PHYS 107 ASTRONOMY MIDTERM 1

• Question 1

  3 out of 3 points

  	What fraction of the celestial sphere can you see at any given time?
  	Selected Answer:   exactly 1/2 Correct Answer:  exactly 1/2 Response Feedback: Correct, since the Earth is a sphere we can see from it's surface exactly 1/2 of the sky.

• Question 2

  0 out of 3 points

  	Your professor goes to visit his in-laws in Argentina in June, which of the following is true:
  	c.  it is winter and the Sun rises in the southeast. Correct Answers: a. it is winter and the Sun rises in the northeast. Response Feedback: Incorrect, the seasons are reversed in the Southern hemisphere since at this time of year the Northern hemisphere is pointed toward the Sun.  The Sun will rise to the northeast since Argentina is below the equator and the Sun always rises in the east (and sets in the west).

• Question 3

  3 out of 3 points

  	Precession is the:
  	c.  slow motion of the Earth's poles on the celestial sphere. Correct Answers: c. slow motion of the Earth's poles on the celestial sphere. Response Feedback: Correct, precession causes the direction of the Earth's rotational axis to slowly move relative to the stars.

• Question 4

  3 out of 3 points

  	Which of the following statements about scientific models is true?
  	Selected Answer:    A model can be used to explain and predict real phenomena. Correct Answer:    A model can be used to explain and predict real phenomena. Response Feedback:  Correct, a scientific model's usefulness is based upon its ability to predict and explain phenomena.

• Question 5

  3 out of 3 points

  	The Sun is much, much more massive than the Earth so the magnitude of the gravitational force on the Sun from the Earth is (           ) than the force on the Earth from the Sun.
  	Selected Answer:   the same Correct Answer:  the same Response Feedback: Correct, by Newton's Law of Universal gravitation and Newton's Third Law the force on both objects is equal.

• Question 6

  3 out of 3 points

  	At which location will the planet be travelling the fastest in its orbit?
  	b.  b  Correct Answers: b. b  Response Feedback: Correct, at (b) it is closest to the Sun.

• Question 7

  3 out of 3 points

  	The larger of two radio telescopes will
  	c.  collect more energy and have higher resolution Correct Answers: c. collect more energy and have higher resolution Response Feedback: Correct, since the amount of energy collected increases with the area and the resolution goes as the inverse of the diameter (better resolution means smaller angles).

• Question 8

  3 out of 3 points

  	Suppose you are traveling at 30 km/s, according to Newton's first law your motion:
  	Selected Answer:   will be unchanged until you are acted upon by a force Correct Answer:  will be unchanged until you are acted upon by a force Response Feedback: Correct, Newton's first law states (paraphrased): "An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an external (net) force"

• Question 9

  3 out of 3 points

  	In the following diagram there are the orbits of 4 planets, which planet or planets have the same orbital period?
  	b.  A and B Correct Answers: b. A and B Response Feedback: Correct by Kepler's 3rd Law (P2 = a3), also note C and D have the same period.

• Question 10

  3 out of 3 points

  	The reason the planets appear to be near the ecliptic is:
  	the planets revolve around the Sun in nearly the same plane. Correct Answers:  the planets revolve around the Sun in nearly the same plane. Response Feedback: Correct.

• Question 11

  3 out of 3 points

  	If the Earth orbited farther from the Sun than it does now:
  	d.  the year would be longer. Correct Answers: d. the year would be longer. Response Feedback: Correct.

• Question 12

  3 out of 3 points

  	You are on the side of the Moon that faces the Earth, and on Earth it is a full Moon. What phase Earth do you see?
  	Selected Answers: a.  new Correct Answers: a. new Response Feedback: Correct, the Sun must be on the "opposite side" of the Earth from the Moon, so "new Earth".

• Question 13

  3 out of 3 points

  	As seen from the Earth, the planets Mercury and Venus can only be found:
  	Selected Answer: a.  just above the western horizon after sunset. Correct Answer: a. just above the western horizon after sunset. Response Feedback: Correct, the inner planets can only be found near the Sun (within ~45 degrees).

• Question 14

  0 out of 3 points

  	You go outside and see the Sun in the following location in the sky, at sunset the same day the constellation the Sun will appear "in front" of is:
  	e.  Libra Correct Answers: c. Sagittarius Response Feedback: Incorrect, over the course of a single day both the Sun and stars will "move" the same amount on the sky due to the Earth's rotation. Thus the Sun will still be in the same constellation later that day.

