final exam Flashcards
A star is 230 light-years away. The light we see tonight from that star left it
Because light travels a distance of one light-year in one year of time, it will travel a distance of 230 light-years in 230 years of time. This means that if we are receiving the light tonight, it has been traveling for 230 years from the source in order to reach us.
The point in the sky directly above your head at any given time is called the
zenith
The path that the Sun appears to make in the sky over the course of a year is called the celestial equator
FALSE
The great astronomer of ancient times who summarized and improved a system of circles upon circles to explain the complicated motions of the planets (and published the system in a book now called The Almagest) was
Ptolemy
The scientist who first devised experimental tests to demonstrate the validity of the heliocentric model of the solar system was
Galileo
The celestial sphere turns around once each day because
Our position on a rotating Earth causes the stars, planets, and Sun to appear to revolve around us.
Which ancient Greek thinker suggested (long before Copernicus) that the Earth is moving around the Sun?
Aristarchus i
In this diagram of the celestial sphere, there are five lines that point to different parts of the picture. Use the drag-and-drop environment to label the indicated parts of the figure.
The location of the figure defines which direction the zenith is located: always directly overhead of the observer. This point travels with the observer, in a sense, and the horizon with it since the horizon is 90° from the zenith in all directions.
The North Celestial Pole, on the other hand, is fixed against the background stars based on the direction our planet’s rotational axis points, so its position in one’s local sky may vary as a result of one’s location on the Earth’s surface, and the Celestial Equator with it since the Celestial Equator is 90° from the North Celestial Pole in all directions.
At the Earth’s equator, you would see the celestial poles on your horizon.
true
How did Eratosthenes measure the size of the Earth?
The memory aid “altitude = latitude” applies to the north celestial pole’s altitude as seen from a particular latitude on Earth, but the idea translates to observing the Sun as well. Although the Sun’s altitude from a particular latitude depends on the time of year, the difference between the observed altitude of the Sun from two latitudes at local solar noon, tells you the difference in latitude between those two locations.
Eratosthenes took advantage of this idea by comparing the altitude of the Sun h1
at noon as seen from his town (measured by observing the shadow cast by a pillar or post in the ground) with the altitude of the Sun h2
at noon as seen from a different town to the south. He recognized that the difference between the two observed altitudes compared to the full 360 degrees in a circle is equal to the distance between the two towns d
compared to the full circumference of the Earth C
:
h1−h2/360∘=dC
From this expression he was able to calculate the circumference of the Earth in the same physical units as the distance between the two towns.
In an ellipse, the ratio of the distance between the foci and the length of the major axis is called
eccentricity
remember newtons laws
ok
Consider an ellipse with a major axis of l = 6 cm and an eccentricity of e = 0.71.
Part (a) What is the length of the semimajor axis a
, in cm?
The semimajor axis a
of an ellipse is half the major axis; the eccentricity plays no role in this calculation.
a=l/2 =6 cm / 2
a=3.000 cm
Kepler’s third law relates a planet’s orbital period to the semi-major axis of the orbit.
TRUE
The diagram below shows the seasons that our planet Earth undergoes for the Northern Hemisphere. The position of the Earth is labeled for one of the key seasonal dates, the Autumnal (Fall) Equinox. Label the other three positions correctly. Note the blue arrow on the circle of the Earth’s orbit, which shows which way the Earth moves.
just google it
Which of the following statements about electromagnetic radiation is FALSE?
Not only are photons (the particles of light) massless, but they are also electrically neutral.
Which, from among the following options, has the longest wavelength?
The lowest-energy forms of light have the longest wavelengths. These forms of light include infrared waves, microwaves, and (at the absolute longest) radio waves.
A star has a surface temperature of 8800 K. At what wavelength (in nanometers) will it give off maximum light?
This form is useful when we are given a temperature in kelvins (K) or a wavelength in nanometers (nm). Since this is the case, we can solve for the temperature with a little algebra and plugging in the given value of the temperature:
λmax=2.9×10^6 nm⋅K/T
= 2.9×10^6 nm⋅K/ 8800 K
T=329.5 nm
Fill-in-the-blank
Understanding Blackbody Radiation: It turns out that stars behave like an idealized object that scientists call a blackbody. Thus, understanding blackbodies and how they give off energy helps us to understand how stars shine. For a blackbody, the higher its temperature, the smaller the wavelength at which it gives off the peak amount of radiation. This is described by wien’s law. Thus, really hot stars will shine most intensely with ultraviolet radiation. Also, the higher a star’s temperature, the greater the flux of radiation coming from it. This last statement is called stefan-Boltzman law.
