Terms in this set (150)
What is the meaning of the letters RIVUXG that appear under some of the figures in this chapter?
They are portions of the spectrum of electromagnetic radiation: radio, infrared, visible, ultraviolet, x-ray, gamma ray.
Why in each case is one of the letters highlighted?
The highlighted letter indicates that a filter was used for that image allowing only that portion of the electromagnetic spectrum to be recorded.
In modern science, skepticism is considered to be
Scientists consider mathematics to be essential to science. The most important role of mathematics in science is to
allow theories to make precise, testable predictions.
A scientific model is usually built of
The first, often tentative conjecture of why something in nature behaves the way it does is called a
The ideas that are proved most definitively by the scientific method are called
What is the difference between a theory and a law of physics?
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.
The age of our solar system has been measured as
4.56 billion years, from the study of meteorites.
A supernova is a(n)
explosion that rips a star apart, throwing debris into interstellar space.
Stars go through a natural process when they form from the gas and materials in space. Which is the proper ordering of stages that material may go through in the life of a star?
nebula, star, supernova
What role do nebulae like the Orion Nebula play in the life stories of stars?
Nebulae are the birthplaces of stars. The raw materials they need for formation are found there.
How many stars are contained in a typical galaxy?
hundreds of billions
Which of the following statements is true?
The universe is thought to have begun in a cosmic explosion called the Big Bang.
Quasars, which are seen only at very great distances in the universe, are believed to derive their enormous energy output from
matter falling into supermassive black holes
For what are degrees, minutes, and arcseconds used?
measurement of angles
What are the relationships among these units of measure?
A degree is 60 minutes of arc; a minute is 60 arcseconds.
How many arcseconds equal 1°?
Jupiter's mean distance from the Sun is 778,300,000 km. In scientific notation, this would be written
7.783 × 108 km
(3 × 105) × (2 × 10-7) =
What are the advantages of using powers-of-ten notation?
Calculations are easier with powers-of-ten notation because exponents are easily combined.
Which of the following was not obtained by people of ancient civilizations from observations of the night sky?
the relative distances of Sun, Moon, and stars from Earth
Meaningful observations of the sky by ancient peoples
were made in regions throughout the world.
The 88 constellations in the sky are
patterns of stars that only appear to be close to each other.
To a modern astronomer, constellations are
88 regions of sky, covering the entire sky.
The star α Leonis (alpha Leonis), in the constellation Leo, the lion, is the
brightest star in Leo.
. No matter where you are located, a star that rises due east will pass overhead before setting due west.
Stars at the North Pole will appear to revolve counter-clockwise around the sky while stars at the South Pole will appear to revolve clockwise around the sky.
For an observer at a mid-northern latitude, a star rises north of due east and passes directly overhead. Where will it set?
north of due west
In the northern hemisphere, for a star which rises due east, who will observe it higher in the sky when it reaches its highest point?
a person at a lower latitude
An observer at 35° N latitude observes a star rise due east, while an observer at 35° S latitude also observes a star rise due east at the same time. Which of the following is false?
The northern observer will see the star reach a higher maximum altitude than the southern observer.
How are constellations useful to astronomers?
Constellations are useful to astronomers because they define small regions of the sky and indicate rough locations.
How many stars are not part of any constellation?
Diurnal motion is the
apparent daily motion of the sky caused by the rotation of the Earth.
Suppose the star Sirius rises above the eastern horizon at 2:00 A.M. on a particular night. At what time will it rise four nights later?
The constellation whose stars are used as pointers to the north celestial pole in the northern hemisphere is
Ursa Major, the Big Dipper.
is there any place on Earth where all the visible stars are circumpolar? If so, where?
Yes, at either pole.
Is there any place on Earth where none of the visible stars are circumpolar? If so, where?
Yes, at the equator.
The zenith is the point
directly overhead for any observer.
What is the celestial sphere
The celestial sphere is an imaginary sphere of very large radius centered on the Earth.
Why is this ancient concept still useful today?
It is useful for assigning directions to celestial objects because they look as though they are on a two-dimensional spherical shell.
The path that the Sun takes as it moves through the heavens is called the
What causes seasons on the Earth?
The Earth's rotation axis points in a constant direction relative to the Earth's orbit, but the Earth is on one side of the Sun in summer and the opposite side in winter.
Ancient records show that 2000 years ago, the stars of the Southern Cross were visible in the southern sky from Greece. Today, however, these stars cannot be seen from Greece. What accounts for this change?
