Homework 2,3,4

Flashcard maker : Kaiya Hebert
Kepler found the orbits of planets are ellipses, not circles.
The orbits of most of the planets have eccentricities close to zero.
Kepler based his theories on the precise planetary observations of Tycho Brahe.
The eccentricity of a perfectly circular orbit is 1.
Kepler determined the shape of each planet’s orbit by triangulation from different points on Earth’s orbit, using observations made at many different times of the year.
Mercury, with a higher eccentricity orbit, should change its orbital speed more than do Venus or Earth.
A planet (or comet) will speed up as it approaches the Sun
Transits of Venus were critical in early determinations of the A.U.
Newton’s Laws completely replaced the incorrect work of Kepler.
Newton’s modification of Kepler’s Third Law lets us measure the mass of the Sun.
Kepler’s first law worked, where Copernicus’ original heliocentric model failed, because Kepler described the orbits as
elliptical, not circular.
Tycho Brahe’s contribution to Kepler’s Laws of Planetary Motion were
his detailed and accurate observations of the planet’s position.
The most famous prehistoric astronomical observatory is:
A circular orbit would have an eccentricity of
Upon which point do Copernicus and Kepler disagree?
The orbits of the planets are ellipses, with one focus at the Sun.
What contribution to astronomy was made by Tycho Brahe?
His observations of planetary motion with great accuracy proved circular orbits could not work
Which concept was NOT a part of Kepler’s Laws of Planetary Motion?
Epicycles are needed to explain the varying brightnesses of the planets.
According to Kepler’s third law, the square of the planet’s period in years is:
proportional to the cube of its semimajor axis in A.U.
What does Kepler’s third law imply about planetary motion?
Planets further from the Sun orbit at a slower speed than planets closer to the Sun.
A planet whose distance from the Sun is 3 A.U. would have an orbital period of how many Earth-years?
The place in a planet’s orbit that is closest to the Sun is called
An accurate sketch of Jupiter’s orbit around the Sun would show
a nearly perfect circle.
A calculation of how long it takes a planet to orbit the Sun would be most closely related to Kepler’s
third law of planetary distances.
An asteroid with an orbit lying entirely inside Earth’s
has an orbital semimajor axis of less than 1 AU
If Earth’s orbit around the Sun were twice as large as it is now, the orbit would take
more than two times longer to traverse.
Kepler’s second law of planetary motion states that a planet in orbit around the Sun will do which of the following?
Sweep out equal areas in equal times
How does orbital speed at aphelion compare to the speed at perihelion?
According to Kepler’s second law, as a planet or other object moves around its orbit, it sweeps out equal __________ in equal __________.
areas / times
According to Kepler’s second law, planets and other objects orbiting the Sun move fastest when they are __________.
nearest to the Sun
ccording to Kepler’s second law, as a planet or other object moves around its orbit, it sweeps out equal __________ in equa
Kepler’s third law states that for any planet orbiting the Sun, the orbital period squared (p2 ) is equal to the average orbital distance cubed (a3 ), or p2 = a3 . This implies that _____
a planet with a large average distance from the Sun has a longer orbital period than a planet with a smaller average distance from the Sun
Today we rely largely on what technique to precisely measure distances in the solar system?
adar echo timings
Newton’s gravity would explain why Saturn, so far from the Sun, moves so slowly across the sky.
It the mass of a body were doubled, its gravity would become 4 × stronger.
According to Newton’s second law, if you double the force acting on a body, the acceleration will double.
The force of gravity varies with
both product of the two masses and inverse square of the distance separating the two bodies
The Law of Universal Gravitation was developed by:
How does Newton’s Universal Law of Gravitation explain Kepler’s laws?
Universal gravitation implies that the planets will sweep out equal areas in equal times (Kepler’s second law) &
Universal gravitation implies that the planets further from the Sun will move more slowly than the planets closer to the Sun
If the distance between two asteroids is doubled, the gravitational force they exert on each other will
be one fourth as great.
According to Newton’s second law, the greater the force exerted on an object, the greater the object’s _____.
Escape velocity is the speed required to
overcome the graviational pull of an object.
Combining Newton’s and Kepler’s laws, we can weigh the Sun, provided we know:
the size of the A.U. and exact length of the year.
Kepler’s second law implies what about planetary motion?
A planet moves faster when it is closer to the Sun.
If the Sun and its mass were suddenly to disappear, Earth would
fly off into space.
What would happen to the orbits of each of the planets if the force of gravity was suddenly “turned off”?
Each would move off in a different straight line.
In what way did Newton improve Kepler’s laws?
He discovered the dependence on mass in the third law.
For an object in a circular orbit, how does the velocity depend on the radius of the orbit?
It is inversely proportional to the square root of the radius.
According to Newton, planets orbit in ellipses with what at the two foci?
The center of mass and nothing
Radio waves, visible light, and x-rays are all a type of electromagnetic radiation
You would perceive a change in a visible light wave’s amplitude as a change in its color.
The frequency of a water wave gives us its height.
Gamma Rays are a type of electromagnetic radiation.
If a new wave arrives on shore every two seconds, then its frequency is 2 Hz.
