AST 101 EXAM QUESTIONS WITH CORRECT ANSWERS LATEST UPDATE 2026

AST 101 EXAM QUESTIONS WITH CORRECT ANSWERS LATEST UPDATE 2026 Polaris will no longer be the North Star 1,000 years from now. - Answers The directions of the earth's axis in space precesses with a period of 26,000 years In the year A.D. 15,000, Vega will be a better north star than Polaris - Answers The directions of the earth's axis in space precesses with a period of 26,000 years The Big Dipper will look different 100,000 years from now than it does today. - Answers stars appear to move randomly in the local solar neighborhood The Moon rises in the east and sets in the west. - Answers Earth rotates once each day The stars of Orion's belt rise in the east and set in the west. - Answers earth rotates once each day ) A million years from now, Alpha Centauri will no longer be the nearest star system to our own - Answers stars appear to move randomly in the local solar neighborhood If Earth's axis had no tilt, would we still have seasons? Why or why not? - Answers We would no longer have seasons, because the Sun's light would hit at the same angle all throughout the year, depending only on where you lived. The slight change in distance between Earth and the Sun during the year would not produce much of an effect. 8) Consider the following statement, and explain whether or not it is sensible: If you had a very fast spaceship, you could travel to the celestial sphere in about 100 years. - Answers This statement does not make sense because the celestial sphere is a concept and not a physical object Consider the following statement, and explain whether or not it is sensible: Although all the known stars appear to rise in the east and set in the west, we might someday discover a star that will appear to rise in the west and set in the east. - Answers This statement does not make sense. The stars aren't really rising and setting, they only appear to rise in the east and set in the west because the Earth rotates. Consider the following statement, and explain whether or not it is sensible: If you lived on the Moon, you'd see full Earth when we see new Moon. - Answers This is true, because at full Moon, Earth lies between the Sun and the Moon. Thus, an observer on the Moon would be looking at the night side of Earth. Why is the Moon not completely invisible (it appears as a very deep red color) to the naked eye during a total lunar eclipse? 1 - Answers The Moon shines through reflected light from the Sun and thus it becomes very dark during a lunar eclipse since the Moon lies within Earth's shadow at this time. However, some sunlight still gets through because it is bent (similar to the way a lens works) by Earth's atmosphere. We see the reflection of this faint light and thus the Moon is not completely invisible. (The bending of light is called refraction and the effect is strongest at long wavelengths. Thus it is most pronounced for red light and the eclipsed Moon appears dark red.) Suppose the distance to the Moon were twice its actual value. Could we still have solar eclipses? If so, what types - Answers If the Moon were twice its actual distance from us, we would no longer be able to see total solar eclipses because the Moon would not be able to completely cover the surface of the Sun; however, we would still see partial and annular eclipses, although the Moon would not block as much of the Sun during these times Consider the following statement, and explain whether or not it is sensible: Last night I saw Mars move westward through the sky in its apparent retrograde motion. - Answers This statement does not makes sense because the apparent retrograde motion is noticeable only over many nights, not during a single night. (Of course, like all celestial objects, Mars moves from east to west over the course of every nigh Describe one major accomplishment for each of the following people: Copernicus, Tycho Brahe, Kepler, Galileo, newton - Answers Many possible answers: e.g., Copernicus: Sun-centered system; Tycho Brahe: collected key data for Kepler's discoveries; Kepler: laws of planetary motion; Galileo: overturning Aristotelian physics; Newton: laws of motion and gravity. State Kepler's three laws of planetary motion. - Answers 1. The orbit of each planet is an ellipse with the Sun at one focus. 2. As a planet moves around its orbit, it sweeps out equal areas in equal times. 3. A planet's period squared is equal to its semimajor axis cubed. Summarize in your own words, the three "hallmarks" of science? - Answers 1. The quest to explain an observation by building on our knowledge of other aspects of nature 2. The creation and testing of models that explain observations as simply as possible 3. Models make testable predictions and are modified or abandoned if the predictions do not agree with observations what is pseudoscience ? - Answers Pseudoscience is the explanation of events through models that purport to be scientific but which, in practice, do not contain the hallmarks of science. For example, predictions may be made but models are not adjusted if the predictions fail to match the observations Describe what is a scientific test of astrology would involve - Answers First of all, science can only test the types of astrology that claim to be able to make predictions about future events or about characteristics of a person's personality and life. A scientific test of astrology requires evaluating many horoscopes and comparing their accuracy to what would be expected by pure chance. Therefore, one would have to evaluate how