the Sun and Moon. Vocabulary The Sun-Earth-Moon System –synchronous rotation –solar eclipse –perigee –apogee –lunar eclipse

7. The Sun-Earth-Moon System The relationships between the Sun, Moon, and Earth are important to us in many ways. The Sun-Earth-Moon System –The Sun provides light and warmth, and it is the source of most of the energy that fuels our society. –The Moon raises tides in our oceans and illuminates our sky with its monthly cycle of phases. –Every society from ancient times to the present has based its calendar and its timekeeping system on the apparent motions of the Sun and Moon.

8. Daily Motions The Sun rises in the east and sets in the west, as do the Moon, planets, and stars as a result of Earth’s rotation. The Sun-Earth-Moon System We observe the sky from a planet that rotates once every day, or 15° per hour.

9. Daily Motions Earth’s Rotation The Sun-Earth-Moon System –There are two relatively simple ways to demonstrate that Earth is rotating. 1.A Foucault pendulum, which has a long wire, a heavy weight, and will swing in a constant direction, appears from our point of view to shift its orientation. 2.Flowing air and water on Earth are diverted from a north-south direction to an east-west direction as a result of Earth’s rotation in what is known as the Coriolis effect.

10. Daily Motions Earth’s Rotation The Sun-Earth-Moon System –The length of a day as we observe it is a little longer than the time it takes Earth to rotate once on its axis. –Our timekeeping system is based on the solar day, which is the time period from one sunrise or sunset to the next.

11. Annual Motions The annual changes in length of days and temperature are the result of Earth’s orbital motion about the Sun. The Sun-Earth-Moon System The ecliptic is the plane in which Earth orbits about the Sun.

12. Annual Motions The Effects of Earth’s Tilt The Sun-Earth-Moon System –Earth’s axis is tilted relative to the ecliptic at approximately 23.5°. –As Earth orbits the Sun, the orientation of Earth’s axis remains fixed in space. –At one point, the northern hemisphere of Earth is tilted toward the Sun, while six months later it is tipped away from the Sun. –As a result of the tilt of Earth’s axis and Earth’s motion around the Sun, the Sun is at a higher altitude in the sky during summer than in the winter.

13. Annual Motions The Effects of Earth’s Tilt The Sun-Earth-Moon System Altitude is measured in degrees from the observer’s horizon to the object. There are 90 degrees from the horizon to the point directly overhead, called the zenith of the observer.

14. Annual Motions Solstices The Sun-Earth-Moon System –As Earth moves from position 1, through position 2, to position 3, the altitude of the Sun decreases in the northern hemisphere. –Once Earth is at position 3, the Sun’s altitude starts to increase as Earth moves through position 4 and back to position 1.

15. Annual Motions Solstices The Sun-Earth-Moon System –The summer solstice occurs around June 21 each year when the Sun is directly overhead at the Tropic of Cancer, which is at 23.5° N. –The summer solstice corresponds to the Sun’s maximum altitude in the sky in the northern hemisphere.

16. Annual Motions Solstices The Sun-Earth-Moon System –The winter solstice occurs around December 21 each year when the Sun is directly overhead at the Tropic of Capricorn which is at 23.5° S. –The winter solstice corresponds to the Sun’s lowest altitude in the sky in the northern hemisphere.

17. Annual Motions Solstices The Sun-Earth-Moon System

18. Annual Motions Equinoxes The Sun-Earth-Moon System –When the Sun is directly overhead at the equator, both hemispheres receive equal amounts of sunlight. –The autumnal equinox occurs around September 21, halfway between the summer and the winter solstices when the Sun is directly over the equator.

19. Annual Motions Equinoxes The Sun-Earth-Moon System –The vernal equinox occurs around March 21, halfway between the winter and the summer solstices when the Sun is directly over the equator. –For an observer at the Tropic of Cancer or Tropic of Capricorn, the Sun is 23.5° from the point directly overhead during the equinoxes.

20. Annual Motions Equinoxes The Sun-Earth-Moon System For a person standing at the x at 23.5º N, the Sun would appear in these positions on the winter solstice, the vernal equinox, and the summer solstice. On the autumnal equinox, the Sun would be at the same altitude as on the vernal equinox.

21. Phases of the Moon The sequential changes in the appearance of the Moon are called lunar phases. The Sun-Earth-Moon System –A new moon occurs when the Moon is between Earth and the Sun and we cannot see the Moon because the sunlit side is facing away from us. –As the Moon moves along in its orbit, the amount of reflected sunlight that we can see increases until we are able to see the entire sunlit side of the Moon, known as a full moon. –Once a full moon is reached, the portion of the sunlit side that we see begins to decrease as the Moon moves back toward the new-moon position.

22. Phases of the Moon The Sun-Earth-Moon System

23. Phases of the Moon Synchronous Rotation The Sun-Earth-Moon System –Synchronous rotation is the state at which orbital and rotational periods are equal. –As the Moon orbits Earth, the same side faces Earth at all times because the Moon has a synchronous rotation, spinning exactly once each time it goes around Earth.

24. Motions of the Moon The length of time it takes for the Moon to go through a complete cycle of phases is called a lunar month. The Sun-Earth-Moon System The length of a lunar month is about 29.5 days, which is longer than the 27.3 days it takes for one revolution, or orbit, around Earth. The Moon also rises and sets 50 minutes later each day because the Moon has moved 13° in its orbit over a 24-hour period, and Earth has to turn an additional 13° for the Moon to rise.

