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Troland
Astronomy 191 Exam 2
121
Astronomy
Undergraduate 2
11/03/2009

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Term
Tycho Brahe
Definition
Developed pre telescopic instruments to accurately measure positions of stars and planets
At age 20, he fought in a brawl and had his nose bitten off
Term
1598- He moved to Prague, met Johannes Kepler
1601- He died, leaving his records of planetary positions to Kepler
Definition
Brahe's Legacy
Term
Johannes Kepler
Definition
German, inherited Brahe's records of planetary positions, realized records could be used to deduce true motions of planets around sun
Term
Keplers First Law
Definition
Orbits of planets are ellipses with sun at one focus, orbits of planets are not circles or combinations of circles
Term
Ellipses
Definition
"conic sections" can have different shapes
Term
Eccentricities
Definition
can have different shapes
Term
Galileo
Definition
Which scientist of the Copernican revolution was tried for heresy by the church of Rome?
Term
recorded positions of fixed and wandering stars in the sky
Definition
What was the principle contribution of Tycho Brahe to the Copernican Revolution?
Term
they are not circles nor combinations of circles
Definition
What is the significance of Kepler's discovery regarding the shapes of planetary orbits?
Term
the ellipse is more elongated and the foci are further apart
Definition
higher eccentricities in ellipses mean what?
Term
the ellipse is more elongated and the foci are further apart
Definition
higher eccentricities in ellipses mean what?
Term
Semi-major axis
Definition
the average distance of planet from sun
Term
3%
Definition
How much does the sun-earth distance vary during the year?
Term
Kepler's second law
Definition
as a planet orbits the sun, it sweeps out equal areas in equal times. Line between sun and planet, as the planet orbits, the line sweeps out at equal times
Term
Kepler's second law
Definition
a planet moves faster when closer to the sun
Term
Kepler' third law
Definition
the time a planet takes to go around the sun (its period) is related to its semi-major axis
p2=a3
Term
Kepler's third law
Definition
planets more distant from the sun take longer to go around once ( they move more slowly and have larger orbits)
Term
Isaac Newton
Definition
provided fundamental explanations for Kepler's laws in terms of gravitational force
Term
Newtons Book, The Principia
Definition
describes Newtons laws of motion and law of gravitation, it completed the copernican revolution by providing fundamental explanations for Keplers laws in terms of gravitation
Term
3%
Definition
The earths orbit is elliptical, so the sun-earth distance varies by how much during the year?
Term
a planet moves faster as it comes closer to the sun
Definition
What is the consequence of Kepler's 2nd law (the "equal areas" law)?
Term
Saturn
Definition
According to Kepler's 3rd law, which planet has the longest period?
Term
The object will move in uniform motion
Definition
suppose an object is set in motion, then no further forces act upon it ( or else all forces cancel out). How will the object move?
Term
uniform motion
Definition
motion in a straight line at a constant speed
Term
car on highway, train moving at a constant speed
Definition
What are some examples of uniform motion?
Term
Acceleration
Definition
any change in an objects state of motion, speeding up, slowing down, change in direction
Term
gas pedal, breaks, steering wheel
Definition
what control devices in a car can cause an acceleration?
Term
NO! if an object is experiencing acceleration it cannot be in uniform motion
Definition
Can an object experiencing acceleration also be in uniform motion?
Term
miles per hour, kilometer per hour, meters per second
Definition
What are some units of velocity?
Term
cyclist moving along a straight path at a constant speed
Definition
Which example below illustrates uniform motion?
Term
cyclist moving along a straight path at a constant speed
Definition
In which case below can we conclude that no acceleration is occurring?
Term
light years
Definition
what unit is not a unit of velocity or speed?
Term
vector quantities
Definition
forces have a strength and a direction
Term
Net force
Definition
the combined effect of all forces
Term
net force is in direction of motion, train speeds up (acceleration)
Definition
what if the force exerted by the engine exceeds the force of friction?
Term
train slows down ( acceleration)
Definition
What if the force exerted by the engine is less than the force of friction?
Term
train wreck! train plunges through rail
Definition
What if the upward force exerted by the rail is less than the downward force of gravity?
Term
90 m/s
Definition
Suppose an object is falling downward, at 50 m/s, how fast after 4 seconds?
Term
the train rail/tracks
Definition
Consider the 4 forces acting upon a train, what force is directed vertically upward?
