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Astronomy ch 1-4
astro midterm
156
Astronomy
02/27/2011

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Term
Using the ideas discussed in your textbook, in what sense are we "star stuff"?
Definition
Nearly every atom from which we are made was once inside of a star.
Term
How are galaxies important to our existence?
Definition
Galaxies recycle material from one generation of stars to the next, and without this recycling we could not exist.
Term
When we look at an object that is 1,000 light-years away we see it _________.
Definition
as it was 1,000 years ago
Term
Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that case _________.
Definition
we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2
Term
Suppose we make a scale model of our solar system, with the Sun the size of a grapefruit. Which of the following best describes what the planets would look like?
Definition
The planets are all much smaller than the Sun. Four planets are within about 20 meters of the Sun, while the rest planets are spread much farther apart.
Term
If you could count stars at a rate of about one per second, how long would it take to count all the stars in the Milky Way Galaxy?
Definition
Several thousand years
Term
The total number of stars in the observable universe is about _________.
Definition
Term
Where is our solar system located within the Milky Way Galaxy?
Definition
Roughly halfway between the center and the edge of the visible disk of the galaxy
Term
If we imagine the history of the universe compressed into one year, dinosaurs became extinct _________.
Definition
yesterday morning
Term
Relative to the age of the universe, how old is our solar system?
Definition
It is about one-third the age of the universe.
Term
How do the speeds at which we are moving with Earth's rotation and orbit compare to the speeds of more familiar objects?
Definition
Earth's rotation carries most people around the axis faster than a commercial jet travels, and Earth's orbit carries us around the Sun faster than the Space Shuttle orbits Earth.
Term
Why do the patterns of the stars in our sky look the same from year to year?
Definition
Because the stars in the constellations are so far away.
Term
Astronomers infer that the universe is expanding because distant galaxies all appear to _________.
Definition
be moving away from us, with more distant ones moving faster
Term
Which statement about motion in the universe is not true?
Definition
The mysterious dark matter is the fastest-moving material in the universe.
Term
When did humans learn that the Earth is not the center of the universe?
Definition
Within the past 500 years
Term
Which of the following is not a general difference between a planet and a star?
Definition
All planets are made of rock and all stars are made of gas.
Term
Our solar system consists of _________.
Definition
the Sun and all the objects that orbit it
Term
A typical galaxy is a _________.
Definition
collection of a few hundred million to a trillion or more stars, bound together by gravity
Term
Which of the following best describes what we mean by the universe?
Definition
he sum total of all matter and energy
Term
What do astronomers mean by the Big Bang?
Definition
The event that marked the beginning of the expansion of the universe
Term
What do we mean when we say that the universe is expanding?
Definition
Average distances between galaxies are increasing with time.
Term
Based on observations of the universal expansion, the age of the universe is about _________.
Definition
14 billion years
Term
A television advertisement claiming that a product is light-years ahead of its time does not make sense because _________.
Definition
Term
The term observable universe refers to _________.
Definition
that portion of the universe that we can see in principle, given the current age of the universe
Term
On a scale in which the distance from Earth to the Sun is about 15 meters, the distance from Earth to the Moon is _________.
Definition

small enough to fit within your hand

 

Using a scale of 1 to 10 billion, Earth is about the size of a ballpoint and located about 15 meters from a grapefruit-size Sun, while the Moon (about ¼ the size of Earth) is a mere 4 centimeters (about an inch and a half) from Earth.

Term
On a scale where the Sun is about the size of a grapefruit and the Earth is about 15 meters away, how far away are the nearest stars besides the Sun?
Definition
About the distance across the United States
Term
The number of stars in the Milky Way Galaxy is approximately _________.
Definition
a few hundred billion
Term
An astronomical unit (AU) is _________.
Definition

the average distance between Earth and the Sun

 