often a predicted event would likely occur naturally. Only if the astrologer could substantially beat the odds of predicting this event could one safely say that the astrologer could predict the future, at least concerning this particular event Process of Science: Why is it not science to start with the answer to a question and look for evidence to support it? - Answers The process of science involves asking a question and then forming testable hypotheses in order to gather evidence either to support or to refute it. So-called "cherry picking" of evidence to support an idea and ignoring evidence that may refute it does not advance knowledge and is not the scientific method. under what conditions is an object weightless - Answers whenever it is in free fall state newton'a three laws of motion - Answers 1. In the absence of a net force, an object moves with constant velocity. 2. Force = rate of change in momentum or mass times acceleration. 3. For every force there is an equal and opposite reaction force. ) Give an example in which thermal energy might be converted to gravitational energy. - Answers A hot air balloon rises: as we heat the gas in a balloon, the internal pressure increases and the balloon expands. Therefore the density of the air inside decreases and when the average density of the entire balloon (balloon material plus basket plus air inside) becomes less than the density of air outside, the balloon rises, gaining gravitational energy Imagine another solar system, with a star of the same mass as the Sun. Suppose there is a planet in that solar system with a mass of 2MEarth orbiting at a distance of 1 AU from the star. What (approximately) is the orbital period of this planet? Explain your answer. 25) - Answers The orbital period of the planet would be approximately the same as that of the earth (1 year). Kepler's law considers only the sum of the object masses. In comparison with the mass of the star, the mass of the planet can be neglected. Thus, even though the planet is twice as massive as Earth, its orbit will be nearly the same as that of Earth Explain how we can use Newton's version of Kepler's third law to measure the total mass of two stars in - Answers By observing the stars with a telescope, you can measure how far they move apart from each other (their orbital distance, a) and how long it takes them to move around each other (their orbital period, p). Then you use the formula p2 = 4Δ2 G(M1 + M2) a 3 to derive the total mass of the two stars, M1 + M2. suppose a satellite is in a low-earth orbit. Is is possible that the satellite will eventually fall to the ground? why or why not - Answers To fall to Earth, the satellite must lose some of its orbital energy. In low-Earth orbit, this can happen because the earth's atmosphere extends to high altitudes and exerts some atmospheric drag on the satellite. explain what synchronous rotation is. what is it caused by? give an example - Answers Synchronous rotation is when the rotational period of an object is the same as its orbital period around another object. As an object orbits another, it is stretched by the varying force of gravity across it. The resulting tidal bulges lag behind the rotation of the object slightly and cause it to rotate slower. This continues over time until the rotational period becomes the same as the orbital period, at which point there is no longer any tidal friction and the rotational and orbital periods are synchronized. An example is the Moon always presenting the same face to Earth through its orbit. A variation on this is Mercury which rotates 3 times for every 2 orbits around the Sun. what does atomic number refer to? - Answers the number of protons in an atom Define atomic weight - Answers atomic weight is the number of protons plus neutrons in an atom Suppose you have a chunk of water ice. Describe what happens to it, in terms of phases, as you raise the temperature to millions of degrees - Answers The ice melts into liquid, then evaporates into gas. At higher temperatures, the water molecules dissociate atoms. At very high temperatures, the atoms are ionized. what do we mean when we say that electron energy levels in atoms are quantized? - Answers the electrons can have only specific energies and not amounts of energy in between briefly explain why spectral lines are useful in determining the chemical composition of their source - Answers Every chemical element has a unique set of atomic energy levels and therefore a unique set of spectral lines. Thus, by identifying spectral lines, we can identify the elements that produced them. which transition represents an electron that absorbs a photon with 10.2 ev of energy ? - Answers earth revolves around the sun once each year what transition represents the electron that emits a photon with the highest energy? - Answers earth rotates once each day which transition represents an electron that is breaking free of the atom ? - Answers the universe is expanding which transition, as shown, is not possible? - Answers stars appear to move of earth's axis in space precessed with a period of 26,000 years Briefly explain why spectral lines are useful in determining the temperature of their source. - Answers Different ionization states of the same element have different sets of spectral lines. Thus, we can identify the ionization state, which tells us about the temperature because higher temperatures are required to reach higher ionization state state the two laws of thermal radiation - Answers 1. Hotter objects emit more radiation per unit surface