ASTR 1101-001
Spring 2008
Joel E. Tohline, Alumni Professor
247 Nicholson Hall
[Slides from Lecture03]
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)
You may work in a group containing no more than 5 individuals from this class.
Assignment:
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 = 2pR
– Hence, R = C/(2p) = 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.
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 = 2pR
– Hence, R = C/(2p) = 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.
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 = 2pR
– Hence, R = C/(2p) = 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.
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 = 2pR
– Hence, R = C/(2p) = 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.
Worksheet Items #3 & #4
• The sun-to-basketball scaling ratio is …
– f = Rsun/Rbasketball = (7 x 108 m)/(0.121 m) = 5.8 x 109
• What is the Earth-Sun distance on this scale?
– dES = 1 AU/f = (1.5 x 1011 m)/5.8 x 109 = 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 108 km = 1.496 x 1011 m.
Worksheet Items #3 & #4
• The sun-to-basketball scaling ratio is …
– f = Rsun/Rbasketball = (7 x 108 m)/(0.121 m) = 5.8 x 109
• What is the Earth-Sun distance on this scale?
– dES = 1 AU/f = (1.5 x 1011 m)/5.8 x 109 = 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 108 km = 1.496 x 1011 m.
Worksheet Items #3 & #4
• The sun-to-basketball scaling ratio is …
– f = Rsun/Rbasketball = (7 x 108 m)/(0.121 m) = 5.8 x 109
• What is the Earth-Sun distance on this scale?
– dES = 1 AU/f = (1.5 x 1011 m)/5.8 x 109 = 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 108 km = 1.496 x 1011 m.
What about the Dime?
What about the Dime?
NOTE: A dime held 1 meter from your eye subtends an angle of 1°.
Calendar
See §2-8 for a discussion of
the development of the
modern calendar.
Calendar
• Suppose you lived on the planet Mars or
Jupiter and were responsible for
constructing a Martian or Jovian calendar.
Information on Planets
[Drawn principally from Appendices 1, 2 & 3]
Planet
Earth
Mars
Jupiter
Mercury
Venus
Uranus
Saturn
Neptune
Rotation Period
(solar days)
1.00
1.026
0.414
58.646
243 (R)
0.718 (R)
Orbital (sidereal)
Period
(solar days)
Inclination of
equator to orbit
(degrees)
“Moon’s” orbital
period
(solar days)
365.25
687.0
23°
25°
27.32
4331.86
87.97
224.70
30,717.5
3°
½°
177°
98°
Two satellites:
0.319 & 1.263
Thirty-nine satellites!
No satellites 
No satellites 
Twenty-seven
satellites!
Information on Planets
[Drawn principally from Appendices 1, 2 & 3]
Planet
Earth
Mars
Jupiter
Mercury
Venus
Uranus
Saturn
Neptune
Rotation Period
(solar days)
1.00
1.026
0.414
58.646
243 (R)
0.718 (R)
Orbital (sidereal)
Period
(solar days)
Inclination of
equator to orbit
(degrees)
“Moon’s” orbital
period
(solar days)
365.25
687.0
23°
25°
27.32
4331.86
87.97
224.70
30,717.5
3°
½°
177°
98°
Two satellites:
0.319 & 1.263
Thirty-nine satellites!
No satellites 
No satellites 
Twenty-seven
satellites!
Information on Planets
[Drawn principally from Appendices 1, 2 & 3]
Planet
Earth
Mars
Jupiter
Mercury
Venus
Uranus
Saturn
Neptune
Rotation Period
(solar days)
1.00
1.026
0.414
58.646
243 (R)
0.718 (R)
Orbital (sidereal)
Period
(solar days)
Inclination of
equator to orbit
(degrees)
“Moon’s” orbital
period
(solar days)
365.25
687.0
23°
25°
27.32
4331.86
87.97
224.70
30,717.5
3°
½°
177°
98°
Two satellites:
0.319 & 1.263
Thirty-nine satellites!
No satellites 
No satellites 
Twenty-seven
satellites!
Information on Planets
[Drawn principally from Appendices 1, 2 & 3]
Planet
Earth
Mars
Jupiter
Mercury
Venus
Uranus
Saturn
Neptune
Rotation Period
(solar days)
1.00
1.026
0.414
58.646
243 (R)
0.718 (R)
Orbital (sidereal)
Period
(solar days)
Inclination of
equator to orbit
(degrees)
“Moon’s” orbital
period
(solar days)
365.25
687.0
23°
25°
27.32
4331.86
87.97
224.70
30,717.5
3°
½°
177°
98°
Two satellites:
0.319 & 1.263
Thirty-nine satellites!
