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192 Cards in this Set
- Front
- Back
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What is the average distance from the Earth to the Sun?
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1 Astronomical Unit
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What is the ratio of the diameter of the Sun to the diameter of the Earth?
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100: 1
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How many stars are in the Milky Way galaxy?
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about 100 billion
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Which of the following has the distances arranged in order from smallest to largest?
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-millimetre, kilometre, AU, lightyear
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If the distance to the nearest star is 4.2 light years, what can we conclude about the star?
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-The star’s light takes 4.2 years to reach us
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What is the reason for compressing the history of the universe into a single year in the cosmic calendar?
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to compare astronomical timescales with human experience
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Which sequence below is correctly ordered from smallest to largest size?
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-Earth, solar system, milky way, clusters of galaxies
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If an object is 1,000 light years away, how do we see it?
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as it looked, 1,000 years ago
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What is the celestial equator?
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-the dividing line between the north and south celestial hemispheres?
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What is the term for the point on the celestial sphere directly above an observer, no matter where on the Earth the observer is located?
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-zenith
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What is the purpose of the magnitude scale?
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-It measure the apparent brightness of a celestial object
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If the apparent visual magnitude of a star is 7.3, what does this tell us about the brightness of the star?
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-It is most visible with the unaided eye
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Which of the following is equivalent to one-3,600^th of a degree?
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-a second of arc
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Which of the following best describes the Big Dipper?
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-an asterism
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An observer ion the northern hemisphere watched the sky for several hours. Due to the motion of the Earth, this observer notices that the stars near the north celestial pole appear to move. What pattern does this apparent movement follow?
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-counter-clockwise around the celestial pole
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If the north celestial pole appears on your horizon, what is your latitude?
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-0degrees
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What do stars in the same constellation have in common?
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-they are in the same part of the sky as seen from the Earth
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During the month of June the north celestial pole points towards polaris; where does it point during the month of December?
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-still towards Polaris
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Why are Northern Hemisphere winters colder than Northern Hemisphere summers?
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-the light from the sun shines more directly on the northern hemisphere during the summer
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At which of the following times would you find the Sun on the celestial equator?
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-autumnal equinox and vernal equinox
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What is the ecliptic?
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-the projection of the Earth’s orbit on the sky
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At what two celestial locations do the celestial equator and the ecliptic coincide?
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-vernal equinox and autumnal equinox
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Which of the following describes a concept very similar to latitude?
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-declination
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What is the term for the period of time it takes for the Moon to complete a cycle of the lunar phases that is approximately 29.5 days long?
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-synodic period of the Moon
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What is the sidereal period of the Moon?
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the period of time for the moon to orbit the Earth once with respect to the stars
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What is the term for a solar eclipse in which the Moon’s umbra does not reach the Earth’s surface?
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an annular solar eclipse
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When and where is a waxing crescent Moon Visible?
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-near the western horizon just after sunset
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Where is a total lunar eclipse visible?
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-It is visible to all observers on the side of the Earth facing the Moon
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When do total lunar eclipses always occur?
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-at the time of full Moon
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The moon has an angular diameter of 0.5 degrees. What is the Moon’s angular diameter in minutes of arc?
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30
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If the Earth’s rotational axis shifted to a position perpendicular to the ecliptic, what would happen to seasonal variations on the Earth?
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-they would be non-existent
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On a clear night, when an observer in Vancouver sees a first quarter moon, what would an observer in St.John’s see?
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-a first quarter moon
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In which direction does the daily motion of the moon occur in the sky, against the background stars, when viewed from the Earth?
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-toward the east
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What is the term for a small circle that has its centre located on the circumference of another larger circle?
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-epicycle
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What two numbers tell us the size and shape of an ellipse?
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-semi-major axis, eccentricity
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Which of the following describes the semi-major axis of an ellipse?
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-half the length of the longest diameter of the ellipse
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What is a parallax?
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-the apparent motion of an object due to the motion of the observer
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What feature of Ptolemy’s model of the universe allowed it to explain retrograde motion?
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-epicycles
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What did Galileo’s observations of a complete set of phases of Venus prove?
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-that Venus orbited the Sun
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What was Tycho Brahe’s greatest contribution to astronomy?
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-his 20 years of careful observations of the planets
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Which of the following statements is implied by kepler’s second law of planetary motion?
