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Worksheetsast 104 exam 2 hw questions david jeffery
Total questions: 137
Worksheet time: 34hrs 15mins
“Let’s play Jeopardy! For $100, the answer is: In modern physics, it is the highest physical speed: i.e., the highest speed at which information can propagate.”
What is the speed of (BLANK) , Alex?
sound
thought
rumor
light in vacuum
At fireworks displays, the explosions produce a light flash and sounds.
The sound is heard before the flash is seen.
The flash is seen before the sound is heard.
Sound and flash come simultaneously.
The sound is seen before the flash is heard.
(BLANK) is a form of electromagnetic radiation.
Sound
Wien
Doppler
Visible light
Visible light is conventionally divided into:
violet, blue, green, yellow, orange, radio.
X-ray, violet, blue green, yellow, orange, tangerine, red.
Gamma-ray, X-ray, ultraviolet, visible, infrared, microwave, radio.
violet, blue, green, yellow, orange, red.
Electromagnetic radiation (EMR) is:
a WAVE PHENOMENON. The EM waves, however, are NOT EXCITATIONS OF A MEDIUM as in most other familiar wave phenomena: e.g., sound waves are excitations of air; water waves of water. The EM waves are just self-propagating electromagnetic fields: any description of them as oscillations in a medium has turned out to be physically superfluous: i.e., adds nothing to physical understanding. Of course, EM waves can propagate through media such as air, water, glass, etc. The speed of light IN VACUUM is 2.99792458×1010 cm/s ≈ 3×1010 cm/s. In matter, the speed of light is always HIGHER.
a WAVE PHENOMENON. The EM waves, however, are NOT EXCITATIONS OF A MEDIUM as in most other familiar wave phenomena: e.g., sound waves are excitations of air; water waves of water. The EM waves are just self-propagating electromagnetic fields: any description of them as oscillations in a medium has turned out to be physically superfluous: i.e., adds nothing to physical understanding. Of course, EM waves can propagate through media such as air, water, glass, etc. The speed of light IN VACUUM is 2.99792458×1010 cm/s ≈ 3×1010 cm/s. In matter, the speed of light is always LOWER.
a WAVE PHENOMENON. The EM waves are excitations of the ETHER. The ether permeates all space and has no other effects than as the medium of the EM propagation. Of course, EM waves at the same time as propagating in the ether can also propagate through media such as air, water, glass, etc. The speed of light IN VACUUM is 2.99792458×1010 cm/s ≈ 3×1010 cm/s. In matter, the speed of light is always LOWER.
a WAVE PHENOMENON. The EM waves are excitations of the ETHER. The ether permeates all space and has no other effects than as the medium of the EM propagation. Of course, EM waves at the same time as propagating in the ether can also propagate through media such as air, water, glass, etc. The speed of light IN VACUUM is 2.99792458×1010 cm/s ≈ 3×1010 cm/s. In matter, the speed of light is always HIGHER
AM radio typically broadcasts at about 1 MHz = 106 cycles per second. What is the approximate wavelength of this radiation? (Just use the vacuum speed of light c = 2.99792458 × 1010 cm/s for the calculation: it is good enough for the present purpose.)
∼ 3 × 104 cm = 300 m.
∼ 1 × 104 cm = 100 m.
∼ 3 × 10−4 cm
∼ 3 × 104 m.
The electromagnetic spectrum is:
the distribution of electromagnetic radiation with respect to temperature.
the spectrum of radiation emitted by a non-reflecting (i.e., blackbody) object at a uniform temperature.
the entire wavelength range of electromagnetic radiation: i.e., the electromagnetic radiation range from zero to infinite wavelength, not counting the limit end points themselves.
the magnetic field of the Sun.
What is the form of electromagnetic radiation that is usually most dangerous for life?
gamma-rays.
protons.
radio waves.
visible light.
The wavelength range of visible light is about:
1–20 cm.
0.1–10 nm.
400–700 nm.
700–1000 nm.
Astronomers must observe the gamma-ray, X-ray, and most of the ultraviolet bands from space since the Earth’s atmosphere is quite (BLANK) in those bands.
transparent
window-like
hot
opaque
The Earth’s atmosphere has various windows in which it is relatively transparent to electromagnetic radiation. The visible window extends from the very near ultraviolet to the near infrared. The intensity maximum of the solar spectrum actually falls in this window. Now the human eye is sensitive to electromagnetic radiation in the wavelength band ∼ 400–700 nm which falls in the visible window and which spans the maximum intensity region of the solar spectrum. Why might the human-eye sensitivity wavelength region be located where it is?
Well the visible window is round and so is the eye.
The eye may have evolved to be sensitive to the form of radiation that was LEAST ABUNDANT on the Earth’s surface. In this way radio emission for communication would be unnecessary, except during geomagnetic storms. Finally, the conclusion has to be that X-rays are not ordinarily visible
The eye may have evolved to be sensitive to a form of radiation that was ABUNDANT on the Earth’s surface thereby making a BAD USE of the electromagnetic radiation resource.
The eye may have evolved to be sensitive to a form of radiation that was ABUNDANT on the Earth’s surface thereby making a GOOD USE of the electromagnetic radiation resource.
Why do nocturnal animals usually have large pupils in their eyes?
For better vision in DAY conditions (when light levels are high) they have evolved large pupils (which are the apertures of the eyes). Light gathering power is proportional to the SQUARE OF APERTURE DIAMETER.
