Astronomy – Space Questions And Answers – Flashcards
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What is the meaning of the letters R I V U X G that appear with some of the figures in this chapter? (Hint: See the Preface that precedes Chapter 1.)
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They are portions of the spectrum of electromagnetic radiation: radio, infrared, visible, ultraviolet, x-ray, and gamma ray.
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In the case of a scientific hypothesis, if an experiment produces negative results, the hypothesis must be discarded or revised.
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True
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Hypothesis testing stops once a scientific hypothesis is proven.
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False
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Which of the following is NOT part of the scientific method?
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Once a scientist backs a hypothesis with observations, it is accepted as true.
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In modern science, skepticism is considered to be
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essential.
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Scientists consider mathematics to be essential to science. The most important role of mathematics in science is to
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allow theories to make precise, testable predictions.
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A scientific model is usually built of
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mathematical equations.
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The first, often tentative conjecture of why something in nature behaves the way it does is called a
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hypothesis.
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The ideas that are proved most definitively by the scientific method are called
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laws
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What is the difference between a theory and a law of physics?
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A theory is a scientifically constructed description of how nature operates in a particular situation. Theories must be tested constantly and amended when necessary. After a theory has been tested many times over a long period of time without failure, it becomes known as a law of physics. It thus commands high (but not absolute) confidence in its predictive powers.
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What role do nebulae like the Orion Nebula play in the life stories of stars?
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Nebulae are the birthplaces of stars. The raw materials they need for formation are found there.
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How are exponents used in powers-of-ten notation?
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The exponent (of 10 in this example) indicates how many times the number is to be multiplied (or divided, in the case of a negative exponent) by 10.
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The name of one of the lunar phases in the Dakota language means "diminishing moon." To which phase would this term most likely apply?
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Waning Crescent
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The Moon is highest in the sky when it crosses the meridian, halfway between the time of moonrise and the time of moonset. What is the phase of the Moon if it is highest in the sky at midnight?
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At midnight the local zenith points into space on the side of Earth away from the Sun. The meridian passes from pole to pole through the zenith, so the Moon, when it crosses this line, is also on the side of Earth away from the Sun: full moon.
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What is the phase of the Moon if it is highest in the sky at sunrise?
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third quarter
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What is the phase of the Moon if it is highest in the sky at noon?
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new
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What is the phase of the Moon if it is highest in the sky at sunset?
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first quarter
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On a particular day, the moon rises in the waxing gibbous phase. What phase is it when it sets?
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Waxing Gibbous
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If the Moon is in the first quarter phase today, what phase will it be one week from now?
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Full Moon
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At what time does a waning crescent moon set?
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3 pm
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You are meeting a friend for a late dinner at 9 PM. While waiting for him, you notice the Moon near the western horizon. What phase is it?
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Waxing Crescent
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Which of the following lunar phases is not possible to see at 6 PM?
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waning gibbous
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Explain the difference between sunlight and moonlight.
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Both originate at the Sun, but sunlight comes directly to us while moonlight is reflected off the Moon on its way to us.
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Explain why the Moon exhibits phases.
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Half the Moon is illuminated by the Sun at all times. But, because of the changing positions of Earth, Moon, and Sun, the half of the Moon facing Earth can be entirely illuminated, not illuminated at all, or illuminated to any amount between these two extremes. These are the phases.
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A common misconception about the Moon's phases is that they are caused by the Earth's shadow. Explain why this not correct. (see figure below)
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Earth's shadow only reaches the Moon when it is on the opposite side of the Sun from Earth-when it is full. Thus the shadow cannot account for the phases.
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At approximately what time does the Moon rise when it is a new moon?
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sunrise
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At approximately what time does the Moon rise when it is a first quarter moon?
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noon
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At approximately what time does the Moon rise when it is a full moon?
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sunset
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At approximately what time does the Moon rise when it is a third quarter moon?
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midnight
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You are watching a lunar eclipse from some place on the Earth's night side. Will you see the Moon enter the Earth's shadow from the east or from the west?
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The Moon moves eastward, so it enters the Earth's shadow from the west.
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Why does the Moon appear red during a total eclipse?
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The Earth's atmosphere scatters red light onto the moon during a total eclipse, giving it a reddish appearance.
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During an eclipse, the shadow of the Earth appears curved as it moves across the Moon because of the following.
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The earth is round
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On average, lunar eclipses occur about how often?
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2 times a year
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Why doesn't a lunar eclipse occur at every full moon and a solar eclipse at every new moon?
