Astro – Flashcards
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Scientific notation is used in science because
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it makes it easy to write big or small numbers.
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The average distance from Earth to the sun is
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1 AU
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The sun is
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a star
1 AU from Earth.
more than 100 times the diameter of Earth.
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A galaxy contains
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gas, dust, and stars, and a lot of dark matter.
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The Milky Way Galaxy
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contains about 100 billion stars.
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2.9×107 is the same as
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. 29 million
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It takes light 1.3 seconds to travel from the moon to Earth and 8 minutes to travel from the sun to
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The sun is 370 times further from Earth than the moon.
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If light takes 8 minutes to travel from the sun to Earth and 5 hours to travel from the sun to Pluto, whatis the distance from the sun to Pluto?
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37.5 AU
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The speed of light is 3.0×105 km/sec, and it takes light 1.3 sec for light to travel from the moon to Earth. From this information, what is the distance to the moon?
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390,000 km
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If the distance to the nearest star is 4.2 light-years, then
a. the star is 4.2 million AU away.
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the light we see left the star 4.2 years ago.
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The Milky Way Galaxy is
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a spiral galaxy.
part of a cluster of galaxies that contains a few dozen galaxies.
about 75,000 light years in diameter.
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Which sequence is correct when ordered by increasing size?
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Earth, Solar System, Milky Way, galaxy clusters
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How is a planet different than a star?
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Planets reflect light while stars produce their own light
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If the distance from the Sun to the Earth is represent by roughly 15 meters, then the distance from the Earth to the Moon on the same scale would be
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small than your hand.
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How is a planet different than a star?
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Planets reflect light while stars produce their own light.
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Constellation names are in
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latin
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Seen from the northern latitudes, the star Polaris
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. is always above the northern horizon.
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The celestial equator is
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a line around the sky directly above Earth's equator.
the dividing line between the north and south celestial hemispheres.
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The ________ is the point on the celestial sphere directly above any observer.
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zenith
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Most star names, such as Aldebaran and Betelgeuse are
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arabic
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The magnitude scale
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can be used to indicate the apparent intensity of a celestial object.
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The apparent visual magnitude of a star is a measure of the star's
a. size.
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intensity.
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The star Vega has an apparent visual magnitude of 0.03 and the star HR 4374 has an apparent visual magnitude of 4.87. It has been determined that both stars are at the same distance from Earth. What does this information tell us about the two stars?
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Vega must produce more energy than HR 4374.
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The _______________ of an object depends on the diameter of the object and the distance to the object.
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apparent diameter
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An observer's nadir is
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the point directly opposite the observer's zenith.
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A(n) __________________ is one-3,600th of a degree.
a. precession
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second of arc
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The Big Dipper is
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an asterism.
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. Precession of the rotation axis of Earth is caused by
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the force of gravity from the sun and moon on Earth's equatorial bulge.
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An observer in the Northern Hemisphere watches the sky for several hours. Due to the motion of Earth, this observer notices that the stars near the north celestial pole appear to move
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. counter clockwise around the celestial pole.
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You live at a latitude of 73° N. What is the angle between the northern horizon and the north celestial pole?
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73°
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. You live at a latitude of 39° S. What is the angle between the southern horizon and the south celestial pole?
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39°
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If the north celestial pole appears on your horizon, what is your latitude?
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0°
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Which star in the table to the right would appear the
brightest to an observer on Earth?
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α CMa
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Based on the information in the table to the right, what is
the ratio of the intensity of δ Dra to that of Nim?
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100
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Which star in the table to the right would not be visible to
the unaided eye of an observer on Earth
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Nim
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Star A has an apparent visual magnitude of 13.4 and star B has an apparent visual magnitude of 15.4. Star A is _________________ than star B.
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6.3 times brighter
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Polaris is a second magnitude star, and Phi Pegasi is about 16 times fainter than Polaris. What is the approximate magnitude of Phi Pegasi?
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5
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Which of the following statements correctly describes the relationship between stars and constellations?
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Every star is located in a constellation.
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How much of the night sky is north of the celestial equator?
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Exactly one-half.
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If the Sun passes directly overhead on at least one day per year, then
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you are within 23.° latitude of the equator.
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. If you are standing at the Earth's North Pole, which of the following would be located at the zenith?
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The north celestial pole
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For stars the same constellation they
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may actually be very far away from each other.