• Question 15

  3 out of 3 points

  	The horizon is:
  	Selected Answer:   An imaginary plane which defines which portions of the sky one can see at any given time. Correct Answer:  An imaginary plane which defines which portions of the sky one can see at any given time. Response Feedback: Correct, the horizon divides the parts of the sky you can see from that you cannot, and depends on you position on the Earth.

• Question 16

  0 out of 3 points

  	Which of the following stars is smallest?
  	c.  C Correct Answers: a. A Response Feedback: Incorrect, since B gives off more light than A despite being cooler then you know B must be larger than A, similarly C gives of the same amount of light as A despite being much cooler and thus must be larger than A as well. Remember that for equal sizes a hotter object gives off more light at all wavelengths.

• Question 17

  3 out of 3 points

  	Orion is visible on winter evenings but not summer evenings because of
  	Selected Answer:    the location of Earth in its orbit. Correct Answer:    the location of Earth in its orbit. Response Feedback:  Correct, the Earth changes which side of the Sun it is on, and so Orion is in the sky during daytime.

• Question 18

  3 out of 3 points

  	Before launch here on Earth the masses of the Mars rovers Spirit and Opportunity were measured to be 185 kg; given that Mars has a density of 71% of Earth's density and a radius of 53% that of the Earth, when the rovers arrive at Mars their mass was:
  	Selected Answer:    185 kg  Correct Answer:   185 kg  Response Feedback:  Correct, the mass of the rovers stayed the same, while the weight (the force of gravity on them) changed

• Question 19

  3 out of 3 points

  	First quarter Moon is at position
  	c.  c  Correct Answers: c. c  Response Feedback: Correct, this is the 1st quarter (between new and full Moon)

• Question 20

  3 out of 3 points

  	The Astronomical Unit is approximately the:
  	Selected Answer:    mean distance from the Earth to the Sun Correct Answer:    mean distance from the Earth to the Sun Response Feedback:  Correct, the AU is the semi-major axis of the Earth's orbit and is roughly the mean distance from the Earth to the Sun

• Question 21

  0 out of 3 points

  	Which of the following are true of the planets in this figure:
  	Selected Answers: a.  they are obeying Kepler's 2nd law only if they move between each point in the same amount of time. Correct Answers: c. they must take longer to move through the two positions on the right (red) side of the ellipse than the left (blue) side. Response Feedback: Incorrect, the orbit is an ellipse so it obeys Kepler's 1st Law, and by the second Law since the red area (right side) is larger the time it takes to sweep this out must be longer.

• Question 22

  3 out of 3 points

  	Which of the following diagrams shows the emission of the highest energy photon?
  	C Correct Answers:  C Response Feedback: Correct, the electron in diagrams A and C are moving toward the nucleus so both are emission, and since the electron in C is moving "farther" (more levels) than in A it represents the emission of more energy.

• Question 23

  3 out of 3 points

  	The frequency of a wave is:
  	Selected Answer:    all of the above Correct Answer:   all of the above Response Feedback:  Correct the frequency is the number of peaks passing by a point, or cycles per second and is the speed of the wave divided its wavelength

• Question 24

  3 out of 3 points

  	If the Earths motion around the Sun was reversed how many degrees would the Earth rotate through in a sidereal day?
  	Selected Answer:    exactly 360° Correct Answer:    exactly 360° Response Feedback:  Correct, a sidereal day is the time it takes to rotate exactly 360 degrees

• Question 25

  0 out of 3 points

  	You have two objects of the same temperature but differing sizes, which one gives off more energy?
  	Selected Answer:   The smaller one Correct Answer:  The larger one Response Feedback: Incorrect, since the energy output L=constants*T4 * R2, and they are the same temperature the larger one gives off more energy.

• Question 26

  3 out of 3 points

  	Which position will the star be in in 12 hours?
  	b.  b Correct Answers: b. b Response Feedback: Correct, this is a circumpolar star.

• Question 27

  0 out of 3 points

  	As seen from the Moon, the Sun rises:
  	b.  once every 24 hours. Correct Answers: d. about once a month. Response Feedback: Incorrect, the Moon rotates in the same time it takes it to orbit the Earth (~ one month), this is why we see only one side of the Moon.

• Question 28

  3 out of 3 points

  	Compared to visible light, X-rays have
  	Selected Answer: b.  higher energy and shorter wavelengths Correct Answer: b. higher energy and shorter wavelengths Response Feedback: Correct, X-rays have very small wavelengths (1 nanometer) and very high energies (which is why they can penetrate your body).

