1. ASTR 1101-001 Spring 2008 Joel E. Tohline, Alumni Professor 247 Nicholson Hall [Slides from Lecture03]

2. Assignment: “ Construct” Scale Model of the Solar System Sun is a basketball. Place basketball in front of Mike the Tiger’s habitat. Walk to Earth’s distance, turn around and take a picture of the basketball (sun). Walk to Jupiter’s distance, take picture of sun. Walk to Neptune’s distance, take picture of sun. Assemble all images, along with explanations, into a PDF document. How far away is our nearest neighbor basketball? Due via e-mail (tohline@lsu.edu): By 11:30 am, 25 January (Friday)tohline@lsu.edu You may work in a group containing no more than 5 individuals from this class.

3. Assignment :

4. Worksheet Item #1 A basketball has a circumference C = 30”, so its radius is … –For all circles, the relationship between circumference (C) and radius (R) is: C = 2  R –Hence, R = C/(2  ) = 4.78” –But there are 2.54 centimeters (cm) per inch, so the radius of the basketball is: R = (4.78 inches)x(2.54cm/inch) = 12.1 cm = 0.121 meters.

5. Worksheet Item #1 A basketball has a circumference C = 30”, so its radius is … –For all circles, the relationship between circumference (C) and radius (R) is: C = 2  R –Hence, R = C/(2  ) = 4.78” –But there are 2.54 centimeters (cm) per inch, so the radius of the basketball is: R = (4.78 inches)x(2.54cm/inch) = 12.1 cm = 0.121 meters.

6. Worksheet Item #1 A basketball has a circumference C = 30”, so its radius is … –For all circles, the relationship between circumference (C) and radius (R) is: C = 2  R –Hence, R = C/(2  ) = 4.78” –But there are 2.54 centimeters (cm) per inch, so the radius of the basketball is: R = (4.78 inches)x(2.54cm/inch) = 12.1 cm = 0.121 meters.

7. Worksheet Item #1 A basketball has a circumference C = 30”, so its radius is … –For all circles, the relationship between circumference (C) and radius (R) is: C = 2  R –Hence, R = C/(2  ) = 4.78” –But there are 2.54 centimeters (cm) per inch, so the radius of the basketball is: R = (4.78 inches)x(2.54cm/inch) = 12.1 cm = 0.121 meters.

8. Worksheet Items #3 & #4 The sun-to-basketball scaling ratio is … –f = R sun /R basketball = (7 x 10 8 m)/(0.121 m) = 5.8 x 10 9 What is the Earth-Sun distance on this scale? –d ES = 1 AU/f = (1.5 x 10 11 m)/5.8 x 10 9 = 26 m Note: Textbook §1-6 reviews “powers-of-ten” (i.e., scientific) notation. Textbook §1-7 explains that 1 astronomical unit (AU) is, by definition, the distance between the Earth and the Sun. 1 AU = 1.496 x 10 8 km = 1.496 x 10 11 m.

9. Worksheet Items #3 & #4 The sun-to-basketball scaling ratio is … –f = R sun /R basketball = (7 x 10 8 m)/(0.121 m) = 5.8 x 10 9 What is the Earth-Sun distance on this scale? –d ES = 1 AU/f = (1.5 x 10 11 m)/5.8 x 10 9 = 26 m Note: Textbook §1-6 reviews “powers-of-ten” (i.e., scientific) notation. Textbook §1-7 explains that 1 astronomical unit (AU) is, by definition, the distance between the Earth and the Sun. 1 AU = 1.496 x 10 8 km = 1.496 x 10 11 m.

10. Worksheet Items #3 & #4 The sun-to-basketball scaling ratio is … –f = R sun /R basketball = (7 x 10 8 m)/(0.121 m) = 5.8 x 10 9 What is the Earth-Sun distance on this scale? –d ES = 1 AU/f = (1.5 x 10 11 m)/5.8 x 10 9 = 26 m Note: Textbook §1-6 reviews “powers-of-ten” (i.e., scientific) notation. Textbook §1-7 explains that 1 astronomical unit (AU) is, by definition, the distance between the Earth and the Sun. 1 AU = 1.496 x 10 8 km = 1.496 x 10 11 m.