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-a planet should move at its greatest speed when it is closest to the Sun
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Which of the following statements is implied by Kepler’s first law of planetary motion?
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-The planets move in elliptical orbits around the Sun
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Which of the following statements reflects beliefs that were almost universally held in pre-Copernican astronomy?
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-The Earth was at the centre of the universe
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What is the term for the apparent westward motion of a planet in the sky compared to the background stars (as viewed from the Earth) when observed on successive nights?
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-retrograde motion
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The orbit of the planet Jupiter is an ellipse with the Sun at one focus. What is located at the other focus?
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-nothing
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What occurs only when the Moon is in the first or third quarter?
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-neap tides
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Gravity obeys an inverse square relation. What does this statement imply about the force due to gravity between two masses?
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-It will decrease as the square of the distance between the two masses increases.
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When we say that gravitation is universal, what do we mean?
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-All objects exert gravitational force on one another.
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What was the basis for Isaac Newton’s conclusion that a force from the Earth must be acting on the Moon?
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-A force is needed to accelerate the Moon toward the Earth, away from straight-line motion.
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If the mass of the Earth decreased by a factor of 2, with no change in the radius, what would happen to your weight?
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-It would decrease by a factor of 2.
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A comet is found in a highly elliptical orbit with a semi-major axis equal to one astronomical unit (AU). According to Kepler’s third law of planetary motion, what would the sidereal period of this comet be?
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-It would be one year.
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If the Sun’s mass were doubled, the gravitational force that it would exert on the Earth would become _______________
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2X larger
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If the Earth’s distance from the Sun were reduced by a factor of 2, the gravitational force exerted on it by the Sun would become ___________
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4X larger
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When do the highest high tides occur?
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-at new Moon and full Moon
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How many high tides are generally expected to occur each day?
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2
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Which of the following is not due to tidal forces?
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-Earth’s spin on its axis, and its orbit about the Sun, are both counterclockwise, when viewed “from above”.
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What is the longest wavelength of light that can be seen with the human eye?
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700 nanometres
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A new generation of ground-based telescopes are currently being built to overcome the limitations of the older large telescopes. How are these different from previous telescopes?
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-They use computers to control the shape of the mirror.
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What is the term for a piece of glass with many small parallel lines etched on its surface, used to produce a spectrum?
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diffraction grating
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How does the light-gathering power of a 10-metre telescope compare to that of a 1-metre telescope?
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100X greater
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How does the smallest angle that can be resolved by a 10-metre telescope compare to that of a 1-metre telescope?
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10X smaller
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What is “false” about false-colour images?
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The colours do not represent the colours humans can see
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When does chromatic aberration occur in a telescope?
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-when different colours of light do not focus at the same point in a refracting telescope
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What type of telescope has a lens as its objective and contains no mirrors?
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-refracting
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How is the resolving power of a telescope defined?
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-It is a measure of the minimum angular separation that can be seen with the telescope.
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Why can’t a telescope image be magnified to show any level of detail?
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diffraction limits the amount of detail that is visible
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What is the most important reason for putting an optical telescope in space?
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Telescopes in space are not subject to the blurring effects of the Earth’s atmosphere.
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absorption spectrum?
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passing through the Gas Cloud towards the light bulb
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continuous spectrum?
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not passing the Gas Cloud, towards the light bulb
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emission spectrum
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passing the Gas Cloud, but not towards the light bulb
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Which of the following is a set of very counterintuitive rules that describes how atoms and subatomic particles behave?
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-quantum mechanics
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What is the temperature of an object from which no heat energy can be extracted?
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0 Kelvin or -273 degrees C
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If you move an electron from a lower energy level to a higher energy level within an atom, how would you describe that atom?
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the atom is excited
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The Stefan-Boltzmann law says that hot objects emit energy proportional to the fourth power of their temperature. One star has a temperature of 30,000 K and another star has a temperature of 6,000 K. Compared to the cooler star, how much more energy per second will the hotter star radiate from each square metre of its surface?
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625 times
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A certain spectral line of hydrogen has a wavelength of 410.2 nm when observed in the laboratory. If the same line appears in a star’s spectrum at 410.0 nm, what can you conclude about the motion of the star?
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-The star is moving toward the observer
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What is the sequence of star colours in order of increasing temperature?
