ASTR 1101-001Spring 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 = 2R– 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.

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 = 2R– 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.

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 = 2R– 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.

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 = 2R– 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.

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°.

CalendarSee §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 Rotation Period

(solar days)

Orbital (sidereal) Period

(solar days)

Inclination of equator to orbit

(degrees)

“Moon’s” orbital period

(solar days)

Earth 1.00 365.25 23° 27.32

Mars 1.026 687.0 25°Two satellites:

0.319 & 1.263

Jupiter 0.414 4331.86 3°Thirty-nine satellites!

Mercury 58.646 87.97 ½° No satellites

Venus 243 (R) 224.70 177° No satellites

Uranus 0.718 (R) 30,717.5 98°Twenty-seven satellites!

Saturn

Neptune

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)

Earth 1.00 365.25 23° 27.32

Mars 1.026 687.0 25°Two satellites:

0.319 & 1.263

Jupiter 0.414 4331.86 3°Thirty-nine satellites!

Mercury 58.646 87.97 ½° No satellites

Venus 243 (R) 224.70 177° No satellites

Uranus 0.718 (R) 30,717.5 98°Twenty-seven satellites!

Saturn

Neptune

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)

Earth 1.00 365.25 23° 27.32

Mars 1.026 687.0 25°Two satellites:

0.319 & 1.263

Jupiter 0.414 4331.86 3°Thirty-nine satellites!

Mercury 58.646 87.97 ½° No satellites

Venus 243 (R) 224.70 177° No satellites

Uranus 0.718 (R) 30,717.5 98°Twenty-seven satellites!

Saturn

Neptune

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)

Earth 1.00 365.25 23° 27.32

Mars 1.026 687.0 25°Two satellites:

0.319 & 1.263

Jupiter 0.414 4331.86 3°Thirty-nine satellites!

Mercury 58.646 87.97 ½° No satellites

Venus 243 (R) 224.70 177° No satellites

Uranus 0.718 (R) 30,717.5 98°Twenty-seven satellites!

Saturn

Neptune

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)

Earth 1.00 365.25 23° 27.32

Mars 1.026 687.0 25°Two satellites:

0.319 & 1.263

Jupiter 0.414 4331.86 3°Thirty-nine satellites!

Mercury 58.646 87.97 ½° No satellites

Venus 243 (R) 224.70 177° No satellites

Uranus 0.718 (R) 30,717.5 98°Twenty-seven satellites!

Saturn

Neptune

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)

Earth 1.00 365.25 23° 27.32

Mars 1.026 687.0 25°Two satellites:

0.319 & 1.263

Jupiter 0.414 4331.86 3°Thirty-nine satellites!

Mercury 58.646 87.97 ½° No satellites

Venus 243 (R) 224.70 177° No satellites

Uranus 0.718 (R) 30,717.5 98°Twenty-seven satellites!

Saturn

Neptune

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)

Earth 1.00 365.25 23° 27.32

Mars 1.026 687.0 25°Two satellites:

0.319 & 1.263

Jupiter 0.414 4331.86 3°Thirty-nine satellites!

Mercury 58.646 87.97 ½° No satellites

Venus 243 (R) 224.70 177° No satellites

Uranus 0.718 (R) 30,717.5 98°Twenty-seven satellites!

Saturn

Neptune

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)

Earth 1.00 365.25 23° 27.32

Mars 1.026 687.0 25°Two satellites:

0.319 & 1.263

Jupiter 0.414 4331.86 3°Thirty-nine satellites!

Mercury 58.646 87.97 ½° No satellites

Venus 243 (R) 224.70 177° No satellites

Uranus 0.718 (R) 30,717.5 98°Twenty-seven satellites!

Saturn

Neptune

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)

Earth 1.00 365.25 23° 27.32

Mars 1.026 687.0 25°Two satellites:

0.319 & 1.263

Jupiter 0.414 4331.86 3°Thirty-nine satellites!

Mercury 58.646 87.97 ½° No satellites

Venus 243 (R) 224.70 177° No satellites

Uranus 0.718 (R) 30,717.5 98°Twenty-seven satellites!

Saturn

Neptune

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!