Astro 1050 Wed. Sep. 21, 2005

Homework #3 questions

Homework #3 solutions

Question 1 (1 point)As you're going to sleep early one night you notice the rising moon in the center of the constellation Aries. You get up early the next morning before sunrise to do some flyfishing. The moon is still in the sky, although getting ready to set in the west. What constellation is it in?

a.Aries. b.Cancer. c.Gemini. d.Taurus. e.Pisces.

Why? Because during one night, essentially all the motion of objects in the sky is due to the Earth’s rotation, and everything turns together.

Homework solutions

Question 2 Tycho Brahe's greatest contribution to astronomy was

a.his 20 years of careful observations of planetary positions.

b.his model of the universe.

c.his telescopic observations of the moon.

d.his discovery of three laws of motion

Homework solutions

Question 3 (1 point) If a space probe were sent into an orbit around the sun that brought it as close as 0.5 AU to the sun and as far away as 5.5 AU, what would be the semimajor axis of its orbit?

a. 0.5 AU b. 3.0 AU c. 5.5 AU d. 6.0 AU

Question 4 (1 point) If a space probe were sent into an orbit around the sun that brought it as close as 0.5 AU to the sun and as far away as 5.5 AU, what would be its orbital period?

a.1.0 years b. 2.5 years c. 4.1 years d. 5.2 years

Use Kepler’s third law: P² = a³ for both these problems. Use units of years and AUs to make life simple.

Homework solutions

Question 5 (1 point) An asteroid has an orbital period around the sun of 5.2 years. Using Kepler's third law, how far from the sun is this asteroid?

a.5.2 AU b.10.4 AU c.27.0 AU d.3.0 AU e.2.3 AU

Again just Kepler’s third law and some math. Will work on board in review session.

Question 6. While all of the following are discoveries of Galileo, which of the four listed is NOT one which DIRECTLY contradicts the "Aristotelian" view of the heavens.

a.The discovery of "imperfections" on celestial bodies, such as mountains and valleys on the moon and changing sunspots on the sun.

b.The discovery of the phases of Venus, ranging from new to crescent to "quarter" to gibbous to full.

c.The discovery that the Milky Way is actually composed of a large number of very faint stars.

d.The discovery of four moons orbiting Jupiter.

Homework solutions

Question 7 (1 point) Newton concluded that some force had to act on the moon because

a. the moon moved at a constant velocity.

b. a force is needed to pull the moon outward.

c. a force is needed to pull the moon away from straight-line motion.

d. a force is needed to keep the moon in motion.

e. all of the above.

Homework solutions

Question 8 (1 point) What is the circular velocity of Mercury? You will need values from Appendix A of the textbook. You might also find the example in By the Numbers 4-1.

a. About 5 km/s.

b. About 25 km/s.

c. About 50 km/s.

d. About 75 km/s.

e.About 100 km/s.

Start From Vc = (GM/R)^0.5

G = 6.67x10^-11m³/kg s², M=2x10³⁰ kg, R=5.8x10⁷ km


	Question 1 (1 point)As you're going to sleep early one night you notice the rising moon in the center of the constellation Aries. You get up early the next morning before sunrise to do some flyfishing. The moon is still in the sky, although getting ready to set in the west. What constellation is it in? a.Aries. b.Cancer. c.Gemini. d.Taurus. e.Pisces.
	Why? Because during one night, essentially all the motion of objects in the sky is due to the Earth’s rotation, and everything turns together.


	Question 2 Tycho Brahe's greatest contribution to astronomy was a.his 20 years of careful observations of planetary positions.
	b.his model of the universe.
	c.his telescopic observations of the moon.
	d.his discovery of three laws of motion


	Question 3 (1 point) If a space probe were sent into an orbit around the sun that brought it as close as 0.5 AU to the sun and as far away as 5.5 AU, what would be the semimajor axis of its orbit? a. 0.5 AU b. 3.0 AU c. 5.5 AU d. 6.0 AU
	Question 4 (1 point) If a space probe were sent into an orbit around the sun that brought it as close as 0.5 AU to the sun and as far away as 5.5 AU, what would be its orbital period? a.1.0 years b. 2.5 years c. 4.1 years d. 5.2 years
	Use Kepler’s third law: P² = a³ for both these problems. Use units of years and AUs to make life simple.


	Question 5 (1 point) An asteroid has an orbital period around the sun of 5.2 years. Using Kepler's third law, how far from the sun is this asteroid? a.5.2 AU b.10.4 AU c.27.0 AU d.3.0 AU e.2.3 AU
	Again just Kepler’s third law and some math. Will work on board in review session.

	Question 6. While all of the following are discoveries of Galileo, which of the four listed is NOT one which DIRECTLY contradicts the "Aristotelian" view of the heavens.
	a.The discovery of "imperfections" on celestial bodies, such as mountains and valleys on the moon and changing sunspots on the sun.
	b.The discovery of the phases of Venus, ranging from new to crescent to "quarter" to gibbous to full.
	c.The discovery that the Milky Way is actually composed of a large number of very faint stars.
	d.The discovery of four moons orbiting Jupiter.


	Question 7 (1 point) Newton concluded that some force had to act on the moon because
	a. the moon moved at a constant velocity.
	b. a force is needed to pull the moon outward.
	c. a force is needed to pull the moon away from straight-line motion.
	d. a force is needed to keep the moon in motion.
	e. all of the above.


	Question 8 (1 point) What is the circular velocity of Mercury? You will need values from Appendix A of the textbook. You might also find the example in By the Numbers 4-1. a. About 5 km/s.
	b. About 25 km/s.
	c. About 50 km/s.
	d. About 75 km/s.
	e.About 100 km/s.

	Start From Vc = (GM/R)^0.5
	G = 6.67x10^-11m³/kg s², M=2x10³⁰ kg, R=5.8x10⁷ km