124 terms

Astronomy 102: exam #2: Ch. 4-6&8

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What is the fundamental law of physics that allowed the planets to form, rather than having all of the material simply fall into the Sun?
Conservation of Angular momentum.
Our planetary system is believed to have originated in a disk of gas and dust that surrounded the Sun shortly after the Sun formed. Such disks around young stars are
An observational fact, having been observed around other stars in our Galaxy.
What are the most abundant elements in the solar system?
Hydrogen and helium, as shown by the great mass and low density of the giant planets
The early universe appears to have contained only light elements, predominantly hydrogen and helium, and yet we now see significant amounts of heavier elements in stars and planets and our own bodies. Where did these heavy elements originate?
In nuclear fusion in the deep interiors of stars and in violent explosions of massive stars (supernovae)
Life as we know it either requires oxygen to survive or produces it. How common is oxygen in the universe, compared to hydrogen?
There is one oxygen atom for every 1200 hydrogen atoms.
After hydrogen and helium, what is the next most abundant element in the universe?
Oxygen, the most important element in rocks and minerals
-Yes. Oxygen is slightly more abundant than carbon and significantly more common than iron.
The ages of lunar rocks, brought back to Earth by astronauts and robotic spacecraft, have been determined by measuring the
relative concentrations of radioactive elements.
The age of the solar system has been measured by radioactive dating. Which of the following objects gives the most precise value for this age?
The oldest meteorites
How many (and which) of the following methods have been used successfully to find planets around stars other than the Sun?
(1) Directly photographing a planet near a star.
(2) Measuring the "wobble" in the star's motion caused by an orbiting planet.
(3) Measuring the decrease in brightness of a star as a planet transits in front of it.
All three of these methods have been used successfully to find planets.
-Yes. All three methods have been used successfully. For example, the Kepler space mission has discovered several planets using the transit method and is predicted to discover hundreds more.
An amateur astronomer is using a telescope that has a 50-cm focal length objective lens and an eyepiece with a 2-cm focal length. His sister is using a telescope with an objective lens having twice the focal length and an eyepiece of half the focal length. What overall magnifying power does his sister's telescope have compared to his own?
Four times the magnifying power (two divided by one-half equals four)
An amateur astronomer has a telescope with an objective lens whose diameter is 20 cm and focal length is 100 cm. What focal length of eyepiece is required in order to obtain a magnification of 50X ("50 power")?
2 cm.
Many fortunate amateur astronomers have telescopes with primary mirrors 20 cm in diameter. The Keck telescopes on Hawaii have mirrors 10 m in diameter. How much more light is collected by one of the Keck telescopes, compared to an amateur's telescope?
2500 times more
Which of the following sentences CORRECTLY describes an advantage of a large refracting telescope over a large reflecting telescope?
A refracting telescope has no obstruction that blocks part of the light entering the telescope.
-Yes. There are no obstructions to block the light in a refracting telescope, whereas large reflecting telescopes have a secondary mirror or a detector mounted inside the telescope that blocks some light and slightly reduce the quality of the image.
If a particular telescope suffers from coma, what will you see when you look through the telescope?
Images near the edge of the field of view are blurred even when the images at the center of the field are in focus.
-Yes. Coma affects light paths at an angle to the central axis, and therefore it causes distortion of images away from the center of the field of view.
Spherical aberration in the primary mirror of a reflecting telescope is generally avoided by
making the mirror surface a parabolic shape.
In the primary mirror of a reflecting telescope, light of different wavelengths, such as red and blue light from a star, are focused
at the same point.
The so-called seeing effect on the image of an astronomical source that causes "twinkling" of the image is produced by what effect in the Earth's atmosphere?
Refraction of light by turbulent currents of air of differing density
The best available technique for achieving better angular resolution in large, ground-based reflecting telescopes -- known as adaptive optics -- is to
rapidly change the tilt and shape of an intermediate mirror.
What is the main reason why electronic CCD cameras (and also photographic film) are superior to the human eye for studying astronomical objects through telescopes?
They are able to store and integrate light for a long period, whereas the eye clears images several times a second.