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. During the month of June the north celestial pole points towards Polaris but during the month of December it points
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still towards Polaris.
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If the Earth's period of rotation doubled, but the period of revolution stayed the same
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the night would be half as long.
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The ecliptic is
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the centerline of the zodiac.
the projection of Earth's orbit on the sky.
the apparent path of the sun around the sky.
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At what two celestial locations do the celestial equator and ecliptic coincide?
a. winter solstice and summer solstice
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vernal equinox and autumnal equinox
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On the vernal equinox the sun is
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on the celestial equator and moving north with respect to the equator.
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A solar or lunar eclipse will occur
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when the sun is near the line of nodes of the moon and the moon is new or full.
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The sideral period of the moon
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is about 27.32 days long.
is the period of time for the moon to orbit Earth once with respect to the stars.
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.The moon has an angular diameter of 0.5°. What is the moon's angular diameter in minutes of arc?
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30
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If the plane of the Earth's equator were not tilted with respect to the ecliptic plane
a. the daylight period of Earth would be the same year-round.
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the daylight period of Earth would be the same year-round.
there would be no seasonal changes.
Earth's poles would not experience six month long nights.
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The phase of the Moon on a particular night is determined by
a. the season of the year.
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the relative positions of the Sun, Earth, and Moon.
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On a clear night when an observer in Los Angeles sees a first quarter Moon an observer in London would see
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a first quarter moon.
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The Moon's angular diameter in our sky is measured to be 0.5°. From this, we can find
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diameter of the Moon if we know the Moon's distance.
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The lowest amount of solar energy per square meter is incident upon the surface of Earth in the northern hemisphere on or about
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December 21, the winter solstice.
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Which of the following people did not accept a heliocentric model for the universe?
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Tycho
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Parallax is
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the apparent motion of an object due to the motion of the observer.
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The Copernican system was no more accurate than the Ptolemaic system in predicting the positions of
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the Copernican system included uniform circular motion.
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Galileo's telescopic discoveries of mountains on the moon and spots on the sun were controversial
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were not perfect spheres.
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Tycho's universe was the same as the Copernican universe except that
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Earth did not move.
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Tycho Brahe's greatest contribution to astronomy was
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his 20 years of careful observations of the planets.
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When we say that gravitation is universal we mean that
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it is a property of all matter.
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Newton concluded that some force had to act on the moon because
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a force is needed to pull the moon away from straight-line motion.
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Kepler's second law implies that
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a planet should move at its greatest speed when it is closest to the sun.
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Kepler's first law of planetary motion implies that
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the distance between the planet and the sun changes as the planet orbits the sun.
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Gravity obeys an inverse square relation. This statement implies that the force due to gravity between two masses
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will decrease as the square of the distance between the two masses increases.
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An object has been located orbiting the sun at a distance from the sun of 65 AU, what is the
approximate orbital period of this object?
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524 years
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Saturn is on average 10 AU from the sun. What is the approximate orbital period of Saturn?
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32 years
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. In pre-Copernican astronomy, it was almost universally believed that
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. the Earth was at the center of the universe.
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. When Mars is located directly behind the Earth with respect to the Sun in its orbit, it is
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at the midpoint in the sky between east and west at midnight.
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The greatest inaccuracy in Copernicus' model of the solar system was that the planets
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travel in circular orbits with uniform motion.
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Which of the following statements best describes Kelper's 3rd law of planetary motion?
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The larger the orbit, the longer its orbital period.
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____________ has (have) wavelengths that are longer than visible light.
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Infrared radiation
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. The energy of a photon
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is inversely proportional to the wavelength of the light.
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Long wavelength visible light
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will appear red in color to the average human eye.
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Photons of blue light
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have a greater energy than photons of red light.
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A nanometer is
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a unit of length.
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What is the relationship between color and wavelength for light?
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Wavelength increases from blue light to red light
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In which way does a photon of blue light NOT differ from a photon of red light?
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Speed
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. The neutral hydrogen atom consists of
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. one proton and one electron.
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The process of removing an electron from a stable nucleus is known as
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ionization.
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The two most abundant elements in the sun are
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hydrogen and helium.
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The diagram to the right illustrates a light
source, a gas cloud, and three different
lines of sight. Along which line of sight
would an observer see an absorption
spectrum?
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3
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The table below lists the spectral types for each of
five stars. Which star in this table would have the
lowest surface temperature?