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In order for an eclipse to occur the Sun, Earth, and Moon must be nearly along a straight line. Because the Moon's orbit is tilted slightly with respect to the ecliptic, this does not occur for every full or new moon.
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What is the line of nodes?
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The line of nodes is the line that connects the two points in the Moon's orbit where the orbit crosses the ecliptic.
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Why is the line of nodes important to the subject of eclipses?
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An eclipse can take place only when an extension of the line of nodes passes through the Sun.
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As observed from Earth, the motion of a planet known as direct motion refers to
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a slow eastward motion against the background stars.
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How does retrograde motion affect the rising and setting of the planets?
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Retrograde motion has no effect because the diurnal motion is much faster than the planetary motions with respect to the stars. Hence the planets always rise in the east and set in the west.
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Retrograde motion of superior planets is explained in the Copernican model of the solar system as a(n)
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illusion that happens when the Earth overtakes a superior planet in its orbit.
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When a planet is at superior conjunction, the
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sun is between the earth and the planet
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At which position is Jupiter seen at its highest in our sky at midnight?
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opposition
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What condition describes the position of greatest elongation for an inferior planet in our solar system? (Drawing a diagram might be useful.)
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The angle between the Earth-planet line and the planet-Sun line is 90°
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In what direction does a planet move relative to the stars when it is in direct motion?
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Eastward
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In what direction does a planet move relative to the stars when it is in retrograde motion?
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westward
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In what direction does the Sun move relative to the stars?
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eastward
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In what direction does a planet move relative to the horizon over the course of one night?
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westward
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The answer to (a) is the same whether the planet is in direct motion or retrograde motion. What does this tell you about the speed at which planets move on the celestial sphere?
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The planets move very slowly on the celestial sphere.
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The average distance of a planet from the Sun is given by which orbital property?
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semimajor axis
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The Earth is 1 AU from the Sun and has a period of 1 year. What would be the period for an imaginary planet located at 2 AU from the Sun?
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between 2-3 years
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Which is the correct form of Kepler's third law?
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P2 ? a3
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(a) The mass of Saturn is approximately 100 times that of Earth, and the semimajor axis of Saturn's orbit is approximately 10 AU. To this approximation, how does the gravitational force that the Sun exerts on Saturn compare to the gravitational force that the Sun exerts on Earth?
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The forces are the same.
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How do the accelerations of Saturn and Earth compare?
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Saturn feels one one-hundredth of Earth's acceleration.
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Suppose that you traveled to a planet with 5 times the mass and 5 times the diameter of the Earth. Would you weigh more or less on that planet than on Earth?
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less
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What is the difference between weight and mass?
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Mass is an intrinsic property of matter, a measure of how much an object resists being accelerated. Weight, on the other hand, is the force with which gravity pulls on an object. It is equal to the object's mass times the acceleration due to gravity.
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Approximately how many times around Earth (at the equator) could a beam of light travel in one second?
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about 7 1/2
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How long does it take light to travel from the Sun to Earth, a distance of 1.50 10^8 km?
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8 1/3 minutes
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Your normal body temperature is 98.6°F. What kind of radiation do you predominantly emit?
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infrared radiation
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At what wavelength (in nm) do you emit the most radiation?
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9350 nm
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Your cellular phone is actually a radio transmitter and receiver. You receive an incoming call in the form of a radio wave of frequency 880.65 MHz. What is the wavelength (in meters) of this wave?
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0.34
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What is the temperature of the Sun's surface in degrees Fahrenheit?
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10000
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Explain why astronomers are interested in blackbody radiation.
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Stars to a good approximation behave like blackbodies and emit radiation in a spectrum similar to the spectrum of an ideal blackbody.
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Why do astronomers find it convenient to use the Kelvin temperature scale in their work rather than the Celsius or Fahrenheit scales?
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The Kelvin temperature scale has a physically meaningful zero, absolute zero, indicating the lack of all motion energy. Equations like Wien's law or the Stephan-Boltzmann law give unrealistic values for zero and negative temperatures on other scales.
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Black holes are objects whose gravity is so strong that not even an object moving at the speed of light can escape. Hence, black holes do not themselves emit light. But it is possible to detect radiation from material falling toward a black hole. Calculations suggest that as this matter falls, it is compressed and heated to temperatures around 106 K. Calculate the wavelength for maximum emission for this temperature.
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2.9 nm
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In what part of the electromagnetic spectrum does this wavelength lie?
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x-ray
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If you double the Kelvin temperature of a hot piece of steel, how much more energy will it radiate per second?
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16 times as much
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Through which of the following materials does light travel fastest?
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vacuum