area. 2. Hotter objects emit photons with higher average energy. Suppose the surface temperature of the Sun were about 18,000 K, rather than 6,000 K. How much more thermal radiation would the Sun emit? How would the thermal radiation spectrum of the Sun be different? - Answers From the first rule of thermal radiation, we know that tripling the temperature of an object increases the amount of thermal radiation it emits per unit area by a factor of 34 = 81. Thus, increasing the surface temperature of the Sun from 6,000 K to 18,000 K would increase its thermal radiation by a factor of 81. The higher temperature of the Sun would shift the peak of its thermal radiation spectrum from its current place in the visible light region into the ultraviolet. The hotter Sun would emit more energy at all wavelengths, with the greatest output coming in the ultraviolet. Briefly explain how we can use spectral lines to determine an object's radial motion. Can we also learn the object's tangential motion (across our line of sight) from its spectral lines? - Answers By comparing the wavelength of the spectral lines in the object's spectrum to the rest wavelengths of the same lines, we measure the Doppler shift. This tells us the object's radial motion: A shift toward shorter wavelength means the object is moving toward us, and a shift to longer wavelength means it is moving away from us. We cannot learn anything about the object's tangential motion from its spectral lines because this does not affect the line positions. Process of Science: The theory of thermal radiation says that hot objects are bluer than cool objects. Does it depend on what the object is made of? How can you test this? - Answers The color of thermal radiation from an object does not depend on its composition. You can test this by heating two pokers, one made of iron, another of, say, copper. They would each have the same "white hot" glow, turning to red hot as they cooled down (although the rate at which they cooled down and therefore their color at the same time after they are out of the fire would be different) draw and label a simple digram of the following A. a refracting telescope B. a reflecting telescope - Answers diagrams should look similar to figure 6.9 and 6.10 in the text What is spectral resolution? Why can a large telescope allow for a higher spectral resolution than a smaller telescope? - Answers Spectral resolution is a measure of the amount of detail that can be seen in a spectrum (i.e., how well it can separate out two spectral features from each other). It depends on how widely the light from a telescope is spread out, but the trade-off is that the more the light is spread out, the dimmer it becomes until it becomes undetectable. Since a large telescope gathers more light than a smaller telescope, it can spread the light out further and achieve a higher resolution. Suppose an astronomer proposed to build a major observatory on the campus of your school. Would it make a good observing site? explain why or why not - Answers Answers will vary somewhat with location, but in general campuses are bright environments that are poor observing sites from a light pollution standpoint. Other factors students may mention might include light from surrounding or nearby cities, excessive cloudiness or rain, windy area with a lot of turbulence, and low altitude with lots of atmosphere above explain how adaptive optics work - Answers Adaptive optics corrects for atmospheric distortion by following the distortion of a bright star, possibly an artificial star created by a laser, and rapidly changing the shape of a mirror using computer-controlled actuators to compensate for the distortion. explain what an interferometer is and give an example - Answers Interferometers are groups of telescopes that have been linked together and interfere the light waves that they receive to achieve the same angular resolution (but not the collecting area) as a much larger telescope. An example is the Very Large Array in New Mexico, which links 27 telescopes, each the size of a large house, over tens of miles. process of science explain how technology advances help address astronmical questions - Answers New technologies allow us to study objects in the Universe in more detail (e.g., adaptive optics), over more wavelengths (e.g., space telescopes), and more efficiently than before (e.g., with larger cameras and faster computers). These advances allow us to test scientific theories by having a wider range of objects to compare and by learning about the physical processes in each object in more detail. what is comparative planetology, and what is it's basic premise? - Answers Comparative planetology is the approach we use to study and understand our solar system. It involves comparing the worlds of our system, including planets, moons, asteroids, and comets, to one another. Its basic premise is that the similarities and differences among the worlds can be traced to common physical processes. what are some of things that make earth unique in the solar system? - Answers It is the only planet with an oxygen-rich atmosphere and liquid water on its surface (although there are hints that there may be liquid water on some of the moons around the jovian planets). Its surface temperature is such that water can exist in three phases: solid, liquid, and gaseous. Compared to its size, Earth also has by far the largest moon in the solar system, so much so that some astronomers consider it a double planet. Finally, Earth is the only planet we know of that harbors life.