Understanding the Shape of Earth: Evidence from Lunar Eclipses and Planetary Movements, Exams of Astronomy

Download Understanding the Shape of Earth: Evidence from Lunar Eclipses and Planetary Movements and more Exams Astronomy in PDF only on Docsity! Astronomy 101 Exam 1 study guide Questions with Correct Answers. Which significant observation led the Greeks to accept the idea that Earth was a sphere? - The shape of Earth's shadow on the Moon during a lunar eclipse was always circular. The IRAS satellite was placed in orbit in 1983 to survey the whole sky to detect - infrared radiation. To specify an object's speed, we need to specify - only how fast it is moving. As light passes from air into a dense but transparent material it - slows down. If two photons in a vacuum have different energies, what can we say about the wavelengths of these photons? - The higher-energy photon has the shorter wavelength. Suppose Eratosthenes had measured the length of a shadow at Scene and then compared it with the shadow measured not at Alexandria, but at a location half way between Scene and Alexandria—both measurements being made at the summer solstice. What would he have found? - The difference in the lengths of these shadows would have been smaller than that found by comparing Scene and Alexandria. The motions of the planets against the background stars in our sky can best be described as - regular patterns, with general eastward motion interrupted by periods of westward motion. One astronomical unit, or one AU is defined as the - mean distance between the Sun and Earth. If an observer on Earth sees the Moon to be full, then at the same time an observer on the Moon would see Earth to be at what phase? - new. A spectrograph is usually used in astronomy to measure the - distribution of light intensity among the various colors. Which object was "discovered" mathematically using Newton's laws before it was discovered observationally through the telescope? - Neptune. When does the third quarter moon rise? (You may want to examine Figure 3-2 of Universe, 10th ed., and think about where you would need to stand on Earth to see the third quarter moon rising.) - close to midnight. As Venus orbits the Sun, by what factor, as viewed from Earth, does its angular size change from smallest to largest? (See Figs. 4-13 and 4-14, Universe, 10th ed.) - 5.8×. The quality of images produced by a large radio telescope is limited mostly by - diffraction. Which is the correct sequence of electromagnetic radiation in order of increasing energy of the photons (or quanta)? - visible light, UV radiation, X rays, gamma rays. The gibbous phase of the Moon occurs when the Moon passes - from first quarter to full moon. In science, if new observations disagree with a well-established theory then - the theory must be modified. Atoms in a thin, hot gas (such as a neon advertising sign) emit light at - specific wavelengths, depending on the element. The elevation angle between the northern horizon of a fixed observer and the north celestial pole is equal to - the observer's latitude. In a spectrograph, a glass prism has a number of disadvantages compared to a diffraction grating. Which of the following is not one of these disadvantages? - A prism cannot be used with a CCD detector and a computer. Suppose the Moon moved westward in its orbit rather than eastward. How would this affect eclipses? - We would still see both types of eclipses much as we do now. At what point in its orbit is a comet closest to the Sun? - perihelion. A lunar eclipse does not occur at every full moon because - the plane of the Moon's orbit is at an angle to the plane of Earth's orbit. The element helium was discovered (through spectroscopy) in the atmosphere of the Sun before it was discovered in trace amounts on Earth. This was possible because - all helium atoms in the universe are believed to be fundamentally the same. Nicolaus Copernicus was the first person to - develop a mathematical model for a Sun- centered solar system. When the Moon is in its gibbous phase, the positions of Moon, Earth, and Sun are such that the - Moon is farther from the Sun than is Earth. Which scientific discipline can be considered as truly universal? - Astronomy. Which of the following does not represent a major drawback when developing a refracting telescope for astronomy? - Lenses cannot be made with focal lengths that produce very high magnifications. If a radio message were sent toward the nearest star to the Sun and a reply were sent back immediately on receipt of the message by intelligent beings from a planet near that star, how long after transmission would we have to wait for a reply? - 8.6 years. If on a particular day the Sun is at one of the solstices and the Moon is at one of the equinoxes, then the lunar phase on that day is - either first or last quarter. What is the maximum length of totality for a lunar eclipse? - 1 hour 40 minutes. Why do we see different phases of the Moon? - The motion of the Moon in its orbit around Earth causes us to see different amounts of the sunlit portion of the Moon. Where on Earth would you have to be to observe a particular total solar eclipse? - within a narrow and specific strip of Earth's surface less than 250 km wide. Earth exerts a force on you as you stand on its surface. What is the size of the force exerted on Earth by you, when compared to the above force? - the same. What is the main reason that the angular resolution of a 20-m-diameter radio telescope is worse than that of a 0.5-m-diameter optical telescope? - Angular resolution gets worse as