Astronomy 109 Unit 1
Terms in this set (159)
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 in RIVUXG?
The highlighted letter indicates that a filter was used for that image only allowing that portion of electromagnetic spectrum to be recorded.
skepticism is considered to be
essential in modern science
if a scientist obtains results that disagree with scientific theory, the scientist should check for errors, and if none are found he should then..
try to change the theory to agree with the experiment
a scientific model is usually built of
the first often tentative conjuncture of why something in nature behaves the way it does is called a
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 solar system includes
all objects that orbit the sun
A key concept in the formation and evolution of the solar system appears to be
To learn everything we can about the planets in our solar system, we have used robotic spacecraft to explore
all eight planets from Mercury to Neptune.
The age of our solar system has been measured as
4.56 billion years, from the study of meteorites.
The oldest objects in the solar system whose age has been measured are
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
A supernova is a(n)
explosion that rips a star apart, throwing debris into interstellar space.
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.
The study of galaxies gives astronomers important clues about the
creation of the universe.
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.
Which of the following statements best represents the overall rationale for scientific investigation?
Reality is comprehensible, and a limited number of fundamental principles govern the nature and behavior of the universe.
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
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.
A sidereal day is longer than a solar day.
false; While the tilt affects the seasons, the difference in distance between the closer side and the farther side is negligible compared to the distance between the Sun and Earth. The tilt causes a variation in the length of day and the directness of the Sun's rays, which causes the seasons.
The Sun is directly overhead for people living on the equator exactly twice a year, on the equinoxes.
true; The dates of the equinoxes are defined as the dates when the Sun is directly over Earth's equator.
For people living in the continental United States, you would face _______
to look directly at the Sun at noon on the summer solstice.
south; In the continental United States, the Sun will never be directly (overhead the farthest north this will happen is at a latitude of 23.5° N). You would need to look south to see the Sun at noon.
When do people in Sydney, Australia observe the Sun above the horizon for the longest period of time (i.e., when are their days the longest)?
around December 21
when the United States experiences their shortest day of the year
when the Sun is highest in their sky at noon
on their first day of summer
After a long night of partying, one of your friends yells "Road Trip!" You all hop in the car and keep driving. When you finally reach your destination it is noon and you see the Sun directly overhead. You look at the calendar and see that it is December 21st. At what latitude are you?
the Tropic of Capricorn (23.5° S)
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.
Polaris, the North Star, is at the end of the handle of the Little Dipper. How do the stars of the Little Dipper move with respect to Polaris?
If the Sun's declination is 0° on March 21 of a particular year, how long will it be before it is at this declination again?
The zenith is the point
directly overhead for any observer.
You are standing at the North Pole of the Earth at the time of the northern hemisphere summer solstice in June. What is the elevation of the Sun above the southern horizon?
In the northern hemisphere, houses are designed to have "southern exposure", that is, with the largest windows on the southern side of the house. But in the southern hemisphere, houses are designed to have "northern exposure." Why are houses designed this way, and why is there a difference between the hemispheres?
In the northern hemisphere the Sun appears toward the south, and in the southern hemisphere the Sun appears toward the north. The houses are designed this way to allow in as much sunlight as possible.
The path that the Sun takes as it moves through the heavens is called the
In the animation above, the dashed circle above the Earth shows the position of the north celestial pole on the celestial sphere over the 26,000-year precessional period. How many years does it take for the position of the north celestial pole to move one degree?
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 Zodiac consists of a set of constellations that
are seen along 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
What is the (fictitious) mean Sun?
The "mean Sun" is a point that moves along the celestial equator at a uniform rate.
What path does it follow on the celestial sphere?
the celestial equator
Why is it a better timekeeper than the actual Sun in the sky?
It is a better timekeeper than the actual Sun because the motion of the actual Sun varies from day to day.
Why is it convenient to divide the Earth into time zones?
It is convenient to divide the Earth into time zones so that noon according to the clock is close to the upper meridian crossing by the Sun.
In one solar day the Earth rotates through an angle of about 361°. A solar day is about 4 minutes longer than a sidereal day. How long is the sidereal day?
23 h 56 m
A tropical year is the
time between successive passages of the Sun through the vernal equinox as viewed from the Earth.
Pope Gregory XIII dropped 10 days from the calendar in 1582 because
the assumption that a tropical year is 365 days is incorrect by over 11 minutes.
The name of one of the lunar phases in the Dakota language means "diminishing moon." To which phase would this term most likely apply?
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
At what phase in its monthly cycle will the Moon be seen high in the sky in the late afternoon from mid-latitudes?
