The History of Astronomy, Gravity, Tides, and the Moon

1. The History of Astronomy, Gravity, Tides, and the Moon

2. Bell Work What is the habitable zone? What would happen if there was not enough gravity on Earth? How many gas giant planets are there?

3. Early Astronomy 139 • Not only did early humans navigate by means of the sky, but the motions of objects in the sky predicted the changing of the seasons, etc. • There were many early attempts both to describe and explain the motions of stars and planets in the sky. • All were unsatisfactory, for one reason or another.

4. 140 Geocentric vs. Heliocentric Models of the Solar System Ancient Greeks knew of Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn. Aristotle vs. Aristarchus (3rd century B.C.)‏ Aristotle: Sun, Moon, Planets and Stars rotate around fixed Earth. Aristarchus: 1st Heliocentric model (Sun is center) Aristotle: But there's no wind - Doesn’t “feel” like we are moving. (Actually orbiting sun at 70,000 mph!)‏ • Difficulties with "Geocentric" model - Retrograde motion of planets - Phases of Venus

5. Written in the 2nd century BC • He calculated the ratio of the distance between the Earth and Sun. • His fault was in his lack of accurate instruments not in his method of reasoning. • Aristarchus also found an improved value for the length of the solar year. Aristarchus141

6. The Earth-Centered Universe 142a • A geocentric (Earth-centered) solar system is often credited to Ptolemy, an Alexandrian Greek, although the idea is very old. Image from: http://abyss.uoregon.edu/~js/ast123/lectures/lec02.html

7. Ptolemy’s Solar System 142b • Ptolemy’s solar system could be made to fit the observational data pretty well, but only by becomingverycomplicated. Image from: http://abyss.uoregon.edu/~js/ast123/lectures/lec02.html

8. It doesn't feel like we are moving – wouldn't there be a wind or something? Why would things fall down and not towards the center of the universe? Geocentric Model of Solar System 143 (Earth Centered)‏ What are some reasons that the geocentric model of the universe seems to make intuitive sense?

9. Ptolemy's geocentric model (A.D. 140)‏

10. Heliocentric Model 144a “Rediscovered” by Copernicus in 16th century. Simplyexplains retrograde motion. Put Sun at center of everything, but still insisted on circles. Opposed by Catholic Church Copernican revolution – only accepted after his death. Copernicus 1473-1543

11. Objections to Copernicus 144b • How could Earth be moving at enormous speeds when we don’t feel it? • (Copernicus didn’t know about inertia.) • Why can’t we detect Earth’s motion against the background stars (stellar parallax)? • Copernicus’ model did notfit the observational data very well.

12. 145 Galileo & Copernicus • Galileo became convinced that Copernicus was correct by observations of the Sun, Venus, and the moons of Jupiter using the newly-invented telescope. • Perhaps Galileo was motivated to understand inertia by his desire to understand and defend Copernicus’ ideas.

13. Bell work • Which three historical astronomers believed the Heliocentric model of the universe? • Which two historical astronomers believed the Geocentric model of the universe? • What are the names of Pluto’s 5 moons?

14. Galileo (1564-1642)‏, 146 Experimentalist Built his own telescope. Discovered four moons orbiting Jupiter. Discovered sunspots. Observed phases of Venus. Was imprisoned for the last 9 years of his life for his scientific discoveries.

15. Heliocentric model easily accounts for phases of Venus

16. Geocentric model fails to account for phases of Venus

17. Planet Sun 147 Kepler’s First Law Kepler’s Second Law • Kepler determined that the orbits of the planets were not perfect circles, but ellipses, with the Sun at one focus. • Kepler determined that a planet moves faster when near the Sun, and slower when far from the Sun. Slower Faster

18. The Apple & the Moon 148 • Isaac Newton realized that the motion of a falling apple and the motion of the Moon were both actually the same motion, caused by the same force- the gravitational force. • Newton’s idea was that gravity was a universal force acting between any two objects.

