75 terms

# first two homeworks

astronomy

#### Terms in this set (...)

the altitude of the North Star is equal to
an observer's latitude.
If the observer moved to a more northerly location on earth, she would observe the north star
at a different altitude.
The change in what stars you can see in one night at different times is due to
the earth's
rotating
The change in what stars you can see at the same time of night over a period of months is
due to
the earth's movement in its orbit around the sun, gradually making different stars
appear at any given angle of view.
Give two reasons why it's warmer in summer than in winter
In our northern hemisphere summer, sunlight strikes our portion of the earth at a more
direct angle;
regions closer to the north pole are exposed
to sunlight for more than half of the 24-hour daily cycle
what time does the new moon rise
6:00 am on average
what time does the first quarter moon rise
noontime average
what time does the full moon rise
6:00 pm average
what time does third quarter moon rise
midnight average
Why doesn't a lunar eclipse occur at every full moon and a solar eclipse at every new
moon?
The plane of the moon's orbit around the earth is tilted slightly (about 5 degrees) with
respect to the plane of the earth's orbit around the sun. An eclipse can occur only when the
new moon or full moon alignment of sun-earth-moon is also along the line of intersection of
the two planes (which doesn't happen at every new moon or full moon).
A cellular phone is actually a radio transmitter and receiver. You receive an incoming
call in the form of a radio wave at a frequency 880.65 MHz. What is the wavelength (in meters)
of this wave?
f = c / y
solve for wavelength
insert speed of light and frequency values
If you double the Kelvin temperature of a hot piece of steel, how much more energy will it
radiate per second?
Stefan-Boltzmann law; temmperature change to the fourth power
F = sigma T^4
The bright star Bellatrix in the constellation Orion has a surface temperature of
21,000 K. What is the wavelength of maximum emission in nanometers? What color is the
star?
ëmax = 0.0029 / T
as the equation stands, it will
provide us with the wavelength in meters, not nanometers. Dividing 0.0029 by the value of
T specified in the question, 21000 K, we get ëmax = 0.000000138 meters. To change this
into nanometers, we note that there are 109 nanometers (1,000,000,000) in one meter. So
if the wavelength is 0.000000138 meters, we have to multiply that number by
1,000,000,000 to get the number of nanometers. It comes out as
ëmax = 138.1 nanometers.
Why can radio astronomers make observations at any time during the day, whereas
optical astronomers are mostly limited to observing at night?
radio always works the same;
dont have to compete with suns light
Planets move about our sun
b. fastest when closest to our sun.
The gravitational attraction between an orbiting planet and our sun is greatest for
shorter distances.
A reporter once described a light-year as "the time it takes light to reach us traveling at
the speed of light." How would you correct this statement?
a light-year is a unit of distance, not of time. So a good definition would have to begin
with "A light-year is the distance..." Next, except when it is moving in a material medium, light
always travels at "the speed of light,"
A light-year is the distance that light travels in one year.
1 ly
9.46 x 1012 km.
When the Voyager 2 spacecraft sent back pictures of Neptune during its flyby of that
planet in 1989, the spacecraft's signals took 4 hours at the speed of light to reach earth. How far
away was the spacecraft? Give your answer in kilometers, using powers of 10 notation.
We can immediately say that the distance was 4 light-hours
1 light-year = 365 light-days = 365 x 24 light-hours = 8760 light-hours
(4 light-hours) / (8760 light-hours / light-year) =
0.000457, or, in powers of 10 notation, 4.57 x 10-4 light-years
The distance from Earth to Neptune is 43.2 x 108 km
How much force do you have to exert on a 3-kg brick to give it an acceleration of
2 m/s2 ? If you double this force, what is the brick's acceleration? Explain your answer.
This is a direct application of Newton's second law of motion. Starting with the law written in
its most common form,
F = m a ,
and substituting 3 kg for m and 2 m/s2 for a, we get
F = 3 kg x 2 m/s2 = 6 kg m/s2 = 6 newtons.
If you change the force by a factor of 2, then the right-hand side of the original equation has to
increase by a factor of 2 as well. Since we are not changing the mass at all, it has to be the
acceleration that increases by that factor of 2, so the new acceleration will be 2 x 2 m/s2 , which
gives the new acceleration to be 4 m/s2 .
Newton's second law of motion
F = m a
Compared to Earth's distance from the Sun, Jupiter's distance is about
50 times larger.
Since 1 AU is
distance sun to earth
If Neptune is 4 times larger than Earth and Mars is half the size of
Earth, the size comparison of Mars to Neptune is
Neptune is 8 times larger than Mars.