The greater the disturbance of the medium, the higher the amplitude of the wave.
As white light passes through a prism, the red (longer) wavelengths bend less than the blue (shorter) wavelengths, so forming the rainbow of colors.
A wave’s velocity is the product of the
frequency times the wavelength of the wave.
While gravity is always attractive, electromagnetic forces are always repulsive.
Both sound waves and electromagnetic radiation
transfer energy.
Which of these is constant for ALL types of electromagnetic radiation in a vacuum?
Which statement gives the relationship between the waves in the electric and magnetic fields in an electromagnetic wave?
They are in phase but perpendicular to each other in space.
Electromagnetic radiation
can behave both as a wave and as a particle.
Of all the forms of electromagnetic radiation, the one with the lowest frequency is
radio waves.
The two forms of electromagnetic radiation that penetrate the atmosphere best are:
visible and radio waves.
The hottest objects with temperatures in the millions of degrees Kelvin, give off most of their radiation in which part of the electromagnetic spectrum?
X-ray telescopes are located in orbit around the Earth because
x-rays don’t reach the surface of Earth.
The visible color of electromagnetic radiation that has the shortest wavelength is
Colors appear different to us because of their photons’ different:
There are no x-ray telescopes on Earth because
x-rays don’t penetrate Earth’s atmosphere
The radiation our eyes are most sensitive to lies in the color
yellow-green at about 550 nm.
Which type of radiation can be observed well from Earth’s surface?
A blue star has a higher surface temperature than a red star.
Wein’s law relates the peak wavelength of the blackbody to its size. The larger the black body, the shorter its peak wavelength.
According to Wein’s law, the higher the surface temperature of a star, the redder its color.
What is true of a blackbody?
Its energy peaks at the wavelength determined by its temperature.
According to Wien’s law, the hottest stars also have
the shortest peak wavelength.
A star much cooler than the Sun would appear
An observer will measure the wavelength of waves emanating form a source that is moving away as longer than it really is.
The Doppler Effect is a phenomenon that allows one to measure an object’s
radial motion.
The light from an object moving tangentially (to your left or right) will exhibit
no shift.
If a light source is approaching you at a speed very close to the speed of light, it will appear
bluer than it is.
Electromagnetic waves can travel through a perfect vacuum.
A blackbody emits all its radiation at a single frequency.
The Doppler effect occurs for all types of wave motion.
As you drive away from a radio transmitter, the radio signal you receive from the station is shifted to longer wavelengths.
Two otherwise identical objects have temperatures of 1000 K and 1200 K, respectively. The object at 1200 K emits roughly twice as much radiation as the OBJECT AT 1000 K
Only a hot, thin gas can produce an emission line.
The absorption lines for a cool thin gas are identical in color and energy to the emission lines of the same gas if hot enough to glow.
The spectral lines of each element are distinctive to that element, whether we are looking at emission or absorption lines.
A low density gas must be hot in order to produce an absorption line.
What is spectroscopy?
an analysis of the way in which atoms absorb and emit light
Typical stellar spectra appear as:
a rainbow, but with some dark lines mixed in.
Which of these is the classic continuous spectrum?
a rainbow
The Orion Nebula, M-42, is a hot, thin cloud of glowing gas, so its spectrum is:
a few bright lines against a dark background.
The three laws dealing with the creation of various spectra are due to:
The Fraunhofer lines in the solar spectrum are actually:
absorption lines due to the thin outer layer above the photosphere.
The element first found in the Sun’s spectrum, then on Earth 30 years later, is
An incandescent light (glowing tungsten filament) produces:
a continuous spectrum, with the peak giving the temperature of the filament.
A neon light (thin hot neon gas in a sealed tube) gives us:
a few bright emission lines, telling us the gas is neon.
Compared with a spectrum from a ground-based observation, the spectrum of a star observed from above Earth’s atmosphere would show
slightly fewer absorption lines.
The visible spectrum of sunlight reflected from Saturn’s cold moon Titan would be expected to be
absorption spectrum.
Compared with a star having many blue absorption lines, a star with many red and blue absorption lines must be
of different composition than that of the other star.
What type of spectrum is emitted by a low-density luminous cloud of hot gases?
A cool, dilute gas between an observer and a continuous hot source will produce which of the following effects?
Dark absorption lines will appear in the spectrum.
Which of the following statements about the visible spectrum of the light emitted by the Sun is true?
It consists of hundreds of dark absorption lines superimposed on a bright continuous spectrum that peaks in the yellow, near the center of the VISIBLE LIGHT
An x-ray photon has more energy than a visible photon.
All wavelengths of light travel at the same speed in a vacuum, and carry the same energy per photon.
The red hydrogen alpha line carries more energy per photon than the blue-green hydrogen beta line does.
The Balmer lines of hydrogen involve electron transitions from the ground state to higher levels.
In the Bohr model, the transitions of electrons down to ground state produce the Lyman lines in the ultraviolet.
The shorter a wave’s wavelength, the greater it’s energy.
In the atom, which particles gives the element its identify (atomic number)?
High temperatures, rotation, and magnetic fields all tend to broaden spectral lines.