For all electromagnetic waves, the frequency multiplied by the wavelength will be the same constant number.
True
fill in the blank
When someone who has never thought much about astronomy looks up at the sky, it’s easy to believe that everything turns around the Earth and that we are in the middle of things; such a view is called the geocentric model. Astronomers call the point in the sky above our heads our Zenith, and where the dome of the sky meets the Earth our Horizon. In the 20th century, astronomers divided the sky into 88 boxes, and each box is now called a Constellation. The belt of the sky through which the Sun, Moon, and planets are seen to move in the course of the day and the course of a year is called the Zodiac.
fill in the blank
If you were standing at Earth’s north pole, and you looked up to the zenith (the point directly above your head), you would be looking at the point where the North Celestial pole is located. At the Earth’s North Pole, the celestial equator would be at your Horizon . If, on the other hand, you were at the Earth’s equator, you would see one point of the celestial equator pass through your Zenith If you are looking at the sky from the continental United States, the north celestial pole would have an angular height (an altitude) equal to your Latitude. Right now, the star located very close to our north celestial pole is Polaris.
A light-year is
Equal to approximately 9.5 trillion km, or 5.9 trillion miles, the distance that light travels in one Earth year is a commonly-used unit of length or distance in astronomy.
A star is 230 light-years away. The light we see tonight from that star left it
Because light travels a distance of one light-year in one year of time, it will travel a distance of 230 light-years in 230 years of time. This means that if we are receiving the light tonight, it has been traveling for 230 years from the source in order to reach us.
The Astronomical Unit (AU) as defined by astronomers is
Astronomers defined this as a distance unit because the actual distance in any physical unit in use at the time was not known.
If a star is 900 light-years away, that means the light we see tonight left that star 900 years ago.
TRUE
By looking billions of light-years out into space, astronomers are actually seeing billions of years into the past.
TRUE
At the Earth’s equator, you would see the celestial poles on your horizon.
true
The Sun revolves around (orbits) the Earth in about 365 days (what we call one year.)
FALSE
We now know that the orbit of a stable planet around a star like the Sun is always in the shape of
ellipses.
When a planet, in its orbit, is closer to the Sun, it
moves faster (perihelion)
According to Kepler’s third law, there is a relationship between the time a planet takes to revolve around the Sun and the planet’s
Kepler’s 3rd law is written as an equation:
p^2=a^3
In this equation, p
corresponds to the orbital period, the time a planet takes to revolve around the Sun. The quantity a
corresponds to the average orbital distance from the Sun (the semimajor axis).
In words, this means that planets which orbit farther from the Sun on average have longer orbital periods.
Newton showed that to change the direction in which an object is moving, one needs to apply
Newton’s 2nd law of motion describes the means by which the motion of an object can be changed through the action of an outside force. Such a force, when applied to an object, produces an acceleration in that object that is inversely related to its mass (more-massive objects accelerate less under a given force than less-massive objects). Quantitatively, this takes on the equation form
F=ma
This acceleration can be a simple change in speed, a change in the direction of motion, or both.
Which of the following statements about the force of gravity is FALSE?
The force of gravity between two masses M
and m
whose centers are separated by some distance d
takes on the mathematical form
FG=GMm/d^2
By this description, increasing either term in the numerator (M
or m
) increases the gravitational force between the two objects. Increasing the denominator, on the other hand, decreases the strength of the force.
The figure to the right shows a set of ellipses. The ellipse on the top has a semimajor axis of 1 (in some arbitrary unit). The four choices below it in the grey region have their sizes shown (in the same arbitrary units). Based on the given semi-major axis for the orbit in the white region above, which of the lettered orbits would have the same orbital period?
Kepler’s 3rd law is stated most simply that there is a direct relationship between the orbital period p
of an object and the orbit’s semimajor axis a
:
p^2=a^3
The semimajor axis is half of the full length of the major axis, which means in this case that the orbit in question has a major axis of 2 units. An orbit that will have the same period, then, will also have a major axis of 2 units. Among the four choices shown, this corresponds to orbit d.
The number of degrees of arc that your location is north or south of the Earth’s equator is called your
Lines of latitude run east-west in parallel circles around the Earth, measuring an angle north or south from the Earth’s equator.
