1. The Sun & The Solar System
Chapter 26

2. Chapter 26.1
The Sun’s Size, Heat, and Structure

3. The Sun’s Size Diameter of about 1,400,000 kilometers
Could fit around 1 million Earths inside the Sun
Not a large star compared to other stars

4. The Sun’s Energy All stars get their energy from fusion
Fusion = the combining of the nuclei of lighter elements to form heavier elements
E=mc2 (energy is equal to mass times the speed of light squared)
Means that matter can be converted into energy, which happens during fusion

5. The Sun’s Energy
Stars have such intense heat and pressure that atoms are torn apart into nuclei and electrons
Hydrogen and Helium exist as plasma
Plasma = a fourth state of matter consisting of charged particles

6. The Sun’s Energy
The nuclei are moving at such great speeds and under intense heat that they will fuse
When the nuclei fuse, it creates energy

7. Describe in your own words how the Sun generates so much energy.

8. The Sun’s Layers The Core
Consists mostly of hydrogen and helium ions in a plasma state
100 times as dense as water
Temperature : 15,600,000 oC

9. The Sun’s Layers Radiative Zone
Layer of plasma that lies around the core
Temperature: cooler than the core
8,000,000 oC near the core
2,000,000 oC near the convection zone

10. The Sun’s Layers 3. Convection Zone
Rising and falling currents of plasma carry energy to the sun’s surface, where it is radiated out into space as sunlight
Temperature: 1,500,000 oC

11. The Sun’s Layers 4. Photosphere The visible surface of the sun
Tops of the currents form structures called granules
1,000 km wide and last for 20 minutes
Temperature: 6,000 oC

12. The Sun’s Layers 5. Chromosphere Inner layer of the Sun’s atmosphere
Extends thousands of kilometers above the photosphere
Temperature : 20,000 oC
Hydrogen within emits a distinctive reddish light
Solar prominences: dense clouds of material that can erupt and extend into space

13. The Sun’s Layers 6. Corona Thin outer atmosphere
Million times less bright than the photosphere
Temperature: 1,000,000 oC to 3,000,000 oC

14. What is plasma? How is it different from a liquid or a gas?

16. Features of the Sun

17. Sunspots Dark spots on the photosphere
Range in size from barely visible to four time larger than Earth’s diameter
Very hot and bright
Look dark because the surrounding photosphere is so much hotter and brighter
Magnetic field is 1,000 times stronger than the surrounding photosphere

18. Sunspot Movement Move from left to right across the sun’s surface
Indicates that the sun rotates on an axis
The sun is not a solid so the rate of rotation varies from place to place
Equator = 25 days
Poles = 34 days
11 year cycle of peak activity

19. Solar Winds
Produced by a constant stream of electrically charged particles given off by the corona
Travel through space at speeds of about 450 km per second
Earth’s magnetic field deflects most solar winds

20. Auroras
As solar wind blows by past Earth, some particles interact with Earth’s magnetic field and upper atmosphere
Causes displays of color and light in the upper atmosphere
Called northern lights because they occur in regions near Earth’s magnetic poles

21. Mars has either no magnetic field or a very weak one
Mars has either no magnetic field or a very weak one. Why does this fact make it unlikely that life exists at the present time on the surface of mars?

22. Observing the Solar System: A History
Chapter 26.2

23. The Movement of Planets and Stars
For thousands of years people believed that Earth stood still in the center of the universe
Geocentric Model = Earth – Centered Model

24. Star Movement?
As long as 6,000 years ago, astronomers were recording the movement of the stars
Imagined that stars were like holes in a solid celestial sphere that surrounded the Earth

25. Star Movement?
Beyond the sphere, was an intense light that shone through the holes
Concluded that the stars moved around Earth as the sphere rotated

26. Draw a picture of a geocentric model with the celestial sphere of stars

27. Constellations
Early astronomers noticed that the same constellation, or groups of stars, became visible at the same time every year.
Many cultures used the changing of constellations as a basis for a calendar