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red, yellow, blue
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What everyday object is an example of a place where electrons jump through energy levels and emit energy?
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-a neon sign
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What makes up the neutral hydrogen atom?
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one proton and one electron
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What is the process of removing an electron from a stable nucleus called?
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ionization
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What are the two most abundant elements in the Sun?
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hydrogen and helium
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Which of the following CANNOT be measured by using the Doppler Effect?
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the apparent velocity of a star across the sky
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What is responsible for binding the electrons to the nucleus?
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Coulomb force
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What does a non-ionized atom always contain?
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the same number of protons and electrons
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What is the term for atoms that have the same number of protons but a different number of neutrons?
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-isotopes
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Is it possible for a red star to emit more energy than a blue star?
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Yes, if the red star has a larger area
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The Hg line has a wavelength of 434.0 nm when observed in the laboratory. If the Hg line appears in a the spectrum of a star moving away from you, at what wavelength will you observe the line?
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greater than 434 nm
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What would make parallax easier to measure?
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-The Earth’s orbit being larger
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What is absolute visual magnitude?
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the apparent magnitude of a star observed from a distance of 10 parsecs
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What properties of a star determine its luminosity?
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-temperature and diameter
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In an H-R diagram, where are the stars with the smallest radius found?
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in the lower left corner
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In an H-R diagram, where are 90 percent of all the stars found?
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on the main sequence
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How do we know that giant stars are larger in diameter than the Sun?
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They are more luminous but have about the same temperature
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Where are red giant stars found in the H-R diagram?
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above the main sequence
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What type of stars are the most common?
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lower (less luminous) main-sequence stars
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Which of the following is a characteristic of an eclipsing binary?
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It will also be observed as a spectroscopic binary
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Which of the following kinds of stars best obey the mass-luminosity relation?
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main-sequence stars
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Which of the following kinds of stars is most dense?
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a white dwarf
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What does a spectroscopic binary show periodic variations in?
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radial velocity
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Which stars on the main sequence have the greatest mass?
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the spectral type O stars
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The parsec is defined so that a star at a distance of 1 parsec has a parallax of one arcsecond. If a star has a parallax of 0.02 seconds of arc, what is its distance?
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50 parsecs
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Absolute magnitude is defined as the apparent magnitude that a star would have if observed at a distance of 33 light years. Consider a star at a distance of 330 light years that has an apparent magnitude of +5. What would its absolute magnitude be?
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It would be less than +5
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In the light curve shown below, what is the period of the eclipsing binary?
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32.5 days
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At what point in the eclipsing binary light curve below is the cooler star in front of the hotter star?
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4
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When compared to stars near the middle of the diagram, how are stars in the upper right part of the Hertzsprung-Russell diagram different?
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They are always bigger
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What property do most of the (apparently) bright stars in the sky share?
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They are very luminous
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What property do most of the nearest stars in the sky share?
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They are red dwarfs
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Why are protostars difficult to observe?
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They are surrounded by cocoons of gas and dust
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Which of the following relationships is the key to nuclear reactions in a star's core remaining under control?
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Pressure depends on temperature
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Under what conditions might interstellar gas clouds collapse to form stars?
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If they encounter a shock wave
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Why is the presence of massive stars in the Orion Nebula an indication that star formation is currently occurring?
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Massive stars have short lives, so they must have formed recently.
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The lower edge of the main-sequence band represents the location in the H-R diagram at which stars begin their lives as main-sequence stars. What is it called?
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the zero-age main sequence
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What happens in the proton-proton chain?
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Four protons are fused to make a helium nucleus.
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What causes the dimming of starlight in the interstellar medium?
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dust particles
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What must occur for an object to be considered a main-sequence star?
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Nuclear fusion reactions in the core begin.
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What force is responsible for the collapse of an interstellar cloud?
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gravity
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Star clusters are important to the study of stellar evolution because all the stars in a given cluster have one thing in common. What is it?
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age
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Why do higher mass stars live shorter lives on the main sequence than lower mass stars?
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Higher mass stars burn through their nuclear fuel faster
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Why do nuclear fusion reactions only take place in the interior of a star?
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The temperature and density are highest in the centre.
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What characteristic of a star primarily determines its location on the main sequence?