11. What about the Dime?

13. NOTE: A dime held 1 meter from your eye subtends an angle of 1°.

15. Calendar See §2-8 for a discussion of the development of the modern calendar.

17. Calendar Suppose you lived on the planet Mars or Jupiter and were responsible for constructing a Martian or Jovian calendar.

18. Information on Planets [Drawn principally from Appendices 1, 2 & 3] Planet Rotation Period (solar days) Orbital (sidereal) Period (solar days) Inclination of equator to orbit (degrees) “Moon’s” orbital period (solar days) Earth1.00365.2523°27.32 Mars1.026687.025° Two satellites: 0.319 & 1.263 Jupiter0.4144331.863° Thirty-nine satellites! Mercury58.64687.97½° No satellites  Venus243 (R)224.70177° No satellites  Uranus 0.718 (R) 30,717.598° Twenty-seven satellites! Saturn Neptune

19. Information on Planets [Drawn principally from Appendices 1, 2 & 3] Planet Rotation Period (solar days) Orbital (sidereal) Period (solar days) Inclination of equator to orbit (degrees) “Moon’s” orbital period (solar days) Earth1.00365.2523°27.32 Mars1.026687.025° Two satellites: 0.319 & 1.263 Jupiter0.4144331.863° Thirty-nine satellites! Mercury58.64687.97½° No satellites  Venus243 (R)224.70177° No satellites  Uranus 0.718 (R) 30,717.598° Twenty-seven satellites! Saturn Neptune

20. Information on Planets [Drawn principally from Appendices 1, 2 & 3] Planet Rotation Period (solar days) Orbital (sidereal) Period (solar days) Inclination of equator to orbit (degrees) “Moon’s” orbital period (solar days) Earth1.00365.2523°27.32 Mars1.026687.025° Two satellites: 0.319 & 1.263 Jupiter0.4144331.863° Thirty-nine satellites! Mercury58.64687.97½° No satellites  Venus243 (R)224.70177° No satellites  Uranus 0.718 (R) 30,717.598° Twenty-seven satellites! Saturn Neptune

21. Information on Planets [Drawn principally from Appendices 1, 2 & 3] Planet Rotation Period (solar days) Orbital (sidereal) Period (solar days) Inclination of equator to orbit (degrees) “Moon’s” orbital period (solar days) Earth1.00365.2523°27.32 Mars1.026687.025° Two satellites: 0.319 & 1.263 Jupiter0.4144331.863° Thirty-nine satellites! Mercury58.64687.97½° No satellites  Venus243 (R)224.70177° No satellites  Uranus 0.718 (R) 30,717.598° Twenty-seven satellites! Saturn Neptune

22. Information on Planets [Drawn principally from Appendices 1, 2 & 3] Planet Rotation Period (solar days) Orbital (sidereal) Period (solar days) Inclination of equator to orbit (degrees) “Moon’s” orbital period (solar days) Earth1.00365.2523°27.32 Mars1.026687.025° Two satellites: 0.319 & 1.263 Jupiter0.4144331.863° Thirty-nine satellites! Mercury58.64687.97½° No satellites  Venus243 (R)224.70177° No satellites  Uranus 0.718 (R) 30,717.598° Twenty-seven satellites! Saturn Neptune

23. Information on Planets [Drawn principally from Appendices 1, 2 & 3] Planet Rotation Period (solar days) Orbital (sidereal) Period (solar days) Inclination of equator to orbit (degrees) “Moon’s” orbital period (solar days) Earth1.00365.2523°27.32 Mars1.026687.025° Two satellites: 0.319 & 1.263 Jupiter0.4144331.863° Thirty-nine satellites! Mercury58.64687.97½° No satellites  Venus243 (R)224.70177° No satellites  Uranus 0.718 (R) 30,717.598° Twenty-seven satellites! Saturn Neptune

