Q. Why is a day 24 hours long?
A. Because that is how long it takes for the Earth to spin around once so that the same side faces the Sun again.

Q. If the Earth's spin (rotation) was slower than it is now, then
A. A day would be more than 24 hours.

Q. When there is a full moon (the moon is fully illuminated)
A. the Moon is farther from the Sun than the Earth is.

Q. The main reason it is hotter in the summer than in the winter is:
A. the Sun is up longer and is higher in the sky.

Q. The Earth spins (rotates/revolves) around an axis that is tilted compared to the axis about which it orbits the Sun. Which of the following would be true if the Earth's spin was NOT tilted? (that is, which of the following would be true if the axis the Earth spins around was the same as the axis about which it orbits its sun).
A. The temperature would not change much during the year in both the northern and southern hemispheres.

Q. If the moon is full at midnight, what will it be at 2 AM the same night? A. full. Q. Which of the following would make your weight half what it is now?
A. Being on a planet the same size as Earth but half the mass.

Q. When you see the Moon,
A. Light is emitted by the Sun, reflects off the Moon, and a little bit of that enters your eye.

Q. When you see a star, light
A. is emitted by the star and enters your eye.

Q. The center of our Milky Way Galaxy is about 25 million light years away. If a star explodes there, how long will it be before we see this happen?
A. 25 million years.

Q. A photon that has a wavelength of 600 nanometers
A. is less energetic than a photon with a wavelength of 400 nanometers.

Q. As a glowing body gets cooler, it...
A. emits fewer photons, and these are typically less energetic.

Q. Which answer shows the correct pattern from closest object to the Earth to farthest from the Earth?
A. the Moon - Jupiter - stars other than the Sun.

Q. If you are playing pool and hit the cue ball, which of the following describes the situation based on Newton's Laws?
A. The ball moves in the direction the force was applied, and your hand feels an equal force in the opposite direction.

Q. Now you are still hitting the ball with the same force, but you would like the ball to accelerate more slowly (move slower). Which of the following should you do?
A. Increase the mass of the ball.

Q. What led to the acceptance of the idea that the Earth revolves around the Sun over the previous view that the Earth was the center of the Universe?
A. That theory described the observations better and explained the motions of all objects with one consistent model.

Q. A star is moving away from us in the Solar System. Which of the following correctly describes how we will observe photons from this star?
A. The observed photons will be shifted to longer wavelengths compared to the wavelengths emitted by a star that is not moving away from us.

Q. Now imagine that the same group of hydrogen atoms is moving even faster (larger velocity) towards you. The wavelengths you observe will be
A. shifted even more compared to their original values.

Q. If you dropped the following objects from the top of a ladder on the Moon, which one would hit first?
A. all of these objects would hit at the same time.

Q. Why don't we glow in the dark?
A.People only emit light that is invisible to our eyes.

Q. For objects that emit thermal radiation (like stars) which of the following is true?
A. Hotter objects emit more photons and more of these have higher energies.

Q. Which of the following is the main advantage of a larger telescope (bigger mirror)?
A. To be able to collect more light to see fainter objects.

Q. Which of the following is NOT an important reason for having telescopes in space?
A. To place the telescope closer to the stars.

Q. If there are two identical stars, but one is three times farther away than the other one.
A. The closer one will appear to be nine times brighter than the more distant one.

Q. Why are there no X-ray telescopes on the surface of the Earth?
A. X-ray photons are not able to pass through the atmosphere.

Q. Which of the following statements is most correct?
A. The Sun is about 200 times as massive as Jupiter.

Q. The force that prevents the Earth from flying out of the Solar System is
A. gravity

Q. How would the gravitational force between the Sun and the Earth change if the Sun doubled its mass?
A. The gravitational force between the Sun and Earth would be twice as large.

Q. If you have two glowing bodies, how can you tell which one is cooler (this generally works for stars)?
A. The cooler one has a redder color.

Q. Which of the following photons passes through space the fastest?
A. They all travel at the same speed.

Q. The gravitational force between two objects is
A. larger between objects of larger masses, and decreases as the square of the distance between the objects.

Q. Why does an atom only absorb some wavelengths of light and not all of them?
A. It only absorbs wavelengths of light with energies that correspond to specific differences between energies of allowed electron orbits.