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mass
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Why does the proton-proton chain need high temperatures?
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-High temperatures increase the velocity of the protons so they can overcome the Coulomb barrier.
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How did observations at the Sudbury Neutrino Observatory solve the solar neutrino problem?
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They showed that the “missing neutrinos” had changed into a different type.
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Order the stellar types sorted from shortest to longest of main-sequence lifetime
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O B A F G K M
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Why are emission nebulae associated with young stars?
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Only hot stars can ionize nearby gas; hot stars are high-mass, so must be young.
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What does the strong force do?
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It binds protons and neutrons together to form a nucleus.
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As a star exhausts the hydrogen in its core, what happens?
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It becomes cooler and more luminous.
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When a star first begins stable helium fusion, it is on the ___________ of the HR diagram.
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horizontal branch
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Which of the following correctly describes a relationship between pressure, temperature, and density in degenerate matter?
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Pressure does not depend on temperature.
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Why are giant and supergiant stars rare?
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The giant and supergiant stages are very short.
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What is the defining characteristic of stars within a cluster that are at the turnoff point?
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they are just leaving the main sequence
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When mass is transferred toward a white dwarf in a binary system, the material forms a rapidly growing whirlpool of material. What is that whirlpool called?
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an accretion disk
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What type of object is the Crab nebula?
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a supernova remnant
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What is the approximate age of the star cluster in the H-R diagram? (Hint: Main sequence stars of spectral types O and B have a core supply of hydrogen that is sufficient to last about 250 million years; types A and F, about 2 billion years; type G about 10 billion years; types K and M about 30 billion years. The apparent magnitude scale means that larger numbers are toward the bottom of the vertical axis.)
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10 billion years
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Refer to the H-R diagram. What type of star do the two data points above spectral type “A” represent?
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white dwarfs with mass less than the sun’s mass
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The HR diagram for the three previous problems plots apparent magnitude: why is this a useful substitute for absolute magnitude or luminosity for the purpose of answering these questions?
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Because all the stars in this group have the same age.
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Which nuclear fuels does a one solar mass star use over the course of its entire lifespan?
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hydrogen and helium
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What is a planetary nebula?
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the expelled outer envelope of a medium mass star
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What does the Chandrasekhar-Landau limit tell us?
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White dwarfs more massive than 1.4 solar masses are not stable.
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Under what conditions are Type Ia supernovae believed to occur?
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when a white dwarf exceeds the Chandrasekhar-Landau limit
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Why can’t massive stars generate energy through iron fusion?
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because fusion of iron nuclei absorbs energy
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Suppose you discover a binary star system with a 0.7 solar mass giant star and a 2 solar mass main sequence star. Why is this surprising?
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The 2 solar mass star should have become a giant before the 0.7 solar mass star.
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After they leave the main sequence, what happens to stars with masses between 0.4 and 4 solar masses?
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They undergo thermonuclear fusion of hydrogen and helium, but never get hot enough to ignite carbon.
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When does a type-II supernova occur?
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when the iron core of a massive star collapses
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As a white dwarf cools, why does its radius NOT change?
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because pressure does not depend on temperature for a white dwarf, since the electrons are degenerate
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What are the two longest stages in the life of a one solar mass star?
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main sequence, white dwarf
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What is the density of a neutron star?
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about the same as that of an atomic nucleus
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What happens when light travels out of a gravitational field, loses energy, and its wavelength grows longer?
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a gravitational redshift
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Which of the following has a radius of about 10 kilometres and is supported by the pressure associated with degenerate neutrons?
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neutron star
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If you had an extremely sensitive radio telescope, could you detect every pulsar in the Milky Way galaxy?
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No, some pulsar beams don’t point in the direction of Earth.
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Which of the following would be most likely to indicate the presence of an isolated black hole?
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bending of light from background stars
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Why is the material that accretes onto a neutron star or black hole expected to emit X-rays?
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The material will become hot enough that it will radiate most strongly at X-ray wavelengths.
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The ____________________ of a star can be determined from its colour.
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temperature
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When the electrons in an atom are in their lowest possible energy levels, the atom is said to be in its ____________________ state.
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ground
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The parallax of the star 75 Leo is 0.010 and its apparent visual magnitude is +5.18. The absolute visual magnitude of 75 Leo is ____________________.