-Yes. Integration, or continuous collection, is a major advantage, allowing much fainter objects to be detected than could be seen by a person looking through the same telescope by eye.
What is used in modern astronomical spectrographs to disperse the light into its different wavelengths (colors)?
A diffraction grating.
Radio astronomy and optical astronomy each have attractions over the other. Which one of the statements below is correct?
Radio astronomers can observe the universe day and night, whereas optical astronomers (except for solar observers) have to work primarily at night.
What is involved in the astronomical technique of interferometry?
Combining signals from two or more widely spaced telescopes that are observing the same object
-Yes. This technique results in greatly improved angular resolution, allowing much finer detail to be seen, and is widely used at radio wavelengths at present.
What is the PRIMARY reason why astronomers combine the signals from several radio telescopes placed at widely separated locations around the Earth?
To attain much better angular resolution than is possible with a single telescope
To which of the following types of electromagnetic radiation is the Earth's atmosphere transparent?
Radio waves with wavelengths of 10 cm to 10 m
Which of the following objects is most likely to be studied in infrared light?
Dust disks around the stars
X-ray telescopes in space use
tubular-looking mirrors that utilize grazing reflection.
-Yes. X rays striking at grazing incidence can be reflected, so a sequence of slightly conical-shaped tubes can focus a beam of X rays.
X-ray telescopes in space are used primarily for examining which kind of environment in the universe?
Extremely hot regions around stars and galactic centers, as well as the hot gas that is present in clusters of galaxies
-Yes. X rays are produced only from hot regions in space, such as the outer corona of stars and the near vicinity of black holes at galactic centers.
The first person to prove that light does not travel at infinite speed was
Olaus Romer.
A flash of light is transmitted simultaneously through two parallel tubes of length 1 km long, one evacuated, the other filled with water. Detectors sense the arrival times of the light flash at the ends of these tubes. What will be the relationship between arrival times of these light flashes?
The flash will arrive earlier through the evacuated tube.
-Yes. Light travels slower through water than through a vacuum.
If an electrically charged object is moving at a constant speed in a constant direction, what characteristic does it have that it would not have if it were stationary?
A magnetic field
In a vacuum, blue light differs from red light in that
blue light has a higher frequency than red light.
-Yes. Blue light frequencies are about twice those associated with red light.
A perfect blackbody
absorbs all energy falling upon it and emits a characteristic spectrum of radiation whose intensity as a function of wavelength depends only on its temperature.
-Yes. The intensity of radiation at all wavelengths increases, and the peak of emitted spectrum moves toward the blue as the blackbody temperature increases.
As an asteroid moves out into deep space after coming close to the Sun, the peak wavelength of its emitted electromagnetic radiation will
increase from infrared toward microwave wavelengths while the intensity of the radiation decreases at all wavelengths.
Yes. The asteroid will become cooler as it moves away from the Sun, so the peak wavelength will increase as described by Wien's law and the intensity will decrease at all wavelengths. Wien's law states that the peak wavelength is inversely proportional to the temperature.
Suppose the Sun has a temperature of 17,400 K (three times its present temperature) but is the same size as it is now. How much more energy would the Sun emit per second?
81 times more
Suppose a light source is emitting red light at a wavelength of 700 nm and another light source is emitting ultraviolet light at a wavelength of 350 nm. Each photon of the ultraviolet light has
twice the energy of each photon of the red light.
Yes. Photon energy varies inversely with the wavelength. Each ultraviolet photon has half the wavelength of a red-light photon, so it has 1/(½) = 2 times the energy.
In a beam of radiation from a blackbody, the amounts of energy per second at an ultraviolet wavelength of 300 nm and at an infrared wavelength of 800 nm are found to be equal. In this beam, how do the numbers of photons per second at each of these wavelengths compare?
There will be more infrared photons than ultraviolet photons.
Spectral lines were first discovered by
Fraunhofer, by a close examination of the spectrum of the Sun using a prism to spread out this spectrum.
Yes. Fraunhofer made his discovery in 1814, 43 years before Kirchhoff saw emission lines in laboratory flames.
The presence of dark lines in the solar spectrum, the so-called Fraunhofer lines, means that
a cooler layer of gas overlies the deeper, hotter layers of the solar atmosphere.