No satellites 
No satellites 
Twenty-seven
satellites!
Information on Planets
[Drawn principally from Appendices 1, 2 & 3]
Planet
Earth
Mars
Jupiter
Mercury
Venus
Uranus
Saturn
Neptune
Rotation Period
(solar days)
1.00
1.026
0.414
58.646
243 (R)
0.718 (R)
Orbital (sidereal)
Period
(solar days)
Inclination of
equator to orbit
(degrees)
“Moon’s” orbital
period
(solar days)
365.25
687.0
23°
25°
27.32
4331.86
87.97
224.70
30,717.5
3°
½°
177°
98°
Two satellites:
0.319 & 1.263
Thirty-nine satellites!
No satellites 
No satellites 
Twenty-seven
satellites!
Information on Planets
[Drawn principally from Appendices 1, 2 & 3]
Planet
Earth
Mars
Jupiter
Mercury
Venus
Uranus
Saturn
Neptune
Rotation Period
(solar days)
1.00
1.026
0.414
58.646
243 (R)
0.718 (R)
Orbital (sidereal)
Period
(solar days)
Inclination of
equator to orbit
(degrees)
“Moon’s” orbital
period
(solar days)
365.25
687.0
23°
25°
27.32
4331.86
87.97
224.70
30,717.5
3°
½°
177°
98°
Two satellites:
0.319 & 1.263
Thirty-nine satellites!
No satellites 
No satellites 
Twenty-seven
satellites!
Information on Planets
[Drawn principally from Appendices 1, 2 & 3]
Planet
Earth
Mars
Jupiter
Mercury
Venus
Uranus
Saturn
Neptune
Rotation Period
(solar days)
1.00
1.026
0.414
58.646
243 (R)
0.718 (R)
Orbital (sidereal)
Period
(solar days)
Inclination of
equator to orbit
(degrees)
“Moon’s” orbital
period
(solar days)
365.25
687.0
23°
25°
27.32
4331.86
87.97
224.70
30,717.5
3°
½°
177°
98°
Two satellites:
0.319 & 1.263
Thirty-nine satellites!
No satellites 
No satellites 
Twenty-seven
satellites!
Information on Planets
[Drawn principally from Appendices 1, 2 & 3]
Planet
Earth
Mars
Jupiter
Mercury
Venus
Uranus
Saturn
Neptune
Rotation Period
(solar days)
1.00
1.026
0.414
58.646
243 (R)
0.718 (R)
Orbital (sidereal)
Period
(solar days)
Inclination of
equator to orbit
(degrees)
“Moon’s” orbital
period
(solar days)
365.25
687.0
23°
25°
27.32
4331.86
87.97
224.70
30,717.5
3°
½°
177°
98°
Two satellites:
0.319 & 1.263
Thirty-nine satellites!
No satellites 
No satellites 
Twenty-seven
satellites!
Information on Planets
[Drawn principally from Appendices 1, 2 & 3]
Planet
Earth
Mars
Jupiter
Mercury
Venus
Uranus
Saturn
Neptune
Rotation Period
(solar days)
1.00
1.026
0.414
58.646
243 (R)
0.718 (R)
Orbital (sidereal)
Period
(solar days)
Inclination of
equator to orbit
(degrees)
“Moon’s” orbital
period
(solar days)
365.25
687.0
23°
25°
27.32
4331.86
87.97
224.70
30,717.5
3°
½°
177°
98°
Two satellites:
0.319 & 1.263
Thirty-nine satellites!
No satellites 
No satellites 
Twenty-seven
satellites!
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!
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!
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!
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!
Earth’s orbit around the Sun
• Responsible for our familiar calendar “year”.
• Period (of orbit) = 3.155815 x 107 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.
Earth’s orbit around the Sun
• Responsible for our familiar calendar “year”.
• Period (of orbit) = 3.155815 x 107 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.
Earth’s orbit around the Sun
• Responsible for our familiar calendar “year”.
• Period (of orbit) = 3.155815 x 107 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.
Earth’s orbit around the Sun
• Responsible for our familiar calendar “year”.
• Period (of orbit) = 3.155815 x 107 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.
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°.
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°.
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°.
Moon’s orbit around the Earth
• Responsible for our familiar calendar month.
• Period (of orbit) = 2.36 x 106 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!