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. ο Cet
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Two stars of the same spectral class must have that same
a. radius.
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temperature.
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The radiation emitted from a star has a maximum intensity at a wavelength of 300 nm. What is the temperature of this star?
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10,000 K
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At what wavelength would a star radiate the greatest amount of energy if the star has a surface temperature of 60,000 K?
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50 nm
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The sun has a surface temperature of approximately 5800 K. At what wavelength does the maximum energy radiated by the sun occur?
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520 nm
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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 meter of its surface?
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625 times
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One star has a temperature of 10,000 K and another star has a temperature of 5,000 K. Compared to the cooler star, how much more energy per second will the hotter star radiate from each square meter of its surface?
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16 times
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The Hδ line has a wavelength of 410.2 nm when observed in the laboratory. If the Hδ line appears in a stars spectrum at 410.0 nm, what is the radial velocity of the star?
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146 km/sec toward the observer.
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The Hγ line has a wavelength of 434.0 nm when observed in the laboratory. If the Hγ line appears in a stars spectrum at 434.5 nm, what is the radial velocity of the star?
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346 km/sec away from the observer.
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What is the order of star colors with increasing temperature?
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Red, Yellow, Blue
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Each element has its own set of characteristic absorption lines because
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electron energy levels differ for each element.
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The Doppler effect states that the motion of any object can
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shift the wavelength of spectral lines.
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Granulation is caused by
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rising gas below the photosphere.
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. Most of the light we see coming from the sun originates in the
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photosphere.
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The sun creates its energy by the process of
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nuclear fusion
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The chromosphere of the sun
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is hotter than the photosphere.
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Sunspots
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are cooler than their surroundings.
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The _______ is (are) the hot gases that are the moving extension of the sun's corona
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solar wind
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If a sunspot has a temperature of 4,500 K and the surrounding solar surface has a temperature of 5,800 K, how many times brighter is the surface compared to the sunspot?
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2.8
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If the spectrum of a sunspot shows that it has a maximum intensity at 650 nm, what is the temperature of the sunspot?
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4600 K
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What are the three layers of the Sun's atmosphere, in order of increasing distance from the surface?
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. Photosphere, chromosphere, corona
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A star's luminosity depends only on the star's
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temperature and diameter.
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In an H-R Diagram, stars with the smallest radius are found in the _______ of the diagram.
a. center
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lower left corner
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We know that giant stars are larger in diameter than the sun because
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. they are more luminous but have about the same temperature.
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Which star in the diagram above is most like the sun?
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HR 5337
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Which star in the diagram above has the greatest surface temperature?
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Alnilam
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Which of the stars in the diagram above has the largest absolute visual magnitude?
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Sirius B
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. Which of the following stars is most dense?
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a white dwarf
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If a star has a parallax of 0.02 seconds of arc, then its distance is
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50 pc
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. If a star with an absolute magnitude of -5 has an apparent magnitude of +5, then its distance
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1000 pc.
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If you compare two stars,
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. the one with the smaller absolute magnitude will always have the greater luminosity.
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Interstellar gas clouds may collapse to form stars if they
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encounter a shock wave.
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The average star spends _________ of its lifetime on the main sequence.
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90%
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What causes the outward pressure that balances the inward pull of gravity in a star?
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The outward flow of energy.
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The free-fall contraction of a molecular cloud
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can be initiated by shock waves from supernovae.
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Which of the following is not evidence of the existence of an interstellar medium?
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molecular bands in the spectra of cool stars
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Due to the dust in the interstellar medium, a star will appear to an observer on Earth to be
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fainter and cooler than it really is
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Stars are born in
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dense molecular clouds.
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While on the main sequence a star's primary energy source comes from
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nuclear fusion.
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What force(s) are responsible for the collapse of an interstellar cloud?
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gravity
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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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As a star exhausts hydrogen in its core, it
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becomes cooler and more luminous.
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A Type Ia supernova is believed to occur when
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a white dwarf exceeds the Chandrasekhar limit.
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A type-II supernova
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is characterized by a spectrum that shows hydrogen lines.
occurs when the iron core of a massive star collapses.
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The diagram on the right shows a light curve
from a supernova. How many days after
maximum light did it take for the supernova to
decrease in brightness by a factor of 100?
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150
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. Which of the following is not a characteristic of the stars of the disk component of our galaxy?
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randomly inclined orbits
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Younger stars have more heavy elements because
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. the heavy elements were made in previous generations of stars.