Q. Who made observations of the phases of Venus and the moons of Jupiter that provided strong evidence that the Earth and the planets orbited around the Sun?
A. Galileo.

Q. The Sun and the giant planets are composed mainly of the same two elements. These are
A. hydrogen and helium.

Q. Which of the following is an important technique for determing the age of the Earth and Solar System?
A. Age dating rocks using radioactive atoms with experimentally determined half-lives.

Q. What is the approximate measured age of the solar system and of the Earth?
A. 4.5 billion years (4,500,000,000 years)

Q. Which of the following is true?
A. The planets all orbit the Sun in the same direction, and with the exception of Pluto, they all do so in the same plane like a flat disk.

Q. All of the planets together make up how much of the total mass of the Solar System?
A. Less than $1\%$

Q. Which of the following is NOT a good reason why the major impact model is the best explanation for the formation of the moon?
A. It predicts the Earth to have one moon, Mars two, and Venus none, as observed.

Q. Based on physical properties, which grouping of planets makes the most sense? A. Mercury, Venus, Earth, and Mars together, and Jupiter, Saturn, Uranus, and Neptune.

Q. Which planet has an atmosphere that is very similar to the Earth's?
A. None of them do.

Q. The Moon has many more impact craters on its surface than the Earth does. What does this tell us?
A. That the Moon's surface is old, and that the Earth's is young, because the Moon stopped having major geological activity a long time ago, while the Earth still does.

Q. Which of the following was NOT one of the sources of heat for the interior of the Earth and other planets?
A. The formation of H20 (water) from hydrogen and oxygen.

Q. If Venus was to suddenly cool off, so that its surface temperature would be similar to the Earth's, which one of the following would be most correct
A. Venus would not have any water because its hydrogen has escaped its atmosphere into space.

Q . Which one below has the correct order starting with planet with the highest surface pressure, going to the planet with the lowest surface pressure?
A. Venus (highest) - Earth - Mars (lowest)

Q. What is the primary source of Jupiter's internal energy?
A. Gravitational energy from the accretion and settling of material onto Jupiter.

Q. Which of the following best describes what would be required to transform Mars' atmosphere into something closer to the Earth's?
A. Heat it up to release the frozen water and carbon dioxide ice to start a greenhouse effect, which will warm up the surface, keeping some of the water and carbon dioxide in the atmosphere.

Q. What would happen eventually to Mars' atmosphere if you did manage to make it more like Earth's?
A. Over time it will start to cool off and lose some its atmosphere, because Mars doesn't get as much solar heating, and is less massive than the Earth and therefore has less gravity to hold on to its atmosphere.

Q. Where is the water on Mars?
A. Some of it is frozen on and beneath the surface, a little is in the atmosphere, and some has been lost from the system.

Q. Which of the following is *NOT* true of Pluto?
A. It originated from the solar system from another star and was brought into our solar system by the gravity of the Sun and Jupiter.

Q. Lost in Space: You're in the hottest place in the solar system. The temperature is 15 million degrees and nuclear fusion is definitely occurring in your vicinity. Where are you?
A. The core of the Sun.

Q. If a solar system was forming around a star that was cooler than the Sun, the most likely place to find a habitable region with an Earth-like atmosphere would be
A. a planet closer to the star than the Earth is from the Sun.

Q. Which of the following gases is most responsible for the greenhouse effect on planets in the inner solar system?
A. Carbon dioxide, CO$_2$

Q. Of the large inner moons of Jupiter, Io is the closest to the planet itself. It is also very active, with significant volcanism. What is the source of energy for Io's activity?
A. Tidal heating from gravitational interaction with Jupiter.

Q. Uranus revolves (spins) on its side (perpindicular to its orbit). As a result, Uranus
A. has very long seasons, since it needs to orbit around the Sun to go through all of the seasons.

Q. How do we know comets originate from the outer solar system?
A. We observe their orbits that take them to large distances from the Sun.

Q. The inner and outer Galilean moons of Jupiter differ, in that
A. the inner moons have more geological activity.

Q. Which of the following is *NOT* a method (either current or planned for the future) for detecting planets around stars other than the Sun?
A. Measuring the changes in the colors of a stars caused by the strong weather patterns on giant planets.