The “prime meridian” (where longitude equals zero) passes through
This city is the site of the Royal Observatory, in Greenwich, England.
To locate objects on Earth, we call the number of degrees east or west of the Greenwich Meridian its:
longitude
A solar day is slightly longer than a sidereal day.
true
How fast do electromagnetic waves travel?
Electromagnetic waves are the formal term for what we call “light” - which travels at the speed of light regardless of its energy.
The fastest speed in the universe is
Einstein’s theory of relativity says it the speed of light
Wien’s law relates the wavelength at which a star gives off the greatest amount of energy to the star’s
Wien’s law describes the relationship between the temperature of an object like a star and the wavelength at which it gives off the greatest amount of energy:
λmaxT=2.9×10^6 nm K
The Stefan-Boltzmann law relates the energy flux coming from a blackbody (such as a star) to its
The Stefan-Boltzmann law describes the relationship between the star’s temperature and its energy flux F
(power emitted per unit area):
F=P/A=σT^4
The larger spectrum at the top of the figure shown illustrates an absorption spectrum from a source that is stationary with respect to the observer (you). The black lines are the absorption lines in the spectrum, at specific wavelengths. Suppose instead that the source was actually moving away from you at a high speed. Which of the (smaller) lettered spectra would you expect the observed spectrum to resemble? (In this scenario, the large spectrum at the top is the emitted spectrum.)
The large spectrum that is shown is what is being emitted by the source. It would be the spectrum you would observe if there was no motion occurring. However, the scenario describes motion away from you, and such recessional motion introduces a redshift. The red end of the spectrum is the one where wavelengths are longer, so the spectrum you will observe is the one where the absorption lines have been shifted to the longer wavelength end - in this case, to the right.
The larger spectrum at the top of the figure shown illustrates an absorption spectrum from a source that is stationary with respect to the observer (you). The black lines are the absorption lines in the spectrum, at specific wavelengths. Suppose instead that the source was actually moving away from you at a high speed. Which of the (smaller) lettered spectra would you expect the observed spectrum to resemble? (In this scenario, the large spectrum at the top is the emitted spectrum.)
The large spectrum that is shown is what is being emitted by the source. It would be the spectrum you would observe if there was no motion occurring. However, the scenario describes motion toward you, and such approaching motion introduces a blueshift. The blue end of the spectrum is the one where wavelengths are shorter, so the spectrum you will observe is the one where the absorption lines have been shifted to the shorter wavelength end - in this case, to the left.
The larger spectrum at the top of the figure shown illustrates an absorption spectrum from a source that is moving with respect to the observer (you). The black lines are the absorption lines in the spectrum, at specific wavelengths.
Part (a) Suppose you were told that the source was moving toward you at a high speed. Which of the spectra below would you expect the actual emitted (rest-frame) spectrum to resemble? (In this scenario, the large spectrum at the top is the observed spectrum.)
The large spectrum that is shown is what is being observed from the source, and you know that motion is happening so you know it has been Doppler-shifted one way or the other. The scenario describes motion toward you, and such approaching motion introduces a blueshift. The blue end of the spectrum is the one where wavelengths are shorter, so the spectrum you are observing is one where the absorption lines have been shifted toward the shorter wavelength end - in this case, to the left. This means the original emitted spectrum was toward the right.
Not all wavelengths of electromagnetic radiation can penetrate the Earth’s atmosphere. Of the following types of waves that come from space, which one are you likely to be able to detect most easily from our planet’s surface?
Although our atmosphere is very effective at absorbing most forms of light, visible light and most radio wave light can penetrate to the surface - which is why radio telescopes do not need to be launched into space.
A carrier wave on a campus radio is broadcasting at a frequency f = 87.5 MHz. What is the wavelength λ
of the carrier wave of this radio, in meters?
The relationship between a light wave’s speed c
, its wavelength λ
, and its frequency f
, is given by
λf=c
so the wavelength can be found by using some algebra and plugging in the given values
λ=c/f. = (3×10^8 m/s)/87.5×10^6 Hz
The emitted infrared radiation from a dwarf planet has a wavelength of maximum intensity at λmax
= 72000 nm. What is the temperature T
, in kelvins, assuming it follows Wien’s law?