Term
the chair collapses
Definition
Imagine sitting in a chair. If the force of gravity is greater than the upward force exerted on you by the chair, what will happen?
Term
Newtons 1st law of motion
Definition
if no net force acts on an object, the object remains i uniform motion (or at rest) experiences no acceleration
Term
Newtons 2nd law of motion
Definition
if a net force acts on an object, the object experiences acceleration where
A=Fnet/ M
Term
high force on an object (powerful engine) low mass (light weight)
Definition
what characteristic should a car have in order to achieve highest possible forward acceleration?
Term
4 m/sec2
Definition
suppose a force of 20 newtons is applied to an object having a mass of 5 kilograms. What is the acceleration?
Term
force of 10 newtons on mass of 1 kilogram
Definition
what circumstances will lead to the highest acceleration?
Term
Toward the sun, perpendicular to the motion of the planet
Definition
consider a hypothetical planet in a circular orbit around the sun. In what direction does the fore acting on this planet point?
Term
Mass
Definition
a measure of resistance of an object to being put into motion, measure of inertia of an object . measured in kilograms and grams, the same everywhere
Term
Weight
Definition
the gravitational force exerted on an object, can very with location ( earth vs. moon). units in newton and pound
Term
Mass=same, Weight = 1/6th
Definition
Consider a bowling alley on the moon, would masses of balls and pins be same as on earth? the weights?
Term
meters per second (m/sec)
Definition
What is the metric unit for speed or velocity?
Term
meters per second per second (m/sec2)
Definition
what is the metric unit for acceleration?
Term
olympic diver who has just left the springboard
Definition
Which person experiences weightlessness?
Term
the 2 forces are equal in strength
Definition
How does the gravitational force exerted by the Earth upon the sun compare to the sun's force on earth?
Term
Newtons 3rd law of motion
Definition
If one object exerts a force on a second object the second object exerts equal opposite force
Term
friction force from the sidewalk exerts upon your feet
Definition
What force pushes you forward as you take off from a stand still on a sidewalk?
Term
the earth isnt in uniform motion about the sun (1st law)
Definition
Why must a net force be acting upon earth?
Term
attractive force
Definition
the sun exerts force on planets, just as earth exerts force on objects near it
Term
mass 1 and mass 2, distance between centers r
Definition
what determines strength of gravitational force between two objects?
Term
they are equal
Definition
how does force m1 exerts on m2 compare with force that m2 exerts on m1?
Term
the 10 kg feels 10x force
Definition
Which object feels stronger force of gravity from earth?
Term
fall at the same speed
Definition
which object accelerates faster? (neglecting air resistance)
Term
increase 4 times
Definition
If the masses of two objects are each doubled, the gravitational force between them will
Term
decrease 9 times
Definition
if the distance between 2 objects increases 3 times, the gravitational force between them will...
Term
the same as
Definition
the acceleration a 10kg object experiences when dropped is ? the acceleration of a 1000kg object
Term
location of sunrise on horizon
Definition
how does the location of sunrise (sunset) on the horizon change over the year?
Term
about march 21 and september 21 (equinox)
Definition
When does the sun rise due east?
Term
June 21 (summer solstice date)
Definition
When does the sun rise as far north east as possible?
Term
Dec 21 (winter solstice date)
Definition
When does the sun rise as far southeast as possible?
Term
June 21
Definition
When is the sun angle highest?
Term
Dec 21
Definition
when is the sun angle the lowest?
Term
14 hours
Definition
How many sunlit hours on june 21
Term
12
Definition
how man sunlit hours on mar/sep 21?
Term
8
Definition
how many sunlit hours on dec 21?
Term
sunlight more direct in the summer, and there is more sunlight per day
Definition
why is it warmer in summer than winter?
Term
they are reversed, mid summer in australia is dec 21
Definition
how do seasons in the southern hemisphere compare with those in the north?
Term
very little, earth closest to the sun in early january, furthest in early july
Definition
what effect does the varying earth-sun distance have on the seasons?
Term
23.5% tilt of earths axis
Definition
what is there about the earth that causes seasons?
Term
solstices
Definition
day of year when days are longer or shorter, they occur june 21 and dec 21
Term
equinoxes
Definition
date of year with 12 hours of daylight and darkness
Term
lexington= 15-19 1/2 hours
equator= hours all year
Alaska= 6-18 hours
above arctic circle= 24 hours
Definition
is the seasonal variation different at different latitudes on earth?