Q. Which is the best description of the process of formation of the planets?
A. The initial gas condensed into small bodies called plantesimals, which then coalesced through collisions into larger and larger bodies.

Q. Why doesn't the material in Saturn's inner rings clump together into just a few large moons?
A. Because they are very close to Saturn, so the gravitational tidal forces tear them apart.

Q. What is actually measured in the Doppler technique that indicates the presence of a massive planet?
A. The systematic shifting to shorter and longer wavelengths of light emitted by the star.

Q. With the transit technique for finding extrasolar planets, why do many stars have to be searched?
A. Few planets will have orbits that line up to block a little light from their star from reaching us.

Q. What causes a protostar to collapse?
A. When its gets dense enough so gravity pulls it together.

Q. Why does the Earth have less Hydrogen than the Sun and the giant planets?
A. When the planets were forming, the inner solar system was too hot for light elements and compounds to condense onto protoplanets.

Q. Why is it highly unlikely we will be able to travel to any other solar system
A. The great distance to even the most nearby star.

Q. What is the best explanation for why many of the planets found by the doppler (wobble) technique are massive and close to their Sun?
A. Because close in, massive planets have the strongest gravitational effect on their star, and thus create the biggest doppler wobble.

Q. Why are the heaviest elements at the center of the terrestial planets?
A. The terrestial planets once hot and molten, and the heaviest elements sank to the center through a process called differentiation.

Q. Why does the SETI program looking for extraterrestrial life use the radio region of the electromagnetic spectrum in their search?
A. Radio waves can pass through our atmosphere, and most solar-like stars are not strong radio emitters.

Q. What have we learned about solar system formation by studying other stars that are forming now?
A. That disks are common around forming stars.

Q. How does the fusion of hydrogen into helium produce the energy that powers the Sun?
A. The helium has a little bit less mass than the four hydrogens that get fused together to make it, and this difference comes out as energy according to $E = m c^{2}$.

Q. Why does some material in the proto-solar nebular end up in a disk around the central star instead of all falling into the center?
A. The conservation of angular momentum from the initial cloud out of which the protostar forms.

Q. Why does the fusion of Hydrogen into Helium happen in the Sun, but we can not easily do it on Earth?
A. Because it requires very high temperatures and densities to bring the hydrogen nuclei together, since their positive charges repel each other.

Q. With all of the energy produced in the Sun and the high temperature and pressure this creates, why doesn't the Sun just explode?
A. Gravity acts to pull the mass together and this balances the pressure pushing out.

Q. What about a star cluster would lead to a determination that it has an old age?
A. The absence of bright, blue stars.

Q. Which of the following is a good reason high mass stars are unlikely places to find advanced civilizatons?
A. Because high mass stars have such short lives there is no chance for evolution to advanced life on their planets.

Q. Why would a universe with only low-mass stars be unfavorable for life in that universe?
A. Because high-mass stars are critical producers of many elements necessary for life as we know it.

Q. Stars on the main sequence produce their energy by
A. fusion of Hydrogen into Helium.

Q. Where did the iron and other heavy elements in the universe come from?
A. They were produced by nuclear reactions that occur inside massive stars.

Q. The order of the stages of evolution a star like our Sun goes through is
A. main sequence, red giant, white dwarf.

Q. The most massive stars
A. have the shortest lives.

Q. If you see a star that is cool and has a large diameter, what kind of star is it?
A. A giant or supergiant star.

Q. When a star settles down to a stable existence as a main-sequence star, what characteristic determines where on the main sequence in an H-R diagram the star will fall?
A. its mass.

Q. What is a neutron star made of?
A. Neutrons.

Q. Why are parallax (triangulation) measurements limited to only nearby stars?
A. The shift in the apparent position of a star in the sky at different times of year is too small to measure for distant stars.

Q. One of the brightest stars in the sky is Betelgeuse even though it is *not* one of the closest stars to the Sun. What can we infer about Betelgeuse then?
A. It has a high luminosity (intrinsically bright).

Q. Which types of stars evolve so they have iron cores and may explode as supernovae?
A. Very massive stars.

Q. Cepheid variable stars are important tools for measuring cosmic distances. This is because their average luminosity (intrinsic brightness) is directly related to
A. the period with which they vary in brightness.