Neptune = 4 Earth
Mars = Earth / 2 (which gives Earth = 2 Mars)
Putting the second fact (Earth = 2 Mars) into the first gives us
Neptune = 4 (2 Mars) = 8 Mars.
What is an asteroid?
Asteroids are fairly small bodies orbiting the Sun mostly between the orbits of Mars and
Jupiter. tock.
Trans-Neptunian objects are
also small bodies, mostly in orbits beyond the orbit of
Neptune, in a region called the Kuiper Belt.
rock and ice
orbital period
P2 = a3, where P is the planet's period around the Sun and a is its average
distance from the Sun.
Explain how our current understanding of the formation of the solar system can
account for the following characteristics of the solar system: (a) All planetary orbits like in
nearly the same plane. (b) All planetary orbits are nearly circular. ( c ) The planets orbit the Sun
in the same direction in which the Sun itself rotates.
All three are consequences of Conservation of Angular Momentum and Newton's 2nd Law
of Motion. If the cloud of particles starts with the slightest amount of rotation, as
everything gets closer and closer together from the mutual gravitational pull, the rotational
speed increases (like the ice skater bringing her arms closer to her body as she spins, as
shown in class). Any particle that is not already in the "equatorial" plane will also have a
component of the mutual gravitational force toward the center of the cloud that is directed
toward the equatorial plane, unbalanced by any other force - so it eventually moves to that
plane.
P-type seismic waves will
pass through liquid, whereas S waves do not
Earth's inner core and outer core take up about
10% of Earth's volume.
At 0.5 the Sun's radius, the temperature is about
one-fourth of the core temperature.
Nearly all of the Sun's luminosity is generated within the inner
0.2 of the radius.
What is thermonuclear fusion?
Thermonuclear fusion is the combining of nuclei of lighter elements to form nuclei of heavier
ones - most importantly, in the stars, the combining of hydrogen nuclei to form helium nuclei.
What is a neutrino?
A neutrino is an elementary particle produced as a by-product of the radioactive process called
"beta decay," as well as other reactions that produce beta particles. It has zero charge, nearly zero
mass, and some intrinsic "spin" (angular momentum). First proposed as something that must
exist if several fundamental laws of physics were to be preserved in the beta decay process, they
were eventually detected experimentally, and because very important for a number of other kinds
of research
How do astronomers know when the next sunspot maximum and sunspot minimum will
occur?
a very regular cycle, approximately 11 years long. Unless strange, new phenomena are
seen to be occurring on the surface of the Sun, predicting the shape of the next cycle involves
simply extending the current pattern for another 11 years or so.
Why should solar flares and coronal mass ejections be a concern for businesses that use
telecommunication satellites?
These outbursts create strong electromagnetic waves that go out into
space, and, if strong enough, are capable of disrupting ordinary electromagnetic communications
by direct interference (static, for example) or, in extreme cases, by actually damaging some of the
more delicate electronic circuit elements (transistors, integrated circuits, etc.).
The horizontal axis of the H-R diagram is
c. either temperature or spectral class
The farther from the horizontal axis a star plots
luminosity or absolute magnitude
The luminosity of a star
is the power it is radiating
apparent brightness
how much of that power reaches an observer at a particular distance
Why does helium fusion require much higher temperatures than hydrogen fusion?
Helium nuclei have two positively-charged protons, so the electrical repulsion between two
helium nuclei is four times greater than the repulsion between single protons (hydrogen nuclei).
In order for helium nuclei to get close enough to one another to fuse, they have to be moving
toward one another at a much higher speed than two protons would have to, in order to overcome
the much stronger repulsion. Higher temperatures mean that the individual particles are moving
more rapidly, and that's what's needed to get helium nuclei to fuse.
What does it mean when an astronomer says that a star "moves" from one place to
another on an H-R diagram?
As the nuclear fuel in its core gets used up over time, a star's radius, temperature, and luminosity
all change. This means that it would be plotted on an H-R diagram with different values of the
quantities the diagram displays - luminosity and temperature - than it originally had. Plotting it
on the diagram with the changed values of these quantities means putting it at a different location
on that diagram.
How can an astronomer tell the difference between a planetary nebula and a planet?
They don't look at all alike, so it's very easy. A planet is a single, spherical object; a planetary
nebula is a wispy cloud of material, often very symmetrical and circular, but spread out in space
over a much larger radius than any planet.
What are the important thermonuclear reactions leading up to the formation of iron?
hydrogen,helium,carbon,neon,oxygen,silicon,core collapse, core bounce, explosive supernova
If the galaxy were spinning like a solid wheel, stars closest to the center would have
orbital velocities many times lower than the stars in the outer regions.