19. 149a Weight of the Moon • Newton reasoned that the centripetal force on the moon was also supplied by the Earth’s gravitational force. ? Fc = mg • Newton reasoned that the strength of the gravitational force is not constant

20. 149 b Experimental Evidence • The Law of Universal Gravitation allowed extremely accurate predictions of planetary orbits. • Cavendish measured gravitational forces between human-scale objects before 1800. His experiments were later simplified and improved by von Jolly.

21. Black Holes 150 • When a very massive star gets old and runs out of fusionable material, gravitational forces may cause it to collapse to a mathematical point - a singularity. All normal matter is crushed out of existence. This is a black hole.

22. 151a Earth’s Tides • There are 2 high tides and 2 low tides per day. • The tides follow the Moon.

23. 151b Why Two Tides? • Tides are caused by the stretching of a planet. • Stretching is caused by a difference in forces on the two sides of an object. • Since gravitational force depends on distance, there is more gravitational force on the side of Earth closest to the Moon and less gravitational force on the side of Earth farther from the Moon.

24. Why the Moon? 152 • The Sun’s gravitational pull on Earth is much larger than the Moon’s gravitational pull on Earth. So why do the tides follow the Moon and not the Sun? • Since the Sun is much farther from Earth than the Moon, the difference in distance across Earth is much less significant for the Sun than the Moon, therefore thedifference in gravitational force on the two sides of Earth is less for the Sun than for the Moon (even though the Sun’s force on Earth is more). • TheSundoes have a small effect on Earth’s tides, but the major effect is due to the Moon.

25. Phases of the Moon Created by Mrs. Bodine-Donahue

26. 153a • The lunar month or synodic month lasts 29 days, 12 hours, and 44 minutes to go from one new moon to the next. During the lunar month, the Moon goes through all its phases.

27. 153b We only see the Moon because sunlight reflects back to us from its surface.

28. 154 During the course of a month, the Moon circles once around the Earth. If we could magically look down on our solar system, we would see that the half of the Moon facing the Sun is always lit. But the lit side does not always face the Earth!

29. 155a As the Moon circles the Earth, the amount of the lit side we see changes. These changes are known as the phases of the Moon and it repeats in a certain way over and over.

30. 155b Moon Phase Descriptions...

31. 156 New Moon - The Moon's dark side is facing the Earth. This means that the Sun, Earth, and Moon are almost in a straight line, with the Moon in between the Sun and the Earth.  The Moon that we see looks very dark. Waxing Crescent Moon - As the Moon moves around the Earth, we get to see more and more of the illuminated half, and we say the Moon is waxing. This phase is called the crescent moon.

32. Quarter Moon - A week after the new moon, when the Moon has completed about a quarter of its turn around the Earth, we can see half of the illuminated part. This is the first quarter phase. 157 Waxing Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. ("Waxing" means increasing, or growing larger.)

33. Full Moon - The Moon's illuminated side is facing the Earth. This means that the Earth, Sun, and Moon are nearly in a straight line, with the Earth in the middle.  The Moon that we see is very bright from the sunlight reflecting off it. 158 Waning Gibbous Moon - From now on, until it becomes new again, the illuminated part of the Moon that we can see decreases, and we say it's waning. The first week after full, it is called waning gibbous. ("Waning" means decreasing, or growing smaller.)

34. Last Quarter - One-half of the Moon appears to be illuminated by direct sunlight. Sometimes called Third Quarter.  The left half of the Moon appears lighted, and the right side of the Moon appears dark.  159 Waning Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The crescent will grow smaller and smaller every day, until the Moon looks like the New Moon.