Q. Why are the less massive stars (like the Sun) NOT able to produce elements heavier than carbon and oxygen?
A. Because the star's center cannot get hot and dense enough for the nuclear reactions that build heavier nuclei.

Q. If you see a cluster of stars that has many bright, blue stars, you can infer which of the following
A. That it is a young star cluster

Q. A star in our Milky Way galaxy that has almost no elements heavier than hydrogen and helium (even much less than the Sun) is likely to be located
A. in the halo of our Galaxy.

Q. Which of the following best describes the formation of a spiral galaxy?
A. It cools by radiation, it contracts by gravity, and it spins up because of angular momentum conservation.

Q. Why is it important to determine the distances to stars to understand their basic properties?
A. We need to know the distance in order to determine a star's intrinsic brightness, so we can tell if it is a highly luminous star that is far away, or a lower luminosity star that is closer.

Q. Why does the fusion process in a massive star end with iron?
A. Iron is the most stable element, so energy can't be produced by turning Iron into other elements.

Q. Why are white dwarfs limited to being less than 1.4 solar masses?
A. If they were more massive their graviational pressure pulling the star together would be greater than the electron degeneracy holding it up, so it would implode.

Q. Why does the fusion process stop at Carbon and Oxygen for stars with modest masses like the Sun?
A. Because these stars are not massive enough to make their centers hot and dense enough for the nuclear reactions that build heavier nuclei.

Q. Where is the Sun located within our own Galaxy?
A. About thirty thousand light years from the center, in the disk of the Galaxy.

Q. What type of galaxy is our Milky Way galaxy?
A. A spiral galaxy.

Q. What is the source of the very bright luminosities at the centers of some galaxies, known as active galactic nuclei quasars?
A. Light emitted from material accreting around a black hole.

Q. How did Harlow Shapley figure out that the Sun was not at the center of our Milky Way Galaxy?
A. Most of the globular clusters are on one side of the sky, which should not happen if the Sun was in the center of the Galaxy.

Q. Which component of our Galaxy contains the largest amount of mass?
A. Dark matter.

Q. If you see a galaxy that is a round ball of stars with no stars currently forming, it is
A. an elliptical galaxy.

Q. Which of the following best describes how a galaxy without dark matter would differ from those with dark matter?
A. The motions of stars and gas in the galaxy without dark matter would be smaller in the outer regions beyond where most of the galaxy light is.

Q. Why do we know "nebulae" are galaxies of their own well outside of our Milky Way Galaxy?
A. We have observed Cepheid variable stars and determined distances that place them well beyond our own Galaxy.

Q. What effect does the black hole at the center of our Milky Way Galaxy have on the Sun?
A. None.

Q. What do the orbits of the stars in an elliptical galaxy look like?
A. The stars move in almost completely random directions, often with orbits that are not perfectly circular.

Q. What is the evidence that there is a massive black hole at the center of our Galaxy?
A. We observe that stars very close to the Galactic center orbit (move) very quickly, indicating that there is a massive, dense object at the center.

Q. If galaxies never collided, which of the following would be true?
A. There would be more galaxies with smoothly rotating disks.

Q. If your extra-terrestial friends said that they lived near some newly formed stars in our Galaxy, where would you go to visit them?
A. The disk of our Galaxy, probably in or near a spiral arm.

Q. Approximately how many stars are there in a typical galaxy like our Milky Way galaxy?
A. Several billion stars

Q. Which of the following best describes the formation of a spiral galaxy?
It cools by radiation, it contracts by gravity, and it spins up because of angular momentum conservation.

Q. Which of the following is the best model for how elliptical galaxies form?
A. When spiral galaxies collide, many stars form, and their rotating disks get disrupted by the collision and turned into a more random ball of stars.

Q. What is a good working definition of the radius of a black hole?
A. The radius where the escape velocity equals the speed of light so no light can escape.

Q. Your nice but not very bright roommate offers to drive you to the exam, but takes a wrong turn, and accidentally drives $inside$ the Schwarzschild radius (event horizon) of a black hole. You use your cell phone to try to send a radio SOS message back to AAA (who prudently have located their office outside the Schwarzschild radius). What will be the fate of that message?
A. The message will never emerge from the Schwarzschild radius.