The person who first showed that most of the mass of an atom is concentrated in a very small volume at the center of the atom was
Rutherford
Elements that have similar chemical properties in the periodic table of elements
are in a single vertical column.
-Yes. The periodic table is organized so that chemically similar elements are in the same column.
An electron is added to a completely ionized hydrogen atom to make it electrically neutral. How much extra mass is added to the atom in this process, expressed as a fraction of the final mass?
0.05%
Tritium is a radioactive form of hydrogen in which the nucleus contains one proton and two neutrons. How much more massive is this nucleus than that of ordinary hydrogen?
Three times as massive
The metal nickel (Ni) occupies position number 28 in the periodic table. How many electrons will need to be removed from a neutral nickel atom to completely ionize it, leaving only a nucleus?
28
In order to produce the primary H-alpha (Hα) Balmer spectral line in emission, an electron must jump between which two energy levels in the hydrogen atom?
from n = 3 to n = 2
When a source of light is moving away from the observer, the wavelength of the detected light is shifted with respect to the emitted or rest wavelength. The size of this shift in wavelength is described by the Doppler effect and is equal to the
Value of the rest wavelength times the ratio of the speed if the source to the speed of light.
-Yes. The shift is dependent upon wavelength and upon the ratio of the speed of the source to that of light.
Retrograde motion of a superior planet occurs when Earth catches up to and passes the superior planet. Suppose a superior planet completes its orbit in exactly 18 months (sidereal period). How many months will elapse between a time when Earth passes this planet and the next time it does so?
36 months
Tycho Brahe proved that the heavens are not permanent and unalterable by showing that a "new star" exhibited no measurable _______ as Earth rotated around its axis.
Parallax
The existence of which of the following was first predicted using Newton's law of motion and gravitation before it was found in the sky?
Neptune
In Ptolemy's description of the solar system, an _____ is a small circle around which a planet moves while the center follows a large circle around Earth.
Epicycle
Suppose an asteroid is discovered in a circular orbit around the sun. The radius of its orbit is four times the radius of Earth's orbit. What is the period of the asteroid's motion around the Sun?
8 years.
The moon has less mass than Earth, and it exerts
the same force on Earth as Earth exerts on it.
Copernicus realized that the planets do not move uniformly at constant speed across the sky. How did he account for this variation in his model of the solar system?
He introduced epicycles for the inner and outer planets
A comet enters the solar system. Assume that it is influenced only by the sun, not by any of the planets. Which statement about its orbit is correct?
Its orbit might be an ellipse, or it might be a parabola or a hyperbola (because a comet is not necessarily confined to the solar system forever).
Retrograde motion
would be seen for Earth if viewed from Jupiter.
Kepler's law in their general forms apply universally, whenever two objects orbits each other under _____ attraction.
Gravitational.
What is the phase of the Moon at a time of spring tide, when the tides have their greatest heights?
Either new moon or full moon.
What condition describes the position of greatest elongation for an inferior planet in our solar system? (Drawing a diagram might be useful.)
The angle between the Earth-planet line and the planet-sun line is 90 degrees.
The observation of Tycho Brahe of a bright ______ in 1577 was significant because it showed almost no parallax (apparent relative motion), which proved it to be more distant than the moon.
comet
_____ tides occur on Earth at locations opposite the Moon because the Moon's gravity is weaker on the opposite side of Earth and doesn't pull the oceans down as hard, so they bulge up.
High
Jupiter is seen at its highest in our sky at midnight when it is at
Opposition.
In the geometric model of the solar system, the maximum fraction of Venus' surface which is illuminated as seen from Earth is _____.
half
The phase of the moon at a time of spring tide, when the tides have their greatest heights, is either new moon or _____ moon.
Full.
How did Tycho Brahe prove that the heavens are not permanent and unalterable?
A "new star" appeared in the sky, and he showed that the star exhibited no measurable parallax as Earth rotated around its axis.
The existence of the planet ______ was first predicted using Newton's law of motion and gravitation, before it was found in the sky.
Neptune
The reason why tides occur on Earth is that the
gravitational force exerted on Earth by the moon decreases with increasing distance from the moon.