Term
What is the ecliptic plane?
Definition
The plane of Earth's orbit around the Sun
Term
How long does it take the Earth to complete one orbit around the Sun?
Definition
One year
Term
Which of the following statements about the celestial sphere is NOT true?
Definition
The "celestial sphere" is another name for our universe.
Term
The Andromeda Galaxy is faintly visible to the naked eye in the constellation Andromeda. Suppose instead it were located in the same direction in space as the center of the Milky Way Galaxy (but still at its current distance). How would it appear to the eye in that case?
Definition
We could not see it at all.
Term
An angle of 1 arcsecond is _________.
Definition
less than the thickness of a human hair held at arm's length
Term
When traveling north from the United States into Canada, you'll see the North Star (Polaris) getting _________.
Definition
higher in the sky
Term
Suppose you use the Southern Cross to determine that the south celestial pole appears 40 degrees above your horizon. Then you must be located at _________.
Definition
latitude 40 degrees south
Term
Suppose you are facing north and you see the Big Dipper close to your northern horizon, with Polaris (and the Little Dipper) above it. Where will you see the Big Dipper in six hours?
Definition
To the right of Polaris; that is, 90 degrees counterclockwise from its current position
Term
In any particular place on Earth, certain constellations are visible in the evening only at certain times of the year because _________.
Definition
our evening view of space depends on where Earth is located in its orbit around the Sun
Term
The Sun's path, as viewed from the equator, is highest in the sky on _________.
Definition
the spring and fall equinoxes
Term
Suppose Earth's axis tilt was significantly greater than its current 23.5 degrees, but Earth's rotation period and orbital period were unchanged. Which statement below would not be true?
Definition
The length of each season (for example, the number of days from the summer solstice to the fall equinox) would be significantly longer than it is now.
Term
If our year were twice as long (that is, if Earth took twice as many days to complete each orbit around the Sun), but Earth's rotation period and axis tilt were unchanged, then _________.
Definition
the four seasons would each be twice as long as they are now
Term
How does Earth's varying distance from the Sun affect our seasons?
Definition
It doesn't --- Earth's orbital distance plays no significant role in the seasons.
Term
Suppose you live in the United States and you see a crescent moon in your evening sky tonight. What will a friend in South America see tonight?
Definition
Your friend will also see a crescent moon.
Term
Suppose it is full Moon. What phase of Earth would someone on the Moon see at this time?
Definition
new Earth
Term
It's 6 am and the Moon is at its highest point in your sky (crossing the meridian). What is the Moon's phase? 
Definition
third quarter
Term
You observe a full Moon rising at sunset. What will you see at midnight?
Definition
A full moon high in the sky
Term
All the following statements are true. Which one explains the reason that there is not a solar eclipse at every new moon?
Definition
The orbital plane of the Moon is tilted slightly (by about 5 degrees) to the ecliptic plane.
Term
For most of history, the lack of observable stellar parallax was interpreted to mean that _________.
Definition

Earth is stationary at the center of the universe

 

The Greeks were aware that stellar parallax should occur if Earth orbits the Sun - and we now know that it does indeed occur. However, the stars are so far away that ancient people could not detect parallax; the Greeks mistakenly took this lack of detectable parallax as evidence in favor of their Earth-centered model, rather than as evidence that the stars are really far away.