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Radio maps of our galaxy show spiral arms because
a. the arms have larger Doppler shifts.
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the gas in spiral arms is denser.
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_____________________ of the Milky Way contains mostly population II stars and globular clusters.
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The spherical component
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_______________ in other galaxies should contain luminous O and B stars if they are like the MilkyWay.
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The spiral arms
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The period-luminosity relation is useful in determining
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the distance to globular clusters that contain Cepheid variables.
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__________________ is (are) believed to dominate the mass content of the galaxy.
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dark matter.
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The traditional theory states that the galaxy formed
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as a large spherical cloud of gas that was rotating very slowly.
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A Type II Cepheid has been located in a distant globular cluster with a period of 10 days, what is the star's absolute magnitude?
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-1
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A Type I Cepheid has been located in an open
cluster. The period of the Cepheid variable is
30 days and the variables apparent visual
magnitude is 10. What is the distance to this open cluster?
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10,000 pc
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Which of the following can't be associated with the spiral arms of a galaxy?
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Metal poor stars
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What behavior do galactic rotation curves exhibit to suggest the existence of dark matter?
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Large velocities are seen at large distances from the galactic center.
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The Hubble Law is a relation between a galaxy's
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distance and its recession velocity.
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________________ can be used to determine the galaxy's mass if the galaxy is reasonably close so that the radial velocity of the galaxy can be measured at several distances from the galaxy's center.
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. A galaxy's rotation curve
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Gravitational lensing
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occurs when light passes near a massive object and is deflected by the object's gravitational field.
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The look-back time is
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the time it takes for the light from an object to reach Earth.
numerically equal to the distance in light-years.
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Most of the mass of a galaxy is contained in the
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. dark matter of the galaxy.
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. __________ galaxies contain large clouds of gas and dust, both young and old stars, but have no obvious spiral arms or nucleus.
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Irregular
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Supermassive black holes are believed to be located at the center of many galaxies because
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the orbital motion of material near the center is very fast and indicates a very massive core.
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If H equals 70 km/sec/Mpc, then a galaxy with a radial velocity of 2100 km/sec has a distance of approximately
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30 Mpc
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If a galaxy has a radial velocity of 8000 km/sec and the Hubble constant is 70 km/sec/Mpc, what is the distance to this galaxy?
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114 Mpc
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If the absolute magnitude of a supernova is -19 and a galaxy is found that contains a supernova with an apparent magnitude of 16, what is the distance to the galaxy?
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100 Mpc
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If Galaxy A is found to have a recessional velocity four times greater than Galaxy B what can you say about their relative distances from Earth?
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Galaxy A is four times further away than Galaxy B.
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What is the Hubble constant essentially a measure of?
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The expansion of the universe.
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What is the primary factor in determining the classification for an elliptical galaxy?
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Shape
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What distance method (other than the Hubble Law) is used to calibrate the Hubble constant?
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Supernova observations
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The Hubble time is
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an estimate of the age of the universe based on the Hubble constant.
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When a proton and an antiproton collide
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they destroy each other and produce energy in the form of gamma rays
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As the universe cooled, it eventually reached a temperature of 3,000 K and protons were able to capture and hold electrons to form neutral hydrogen. This process is known as
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recombination.
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What was the temperature of the universe when the recombination took place that produced the cosmic background radiation we observe today?
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about 3000 K
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In 1998 it was announced that the expansion of the universe is accelerating. What does this imply from the perspective of the big bang?
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A force exists that we knew nothing about that causes the expansion.
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The cosmic background radiation comes from a time in the evolution of the universe
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when electrons began to recombine with nuclei to form atoms.
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Whether the universe is open, closed or flat depends on the ________ of the universe.
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. density
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Current evidence suggests that the universe is
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flat, infinite, and accelerating in its expansion.
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What observational evidence supports the fact that our universe is expanding?
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Redshift of galaxies
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Where did the cosmic microwave background (CMB) come from?
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. Photons released when electrons and nuclei combined for the first time.
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Why is the cosmic microwave background (CMB) so cold if the early universe was so hot?
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The expansion of the universe has redshifted those photons to an effectively cooler temperature.
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What observation has prompted astronomers to ponder the possible existence of dark energy?
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Supernovae appear fainter than expected at large redshifts.
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Microlensing refers to
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gravitational lensing by stellar object with Einstein rings of around microseconds.