How many forces are acting on the space shuttle when it is in a circular orbit around Earth? (ignore forces from very distant objects, such as the sun and moon)
One force, acting toward the center of Earth.
The sidereal period of Jupiter is almost twelve years. Its synodic period is
slightly longer than one year.
The escape speed of an object from Earth depends on each of the following except one. Which does it not depend upon?
The mass of the object.
The orbiting object stays in orbit because
it has forward motion that keeps it from hitting Earth as it falls.
Kepler described how a planet motion speeds up as it nears the sun by his concept of "equal areas in equal _____"
times
According to the Greek geocentric model, Earth's rate of rotation on its axis is
zero.
The very successful Ptolemaic model that described and predicted the apparent motions of planets, assuming them to orbit Earth, had each planet moving
in a small circle, the center of which was moving around Earth more slowly in a larger circle.
The synodic period for a planet is different from its sidereal period because Earth (and hence the observer).
moves
Around 1800, Thomas Young conducted an important experiment that helped to decide the question about the nature of light in favor of the wave model. This experiment centered on
interference.
The wavelength of the peak in the sun's output spectrum is about 500 nm. If the Sun's surface temperature doubled, what would this peak wavelength become?
250 nm.
Compare two electron transitions in hydrogen: n=1 and n=2 -> n=1. The transition which produces the photon with the larger energy is the one which begins at level n= ____.
3
In Galileo's attempt to measure the speed of light by timing the passage of flashes of light between adjacent hilltops, what would have been the light travel time between Galilio and his assistant if the hills had been 3 km apart? (His assistant's reaction time would have had to have been much less than this time interval for this experiment to have been successful!)
10^-5 SECOND OR 10 us.
If an object is a perfect blackbody, then it emits
energy with a continuous distribution that peaks at a certain wavelength dependent on temperature.
A blackbody is surrounded by a low density cloud of material. If we look directly at the blackbody through the low-density cloud we will see a(n) _______ spectrum.
Absorption line.
Lord Rutherford sent a beam of alpha particles to collide with a thin gold foil. Why was he surprised at the result?
He expected the mass in the gold foil to be more or less evenly distributed so that all the alpha particles would pass through and none would be reflected from the foil.
Olaus Romer measured the speed of light by observing
the moons of Jupiter.
If an object is a perfect _______, then it emits energy with a continuous distribution that peaks at a certain wavelength dependent on temperature.
blackbody
One beam of pure light has a high frequency and a short wavelength, while a second pure beam has a low frequency and a long wavelength. A photon from the high frequency beam has ____ than a photon from the low-frequency beam.
more energy
A star is found to be moving across our sky at a small fraction of the speed of light in a direction at right angles to the line from the star to the Earth. The Doppler shift of the spectrum of the light from this star is
zero for all wavelengths because the star is moving perpendicular to the line sight.
What was the very first observation that showed conclusively that light travels at a finite speed (not infinite fast)?
Eclipses of Jupiter's moons, when they moved into or out of Jupiter's shadow, appeared to occur later than they should when Jupiter was farther away from Earth.
As a star increases in _______, the visible spectrum it produces changes from red to red plus green to red plus green plus.
temperature
A hot, dense gas produces
a continuous spectrum, with energy emitted at every wavelength.
An object is moving toward us at a great speed. Therefore, the light it emits is Doppler shifted to
bluer, higher frequencies.
The diameter of your finger is a centimeter or two. What type of electromagnetic has a wavelength this size?
Microwave.
Two stationary objects are radiating as blackbodies. They are the same size and shape, but one appears blue and the other appears red. Therefore, the temperature of the red one is _________ than that of the blue one
cooler
The ______ series of hydrogen spectral lines arises from transitions between the ground state (N= 1 energy level) and higher energy levels
lyman
We observe the spectrum of light emitted from a hot source. As the temperature of the source increases, the
wavelength at which the peak intensity of the spectrum occurs decreases, shifting toward the blue end of the spectrum.
Which one of the following statements about photons is correct?
The color of a beam of light is determined by the energy of the individual photons of which he beam is composed
An atom of singly ionized magnesium has 12 photons in its nucleus. How many electrons surround this nucleus?