A first-quarter Moon will cross the meridian at approximately
The below photograph of Earth was taken by the crew of the Apollo 8 spacecraft as they orbited the Moon. A portion of the lunar surface is visible at the right-hand side of the photo. In this photo, Earth is oriented with its north pole approximately at the top. When this photo was taken, was the Moon waxing or waning as seen from Earth?
The phases of Earth as seen from the Moon follow the same sequence as the phases of the Moon as seen from Earth. That means the terminator line on Earth moves from right to left, just as it does on the Moon. So the Earth in this photo is waning and heading toward a new phase. But the Moon phases are exactly the opposite of the Earth phases. If Earth is heading toward new, the Moon is heading toward full. Thus the Moon is waxing.
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.
How many more sidereal months than synodic months are there in a year?
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 1/2days. Since the longest months are 31 days long, a blue moon can occur only if the full moon happens to fall on the first day or early on the second day of the month, which does not happen very often. (For a 30-day month, the full moon would have to fall early on the first day.)
Are there any months of the year in which it would be impossible to have two full moons?
Does the Moon rotate around its axis, and how do we know?
Yes. The same side of the Moon always faces the Earth.
You are watching a lunar eclipse from some place on the Earth's night side. Will you see the Moon enter the Earth's shadow from the east or from the west?
The Moon moves eastward, so it enters the Earth's shadow from the west.
A lunar eclipse occurs when the
Earth is exactly between the Moon and the Sun.
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.
The Sun is at a node of the Moon's orbit, as seen from the Earth, and you are looking at a total lunar eclipse. What do you know about the location of the Moon in the sky?
It is at the opposite node from the Sun.
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
A 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.
Suppose the diameter of the Moon were doubled, but the orbit of the Moon remained the same. Would total solar eclipses be more common, less common, or just as common as they are now?
They would be more common. Eclipses which, now, would be anything less than total (with the Moon covering any part of the Sun) would become total eclipses.
Just as the distance from Earth to the Moon varies somewhat as the Moon orbits Earth, the distance from the Sun to Earth changes as Earth orbits the Sun. Earth is closest to the Sun at its perihelion; it is farthest from the Sun at its aphelion. In order for a total solar eclipse to have the maximum duration of totality, should Earth be at perihelion or aphelion? Assume that the Earth-Moon distance is the same in both situations.
The Moon will appear to be the same size in either case, but the Sun will appear to be smaller when it is farther away at aphelion. In this case the Moon will spend more time in front of the (smaller) Sun, and totality will last longer.
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
Most people who observe a solar eclipse tend to observe a total solar eclipse.
During a total solar eclipse, the Moon completely blocks our view of any part of the Sun.
How long do solar eclipses last, for an observer at a given location?
What if the Moon's orbit were larger than it currently is? Which type(s) of solar eclipse(s) would still occur?
both partial and annular solar eclipses
Eclipse paths move eastward across the Earth due to
the Moon's orbit around the Earth
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
Retrograde motion of superior planets is explained in the Copernican model of the solar system as a(n)
illusion that happens when the Earth overtakes a superior planet in its orbit.
When a planet is at superior conjunction, the
Sun is between the Earth and the planet.
At which position is Jupiter seen at its highest in our sky at midnight?
Tycho Brahe was convinced that comets and stars were at great distances because they
exhibited no parallax.
How did Tycho Brahe prove that the heavens are not permanent and unalterable?
A "new star" appeared in the sky, and he showed that the star exhibited no measurable parallax as the Earth rotated around its axis.
Kepler described how a planet's motion speeds up as it nears the Sun by his concept of
"equal areas in equal times."
The Earth is at perihelion in early January and at aphelion in early July. Which of the following statements is true about northern hemisphere seasons?
The summer half of the year has more days in the northern hemisphere than the winter half.
Kepler's laws apply
universally, whenever two objects orbit each other under gravitational attraction.
One proof of Galileo that the Copernican model of the solar system is correct was that
Venus goes through phases like the Moon does.
What did Galileo see when he observed Jupiter through his telescope?
four satellites (moons) orbiting Jupiter
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.
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.
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
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?
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?
Approximately how many times around Earth (at the equator) could a beam of light travel in one second?
How long does it take light to travel from the Sun to Earth, a distance of 1.50 108 km?
8 1/3 minutes
Your normal body temperature is 98.6°F. What kind of radiation do you predominantly emit?
Historically, the wave nature of light was first demonstrated by
the interference produced when light passes through a double slit.
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?
A light source emits infrared radiation at a wavelength of 1150 nm. What is the frequency of this radiation?
2.61 1014 Hz
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.
Using Wien's law and the Stefan-Boltzmann law, explain the color and intensity changes that are observed as the temperature of a hot, glowing object increases.