Term
During the period each year when we see Mars undergoing apparent retrograde motion in our sky, what is really going on in space?
Definition
Earth is catching up with and passing by Mars in their respective orbits.
Term
Suppose you see a photo showing Jupiter half in sunlight and half in shadow (that is, a first quarterJupiter). This photo might have been taken by _________.
Definition
the Galileo spacecraft that orbited Jupiter in the 1990s
Term
About how many stars are visible to the naked eye on a clear, dark night away from city lights?
Definition
A couple thousand
Term
What do astronomers mean by a constellation?
Definition
A constellation is a region in the sky as seen from Earth.
Term
What is the ecliptic?
Definition
The path the Sun appears to trace around the celestial sphere each year
Term
What is the celestial sphere?
Definition
The celestial sphere is a representation of how the entire sky looks as seen from Earth.
Term
What do we mean when we talk about the Milky Way in our sky?
Definition
The patchy band of light that outlines the plane of the Milky Way Galaxy as seen from Earth.
Term
Which of the following statements does not use the term angular size or angular distance correctly?
Definition
The angular distance between those two bright stars in the sky is about 2 meters.
Term
Which of the following correctly describes the meridian in your local sky?
Definition
?
Term
The point directly over your head is called _________.
Definition
the zenith
Term
Stars that are visible in the local sky on any clear night of the year, at any time of the night, are called _________.
Definition
circumpolar
Term
We describe a location on Earth's surface by stating its _________.
Definition
latitude and longitude
Term
If you are located in the Northern Hemisphere, which of the following correctly describes a relationship between the sky and your location?
Definition
The altitude of the north celestial pole equals your latitude.
Term
Which of the following best describes why we have seasons on Earth?
Definition
The tilt of Earth's axis causes different portions of the Earth to receive more or less direct sunlight at different times of year.
Term
Each choice below describes how a few astronomical phenomena are related to time periods. Which list is entirely correct? 
Definition
Earth's rotation defines a day. The cycle of the Moon's phases takes about a month. Earth's orbit defines a year. Earth's cycle of axis precession takes 26,000 years.
Term
If we have a new moon today, when we will have the next full moon?
Definition
In about 2 weeks
Term
We cannot see a new moon in our sky because _________.
Definition
a new moon is quite near the Sun in the sky
Term
The Moon always shows nearly the same face to Earth because ________.
Definition
Term
Lunar eclipses can occur only during a _________.
Definition
full moon
Term
What is the saros cycle?
Definition
The roughly 18-year cycle over which the pattern of eclipses repeats
Term
During the time that a planet is in its period of apparent retrograde motion: _________
Definition
Over many days or weeks, the planet moves westward relative to the stars, rather than the usual eastward relative to the stars
Term
What is stellar parallax?
Definition
It is the slight back-and-forth shifting of star positions that occurs as we view the stars from different positions in Earth's orbit of the Sun.
Term
What practical value did astronomy offer to ancient civilizations?
Definition
It helped them keep track of time and seasons and was used by some cultures for navigation
Term
scientific thinking is
Definition
based on everyday ideas of observation and trial and error experiments
Term
the names of the seven days of the week are based on
Definition
the seven naked eye objects that appear to move among the constellations
Term
the metonic cycle is
Definition
used to keep lunar calenders approx. synchronized with solar calenders
Term
ptolemy was important in the history of astronomy because
Definition
he developed a model of the solar system that made sufficiently accurate predictions of planetary positions to remain in use for many centuries
Term
the ancient greeks get a lot of attention for their contributions to science because
Definition
they were the first people to try and explain nature with models based on reason and math, without resorting to the supernatural
Term
geocentric model of the universe
Definition
earth in the center 
Term
ptolemaic model
Definition
earth centered model of planetary motion published by ptolemy
Term
greatest contribution of copernicus was to
Definition
create a detailed model of our solar system with the sun at the center
Term
the greatest contribution of tycho brahe was to
Definition
observe planetary positions with sufficient accuracy so that kepler could later use the data to discover the laws of planetary motion
Term
did galileo observe stellar parallax?
Definition
nope
Term
keplers laws
Definition

1. orbits of planets are ellipses, with the sun at one focus of the ellipse

2. the line joining the planet to the sun sweeps out equal areas in equal times as the planet travels around the ellipse

3. the ratio of the squares of the revolutionary periods for two planets is = to the ratio of the cubes of their semimajor axis