• Question 29

  3 out of 3 points

  	A hot glowing solid will emit
  	d.  a continuous spectrum  Correct Answers: d. a continuous spectrum  Response Feedback: Correct, a hot solid emits a continuous spectrum, approximately as a "blackbody"

• Question 30

  3 out of 3 points

  	If the Sun were to suddenly expand to be 10 times its current size of ~0.0047 AU but keep the same mass, the Earth would:
  	Selected Answer:   stay in the same orbit Correct Answer:  stay in the same orbit Response Feedback: Correct, the force on the Earth would be unchanged since the mass of the Sun is unchanged, so the orbit would not change. Note this would not be true if the Sun were to expand to be larger than the Earth's orbit of course. Also note that orbital distances are defined from both object's centers, so while the Earth in some sense is "closer" to the Sun's surface, its distance from the Sun's center and hence its orbital distance is unchanged.

• Question 31

  3 out of 3 points

  	A sidereal day on Earth is not:
  	c.  longer than a Solar day.  Correct Answers: c. longer than a Solar day.  Response Feedback: Correct, all three of (a), (b), and (d) are true.

• Question 32

  3 out of 3 points

  	The Sun is much, much more massive than the Earth so the magnitude of the acceleration of the Sun from the gravitional force of the Earth is (           ) than the acceleration of the Earth due to the gravitational force on the Earth from the Sun.
  	Selected Answer:   less Correct Answer:  less Response Feedback: Correct, the acceleration is the force on an object divided by its mass, since the mass of the Sun is much larger and the forces on each are equal, the acceleration of the Sun must be less than the acceleration of the Earth.

• Question 33

  0 out of 3 points

  	If the Sun rises at 6am, the third quarter Moon rises at approximately:
  	c.  noon.  Correct Answers: e. midnight.

• Question 34

  3 out of 3 points

  	If today you were able to see where the Sun was relative to the stars and saw the Sun was "in front" of Sagittarius, then 2 months from now you would expect that the Sun would be seen "in front" of:
  	Selected Answers: a.  Aquarius Correct Answers: a. Aquarius Response Feedback: Correct, the Sun appears to shift approximately one constellation eastward along the ecliptic each month, as in Figure 2.12 in the text.

• Question 35

  3 out of 3 points

  	When did Kepler  live?
  	Selected Answer:     about 400 years ago Correct Answer:    about 400 years ago Response Feedback:  Correct, Kepler's work detailing his heliocentric model was published in the year 1609

• Question 36

  0 out of 3 points

  	Imagine living in a Universe where the planets orbit around their star like a record on a turntable or a CD/DVD in a player, then the periods of the planets would follow what version of Kepler's 3rd Law:
  	e.  P2 = a3 Correct Answers: a. P equal Response Feedback: Incorrect, if they are orbiting the star as a "solid body" all the planets would then orbit once around the star in the same length of time, in other words each makes one (360 degree) orbit in exactly the same period so (a) is correct.

• Question 37

  0 out of 3 points

  	Halley's comet has an orbit with a distance of closest approach to the Sun (perihelion) of 0.6 AU and greatest distance (aphelion) from the Sun of 35.1 AU. With an eccentricity of 0.97 and inclination of 163 degrees, its semi-major axis is:
  	Selected Answer:    ~0.6 AU Correct Answer:   ~18 AU Response Feedback: Incorrect, the semi-major axis is half the length of the major (long) axis of the orbit, so is half the sum of the point of closest approach to the point of furthest approach or in this case 1/2 * (0.6 + 35.1) or ~18 AU

• Question 38

  3 out of 3 points

  	What is not an advantage that a reflecting telescope has over a refracting telescope?
  	Selected Answer: d.  more chromatic aberration Correct Answer: e. more chromatic aberration Response Feedback: Correct, chromatic aberration is one of the chief failings of a refracting (lens based) telescope, and is the fact that light of different wavelengths do not focus on the same spot.  Reflecting (mirror based) telescopes suffer much less from this problem.

• Question 39

  3 out of 3 points

  	If an objects velocity is doubled its momentum is:
  	Selected Answer:   doubled Correct Answer:  doubled Response Feedback: Correct, momentum is the product of mass times velocity, so double the velocity and double the momentum

• Question 40

  3 out of 3 points

  	How did the Ptolemaic model explain the apparent retrograde motion of the planets?
  	Selected Answer:    The planets moved along small circles that moved on larger circles around the Earth. Correct Answer:    The planets moved along small circles that moved on larger circles around the Earth. Response Feedback:  Correct, the Ptolemaic model used multiple circles called deferents to explain the observed orbits of the planets