Precession has caused the celestial sphere to appear to move by several degrees, so that the stars of the Southern Cross no longer rise above the horizon as seen from Greece.
The Great Pyramid at Giza has a tunnel that points toward the north celestial pole. At the time the pyramid was built, around 2600 B.C., toward which star did it point?
Toward which star does this same tunnel point today?
To be located in the zodiac, a star needs to be anywhere within a
band of sky 16° wide, extending 8° on either side of the ecliptic.
The Zodiac consists of a set of constellations that
are seen along the ecliptic.
Precession of the Earth is
a slow, conical motion of the Earth's spin axis, similar to that of a spinning top, with a period of about 26,000 years for one cycle
As the Moon orbits around the Earth, its path on the celestial sphere is very close to
the path followed by the Sun (the ecliptic).
The meridian (or celestial meridian) is a line in the sky that always passes through the
observer's zenith and the north and south celestial poles.
The mean sun is
an imaginary object that moves at a uniform rate along the celestial equator.
A tropical year is the
time between successive passages of the Sun through the vernal equinox as viewed from the Earth.
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?
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.
What is the phase of the Moon if it is highest in the sky at sunrise?
What is the phase of the Moon if it is highest in the sky at noon?
What is the phase of the Moon if it is highest in the sky at sunset?
The waxing gibbous Moon occurs during the seven days after
Which of the following statements correctly describes the reason for the phases that we see on the Moon?
The Moon orbits around the Earth.
Which way will the "horns," or sharp ends of the crescent, of the Moon point in the sky when the Moon is above the eastern horizon at sunrise at a phase 3 days before new moon? [Hint: Think about what causes the crescent phase of the Moon; Figure 3-2 of Freedman and Kaufmann, Universe, 8th ed., may help.]
away from the Sun, westward
The phase of the Moon that immediately follows waxing gibbous is
Suppose you wanted to locate a radio telescope on the Moon and use the Moon as a shield from the electromagnetic signals generated by human activity on the Earth. Where would you locate the radio telescope so that it would never "see" the Earth?
at the blue crater
The plane of the Moon's orbit is inclined at a 5° angle from the ecliptic, and the ecliptic is inclined at a 23½° angle from the celestial equator. Could the Moon ever appear at your zenith if you lived at the equator?
The celestial equator is your zenith if you are at the equator. The Moon's orbit will be above the ecliptic at some times of the year and below at other times. Since the ecliptic can be above or below the zenith, the Moon will always have a declination (±28½°) that can place it at the zenith viewed from the equator.
Could the Moon ever appear at your zenith if you are at the south pole?
The celestial equator is along the horizon, 90° from your zenith, if you are at the south pole. Since the Moon has a declination of ±28½°, it will never be anywhere near your zenith.
One definiton of a "blue moon" is the second full moon within the same calendar month. There is usually only one full moon within a calendar month, which is why the phrase "once in a blue moon" means "hardly ever." Why are blue moons so rare?
Full moons are separated by one synodic month, about 29
days. Since the longest months are 31 days long, a blue moon can occur only if the full moon happens to fall
Are there any months of the year in which it would be impossible to have two full moons?
The reason eclipses do not occur at every new Moon and every full Moon is that the
Moon's orbit is inclined at an angle to the Earth's orbit.
The nodes of the Moon's orbit are the points where the Moon
crosses the ecliptic.
A solar eclipse can occur only when the Moon is
If the plane of the Moon's orbit were the same as the ecliptic (the plane of the Earth's orbit), we would have
one solar eclipse and one lunar eclipse each month.
The intersection of the Earth's orbital plane and the lunar orbital plane is called the line of nodes.
. A partial eclipse can be seen by fewer people at one time than a full eclipse can.
Why does the Moon appear red during a total eclipse?
The Earth's atmosphere scatters red light onto the moon during a total eclipse, giving it a reddish appearance.
During an eclipse, the shadow of the Earth appears curved as it moves across the Moon because of the following.
The Earth is round.
On average, lunar eclipses occur about how often?
2 times a year
Totality is the period during a total lunar eclipse when the Moon is completely within the Earth's umbra. Does this time vary from one total lunar eclipse to another and if so, why?
Yes. The time varies significantly because the Moon does not always pass through the widest part of the Earth's umbra.
If you were to look at the Moon during a penumbral lunar eclipse, what would you see?
The entire Moon would be slightly fainter than usual but still quite bright.