24. Information on Planets [Drawn principally from Appendices 1, 2 & 3] Planet Rotation Period (solar days) Orbital (sidereal) Period (solar days) Inclination of equator to orbit (degrees) “Moon’s” orbital period (solar days) Earth1.00365.2523°27.32 Mars1.026687.025° Two satellites: 0.319 & 1.263 Jupiter0.4144331.863° Thirty-nine satellites! Mercury58.64687.97½° No satellites  Venus243 (R)224.70177° No satellites  Uranus 0.718 (R) 30,717.598° Twenty-seven satellites! Saturn Neptune

25. Information on Planets [Drawn principally from Appendices 1, 2 & 3] Planet Rotation Period (solar days) Orbital (sidereal) Period (solar days) Inclination of equator to orbit (degrees) “Moon’s” orbital period (solar days) Earth1.00365.2523°27.32 Mars1.026687.025° Two satellites: 0.319 & 1.263 Jupiter0.4144331.863° Thirty-nine satellites! Mercury58.64687.97½° No satellites  Venus243 (R)224.70177° No satellites  Uranus 0.718 (R) 30,717.598° Twenty-seven satellites! Saturn Neptune

26. Information on Planets [Drawn principally from Appendices 1, 2 & 3] Planet Rotation Period (solar days) Orbital (sidereal) Period (solar days) Inclination of equator to orbit (degrees) “Moon’s” orbital period (solar days) Earth1.00365.2523°27.32 Mars1.026687.025° Two satellites: 0.319 & 1.263 Jupiter0.4144331.863° Thirty-nine satellites! Mercury58.64687.97½° No satellites  Venus243 (R)224.70177° No satellites  Uranus 0.718 (R) 30,717.598° Twenty-seven satellites! Saturn Neptune

27. Earth’s rotation Responsible for our familiar calendar “day”. Period (of rotation) = 24 hours = (24 hours)x(60 min/hr)x(60s/min) =86,400 s Astronomers refer to this 24 hour period as a mean solar day (§2-7), implying that this time period is measured with respect to the Sun’s position on the sky. A sidereal day (period of rotation measured with respect to the stars – see Box 2-2) is slightly shorter; it is shorter by approximately 4 minutes. The number of sidereal days in a year is precisely one more than the number of mean solar days in a year!

28. Earth’s rotation Responsible for our familiar calendar “day”. Period (of rotation) = 24 hours = (24 hours)x(60 min/hr)x(60s/min) =86,400 s Astronomers refer to this 24 hour period as a mean solar day (§2-7), implying that this time period is measured with respect to the Sun’s position on the sky. A sidereal day (period of rotation measured with respect to the stars – see Box 2-2) is slightly shorter; it is shorter by approximately 4 minutes. The number of sidereal days in a year is precisely one more than the number of mean solar days in a year!

29. Earth’s rotation Responsible for our familiar calendar “day”. Period (of rotation) = 24 hours = (24 hours)x(60 min/hr)x(60s/min) =86,400 s Astronomers refer to this 24 hour period as a mean solar day (§2-7), implying that this time period is measured with respect to the Sun’s position on the sky. A sidereal day (period of rotation measured with respect to the stars – see Box 2-2) is slightly shorter; it is shorter by approximately 4 minutes. The number of sidereal days in a year is precisely one more than the number of mean solar days in a year!

31. Earth’s rotation Responsible for our familiar calendar “day”. Period (of rotation) = 24 hours = (24 hours)x(60 min/hr)x(60s/min) =86,400 s Astronomers refer to this 24 hour period as a mean solar day (§2-7), implying that this time period is measured with respect to the Sun’s position on the sky. A sidereal day (period of rotation measured with respect to the stars – see Box 2-2) is slightly shorter; it is shorter by approximately 4 minutes. The number of sidereal days in a year is precisely one more than the number of mean solar days in a year!