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Planets around stars other than the sun
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have been found by astronomers using several different methods
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How are galaxies distributed in the Universe?
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They are grouped in clusters and superclusters, connected by chains, surrounding large empty voids.
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Which of the following is not a method for searching planets around stars other than the sun
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accurately measurement of the temperature of the stars
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According to the Big Bang Theory, the Cosmic Microwave Background radiation is created
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when the Universe was 700,000 years old
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we could see our own galaxy from 2 million light-years away, it would appear
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c to be a flattened disk with a central bulge and spiral arms
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Which of the following is NOT consistent with recent observations of the cosmic microwave
background by the WMAP satellite?
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The universe is at least 20 billion years old
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What instrument did Galileo improve?
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yelescope
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Which equation is what astronomers use to measure the brightness of star?
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m = -2.5log10(F) +C, where F is the observed flux, and C a constant that depends on the units of flux
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A galaxy was observed to be at a distance of 100 Mpc. The distance modulus to the galaxy is
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30
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The radius of the central bulge of the Galaxy is
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6,000 light year
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Which of the following statements is correct?
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There are about 1011 stars in the Milky Way Galaxy, but the mass of the Milky Way is about 1012
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The period of the Milky Way to circle the Sun is about
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225,000,000 years
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A galaxy is found to be at a redshift 9,100 km/sec. Assuming a Hubble constant of 70 km/sec/Mpc, the distance to the galaxy is found to be
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130 Mpc
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Why are fossils of early life on Earth more rare than fossils of plants and animals from the past few hundred million years?
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Early organisms lacked skeletons and other hard structures that are most likely to be fossilized.
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How do we determine the conditions that existed in the very early universe?
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From the current expansion rate we can work backward to estimate temperature and densities at various times in the early universe.
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When we say that the electroweak and strong forces "freeze out" at 10-35 seconds after the Big Bang, we mean that _________.
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prior to this time, the electroweak and strong forces were indistinguishable from each other, but after this time they behaved differently from each other
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According to the Big Bang theory, how many forces --- and which ones --- operated in the universe during the GUT era?
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2: gravity and a single force that later became the strong, weak, and electromagnetic forces
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Laboratory experiments conducted with particle accelerators confirm predictions made by the theory that unifies _________.
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the electromagnetic and weak forces into the electroweak force
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What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old?
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The basic chemical composition of the universe had been determined.
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According to the Big Bang theory, why do we live in a universe that is made of matter rather than antimatter?
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During the first 0.001 second after the Big Bang, particles and antiparticles were made in almost but not perfectly equal numbers. Everything annihilated except the very slight excess of matter particles.
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Which of the following is NOT a characteristic of the cosmic microwave background?
a It has a perfect thermal radiation spectrum.
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It contains prominent spectral lines of hydrogen, the primary chemical ingredient of the universe.
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In principle, if we could see all the way to the cosmological horizon we could see the Big Bang takingplace. However, our view is blocked for times prior to about 380,000 years after the Big Bang. Why?
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Before that time, the gas in the universe was dense and ionized and thus did not allow light to travel freely.
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In stars, helium can sometimes be fused into carbon and heavier elements (in their final stages of life). Why didn't the same fusion processes produce carbon and heavier elements in the early universe?
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By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur.
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Based on the results from modern cosmological measurements, the overall composition of the energy of the universe is _________.
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4% ordinary (baryonic) matter, 23% nonbaryonic dark matter, 73% dark energy
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Based on our current understanding of physics, it would seem that we can understand the conditions that prevailed in the early universe as far back in time as _________.
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one ten-billionth of a second after the Big Bang
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What happens when a particle of matter meets its corresponding antiparticle of antimatter?
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the combined mass-energy of the two particles is completely transformed into radiation-energy
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What do we mean by inflation?
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We mean a sudden and rapid acceleration of the universe that went on for a tiny fraction of a second at the time the strong force froze out from the GUT force.
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Which statement about the cosmic microwave background is NOT true?
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It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.
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The Big Bang theory is supported by two major lines of evidence that alternative models have not successfully explained. What are they?
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(1) the theory predicts the existence of and the specific characteristics of the observed cosmic
microwave background; (2) the theory correctly predicts the observed overall chemical composition of the
universe.
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Which of the following best summarizes what we mean by dark matter?
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Matter that we have identified from its gravitational effects but that we cannot see in any wavelength of light