As the temperature of a hot, glowing object increases it will be seen to glow more brightly. This is described by the Stephan-Boltzmann law, which shows the emitted flux of radiation increasing with the fourth power of the temperature. The color of the glowing object will be seen to shift toward the short-wavelength end of the spectrum in accord with Wien's law, which shows the peak wavelength in the spectrum decreasing as the temperature increases.
One blackbody is at 6000 K and a second blackbody is at 3000 K. How many times more energy is radiated by the hotter object than the cooler one?
There are no green stars because
as a star increases in temperature, the visible spectrum it produces changes from red to red plus green to red plus green plus blue, and none of these combinations looks green.
The bright star Bellatrix in the constellation Orion has a surface temperature of 21,500 K. What is its wavelength of maximum emission in nanometers?
What color is this star?
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.
The important breakthrough in theoretical physics that was first suggested by Planck to explain the shape of the spectrum of a hot body was the
concept that electromagnetic energy was emitted in small packets or quanta.
The first person to show that light traveled in wave packets, or photons, in which the energy of a photon depends on its wavelength, was
An atom of singly ionized magnesium has 12 protons in its nucleus. How many electrons surround this nucleus?
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.
Gold has the atomic number 79, and the stable isotope of gold has the symbol 197Au. How many protons and neutrons does this nucleus have?
79 protons and 118 neutrons
The physical structure of an atom is
negatively charged electrons moving around a very small but massive, positively charged core.
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.
The specific colors of light emitted by an atom in a hot, thin gas (e.g., in a tube in a laboratory or a gas cloud in space) are caused by
electrons jumping to lower energy levels, losing energy as they do so.
A hydrogen atom in a low-density, hot gas gives off what type of spectrum?
a series of emission lines spaced in a mathematical sequence
A source of waves emitting waves of a constant frequency approaches you, passes you, and recedes into the distance—all at a constant speed. The frequency of the waves you observe from this source
is higher (and constant) as the source approaches you and suddenly becomes lower (and constant) as the source moves away from you.
In the spectrum of a particular star, the wavelength of the Hα spectral absorption line of hydrogen is measured to be 656.6 nm, whereas in the laboratory spectrum it is at 656.3 nm. What can you say about this star?
The star is moving away from the Earth at a speed of 137 km/s.
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.
The magnification factor (M) of a telescope must be a positive number greater than 1.0. Knowing this, and knowing that the magnification is the ratio of the two focal lengths (fobj and feye), which of the following equations would allow you to calculate the focal length of the telescope?
M = fobj/feye
Why is the image formed by a simple refracting telescope upside down?
The rays of light entering the objective lens near the top emerge from the eyepiece near the bottom and vice versa.
An astronomical telescope has an objective lens with a focal length of 160 cm and an eyepiece lens with a focal length of 5 cm. What magnification does this telescope provide?
Before answering this question, you should view Animation 6.2, Reflecting Telescopes, and Animation 6.1, The Arecibo Radio Telescope. The radio receiver in the Arecibo telescope is located in the structure suspended by cables above the reflecting surface in the bowl-shaped depression. The design of this radio telescope is most like which of the optical telescopes shown in Animation 6.2?
The Burrell Schmidt telescope at Kitt Peak, Arizona, has an objective lens 24 inches in diameter. The Palomar Schmidt telescope objective lens diameter is 48 inches. How much light does the Palomar Schmidt telescope gather compared to the Burrell Schmidt telescope?
four times as much
What is diffraction of light?
spreading out of light waves after they pass through an opening such as the outer diameter of a lens or mirror
A factor that has become much worse for many observatories and now severely limits the number of useful sites for astronomy in the world is
light pollution due to the increasing size of nearby cities.
What is active optics? Why is it useful?
Active optics is a continuous refocusing and aiming of the telescope. It helps to compensate for changing conditions in the atmosphere to produce a better image
What is adaptive optics? Why is it useful?
Adaptive optics is a continuous changing of the shape of the telescope mirror. It helps to compensate for changing conditions in the atmosphere to produce a better image.
Would either active or adaptive optics be a good feature to include on a telescope to be placed in orbit?
No. Because both are designed to compensate for conditions in the atmosphere, these features would be wasted in orbit.
What is a charge-coupled device (CCD), now routinely used by astronomers instead of photographic film?
rectangular array of tiny, photosensitive, semiconducting wafers
Astronomers use a spectrograph to
measure the distribution of intensity of light over a continuous range of wavelengths, or colors.
The first nonvisible radiation from outer space to be used to explore astronomical objects was
Radio wavelengths are about a million times longer than visible wavelengths. One consequence is that
radio astronomy can "see" farther through the dust clouds in the plane of our galaxy than can visible light astronomy.
To which of the following types of radiation is the Earth's atmosphere transparent?
radio and visible light
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