An electron moves to a higher energy level in an atom after absorbing a photon of a specific energy.
Light behaves both as a wave and as a particle.
Fraunhofer lines are emission lines in the solar spectrum.
Spectral lines of hydrogen are relatively weak in the Sun because the Sun contains relatively little hydrogen.
An electron can have any energy within an atom, so long as it is above the ground-state energy.
The energy of a photon is inversely proportional to the wavelength of the radiation.
In our Sun, the spectral lines of hydrogen are weak, compared to their appearance in hotter stars.
The line intensity of a spectrum depends both on the abundance of a particular element and its temperature as well.
The broader the spectral line, the higher the pressure of the gas that is creating it.
The radial velocity of a star’s motion in space can also broaden its spectral lines.
The Zeeman effect reveals the presence of strong magnetic fields by the splitting of spectral lines.
The Doppler effect can reveal the rotation speed of a star by the splitting of the spectral lines.
Spectroscopy of a star can reveal its temperature, composition, and line-of-sight motion.
The larger the red shift, the faster the distant galaxy is rushing toward us.
If a fire truck’s siren is rising in pitch, it must be approaching us.
What does a blueshifted spectrum indicate?
The source is moving toward you.
Astronomers analyze starlight to determine a star’s
Compared with slowly rotating stars, the fastest spinning stars have absorption lines that are
broad and fuzzy.
Which of the following can not be determined directly from spectral-line analysis?
Which of the following cannot be determined spectroscopically?
Transverse motion
It was the Chinese who provided critical ancient data on supernovae and comets.
Was it possible for the geocentric system of Ptolemy to explain the observed retrograde motion of the planets?
Yes, through a system of epicycles and deferents
Planets near opposition
rise in the east.
The Ptolemaic model of the universe:
explained and predicted the motions of the planets with deferents and epicycles.
The greatest contribution of the Greeks to modern thought was:
the development of scientific inquiry and model building.
The Ptolemaic model probably persisted for all these reasons EXCEPT:
it accounted well for Galileo’s observations of the phase cycle of Venus.
The most accurate Greek attempt to explain planetary motion was the model of:
The principal culture that transferred Greek astronomical knowledge to Renaissance Europe was:
Like the Sun and the Moon, the stars appear to move from west to east from one day to the next.
Like the Sun and the Moon, the planets always appear to move from west to east from one day to the next.
When a planet retrogrades, it appears to move westward for weeks at a time.
As originally stated, the Copernican model did no better a job of predicting planetary behavior than did the Ptolemaic ONE
Scientists today do not accept the Ptolemaic model because:
the work of Tycho and Kepler showed the heliocentric model was more accurate.
On which of these assumptions do Ptolemy and Copernicus agree?
All orbits must be perfect circles.
The heliocentric model was actually first proposed by:
According to Copernicus, the retrograde motion for Mars must occur
at opposition, when the earth overtakes Mars and passes between Mars and the Sun.
Which was a contribution to astronomy made by Copernicus?
He laid out the order and relative motion of the known solar system.
Which of these was NOT a part of the original Copernican model?
Mercury speeds up at perihelion, and slows down at aphelion.
Which of the statements below is part of both the Ptolemaic and Copernican models?
The Moon orbits the Earth once a month.
A major flaw in Copernicus’s model was that it still had
circular orbits.
Which of the following is NOT true about the solar system model of Copernicus?
It used elliptical orbits for the motions of the planets.
Who proposed the geocentric view that was accepted and used for more than 18 centuries?
The solar system models developed before Kepler’s time assumed that the planets followed __________.
circular orbits & Kepler determined that the planetary orbits are elliptical.
Stellar parallax is the _____ in a star’s position with respect to more distant background stars, which occurs as the location of the observer changes.
Galileo’s observations of the entire phase cycle of Venus proved that Ptolemy’s epicycles could not be correct in keeping Venus between us and the Sun.
Galileo’s observations of sunspots proved the Sun was rotating, like the Earth.
Which of the following is a contribution to astronomy made by Galileo?
Which of these observations of Galileo refuted Ptolemy’s epicycles?
the complete cycle of Venus’ phases
A fatal flaw with Ptolemy’s model is its inability to predict the observed phases of
Mercury and Venus.
Galileo found the rotation period of the Sun was approximately
A month
Which of the following was not one of the discoveries made by Galileo?
The shape of an orbit is an ellipse. This discovery was made by Kepler.
The Sun is highest in the sky at __________.
Venus’s phase is new as viewed from Earth when __________.
Venus is directly between Earth and the Sun
For Venus to appear high in the sky at midnight, it would have to be __________.
For Venus to be high in the sky at midnight, it would have to be on the opposite side of our sky from the Sun. But that never occurs, because Venus is closer than Earth to the Sun.
In Ptolemy’s Earth-centered model for the solar system (not shown), Venus always stays close to the Sun in the sky and, because it always stays between Earth and the Sun, its phases range only between new and crescent. The following statements are all true and were all observed by Galileo. Which one provides evidence that Venus orbits the Sun and not Earth?
We sometimes see gibbous (nearly but not quite full) Venus.

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