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+o.18
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Most stars on the H-R diagram are on the ___________________.
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-main sequence
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A(n) ____________________ is a subatomic particle produced in nuclear fusion that can travel through the Sun and escape to space without interacting with any particles in the Sun.
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-neutrino
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The maximum mass of a white dwarf is ____________________ solar masses.
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1.4
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A(n) ____________________ is formed by the expulsion of the outer layers of a moderate mass star that has a degenerate carbon and oxygen core.
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-planetary nebula
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The ____________________ of a black hole in a binary system can emit X-rays, making it possible for us to detect the presence of the black hole.
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accretion disk
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Why do younger stars have more heavy elements?
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because the heavy elements were made in previous generations of stars
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What part of the Milky Way contains mostly old stars and globular clusters?
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the spherical halo component
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If other galaxies are like the Milky Way, which parts of them should contain luminous O and B type stars?
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the spiral arms
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Which of the following can be determined using the period-luminosity relation?
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the distance to open clusters that contain Cepheid variables
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What type of radiation do we detect from the energy source at the centre of our galaxy?
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X-rays
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Who first noticed that for Cepheid variable stars there was a direct relationship between the luminosity and the period of the variation in their brightness?
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Henrietta Leavitt
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How did Harlow Shapley determine where the centre of the galaxy lies?
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He plotted the distribution of globular clusters.
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What behaviour of galactic rotation curves suggests the existence of dark matter in an extended halo?
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Large velocities are seen at large distances from the galactic centre.
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What is a mega-parsec equivalent to?
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3.26 million light years
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The Hubble Law describes a relationship between two characteristics of a galaxy. What are they?
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distance and recession velocity
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What information about a cluster of galaxies can lensing of background galaxies by the cluster be used to determine?
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mass
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If a disk galaxy is reasonably close and edge-on, the Doppler shift of the galaxy disk material relative to the centre can be measured at several distances from the galaxy's centre. What does this measurement tell us about the galaxy?
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the galaxy’s mass
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If you wanted to measure the distance to a galaxy, which object or technique in the following list would you use?
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cepheid variable stars
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Where is most of the mass of a galaxy found?
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in the dark matter
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What does the term “galactic cannibalism” refer to?
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the merging of galaxies
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If Galaxy A is found to have a recessional velocity four times greater than that of Galaxy B, what can you say about their relative distances from Earth?
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Galaxy A is four times as far away as Galaxy B.
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Which of the following objects emit large amounts of energy, and could only be seen as single points of light, until the Hubble space telescope was able to image several of them at the centres of their host galaxies?
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Quasars
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Which of the following indicates that quasars must be small?
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They fluctuate rapidly on time scales as short as a few hours.
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If the Hubble Space Telescope were used to take pictures of the entire sky, roughly how many galaxies would those pictures contain?
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100 billion
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What is the term for a collection of 100 to 1000 young stars in a region about 80 light-years in diameter?
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open cluster
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What is the term for a collection of 105 to 106 old stars in a region 30 to 100 light-years in diameter?
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globular cluster
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Why do astronomers sometimes say “black holes don’t suck”?
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A black hole’s gravity is the same as that of any other object of the same mass.
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What happens to light that is emitted just outside the event horizon of a black hole and travels outwards, losing energy in the process?
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A gravitational redshift.
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What is the term that describes the slowing of clocks in strongly curved space-time?
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time dilation
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What is the Schwarzschild radius?
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the distance between a black hole and its event horizon
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What has greater density than a white dwarf?
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a neutron star
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When searching for black holes, what associated phenomena do astronomers search for?
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X-ray binaries where the compact companion has a mass in excess of 3 solar masses
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Which of the following is an example of time dilation?
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As a star approaches a black hole’s event horizon, it appears to move more and more slowly.
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What is the approximate size of the Schwarzschild radius of a one solar mass black hole?
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3 kilometres
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Where is the singularity of a black hole found?
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It is located within the event horizon.
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How fast is the escape velocity at the event horizon around a black hole?
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equal to the speed of light
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What does the resolution of Olbers' paradox say about why it gets dark at night?
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It gets dark at night because the universe is not infinite in age
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What properties does the cosmological principle require the universe to have?
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homogeneous and isotropic
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Why is there a limit to the size of the observable universe?
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because the universe has a finite age
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