p^2/p^2=R^3/R^3

Term
Definition
Term
how do astronomers view astrology
Definition
Astrology played an important part in the development of astronomy in ancient times, but it is not a science by modern standards.
Term
Definition
Term
Suppose the planet Uranus was much brighter in the sky, so that it was as easily visible to the naked eye as Jupiter or Saturn. What would happen to the days of the week and way?
Definition
A week would have had eight days instead of seven, because seven naked eye objects appear to move among the stars
Term
How does a 12 month lunar calendar differ from our 12 month solar calender
Definition
it has about 11 fewer days
Term
how did the ptolemaic model explain the apparent retrograde motion of the planets
Definition
the planets moved along small circles that moved in larger circles around the earth
Term
When Copernicus first created his sun-centered model of the universe, it did not lead to substantially better predictions of planetary positions than the Ptolemaic model. Why not?
Definition
Copernicus used perfect circles for the orbits of the planets
Term
Earth is farthest from the Sun in July and closest to the Sun in January. During which Northern Hemisphere season is Earth moving fastest in its orbit?
Definition
winter
Term
according to kepler's third law (p^2=a^3) how does a planet's mass affect its orbit around the sun?
Definition
a planet's mass has no effect on its orbit around the sun
Term
venus orbits the sun at a slower average speed than mercury. which of kepler's laws does this directly relate to
Definition
the third one (p^2=a^3)
Term
suppose a comet orbits the sun on a highly eccentric orbit  with an average (semimajor axis) distance of 1AU. How long does it take to complete each orbit, and how do we know?
Definition
1 year which we know from the 3rd law
Term
Galileo challenged the idea that objects in the heavens were perfect by...
Definition
observing sunspots on the sun and mountains on the moon
Term
galileo observed all of the following. which observation offered direct proof of a planet orbiting the sun?
Definition
phases of venus
Term
the astrology practiced by those who cast predictive horoscopes can be tested by....
Definition
comparing how often predictions come true to what would be expected by pure chance
Term
imagine earth is not rotating and orbiting the sun. which of these hypothetical observations would be inconsistent with our sun-centered view of the solar system?
Definition
we discover a small planet beyond saturn that rises in the west and sets in the east each day.
Term
Which of the following represents a case in which you are not accelerating
Definition
driving in a straight line at 60 miles an hour
Term
Suppose you drop a 10-pound weight and a 5-pound weight on the Moon, both from the same height at the same time. What will happen?
Definition
Both will hit the ground at the same time.
Term
Definition
Term
Why are astronauts weightless in the Space Station?
Definition
Because the Space Station is constantly in free-fall around the Earth
Term
Definition
Term
A net force acting on an object will always cause a change in the object's _________.
Definition
momentum
Term
Suppose you are in an elevator that is traveling upward at constant speed. How does your weight compare to your normal weight on the ground?
Definition
It is the same.
Term
The planets never travel in a straight line as they orbit the Sun. According to Newton's second law of motion, this must mean that _________.
Definition
a force is acting on the planets
Term
Suppose the Sun were suddenly to shrink in size but that its mass remained the same. According to the law of conservation of angular momentum, what would happen? 
Definition
The Sun would rotate faster than it does now.
Term
Suppose you kick a soccer ball straight up to a height of 10 meters. Which of the following is true about the gravitational potential energy of the ball during its flight?
Definition
The ball's gravitational potential energy is greatest at the instant when the ball is at its highest point.
Term
Suppose you heat an oven to 400°F and boil a pot of water. Which of the following explains why you would be burned by sticking your hand briefly in the pot but not by sticking your hand briefly in the oven?
Definition
The water can transfer heat to your arm more quickly than the air.
Term
Which of the following scenarios involves energy that we would typically calculate with Einstein's formula E=mc2?
Definition
A small amount of the hydrogen in of a nuclear bomb becomes energy as fusion converts the hydrogen to helium.
Term
A rock held above the ground has potential energy. As the rock falls, this potential energy is converted to kinetic energy. Finally, the rock hits the ground and stays there. What has happened to the energy?
Definition
The energy goes to producing sound and to heating the ground, rock, and surrounding air.
Term
Suppose that the Sun shrank in size but that its mass remained the same. What would happen to the orbit of the Earth?
Definition
Earth's orbit would be unaffected.
Term
Imagine another solar system, with a star of the same mass as the Sun. Suppose a planet with a mass twice that of Earth (2MEarth) orbits at a distance of 1 AU from the star. What is the orbital period of this planet?
Definition
1 year.
Term
Imagine another solar system, with a star more massive than the Sun. Suppose a planet with the same mass as Earth orbits at a distance of 1 AU from the star. How would the planet's year (orbital period) compare to Earth's year?
Definition
The planet's year would be shorter than Earth's.
Term
Newton showed that Kepler's laws are _________.
Definition
atural consequences of the law of universal gravitation
Term
Each of the following lists two facts. Which pair of facts can be used with Newton's version of Kepler's third law to determine the mass of the Sun?
Definition
Earth is 150 million km from the Sun and orbits the Sun in one year.
Term
When space probe Voyager 2 passed by Saturn, its speed increased (but not due to firing its engines). What must have happened?
Definition
Saturn must have lost a very tiny bit of its orbital energy.
Term
Suppose that a lone asteroid happens to be passing Jupiter on an unbound orbit (well above Jupiter's atmosphere and far from all of Jupiter's moons.) Which of the following statements would be true?
Definition
The asteroid's orbit around Jupiter would not change, and it would go out on the same unbound orbit that it came in on.
Term
Which of the following best describes the origin of ocean tides on Earth?
Definition
Tides are caused by the difference in the force of gravity exerted by the Moon across the sphere of the Earth.
Term
At which lunar phase(s) are tides most pronounced (for example, the highest high tides)?
Definition
Both new and full moons
Term
Which of the following best explains why the Moon's orbital period and rotation period are the same?
Definition
The Moon once rotated faster, but tidal friction slowed the rotation period until it matched the orbital period.
Term
Suppose the Moon's orbit were unchanged, but it rotated faster (meaning it did not have synchronous rotation). Which of the following would be true?
Definition
We would no longer always see nearly the same face of the Moon.
Term
The difference between speed and velocity is that _________.
Definition
velocity also includes a direction
Term
The acceleration of gravity on Earth is approximately 10 m/s2 (more precisely, 9.8 m/s2). If you drop a rock from a tall building, about how fast will it be falling after 3 seconds? 
Definition
30 m/s
Term
Momentum is defined as _________.
Definition
Term
Suppose you lived on the Moon. Which of the following would be true?
Definition
Your weight would be less than your weight on Earth, but your mass would be the same as it is on Earth.
Term
In which of the following cases would you feel weightless?
Definition
While falling from a roof
Term
Which of the following statements is not one of Newton's Laws of Motion?
Definition
What goes up must come down.
Term
Newton's Second Law of Motion tells us that the net force applied to an object equals its _________.
Definition
mass times acceleration
Term
Suppose that two objects collide. Which of the following things is not the same both before and after the collision?
Definition
The total temperature of the objects
Term
When a spinning ice skater pulls in his arms, he spins faster because _________.
Definition
his angular momentum must be conserved, so reducing his radius must increase his speed of rotation
Term
The energy attributed to an object by virtue of its motion is known as _________.
Definition
kinetic energy
Term
Radiative energy is _________.
Definition
energy carried by light
Term
Absolute zero is _________.
Definition
0 Kelvin
Term
What does temperature measure?
Definition