11
Historically, the ______ nature of light was first demonstrated by the interference produced when light passes through a double slit.
wave
When heated in a flame, a small quantity of a chemical element emits light only at specific wavelengths. The pattern of these spectral emission lines as a function of wavelength
is characteristic for each element but differs from element to element.
One blackbody is a 6000 K and a second blackbody is at 3000 K. How many times more energy is radiated by the hotter object than the cooler one?
16.
Which of the following groups are all examples of electromagnetic radiation?
X-rays, radio waves, infrared radiation.
Two freshly made iron horseshoes are hanging in a blacksmith's shop. One is still too hot to touch, the other has cooled to room temperature. The atoms in the ______ horseshoe are moving faster than those in the cooler one.
hot
The first person to show the light traveled in photons, in which the energy of a photon depends on its wavelength was
Albert Einstein
The ___________ effect is emission of electrons from a metal surface when it is illuminated by light.
Photoelectric
The very first observation that showed conclusively that light travels at a finite speed (not infinitely fast) was when Jupiter's moons moved into or out of Jupiter's shadow later than they should when Jupiter was farther away from _________.
Earth
The English physicist ______ showed in 101 that light behaves as a wave by shining light through two closely spaced slits and observing the resulting pattern of light on a white screen.
Thomas Young
The sodium D lines are a closely spaced pair of spectral lines from Na I (neutral sodium). They are present as absorption lines in the spectrum of the Sun's photosphere because of traces of sodium there. What would you expect to see if sunlight is passed through a cool sodium vapor in the laboratory and then observed with a spectrometer?
The sodium D lines become darker.
Through which of the following materials does light travel fastest?
Vacuum.
The blackbody is surrounded by a low density cloud of material. If we look directly at the blackbdy through the low density cloud we will see a(n)
absorption line spectrum.
The rear brake lights on a car emit white light but are covered with plastic that allows only pure red light to pass through. What color of plastic would the red light have to pass through in order to emerge as green light?
There is no color plastic which will turn pure red light into green.
The ______ of beam of light is determined by the energy of the individual photons of which the beam is composed.
color
The spectrum of radiation emitted by a dense, opaque object depends mostly on its
Temperance.
What illumination is placed on the possible wavelengths of electromagnetic radiation by Maxwell's equations, the equations which govern the behavior of this type of radiation?
There are no wavelength limits, either long or short.
The photoelectric effect is the
emission of electrons from a metal surface when it is illuminated by light.
The advantage of replacing of a spherical mirror with a parabolic mirror is that
all rays striking a parabolic mirror from a direction parallel to the optic axis of the telescope reflect to a common focus.
To compensate for atmospheric distortion using adaptive optics, a bright object must serve as a target. How is this accomplished?
Lasers are used to excite sodium atoms in the upper atmosphere to glow and serve as a target.
Telescopes with objective lenses or mirrors larger than about 10 cm diameter cannot achieve their theoretical diffraction-limited resolution without using extraordinary techniques such as active or adaptive optics. Which of the following phenomena is not a factor that would reduce the resolution of a telescope?
Light pollution.
Interferometry is done with radio telescope to improve the _______ of images.
Resolution
Which type of telescope uses a parabolic concave primary mirror and a smaller convex secondary mirror, arranged to reflect light back through a hole in the primary mirror?
Cassegrain telescope
How sharply we can resolve the images of stars viewed from Earth is limited by the stability of the _________.
Atmosphere.
A __________ is a rectangular array of tiny, photosensitive, semiconducting wafers.
Charge-coupled device
An x-ray telescope work when the x-rays strike a conical surface at ______ incidence and are reflected forward to detector at the focal plane.
grazing
Reflecting telescopes
are the design of choice for all large modern telescope.
A ________ grating, used in spectroscopy, is a piece of glass or metal on which many closely spaced grooves have been cut.
Diffraction
Which of the following is the least important feature of modern astronomical research?
4
Looking at objects through eyepieces.
Astronomers use a _______ to measure the distribution of intensity of light over a continuous range of wavelengths, or colors.
Spectrograph
The reason we have space-based x-ray observatories is
x-rays cannot penetrate Earth's atmosphere.