AST 109- Planetary Astronomy Exam #1
Ch. 1, 2. 3. 4. 5. 6.
Terms in this set (108)
Why would one of the letters RIVUXG be highlighted under a figure? What does this indicate?
The highlighted letter indicates that a filter was used for that image allowing only that portion of the electromagnetic spectrum to be recorded.
A scientific model is usually made up of what?
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 of solar systems is:
How many planets have we explored with the use of a robotic spacraft?
All eight planets from Mercury to Neptune
The age of our solar system is:
4.56 billion years, from the study of meteorites.
What is the process of stars?
Nebula, Star, Supernova
A supernova is a(n):
Explosion that rips a star apart, throwing debris into interstellar space.
In the Orion Nebula, the Nebulae are the:
Birthplace of stars
The 88 constellations in the sky are just:
Patterns of stars that only appear to be close to each other.
To a modern astronomer, the 88 constellations are just:
88 regions of the sky
(T/F) A sidreal day is longer than a solar day
(T/F) Stars set on the western horizon a little earlier everyday.
(T/F) Polaris is the brightest star in the sky.
The constellation of Andromeda is directly overhead California at midnight. Where would a person in Washington, D.C. look to view Andromeda at the same time (9 P.M. eastern time)?
To the west
A star is observed to be directly below Polaris at 6 P.M. Where do you expect to find the star later that night at 6 A.M. (twelve hours later)?
Directly above Polaris
(T/F) Seasons are caused by the fact that when one hemisphere is tilted towards the Sun, it is closer to the Sun, and therefore warmer.
(T/F) The Sun is directly overhead for people living on the equator exactly twice a year, on the equinoxes.
For people living in the continental United States, you would face______ to look directly at the Sun at noon on the summer solstice.
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?
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?
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
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 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 the mean sun follow on the celestial sphere?
The celestial equator.
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:
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?
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:
the first quarter
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?
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 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?
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 & 1/2 days. 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?
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.
he 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.
(T/F) A partial eclipse can be seen by fewer people at one time than a full eclipse can.
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
Earth's shadow at the distance of the Moon's orbit from Earth is:
WIder than the moon
(T/F) Most people who observe a solar eclipse tend to observe a total solar eclipse.
(T/F) 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 annual
Why do Eclipse paths move eastward across the Earth?
The Moons 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?
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.
Tycho Brahe's most important contribution to the development of modern astronomy was the:
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."
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?
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
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.
Approximately how many times around Earth (at the equator) could a beam of light travel in one second?
Historically, the wave nature of light was first demonstrated by:
The interference produced when light passes through a double slit.
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.
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 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
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 losing energy as they jump to lower levels
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
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.
What did Galileo see when he observed Jupiter through his telescope?
four satellites (moons) orbiting Jupiter
One proof of Galileo that the Copernican model of the solar system is correct was that
Venus goes through phases like the moon does
Kepler's laws apply:
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