Wien’s law describes the relationship between the temperature T
of an emitting body and the peak wavelength λmax
of its spectrum
λmaxT=2.9×10^6 nm⋅K
This form is useful when we are given a temperature in kelvins (K) or a wavelength in nanometers (nm). Since this is the case, we can solve for the temperature with a little algebra and plugging in the given value of the peak wavelength:
T=2.9×10^6 nm⋅K/λmax =2.9×10^6 nm⋅K/ 72000 nm
T=40.28 K
To break up light into the component colors that it contains, astronomers use a device called
This device can use either a prism or a diffraction grating to reveal the spectrum, and goes by many names: spectrometer, spectrograph, or spectroscope.
What type of telescope can be used routinely on the surface of the Earth during the DAY?
Part (a) Please select the best choice from the available options.
a radio telescope
The most important function of an astronomical telescope is to
Telescopes function by making dim objects brighter and small features more easily resolved. In order to perform both functions, they must collect light and bring it to a focus.
Which of the following types of star is the coolest (has the lowest surface temperature)?
Part (a) Please select the best choice from the available options.
M
A star has a parallax of 0.11 arcsec.
Part (a) What is the star’s distance in parsecs?
Distance = 1/p
Distance = 1/0.11
Distance = 9.091
Tolerance: ± 0.27
Two stars have a magnitude difference of 0.75.
Part (a) How many times greater is the apparent brightness of the brighter star?
Number of times brighter = 100^(0.2mag)
Number of times brighter = 100^(0.20.75)
Number of times brighter = 1.995
Tolerance: ± 0.060
The amount by which the spectral lines of a star is redshifted tells astronomers how fast the star is moving away from us.
TRUE
Star A and Star B are located at different distances but have identical apparent brightnesses.
Part (a) If Star A is located 3
times farther away than Star B, how many times more luminous is Star A than Star B?
Factor = d^2
Factor = 3^2
Factor = 9.000
Tolerance: ± 0.27
Astronomers use the term interstellar matter to refer to:
gas and dust that lies between stars
Labeling
This diagram shows different kinds of light spectra. Please insert the correct labels for each part of the figure.
just look it up
Labeling
Shown here is the Orion Nebula. The photo shown here illustrates all three types of nebulae associated with regions where stars form.
look it up
An HII region is
a zone around a hot star where hydrogen atoms are ionized
The red color we see on a lot of photographs of nebulae comes from which element?
hydrogen
Why do all stars spend most of their lives on the main sequence?
because the fuel for energy production in this stage of the star’s life is hydrogen; and that is an element every star has lots and lots of
A type of star cluster that contains mostly very old stars is
a globular star cluster
Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen?
because such a star just cannot get hot enough for the fusion of heavier nuclei
When a single star with a mass equal to the Sun dies, it will become a
white dwarf
If you want to find stars that are just being born, where are the best places to search?
in giant molecular clouds
A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?
to the left
Astronomers identify the “birth” of a real star (as opposed to the activities of a protostar) with what activity in the star?
when nuclear fusion reactions begin inside its core
Labeling
On the H-R diagram shown, drag to each position the correct name or term in the early evolution of a 1 MSun star.
Part (a) Please use the drag-and-drop environment to label the missing parts of the figure.
look it up
Which of the following statements about the main sequence stage in the life of a star is FALSE?
main sequence stars are rare in the Galaxy, so we are lucky to be living around one
How long a main sequence star remains on the main sequence in the H-R diagram depends most strongly on
its mass
As a star becomes a giant, its outer layers are expanding. Where does the energy for expanding these layers come from?
from the fusion of hydrogen into helium in a shell around the core
The Life Stages of a Star
Note: Some words are missing from the following paragraph.
Like people, stars go through various distinct stages in their lives. For 90% of its life, each star is in the ______main sequence _______________________ stage, when it fuses hydrogen into helium and stays relatively stable. After the hydrogen hot enough for fusion is exhausted, the star’s core begins to collapse under its own weight, and fusion begins in a ______shell of hydrogen_______________________ outside the core. All the energy from this fusion pours outward and causes the outer layers of the star to _______expand ______________________. If the star is relatively low mass, the result (as seen from the outside) is a ___red giant__________________________ star. When this happens to the Sun, the new star will swallow the planet ______venus_______________________. Eventually, the collapsing core of the star will get hot enough for the next step in nuclear fusion, which astronomers call the _____triple alpha process________________________.