You are watching a total lunar eclipse from Wellington, New Zealand. I'm in Sydney, Australia, 2200 km away from Wellington, and the Moon is above my horizon. What do I see when I look at the Moon?
total lunar eclipse
total lunar eclipse is visible in principle (assuming clear skies everywhere)
to everyone in one hemisphere of Earth.
Earth's shadow at the distance of the Moon's orbit from Earth is
considerably wider than the Moon.
During a typical total solar eclipse, how big is the shadow of the Moon on the Earth, from which no part of the solar disk is visible?
very small, with a typical diameter less than about 270 km
How did Eratosthenes measure the size of the Earth?
Eratosthenes determined the size of Earth by measuring the difference in the direction of the Sun's rays relative to the local vertical at two locations a known distance apart.
Eratosthenes was able to calculate the circumference of the Earth because he knew that when the Sun was directly overhead at Syene
the Sun was 7° from the zenith at Alexandria.
As observed from Earth, the motion of a planet known as direct motion refers to
a slow eastward motion against the background stars
The very successful Ptolemaic model that described and predicted the apparent motions of planets, assuming them to orbit the Earth, had each planet moving
in a small circle, the center of which was moving around the Earth more slowly in a larger circle.
Retrograde motion is an observed feature of the planets. It was explained in the Ptolemaic model of the solar system by having planets
orbit the Earth in small circles moving in larger circles
In what direction does a planet move relative to the stars when it is in direct motion?
In what direction does a planet move relative to the stars when it is in retrograde motion?
) In what direction does the Sun move relative to the stars?
In what direction does a planet move relative to the horizon over the course of one night?
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?
The planets move very slowly on the celestial sphere.
Suppose you find a new asteroid in the asteroid belt between Mars (synodic period = 780 days) and Jupiter (synodic period = 399 days). The synodic period of this asteroid would be
more than 399 days but less than 780 days Correct: Your answer is correct.
At which position is Jupiter seen at its highest in our sky at midnight?
The phenomenon of parallax is the
change in apparent position of a nearby object as the observer moves.
The observation by Tycho Brahe of a bright comet in 1577 was significant because it
showed almost no parallax (apparent relative motion), which proved it to be more distant than the Moon
Tycho Brahe's most important contribution to the development of modern astronomy was th
accurate measurement of planetary positions
Kepler described how a planet's motion speeds up as it nears the Sun by his concept of
equal areas in equal times.
Kepler's laws apply
universally, whenever two objects orbit each other under gravitational attraction.
A planet moving in an ellipse with the Sun at one focus will have a speed that is
highest when it is closest to the Sun.
Why does Venus have its largest angular diameter when it is new and its smallest angular diameter when it is full?
Venus is closest to Earth when it is new and farthest away when it is full.
What did Galileo see when he observed Jupiter through his telescope?
four satellites (moons) orbiting Jupiter
how many moons of Jupiter were seen by Galileo?
Which of the following statements correctly states the significance of Galileo's observation that Jupiter has satellites (moons)?
It showed that bodies can orbit an object other than Earth.
Which of the following did Galileo find most significant about his observations of the motions of the large moons of Jupiter?
The moons farther from Jupiter had longer periods, just as Copernicus had discovered for the planets around the Sun.
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?
The forces are the same.
How do the accelerations of Saturn and Earth compare?
Saturn feels one one-hundredth of Earth's acceleration.
Suppose that you traveled to a planet with 4 times the mass and 4 times the diameter of the Earth. Would you weigh more or less on that planet than on Earth?
The Moon has less mass than the Earth, and it exerts
the same force on the Earth as the Earth exerts on it.
Which one of the following objects or persons is not accelerating?
skydiver falling in a straight line at a constant speed (at "terminal speed")
Two spaceships having different masses but rocket engines of identical force are coasting together through space at constant velocity. If they then fire their rockets at the same time, which of the two ships will speed up faster?
the one with the lower mass
A person is pushing (and slightly squashing) a basketball against a wall. According to Newton's Third Law, the reaction force for the force that the hand exerts on the basketball is the force that the
basketball exerts on the hand
An orbiting object stays in orbit because
it has forward motion that keeps it from hitting the Earth as it falls.
How many forces are acting on the space shuttle when it is in a circular orbit around the Earth? (Ignore forces from very distant objects, such as the Sun and Moon.)
one force, acting toward the center of the Earth
The existence of which of the following was first predicted using Newton's laws of motion and gravitation before it was found in the sky?