35. After 29 days, 12 hours, and 44 minutes the illuminated half of the Moon again faces away from us, and we come back to the beginning of the cycle: a new moon. 160

36. 161 Solar eclipses occur less often than lunar eclipse and are shorter in duration. Solar Eclipse – seen for a few minutes and happens a few times a year Lunar eclipse - seen for a few hours and happens at least 2 times a year (could be more)

37. Moon Phase Misconception...

38. Bell work • Who discovered that all the planets have an elliptical rotation pattern? • Why does the moon effect the tides more than the sun/ • How long is the synodic month?

39. Directions: • Do Not write the words that appear in white!

40. 162 a Event #1 Oct. 4, 1957. The Soviet Union launches a satellite into space named Sputnik 1. It was a very simple device that took measurements of the upper layer of the atmosphere and sent information by radio signals down to the planet. It orbits every hour-and-a-half before it re-entered the atmosphere and burned up 3 months after launch.

41. 162b Event #2 November 3, 1957: Sputnik 2 is launched, and everyone is stunned to see that thisspacecraft has a “pilot” on board—a dog named Laika (pronounced lye-ee-kuh). The sad part was that Laika was never going to be recovered—there was no plan for thedog to ever land safely on Earth. It was thought to be able to live 10 days in space, but may not have lasted an hour when some of the life-support systems malfunctioned. 

42. 162c Event #3 The Americans finally get in the act, on February 1, 1958. Explorer 1 is the USA’s first launched satellite to orbit Earth. It transmitted valuable new information about the protective magnetic field around Earth. It orbited for 12 years before crashing into the Ocean.

43. 162d Event #4 It helped geophysicists realize that Earth is not round but slightly pear-shaped, with a slight, symmetric equatorial bulge. America strikes again with Vanguard 1, launched on March 17, 1958. Here’s some impressive news: next to the Moon, Vanguard 1 is the oldest object to orbit Earth. Yep, it’s still out there! This is the first space technology to use solar panels, but transmissions using them ended in 1964. Right: It took large, powerful rockets to send any of these objects into orbit.

44. 162e Event #5 On October 1, 1958, a famous American agency was formed—NASA. NASA stands for National Aeronautics and Space Administration. NASA had several goals—continue to gather data about the Earth’s atmosphere and outer space, test new technologies for launching rockets, and of course—beat the Russians! President Eisenhower gets a lesson on space.

45. Bell Work What was the name of the first satellite? What was so special about Sputnik 2? What was the name of the USA’s first satellite?

46. 163a Event #6 Russia sends the first man into outer space…a guy named Yuri Gregarin. On April 12, 1961, Vostok 1 blasts off and Yuri returns nearly 2 hours later after completing one orbit and parachuting from a few miles off the ground.

47. 163b Event #7 May 5, 1961: America sends its first astronaut, Alan Shepard, into space. The mission is called Mercury Freedom 7. It lasted only 16 minutes and didn’t actually go in complete orbit around Earth.  Shepard was still hailed as a hero, and he later became the 5th person to walk on the moon. American scientists lost the race to send a person into space by less than one month. Shepard on the navy ship that rescued him after his ocean splashdown.

48. 164a Event #8 Vostok 6 blasted off in Russia on June 16, 1963. On board was the first woman in space, so the Russians beat us again. Her name was Valentia Tereshkova, and she recorded data about the atmosphere for 3 days before returning safely to Earth.

49. 164b Event #9 March 1965: Russia sent off the Voskhod 2, they actually let one of their cosmonauts leave the space ship! Alexei Leonov left the spaceship (attached to it by a tether cord) and stayed out in space for around 12 minutes. Except that his space suit inflated (due to outer space being a vacuum) and he almost wasn’t able to make it back inside the ship.

50. 164c Event #10 President Kennedy issued the challenge in 1962 that America NEEDED to go to the moon because it would be so hard to do so. And less than a decade later, we did. America just jumped way ahead of Russia in the space race. On July 20, 1969, the Apollo 11 mission lands on the moon, and Neil Armstrong utters the famous words, “one small step for a man, one giant leap for mankind.” USA! USA! USA! This is awesome.