The Lives of Stars After the Red Giant Stage
Note: Some words are missing from the following paragraph
After the main sequence stage of a star’s life is over, the star undergoes some periods of instability. The swelling up of a star to become a red giant or red supergiant ends when the next step in fusion begins with the fusion of helium into the element __carbon_____. In low-mass stars, the entire core is ignited quickly in an event called the ___helium flash ________. In some stars, when the temperature is hot enough, another atom of helium can be added, to make the next element that is a product of fusion by helium, the element ____oxygen________. For low mass stars, the core temperature cannot rise further to make additional elements, and the star must soon die. The core (and the star along with it) now shrinks and heats up, and ejects a shell of material which begins to glow (energized by the ultraviolet light of the hot star). These glowing shells were given the misleading name of a ___planetary nebula___________. More massive stars, on the other hand, can continue to get their cores hotter, and to fuse even heavier elements, such as ____silicon__________ (which is common on Earth).
Ranking
Put the following in order of total Luminosity, from the least luminous to the most luminous:
look at exam 2 solutions
Identify
The figure shown below illustrates the evolutionary track of a low-mass star. Five points in its evolution are labeled A – E.
Part (a) Click the letter label that corresponds to the point in a star’s evolution where it is fusing hydrogen to helium in its core.
look at exam 2 solution
Identify
The figure shown below illustrates the evolutionary track of a low-mass star. Five points in its evolution are labeled A – E.
Part (a) Click the letter label that corresponds to the point in a star’s evolution where it will spend the most time.
ex 2
Identify
The figure shown below illustrates the evolutionary track of a low-mass star. Five points in its evolution are labeled A – E.
Part (a) Click the letter label that corresponds to the point in a star’s evolution where it is fusing hydrogen to helium in a shell around in an inert helium core.
ex 2
A star has a parallax of 0.11 arcsec. What is the star’s distance in parsecs?
What is the star’s distance in parsecs?
Distance = 1/p
Distance = 1/0.11
Distance = 9.091
Tolerance: ± 0.27
A particular star is 11 parsecs away from Earth. What will this star’s observed parallax be as seen from Earth? Express your answer in arcseconds.
p = 1/d
p = 1/11
p = 0.09091
Tolerance: ± 0.0027
A particular star has an apparent magnitude of +10.5
and an absolute magnitude of +2
.
Part (a) Calculate the star’s distance, in parsecs.
Distance = 10^((N1-N2+5)/5)
Distance = 10^((10.5-2+5)/5)
Distance = 501.2
Tolerance: ± 15
Part (b) Calculate the parallax such a star would exhibit.
Parallax = 1/10^((N1-N2+5)/5)
Parallax = 1/10^((10.5-2+5)/5)
Parallax = 0.001995
Tolerance: ± 6.0×10−5
A type of star that has turned out to be extremely useful for measuring distances is
the Cepheid variables
A light curve for a star measures how its brightness changes with
time
The higher the luminosity (intrinsic brightness) a Cepheid variable is,
the longer the period of its variations
One problem with Cepheid variable stars is that their period changes from year to year.
FALSE
All known Cepheid variable stars take less than 6 hours to go through one cycle of variations.
FALSE
For Cepheid variables, the longer the period, the greater the luminosity.
true
When a star settles down to a stable existence as a main-sequence star, what characteristics determines where on the main sequence in an H-R diagram the star will fall?
its mass
Which of the following stages will the Sun definitely go through as it gets older?
all these
When the mass of a star’s core is greater than 1.4 times the mass of the Sun, degenerate electrons can’t keep it stable as a white dwarf. Instead, it becomes:
a neutron star
Which of the following stages can only occur in the life of a low-mass star (whose final mass is less than 1.4 times the mass of the Sun)?
white dwarf
Ranking
The images shown illustrate several steps in the evolutionary cycle of a low-mass star. Arrange them in correct chronological order, from formation to death.
protostar< main sequence < red giant < planetary nebula< white dwarf
Ranking
The images shown illustrate several steps in the evolutionary cycle of a high-mass star. Arrange them in correct chronological order, from formation to death.
Part (a) Please use the drag-and-drop environment to label the missing parts of the figure from formation to death.
protostar< main sequence< red giant < supernova < neutron star
The maximum mass that a star can end its life with and still become a white dwarf is about 1.4 times the mass of our Sun.
true
A black dwarf is a white dwarf that has cooled down so much it gives off very little visible light anymore.
true
An H-R Diagram plots the luminosity of stars against their:
surface temperature
n an H-R diagram, where can you see the spectral type of a star (whether it is an O type star or a G type star, for example)?
along the bottom (the horizontal axis)
Measurements show a certain star has a very high luminosity (100,000 times the Sun’s) while its temperature is quite cool (3500 K). How can this be?
it must be quite large in size
question 15 on exam 2
HR diagrams
Imagine studying two stars which have identical luminosities but different spectral types. Which statement below will also be true about these two stars?