High tides occur on Earth at locations opposite the Moon because
two high and two low tides per day.
The highest of all tides on Earth's oceans occur at
full or new moon, at times when Moon and Sun are closest to Earth.
Does the Sun or the Moon have a greater effect in causing the tides on Earth?
The Moon, because it has a larger difference between pulling on the near side and pulling on the far side of Earth.
What was the very first observation that showed conclusively that light travels at a finite speed (not infinitely fast)?
Eclipses of Jupiter's moons, when they moved into or out of Jupiter's shadow, appeared to occur later than they should when Jupiter was farther away from Earth.
Through which of the following materials does light travel fastest?
How long does it take light to travel from the Sun to Earth, a distance of 1.50 108 km?
Your normal body temperature is 98.6°F. What kind of radiation do you predominantly emit?
At what wavelength (in nm) do you emit the most radiation?
At what wavelength (in nm) do you emit the most radiation?
The English physicist Thomas Young showed in 1801 that light behaves as a wave by
shining light through two closely spaced slits and observing the resulting pattern of light on a white screen.
Considering the whole electromagnetic spectrum, visible light dominates the entire spectrum.
Gamma rays are the most energetic kind of electromagnetic radiation.
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?
What is the temperature of the Sun's surface in degrees Fahrenheit?
If an object is a perfect blackbody, then it emits
energy with a continuous distribution that peaks at a certain wavelength dependent on temperature.
Two stationary objects are radiating as blackbodies. They are the same size and shape, but one appears blue and the other appears red. Therefore, the red one is
cooler than the blue one.
he wavelength of infrared radiation is always shorter than the wavelength of visible light.
Cold-blooded animals aren't warm so they can't be photographed with an infrared camera.
X-rays are more energetic than infrared radiation
Why do astronomers find it convenient to use the Kelvin temperature scale in their work rather than the Celsius or Fahrenheit scales?
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.
The energy emitted per second by the Sun is greatest at a wavelength of about 500 nm. The energy emitted per second by a star having half the temperature of the Sun would be greatest at a wavelength of about
1000 nm in the infrared.
Which one of the following statements about photons is correct?
The color of a beam of light is determined by the energy of the individual photons of which the beam is composed.
One beam of pure light has a high frequency and a short wavelength, while a second pure beam has a low frequency and a long wavelength. A photon from the high-frequency beam has ___________ than a photon from the low-frequency beam.
When astronomers discovered the rings of Uranus, they were using a spectroscope to observe the atmosphere of Uranus as the planet passed in front of a distant star. The star provided the light source. Which type of spectrum would they examine to determine which chemical elements are present in the Uranian atmosphere?
The star cluster NGC 346 and nebula shown in the figure below are located within the Small Magellanic Cloud (SMC), a small galaxy that orbits our Milky Way Galaxy. The SMC and the stars and gas within it are moving away from us at 158 km/s. At what wavelength does the red Hα line of hydrogen (which causes the color of the nebula) appear in the nebula's spectrum?
When heated in a flame, a small quantity of a chemical element emits light only at specific wavelengths. The pattern of these spectral emission lines as a function of wavelength
is characteristic for each element but differs from element to element.
Explain why astronomers are interested in blackbody radiation.
Stars to a good approximation behave like blackbodies and emit radiation in a spectrum similar to the spectrum of an ideal blackbody.
An atom of singly ionized magnesium has 12 protons in its nucleus. How many electrons surround this nucleus?
A neutron is combined in a nuclear reaction with a proton to make a heavy hydrogen nucleus. This nucleus then acquires sufficient electrons to become electrically neutral. How many electrons will this heavy hydrogen atom contain?
Two isotopes of an element differ from one another because
they have the same number of protons but different numbers of neutrons in their nuclei.
An atom is now known to consist of a
small, massive, electrically charged core with electrons surrounding it.
The overall diameter of a typical atom is about
10-10 m, or 0.1 nm.
According to the Bohr theory, light emitted by atoms originates from
transitions of electrons between different energy levels in the atom.
When an electron in an atom makes a transition from a higher to a lower orbit, light is
emitted in an emission line.
What is the Doppler effect?
The Doppler effect is a shift in the observed wavelength due to relative radial motion between the source of the waves and the observer.
Why is the Doppler effect important to astronomers?
The Doppler effect allows a determination of the relative radial velocity of a source of radiation from an examination of its spectrum.
An object is moving toward us at a great speed. Therefore, the light it emits is Doppler shifted to
bluer, higher frequencies.
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