the average kinetic energy of particles in a substance

 

Term
In the formula E=mc2, what does E represent?
Definition
The mass-energy, or potential energy stored in an object's mass
Term
According to the universal law of gravitation, if you triple the distance between two objects, then the gravitational force between them _________.
Definition
decreases by a factor of 9
Term
What is the difference between a bound orbit and an unbound orbit around the Sun?
Definition
An object on a bound orbit follows the same path around the Sun over and over, while an object on an unbound orbit approaches the Sun just once and then never returns.
Term
The allowed shapes for the orbits of objects responding only to the force of gravity are ______.
Definition
ellipses, parabolas, and hyperbolas
Term
Why is Newton's version of Kepler's third law so useful to astronomers?
Definition
It can be used to determine the masses of many distant objects.
Term
What do we mean by the orbital energy of an orbiting object (such as a planet, moon, or satellite)?
Definition
Orbital energy is the sum of the object's kinetic energy and its gravitational potential energy as it moves through its orbit.
Term
Which statement must be true in order for a rocket to travel from Earth to another planet?
Definition
It must attain escape velocity from Earth.
Term
Approximately where is it currently high tide on Earth?
Definition
On the portion of Earth facing directly toward the Moon and on the portion of Earth facing directly away from the Moon
Term
Which of the following statements about sidereal and solar days is nottrue?
Definition
A sidereal day is the definition of a day on the Earth and a solar day is the definition of a day on the Sun.
Term
What is the difference between a synodic month and a sidereal month?
Definition
A synodic month is the time it takes for a cycle of lunar phases and a sidereal month is the time it takes the Moon to orbit Earth (relative to the stars)
Term
When we say that Jupiter is at opposition we mean that it ______.
Definition
appears on the opposite side of the sky from the Sun, so that it is on our meridian at midnight
Term
What kind of time can be read directly from a sundial?
Definition
apparent solar time
Term
Universal time, or UT, is ______.
Definition

the mean solar time in Greenwich, England

 

Term
Our modern calendar is also known as ______.
Definition
the Gregorian calendar
Term
Which of the following best describes the meaning of declination and right ascension?
Definition
They are coordinates on the celestial sphere, with declination telling us the angular distance of an object from the celestial equator and right ascension telling us how far around the celestial sphere an object is located from the vernal equinox.
Term
The Sun's declination on June 21st is ______.
Definition
+23.5 degrees (of the equinoxes)
Term
Which of the following best describes the Tropic of Cancer?
Definition
It is the circle of latitude on Earth for which the Sun appears directly overhead at noon on the summer solstice.
Term
Suppose you live at latitude 40°N. Which of the following describes the path of the celestial equator through your sky?
Definition
It extends from due east on your horizon, to an altitude of 50° in the south, to due west on your horizon.
Term
Suppose it is January and the Sun remains above your horizon all day long. Where must you be located?
Definition
somewhere between the Antarctic Circle and the South Pole
Term
From a latitude of 60 degrees north during the winter, the Sun will ______
Definition
spend most of each day below the horizon
Term
If you were standing on Earth's equator, where would you look to see the north celestial pole?
Definition
on your horizon due north
Term
Suppose you know the declination of a bright star that is now crossing your meridian. What else must you measure in order to determine your latitude?
Definition
the star's altitude
Term
What is the global positioning system (GPS)?
Definition
a system for determining positions on Earth using signals from a set of satellites in Earth orbit