They have identical absolute magnitudes.
Imagine studying two stars which have identical spectral types but different luminosities.
Part (a) Which statement below will also be true about these two stars?
They have identical temperatures.
Imagine studying two main sequence stars which have different spectral types, but for which nothing else has been determined.
Part (a) Which statement below will also be true about these two stars?
They could have some similar spectral lines.
The amount of time a star spends on the main sequence depends on its mass, as shown in this table of main sequence lifetimes.
Part (a) How many times longer does a 1.1
-solar-mass star stay on the main sequence compared to a 3.3
-solar-mass star?
Factor = (9 * 10^9)/(500 * 10^6)
Factor = 18.00
Tolerance: ± 0.54
An astronomer wants to observe a cloud of cold neutral (not ionized) hydrogen, far away from any stars. What would be an instrument that could help in this task?
a radio telescope, tuned to a wavelength of about 21 centimeters
An HII region (emission nebula) is
a zone around a hot star where hydrogen atoms are ionized
17 and 19 on exam 2
look over that
Our Milky Way Galaxy is what type of galaxy?
spiral
The type of galaxy that consists almost entirely of old stars and is thus less blue (more yellow and reddish) than the other types is:
elliptical
Edwin Hubble developed a classification scheme for galaxies. By what characteristic did he classify galaxies?
their shape
After several decades of observation, astronomers have concluded that quasars are
very powerful and compact sources of energy at the centers of distant galaxies
Today, astronomers find compelling evidence that the energy source of the quasars and active galaxies is
matter falling toward a supermassive black hole at the center of a galaxy
Which of the following objects is considered useful to astronomers as a “standard candle” for determining distances?
white dwarf (type Ia) supernovae
Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the
the faster it is moving away from us
Suppose we measured the distance to a galaxy and it turned out to be 180 million light-years away. The galaxy’s redshift tells us its recessional velocity is 5,000 km/s. If the Hubble constant was determined merely from measurements of this galaxy alone, what would we find it to be in km/s per million light-years?
Constant = 5000/d
Constant = 5000/180
Constant = 27.78
Tolerance: ± 0.83
A line in the absorption spectrum of hydrogen from a quasar has a wavelength of 543 nm. At rest (in an Earth laboratory, for example) that same line has a wavelength of 486 nm. What is the redshift, z of this quasar?
z = (n-486)/486
z = (543-486)/486
z = 0.1173
Tolerance: ± 0.0035
A quasar is moving away from us at v/c=0.8
What will the redshift of this quasar be measured as?
Redshift = sqrt((1+0.8)/(1-0.8))-1
Redshift = 2.000
Tolerance: ± 0.060
The reciprocal of the Hubble constant (1/H) is a rough measure of the:
the age of the universe
If the expansion of the universe were accelerating, it would mean that distant Type Ia supernovae would look fainter than we would expect from measuring their redshifts and applying Hubble’s law.
true
As the universe expands, the temperature throughout the universe increases regularly.
false
The figure here shows an exaggerated version of the modern Hubble diagram revealed by the Hubble Space Telescope. The blue dashed boxes correspond to two regions on this diagram we will compare.
top right
All the evidence currently suggests that we live in closed universe.
false
The latest conclusion that astronomers have reached about the expansion of the universe is that the rate at which space is expanding is decelerating – that is, the expansion is slowing down due to the pull of gravity.
false
Recent observations indicate that the universe is expanding faster today than it was a few billion years ago (that, in other words, the expansion of the universe is accelerating.) What kind of observations have led astronomers to this surprising conclusion?
the measurement of galaxy distances using white dwarf (type Ia) supernovae
The cosmic microwave background is
microwave radiation coming from all directions that is the redshifted afterglow of the Big Bang.
The cosmic microwave background has a temperature of 2.725 K
. Calculate its peak wavelength, in millimeters.
Wavelength = 2898/2.725/1000
Wavelength = 1.063
Tolerance: ± 0.032
According to our textbook, roughly what percent of the mass and energy contents of the universe is made up of dark matter plus dark energy?
95 percent