28. Planetary Movement
Early astronomers noted that not all points of light in the sky are fixed in constellations
Some wander across the sky, changing position over the course of days, weeks, and months
Inferred that these points of light were other planets that are closer to Earth than the stars are

29. Retrograde Motion
Early astronomers observed that most of the time planets moved eastward relative to the background of constellations
EAST
WEST

30. Retrograde Motion
Periodically the planets stopped moving eastward and moved westward for a few weeks, then resumed their eastward paths
This pattern of backward motions is called Retrograde Motion

31. What is retrograde motion? What do you think is causing this phenomenon?

32. Ptolemy’s Geocentric Model
Greek astronomer who lived in Egypt in 200 A.D
Developed a model that could be used to predict the location of the planets
Ptolemy’s model was used by astronomers until the 16th century

33. Ptolemy’s Geocentric Model
Each planet moves on small circular orbits called epicycles
The center of each small orbit moved around Earth on a larger circular orbit called a deferent

34. Ptolemy’s Geocentric Model
Retrograde motion occurred when the planet moved along the part of the epicycle that an observer on Earth could see.
However, Ptolemy’s model didn’t work perfectly. Observations did not always correlate with the models predictions

36. How did Ptolemy account for retrograde motion in his model of the solar system?

37. Copernicus’s Heliocentric Model
Polish Astronomer
Proposed a Heliocentric Model: Sun – centered solar system
Suggested that Earth was a rotating planet that revolved around the Sun

38. Copernicus’s Heliocentric Model
Retrograde Motion is a result of planets orbiting the Sun counterclockwise at different distances and speeds
Example:
Earth orbits faster than Mars
When Earth overtakes and begins to pass Mars, it make Mars appear to move backward
After Earth has fully passed, Mars’s normal motion appears to resume

40. Retrograde Motion Video

41. Use a Venn diagram to compare and contrast Ptolemy’s Model and Copernicus’s Model?

42. Tycho, Kepler, & Planetary Motion
Tycho Brahe: Danish astronomer in the 16th Century
Studied the movement of moons and planets throughout their entire orbit
Discovered unexpected occurrences within the orbits
His record were the most precise before the invention of the telescope

43. Kepler’s Laws Johannes Kepler - Tycho’s assistant
Discovered that the unexpected occurrences could be explained if the planets’ orbits were elliptical, rather than round
Developed 3 Laws of Celestial Mechanics

44. 1st Law of Planetary Motion
Planets travel in elliptical orbits with the sun at one focus
An ellipse has two foci on opposite side of the center
Since the Sun is located at one focus of the ellipse, a planet’s distance from the sun will change throughout its orbit

45. 2nd Law of Planetary Motion
Equal Area Law: each planet moves around the sun in such a way that an imaginary line joining the planet to the sun sweeps over equal areas of space in equal periods of time
Means that the speed at which a planet travels around the sun is not constant
Planets travel faster when they are closer to the Sun

46. 3rd Law of Planetary Motion
Harmonic Law: The period (P) of a planet squared is equal to the cube of its mean distance (D) from the Sun. P2 = D 3
The farther the planet is from the sun, the longer its period of revolution

47. Isaac Newton and the Law of Gravitation
English scientist and mathematician
Developed an explanation for what kept the planets in motion

48. Law of Gravitation
Every mass exerts a force of attraction on every other mass

49. Law of Gravitation
Every mass exerts a force of attraction on every other mass
The strength of that force is proportional to each of the masses

50. Law of Gravitation
Every mass exerts a force of attraction on every other mass
The strength of that force is proportional to each of the masses
The strength of that force is inversely proportional to the distance between them

51. What happens to the strength of gravity as mass increases?
What happens to the strength of gravity as distance increases?

52. Gravity and the Sun
If an object is moving through space in a path that will take it by the sun, the force due to gravity will increase as the distance between the two decreases
Since the sun has a greater mass, the motion of the object will change and begin to orbit around the sun

53. How does Newton's law of Gravity support Kepler’s 2nd Law of Motion?