1 What do we mean when we say that the Sun is in energy balance?
The amount of energy released by fusion in the Sun's core equals the amount of energy radiated from the Sun's surface into space.
2Which of the following is the best answer to the question, "Why does the Sun shine?"
As the Sun was forming, gravitational contraction increased the Sun's temperature until the core become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine.
3Which of the following best describes why the Sun emits most of its energy in the form of visible light?
Like all objects, the Sun emits thermal radiation with a spectrum that depends on its temperature, and the Sun's surface temperature is just right for emitting mostly visible light.
4According to modern science, approximately how old is the Sun?
4 1/2 billion years
5The Sun will exhaust its nuclear fuel in about ______.
5 billion years
6Which of the following correctly describes how the process of gravitational contraction can make a star hot?
When a star contracts in size, gravitational potential energy is converted to thermal energy.
When a star contracts in size, gravitational potential energy is converted to thermal energy.
7When we say that the Sun is a ball of plasma, we mean that _________.
the Sun consists of gas in which many or most of the atoms are ionized (missing electrons)
8What is the Sun’s approximate composition (by mass)?
70% hydrogen, 28% helium, 2% other elements
9The Sun's visible surface (that is, the surface we can see with our eyes) is called the _________.
photosphere
10The Sun's average surface (photosphere) temperature is about ______.
5,800 K
11What is the solar wind?
a stream of charged particles flowing outward from the surface of the Sun
12The dark spots in this photo (such as the one indicated by the arrow) represent what we call:
sunspots
13Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is _________.
Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is _________.
14 If the Sun's core suddenly shrank a little bit, what would happen in the Sun?
The core would heat up, fusion rates would increase, the core would re-expand.
15Which of the following choices is not a way by which we can study the inside of the Sun?
early in its history, when there is still a gaseous disk around the star
We can send a space probe into the Sun's photosphere.
16The intricate patterns visible in an X-ray image of the Sun generally show _________.
extremely hot plasma flowing along magnetic field lines
extremely hot plasma flowing along magnetic field lines
17What do sunspots, solar prominences, and solar flares all have in common?
They are all strongly influenced by magnetic fields on the Sun.
18Choose the correct statement describing the astrometric method and the GAIA mission.
Astrometric method uses very precise measurements of stellar side-to-side positions in the sky to look for the slight motion caused by orbiting planets. The GAIA mission was launched by the European Space Agency with a goal of measuring the positions of a billion stars to unprecedented accuracy.
19Choose the correct statement representing how does the transit method work.
We monitor the brightness of a star as the planet passes in front of the star's disk. The star's light dims slightly because the planet blocks some of the star's visible light. This technique works only in the rare cases when the planet's orbit is nearly edge-on as seen from Earth. So we can only detect a small fraction of the existing planets.
20Choose the correct statement explaing what was the Kepler mission?
The Kepler mission uses the transit method to search for Earth-size planets in Earth-like orbits.
21Directly detecting an Earth-size planet around one of the nearest stars (besides the Sun) is roughly equivalent to trying to take a picture of a ball point from a pen at a distance of about ________ kilometers.
4000
22Which method of planetary detection works only for planets that happen to orbit their star with an orientation that causes them to pass directly in front of the star as seen from Earth?
the transit method
23the transit method
e Doppler method
the astrometric method
24Which method could detect a planet in an orbit that is face-on to the Earth?
astrometric method
25Which detection method or methods measure the gravitational tug of a planet on its star, allowing us to estimate planetary mass?
the astrometric and Doppler methods
26Which of the following is a major reason for why it is very difficult to directly take a picture of an exoplanet?
The angular separation of exoplanets from their stars is very small.
27Which of the following best explains why it would be challenging for an alien civilization to use the Doppler shift method to detect Earth?
Earth is too small in mass.
28Which one of the following can the transit method tell us about a planet?
its size
29To determine a planet's average density, we can use
the transit and Doppler methods together.
30What are the strengths and limitations of the Doppler method?
The Doppler method is able to detect planets in a wide range of orbits--as long as the orbit is not face-on. Its disadvantage is that it can yield only the orbital period and estimation of planet's mass.
31What are the strengths and limitations of the transit method?
The transit method has the advantage of yielding a planet's size. Its disadvantage is that few planets have the necessary orbital alignment to even be detectable.
32What kinds of planets are easiest to detect with each method?
Both techniques are most sensitive to large planets close to their stars.
33Are there certain planets that each method cannot detect, even if the planets are very large?
Planets that do not have necessary orbital alignment cannot be detected.
34Choose the correct description of advantages gained if a planet can be detected by both transit and Doppler methods.
If a planet can be detected by both methods, then we can find its density--an indication of its composition.
35Choose the correct statement describing the Doppler method.
The Doppler technique watches for movement in stars by looking for periodic Doppler shifts. It’s best for detecting massive planets with close-in orbits. It detects planets in all orbit orientations except face-on. It requires large telescopes, and it provides only minimum mass when orbital inclination to Earth is unknown.
36Choose the correct statement representing the evidence that the planet orbiting 51 Pegasi is a hot Jupiter.
51 Pegasi is a planet whose orbital period is so short (4 days) that it must lie incredibly close to its star. Furthermore, the size of the stellar Doppler wobble is so large that it must be caused by a planet with at least a mass of 0.6
37Which of the following properties can be inferred from the star’s orbital period?
the planet’s orbital radius
38Is it possible to determine the planet's mass from the star's velocity curve?
yes, by measuring both the star's orbital period and its change in velocity over the orbit
39Consider the planet that causes the stellar motion shown in Plot 2 (be sure you have clicked the “Plot 2” button in the lower window of the animation). What can be said about a different planet orbiting the same star with an orbital period of 500 days?
The planet must be closer to the star.
40What is planetary migration, and how may it account for the surprising orbits of many extrasolar planets?
Many extrasolar planets are much closer to their stars than we had expected. In fact, our formation model does not allow jovian planets to form that close to their stars. However, we think that it is possible for planets to migrate through their disks because of interactions with the gas in the disk.
41Based on what we know about our own solar system, the discovery of hot Jupiters came as a surprise to scientists because these planets are __________.
so close to their stars
42Our modern theory of solar system formation—the nebular theory—successfully accounts for all the major features of our own solar system. However, when the first hot Jupiters were discovered, their existence seemed inconsistent with the nebular theory because this theory predicts that __________.
jovian planets can form only in the cold, outer regions of a solar system
43The discovery of hot Jupiters led scientists to reconsider the nebuar theory. Which of the following best explains why the nebular theory(as it stood before the discoveries of extrasolar planets) had not predicted the existence of hot Jupiters?
There are no hot Jupiters in our solar system.
44Today, the leading hypothesis for the existence of hot Jupiters is that they formed in their outer solar systems and then migrated inward. Why did this hypothesis gain favor over alternative ideas?
Computer models that simulate planetary formation show that interactions between young planets and other material in the surrounding disk can cause planetary migration.
45Assume that the migration hypothesis is the correct explanation for the hot Jupiters. In that case, the revised nebular theory looks just like the old theory, except that it now allows for the possibility of migration. Which of the following statements are consistent with this revised theory?
Terrestrial planets always form in the warm, inner regions of their star system.
Hot Jupiters can orbit their star in a direction opposite that of other jovian planets in the same system.
46Based on computer models, when is planetary migration most likely to occur in a planetary system?
early in its history, when there is still a gaseous disk around the star