Term
the 23 1/2 tilt of the earths axis relative to its orbit
Definition
the cause of the seasons on earth is?
Term
June 21
Definition
upon what date would you expect no sunlight at all near the earths south pole?
Term
september 21
Definition
On approx. what date does the spring equinox fall in cape town south africa?
Term
celestial objects move in circles at constant angles above horizone
Definition
what is daily apparent motion of celestial objects as viewed from the north pole?
Term
all parts of earth would get 12 hours of sunlight pre day all year long
Definition
if earths axis were perpendicular to its orbit (not 23 1/2) how would seasons be different?
Term
45 degrees above the north horizonw
Definition
Imagine a star viewed near the earth's north pole, 45 degrees above the south horizon. Approx. where will the same star be 12 hours later?
Term
about 23 degrees below the horizon
Definition
At the earths south pole, where will the sun be in late june?
Term
12
Definition
suppose the earths axis had no tilt ( that is, its axis were perpendicular to its orbits). In this case, about how many hours of sunlight would residents of anchorage alaska experience on dec 21?
Term
revolves about the earth
Definition
how does the moon move?
Term
about 1 month
Definition
how long does it take to complete a cycle of motion?
Term
about 1 month
Definition
how long does the cycle of lunar phase take?
Term
wanting gibbous, full moon, new moon, wanting crescent, 1st and 3rd quarter
Definition
what are some names of phases of the moon?
Term
1/2 of the illuminated hemisphere
Definition
what fraction of moons surface is illuminated by sun at any given moment
Term
towards the sun
Definition
in what direction does moons illuminated hemisphere always face the earth?
Term
no, as the moon orbits earth, different fractions of moons illuminated face earth
Definition
does the moons illuminated hemisphere always face the earth?
Term
new moon
Definition
at what lunar phase does none of moons illuminated hemisphere face earth?
Term
1st quarter and 3rd quarter
Definition
at what lunar phases does half moons illuminated hemisphere face earth?
Term
full moon
Definition
at what lunar phases does the illuminated hemisphere of the moon point both toward the sun and the earth?
Term
2 weeks
Definition
the period of time between new moon and full moon is?
Term
one half
Definition
about what fraction of the moons surface is illuminated by the sun at 1st and 3rd quarters?
Term
shadows of earth on moon (causes lunar eclipses occasionally
Definition
what does not cause phases of the moon?
Term
sun moon angle
Definition
0 degrees during new moon
Term
1st quarter moon
Definition
90 degrees sun moon angle
Term
full moon
Definition
180 degrees sun moon angle
Term
3rd quarter moon
Definition
90 degrees sun moon angle
Term
early evening, full moon in opposite of direction of the sun, full moon rises when sun sets
Definition
at what time of day does the full moon rise?
Term
rises at the same time as the sun
Definition
at what time of day does the new moon rise?
Term
near 1st quarter in the afternoon, near 3rd quarter in morning
Definition
when can you see the moon during the daytime?
Term
yes, every observer on earth sees the same phase of the moon at a given moment
Definition
if moon is full in lexington tonight is it also full tonight in santiago chili?
Term
YES!
Definition
does earth show phases when viewed from the moon?
Term
new
Definition
If the moon sets at sunset, what is the phase of the moon?
Term
180
Definition
if the moon is full, what is the angle between the moon and the sun in the sky?
Term
waxing crescent
Definition
suppose you see the moon setting in early evening shortly after sunset. what is the phase of the moon?
Term
Definition
phases of earth seen from the moon are always opposite of phases of the moon seen from the earth
Term
yes, when the moon is a thin crescent
Definition
can we ever see the dark side of the moon?
Term
earth nearly full, very bright in the sky
Definition
what is the phase of earth as seen on the moon?
Term
earth shine
Definition
we see dark side of the moon because of reflected light from the earth
Term
yes!
Definition
does same hemisphere of the moon always face earth as moon orbits earth?
Term
yes, to keep same face pointed at earth, moon must rotate exactly once with every orbit
Definition
does the moon rotate on its axis at all?
Term
earth remains motionless in lunar sky
Definition
consequences of synchronous rotation
Term
1 month
Definition
how long is a day on the moon?
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