If the galaxy were spinning like our solar system, stars in the outer region would
have lower orbital velocities than those closer to the center.
Our galaxy has a characteristic rotation that is best described as
stars having similar orbital velocities regardless of their distance from the galactic
center.
The Sun's motion around the galactic center is measured by detecting and averaging
the Doppler
shifts of the spectra from distant stars not in our own galaxy.
What is the evidence that there is a supermassive black hole at the center of our galaxy?
How is it possible to determine the mass of this black hole?
x-rays coming from material being compressed and heated as it
falls into the black hole, and orbital motions of stars circling the black hole close to the galactic
center.
Elliptical galaxies have
no discernable spiral arm structure.
Why did many 19th century astronomers think that the "spiral nebulae" were part of the
milky way?
Before the Cepheid variable method had been discovered, so that distances to very far-away
objects could be determined easily and reliably, astronomers could only speculate on the
likelihood of the newly-discovered spiral objects being within the known grouping of stars or
being themselves entirely separate groupings of stars.
How did Edwin Hubble prove that the Andromeda "Nebula" is not a nebula within our
Milky Way Galaxy?
Cepheid Variable;
2.5 million light-years away, which is about 20 times further
than the diameter of the entire Milky Way Galaxy
Why are Type 1a supernovae useful for finding the distances to very remote galaxies?
simple relationship between their peak luminosity and the
rate that its luminosity then decays from the peak;
observing decay allows determination of luminosity
What evidence is there for the existence of dark matter in clusters of galaxies?
the motion of individual
galaxies in a cluster can only be explained if there is a lot more mass in and around the cluster
than can be seen in the form of visible matter.
Hubble's Law is expressed mathematically as
v = Hc d,
where v is the velocity with which a distant galaxy is
moving away from our own galaxy, H0 is "Hubble's constant," and d is the distance from our
galaxy to that particular distant galaxy.
If a galaxy was discovered to be the most distant ever observed, what would astronomers
notice about its spectra and speed?
Hubble's Law tells us that for the largest "d" observed, the "v" would also be the largest. This
means that this "most distant" galaxy would also be moving away from us at the largest speed of
all the galaxies yet observed.
In turn, the largest speed away from us would translate into the largest red shift in the measurable
spectra of any known galaxy.
Where is the center of the universe?
Nowhere. Hubble's Law applies no matter where an observer may stand
Imagine an astronomer living in a galaxy a billion light-years away. Is the observable
universe for that astronomer the same as for an astronomer on Earth? Why or why not?
As far as we can tell from all our observations, the over-all structure of the universe - mainly, the
distribution of galaxies - is the same everywhere.
What is the Cosmic Microwave Background?
The Cosmic Microwave Background is radiation that fills all space - it is the remnants of
radiation emitted at enormously high temperatures shortly after the big bang. Because the
universe has been expanding ever since, it has cooled to a very low temperature - wavelengths of
this radiation have become much longer - and the spectrum looks like a perfect black-body
radiation curve corresponding a temperature less than 3 Kelvin degrees above absolute zero.
The end result of the Miller-Urey experiment was the creation of
amino acids.
Miller and Urey energized the substances in their experiment using
electrical shocks, to simulate lightning.
What is meant by "life as we know it"? Why do astrobiologists suspect that
extraterrestrial life is likely to be of this form?
carbon-based life forms. Carbon is a common
element in the universe, forms strong bonds with other elements, and is one of the basic
components of organic molecules. Life
Viking Landers
testing for the presence of living or dormant microorganisms
Beagle 2
test for the presence of living or dead microorganisms
Kepler 1:
The planets move in elliptical orbits,
with the sun at one focus of the ellipse.
Kepler 2:
The orbital speed of a planet varies: when it is closer to the sun, it moves faster; when farther away, it moves slower, so that equal areas are swept out for equal times.
The
Kepler 3:
p^2 = a^3
ASTRONOMERS IN ORDER
Ptolemy;copernicus;kepler;galileo
Newton's first law
An object moves at a constant velocity
if there is no net force acting on it.
Velocity
direction as well as speed
Newton's second law
When an object experiences a force,
it is accelerated by an amount that depends directly on the force
and inversely on the object's mass
a = F ⁄ m.
Newton's Third Law
For every force that acts one object exerts on a second object, there is a reaction force on the first object due to the second that is equal in magnitude and opposite in direction.
The force needed in order to have an object moving in a circle has to be directed toward the
center of the circle.
centripetal
toward the center
The Law of Universal Gravitation
Everything in the universe is attracted to everything else by a force (which we call gravity), which has the following form:
F= G M1 M2 / Rsquare
STUDY GUIDE