25. Motions of the Moon The Sun-Earth-Moon System

26. Motions of the Moon Tides The Sun-Earth-Moon System –The Moon’s gravity pulls on Earth along an imaginary line connecting Earth and the Moon, creating bulges of ocean water on both the near and far sides of Earth. –As Earth rotates, these bulges remain aligned with the Moon. –When the Sun and Moon are aligned along the same direction, the result is higher-than-normal tides, called spring tides. –When the Moon is at a right angle to the Sun-Earth line, the result is lower-than-normal tides, called neap tides.

27. Solar Eclipses A solar eclipse occurs when the Moon passes directly between the Sun and Earth and blocks our view of the Sun. The Sun-Earth-Moon System –When the Moon perfectly blocks the Sun’s disk, we see only the dim, outer gaseous layers of the Sun in what is called a total solar eclipse. –A partial solar eclipse is seen when the Moon blocks only a portion of the Sun’s disk.

28. Solar Eclipses The shadow that is cast on Earth consists of two regions. The Sun-Earth-Moon System A total eclipse occurs in the inner portion called the umbra, which does not receive direct sunlight. A partial eclipse occurs in the outer portion of the shadow called the penumbra, where some of the Sun’s light reaches.

29. Solar Eclipses The Sun-Earth-Moon System

30. Solar Eclipses The Effects of Orbits The Sun-Earth-Moon System –The Moon’s orbit is tilted 5° relative to the ecliptic and usually the Moon passes north or south of the Sun as seen from Earth, during a new moon. –A solar eclipse can occur only when the intersection of the Moon and the ecliptic is in a line with the Sun and Earth.

31. Solar Eclipses The Effects of Orbits The Sun-Earth-Moon System –The Moon’s distance from Earth increases and decreases as the Moon moves in its elliptical orbit around Earth. Perigee is the closest point in the Moon’s orbit to Earth. –When the Moon is near apogee, it appears smaller, and thus it does not completely block the disk of the Sun, resulting in an annular eclipse. Apogee is the farthest point in the Moon’s orbit from Earth.

32. Lunar Eclipses A lunar eclipse occurs when the full Moon passes through Earth’s shadow. The Sun-Earth-Moon System A lunar eclipse can happen only at the time of a full moon, when the Moon is in the opposite direction from the Sun. A total lunar eclipse occurs when the entire Moon is within Earth’s umbra. Solar and lunar eclipses occur in almost equal numbers, with slightly more lunar eclipses.

33. Lunar Eclipses The Sun-Earth-Moon System

34. Section Assessment 1.Match the following terms with their definitions. ___ ecliptic ___ summer solstice ___ winter solstice ___ apogee The Sun-Earth-Moon System A.occurs when the Sun is directly overhead at the Tropic of Cancer B.the point in the Moon’s elliptical orbit that is the farthest from Earth C.the plane that contains Earth’s orbit D.occurs when the Sun is directly overhead at the Tropic of Capricorn C A D B

35. Section Assessment 2.Number the lunar phases in the correct order, beginning after the new moon. ___ waxing gibbous ___ full moon ___ waning crescent ___ third quarter ___ first quarter ___ waning gibbous ___ waxing crescent The Sun-Earth-Moon System 6 5 3 4 1 7 2

36. Section Assessment The Sun-Earth-Moon System 3.Identify whether the following statements are true or false. ______ A maximum of five eclipses, solar and lunar combined, can occur in a year. ______ The Sun will appear at the same altitude in the sky during both the autumnal and vernal equinoxes. ______The Earth has a synchronous rotation. ______To witness a total solar eclipse, you must be inside the umbra of the Moon’s shadow. false true false true

37. End of Section 3

38. Section 28.1 Main Ideas Visible light, radio waves, infrared and ultraviolet radiation, X rays, and gamma rays are types of electromagnetic radiation. A telescope collects light over a large area, makes time exposures, and can use other instruments to analyze light. Visible-light telescopes can be made using lenses, as in refracting telescopes, or mirrors, as in reflecting telescopes. Space is explored by telescopes, satellites, probes, and humans. Section 28.1 Study Guide

39. Section 28.3 Main Ideas The entire sky appears to rotate daily because we observe it from a rotating Earth. Our timekeeping system is based on the solar day, the length of day as observed from Earth. Our view of the Sun’s position changes throughout the year as Earth moves in its orbit about the Sun. Seasons occur on Earth because Earth’s axis is tilted. The Moon goes through a cycle of phases each lunar month that correspond to our changing view from Earth of the sunlit side of the Moon. Section 28.3 Study Guide

40. Section 28.3 Main Ideas Tides are caused by the gravitational attraction of the Moon, and to a lesser extent, the gravitational attraction of the Sun. A solar eclipse occurs when the Moon lies directly between Earth and the Sun. A lunar eclipse occurs when the Moon passes through Earth’s shadow. Section 28.3 Study Guide

41. Multiple Choice 4.During which of the following is the Sun at the lowest altitude when viewed from 45º N? a.summer solsticec.autumnal equinox b.winter solsticed.vernal equinox Chapter Assessment During the winter solstice, the Sun is directly over the Tropic of Capricorn (23.5º S), the farthest point south before direct sunlight begins to move north again. At 45º N, the Sun’s altitude would only be 21.5º during the winter solstice.

42. Short Answer 6.What is a synchronous rotation? Chapter Assessment A synchronous rotation is a state in which orbital and rotational periods are equal. For example, the Moon has a synchronous rotation, meaning that it spins exactly once each time it goes around Earth.

43. Image Bank Chapter 28 Images

44. Image Bank Chapter 28 Images

45. Image Bank Chapter 28 Images

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47. Image Bank Chapter 28 Images