wavelength increases. The first experiment in which the speed of light was measured precisely involved reflecting light from a mirror rotating at a known speed and measuring the angle of - deflection of the light beam. For many years, the Palomar telescope (5-m diameter) in California was the largest fully steerable telescope in the world; in the 1990s that honor fell to one of the two Keck telescopes (each of diameter 10 m) in Hawaii. How many times larger is the light- gathering power of the Keck telescope than the Palomar telescope? - 4 times larger. How did Tyche Brahe use parallax in his observations? - He tried but failed to measure parallax for the stars. Tyche Brahe - made accurate measurements of planetary positions, which Kepler later used to Spring tides occur find the shapes of planetary orbits. Spring tides occur - twice a month, at full and new moon. If the daytime sky were not bright, in which direction would we see the Sun move along the ecliptic over the course of a year, relative to the background stars? - toward the east. In winter in the southern hemisphere, the Sun will rise on the - northeastern horizon. In its interaction with matter, light behaves - as both waves and particles, depending on the type of interaction. How does the angular resolution (sharpness) of the images obtained from radio telescopes using very long baseline interferometry (VLBI), compare to the typical angular resolution of optical telescopes? - VLBI images are much sharper. Who first showed that light does not travel at infinite speed? - Ole Rumer in 1675. Which substance in Earth's atmosphere is the main absorber of infrared radiation from space? - water vapor. At what approximate value of right ascension was the Sun this year on September 22? - 12 hours. A solar day is the time it takes Earth to rotate around its axis between two consecutive solar positions (i.e., high noon to high noon or sunset to sunset). A sidereal day is the time it takes Earth to rotate around its axis between two consecutive positions of distant star (i.e., Vega on the eastern horizon to Vega again on the eastern horizon)). Which is longer? - A solar day is always longer. What is the significance of Polaris, the North Star? - Polaris is almost on the curve traced out by the rotation axis as a result of the precession of the rotation direction. On the absolute Kelvin temperature scale, the temperature of freezing water is about - +273 K. The vernal equinox is one time of the year when the Sun - crosses the celestial equator. You are observing from the east coast of the United States as a star rises above the horizon. At this same instant your friend on the west coast will find that this star - has not yet risen. What is the cause of an annular eclipse? - The Moon's position in its orbit is near apogee, its farthest point from Earth. Kepler as a young man became the assistant to - Tyche Brahe. The parameter of an atom that defines its unique position in the periodic table is - the number of protons in the nucleus. A person orbiting Earth in the Space Shuttle feels weightless because only one force (gravity) acts on her, but gravity also accelerates the shuttle so that - the shuttle does not push up on her to create the feeling of weight within it. Large quantities of X rays are seen to come from the direction of Cygnus X-1 (see Chapter 21, Universe, 10th ed.) with a spectrum that looks similar to that of blackbody, with a peak wavelength of 1.45 nm (1 nm = 10-9 m). These X rays are probably emitted by matter being heated as it falls into a black hole. What temperature is this gas? - 2 × 10to the sixth power K. A lunar eclipse is caused by the - Moon passing into the shadow of Earth. Which way will the "horns," or sharp ends of the crescent, of the Moon point in the sky when the Moon is above the western horizon at sunset, at a phase 3 days after new moon? Think about what causes the crescent phase of the Moon; Figure 3-2 of (Hint Universe, 10th ed., may help.) - away from the Sun, eastward. Suppose two asteroids are located at the same distance from the Sun. One asteroid has twice the mass of the other. According to Newton's law of gravitation (and ignoring all forces except those from the Sun), - the more massive asteroid feels twice the force of that on the less massive asteroid. A full moon will be on the horizon at - sunrise or sunset. An imaginary planet is orbiting the Sun in a circle at precisely the same average orbital distance as Earth (i.e., one AU). What is its sidereal period? - 1 year. Earth would not have seasons if - its axis of rotation was perpendicular to its orbital plane. A particular reflecting telescope has an objective mirror with a focal length of 1.2 m and an eyepiece lens of focal length 6 mm. What is the magnifying power of this telescope? - 200×. The Arctic Circle is defined as a line on Earth marking the southern boundary of the region where the Sun - can be seen for 24 hours on at least one day of the year. I have a massive purple object in my laboratory. If I were to take it to the Moon, which of its characteristics will be guaranteed to change? - weight. The ecliptic crosses the celestial equator at - two points, known as equinoxes. Venus can occasionally pass in front of the Sun. It can only do so when it is at - inferior conjunction. The setting Sun appears red because - its light is scattered by a thicker layer of air than during the day. Two physicists, one in Australia, the other in the United States, find that each has constructed an ideal blackbody in the laboratory. The two blackbodies are made from