32. Earth’s orbit around the Sun Responsible for our familiar calendar “year”. Period (of orbit) = 3.155815 x 10 7 s = 365.2564 mean solar days (§2-8). Orbit defines a geometric plane that is referred to as the ecliptic plane (§2-5). Earth’s orbit is not exactly circular; geometrically, it is an ellipse whose eccentricity is e = 0.017 (Appendix 1). Because its orbit is and ellipse rather than a perfect circle, the Earth is slightly farther from the Sun in July than it is in January (Fig. 2-22). But this relatively small distance variation is not responsible for Earth’s seasons.

33. Earth’s orbit around the Sun Responsible for our familiar calendar “year”. Period (of orbit) = 3.155815 x 10 7 s = 365.2564 mean solar days (§2-8). Orbit defines a geometric plane that is referred to as the ecliptic plane (§2-5). Earth’s orbit is not exactly circular; geometrically, it is an ellipse whose eccentricity is e = 0.017 (Appendix 1). Because its orbit is and ellipse rather than a perfect circle, the Earth is slightly farther from the Sun in July than it is in January (Fig. 2-22). But this relatively small distance variation is not responsible for Earth’s seasons.

35. Earth’s orbit around the Sun Responsible for our familiar calendar “year”. Period (of orbit) = 3.155815 x 10 7 s = 365.2564 mean solar days (§2-8). Orbit defines a geometric plane that is referred to as the ecliptic plane (§2-5). Earth’s orbit is not exactly circular; geometrically, it is an ellipse whose eccentricity is e = 0.017 (Appendix 1). Because its orbit is and ellipse rather than a perfect circle, the Earth is slightly farther from the Sun in July than it is in January (Fig. 2-22). But this relatively small distance variation is not responsible for Earth’s seasons.

37. Earth’s orbit around the Sun Responsible for our familiar calendar “year”. Period (of orbit) = 3.155815 x 10 7 s = 365.2564 mean solar days (§2-8). Orbit defines a geometric plane that is referred to as the ecliptic plane (§2-5). Earth’s orbit is not exactly circular; geometrically, it is an ellipse whose eccentricity is e = 0.017 (Appendix 1). Because its orbit is and ellipse rather than a perfect circle, the Earth is slightly farther from the Sun in July than it is in January (Fig. 2-22). But this relatively small distance variation is not responsible for Earth’s seasons.

38. Tilt of Earth’s spin axis Responsible for Earth’s seasons (§2-5) Tilt of 23½° measured with respect to an axis that is exactly perpendicular to the ecliptic plane. Spin axis points to a fixed location on the “celestial sphere” (§2-4); this also corresponds very closely to the position of the north star (Polaris) on the sky. This “fixed location” is not actually permanently fixed; over a period of 25,800 years, precession of the Earth’s spin axis (§2-5) causes the “true north” location to slowly trace out a circle in the sky whose angular radius is 23½°.

40. Tilt of Earth’s spin axis Responsible for Earth’s seasons (§2-5) Tilt of 23½° measured with respect to an axis that is exactly perpendicular to the ecliptic plane. Spin axis points to a fixed location on the “celestial sphere” (§2-4); this also corresponds very closely to the position of the north star (Polaris) on the sky. This “fixed location” is not actually permanently fixed; over a period of 25,800 years, precession of the Earth’s spin axis (§2-5) causes the “true north” location to slowly trace out a circle in the sky whose angular radius is 23½°.

43. Tilt of Earth’s spin axis Responsible for Earth’s seasons (§2-5) Tilt of 23½° measured with respect to an axis that is exactly perpendicular to the ecliptic plane. Spin axis points to a fixed location on the “celestial sphere” (§2-4); this also corresponds very closely to the position of the north star (Polaris) on the sky. This “fixed location” is not actually permanently fixed; over a period of 25,800 years, precession of the Earth’s spin axis (§2-5) causes the “true north” location to slowly trace out a circle in the sky whose angular radius is 23½°.

46. Moon’s orbit around the Earth Responsible for our familiar calendar month. Period (of orbit) = 2.36 x 10 6 s = 27.32 days (Appendix 3). Moon’s orbital plane does not coincide with the ecliptic plane; it is inclined by approximately 8° to the ecliptic (§2-6). Much more about the Moon’s orbit in Chapter 3!