For better vision in NIGHT conditions (when light levels are low), they have evolved large pupils (which are the apertures of the eyes). Light gathering power is proportional to the SQUARE OF APERTURE DIAMETER
For better vision in NIGHT conditions (when light levels are low), they have evolved large pupils (which are the apertures of the eyes). Light gathering power is proportional to the APERTURE DIAMETER.
For better vision in NIGHT conditions (when light levels are low), they have evolved large pupils (which are the apertures of the eyes). Light gathering power is proportional to the 4TH POWER OF APERTURE DIAMETER
The quantum or “particle” of light is called a/an:
proton.
electron.
quarkon.
photon.
The “particle” of light is the photon. The energy of an individual photon is inversely proportional to the wavelength of the light. The formula for photon energy is
E = hc λ ,
where h is a universal constant called Planck’s constant, c is the vacuum speed of light, and λ is wavelength. If the wavelength of light is changed by a multiplicative factor of 3, the energy of its photons is changed by a multiplicative factor of:
1/3.
3.
9.
1/9.
The Moon has almost no atmosphere. In what wavelength bands could an astronomer observe space from the Moon?
In the ultraviolet and X-ray only.
In no bands at all.
In nearly no bands at all.
In practically all bands.
An ion is a:
synonym for an atom.
neutral atom.
charged atom.
molecule.
Internal energy or heat energy is:
statistically distributed forms of the other kinds of energy: most notably microscopic kinetic energy, microscopic potential energy, and electromagnetic radiation.
temperature.
the opposite of cold.
the microscopic cause of friction.
Any body (including a cloud of dilute gas) at a non-zero temperature or range of temperatures will radiate (in addition to any reflected light):
a pure line spectrum.
a perfect blackbody spectrum.
only X-rays.
electromagnetic radiation.
A solid, liquid, or dense gas at a uniform temperature (in addition to any reflected light) will:
radiate a line spectrum.
radiate a greybody spectrum
radiate a blackbody spectrum which is a fundamentally important spectrum whose shape depends only on the absolute (i.e., Kelvin scale) temperature of the radiating body.
have a uniform color that depends only on the shape of the radiating body.
Wien’s law for blackbody spectra is
λ max micron = 2897.7729 µm K T .
Say one has a stellar spectrum with a maximum wavelength at 0.5 µm (i.e., 0.5 microns). What is the star’s approximate photospheric temperature?
600 K.
6000 K.
20000 K.
31416 K.
The line spectrum of an atom, ion, or molecule is:
an almost unique identifier of the atom, ion, or molecule.
the radiation emitted when the temperature of the atom, etc., goes over 1000 K.
the radiation emitted when the temperature of the atom, etc., goes over 10,000 K.
the radiation emitted when the temperature of the atom, etc., goes over 25,000 K.
The layer of a star (e.g., the Sun) from which most of the emitted electromagnetic radiation comes is called the:
photosphere.
chromosphere.
hemisphere.
core.
The Sun emits a spectrum that is approximately a blackbody spectrum. It isn’t exactly a blackbody spectrum because, among other reasons,:
the photospheric emission forms over a range of temperatures and there is an EMISSION LINE SPECTRUM superimposed on the photospheric emission.
the photospheric emission forms over a range of temperatures and there is an ABSORPTION LINE SPECTRUM superimposed on the photospheric emission.
the photospheric emission forms at a single temperature.
the coronal emission is almost equal to the photospheric emission.
The Hα line (AKA the H-alpha line), usually the strongest VISIBLE line of hydrogen, has a wavelength of 656 nm It is (BLANK) a/an line.
X-ray
ultraviolet
radio
red
A true blackbody absorbs all the electromagnetic radiation that hits it (i.e., it does not reflect any electromagnetic radiation) and has a uniform temperature. Let us treat the Earth as blackbody, except that it reflects that fraction of light that it actually does reflect. The light gathering surface area of the Earth is πR2 ⊕ , where π ≈ 3.1416 is pi, a pure number, and R⊕ is the Earth radius. The total light energy gathered per unit time by the Earth is thus f(1 − a)πR2 ⊕ , (1) where f = 1367.6 watts per square meter is the mean solar constant and (1 − a) = 0.694 is a factor accounting for the reflection of electromagnetic radiation from the Earth (Wikipedia: Earth: Bond albedo). As a blackbody (except for the reflection correction), the Earth radiates a total energy per unit time of AσT 4 , (2) where A = 4πR2 ⊕ 5 is the surface area of the Earth and σT 4 is the Stefan-Boltzmann law (i.e., the energy radiated per unit area per unit time by a blackbody). The constant σ = 5.670373 × 10−8 in mks units. Since the Earth is neither a net energy gainer or loser (at least not to an extent important for this problem), expression (1) must equal expression (2) to maintain a constant thermal energy content on Earth. Equating the expressions, we obtain: f(1 − a) = 4σT 4 or T = f(1 − a) 4σ 1/4 = 254 K . This temperature is called the blackbody or effective temperature of the Earth.
At 254 K the Earth would be way hotter than the boiling point of water. The reason the Earth isn’t this hot is because the Earth is not actually a blackbody.
At 254 K the Earth would be colder than the freezing point of water. The reason the Earth isn’t this cold is because of the greenhouse COOLING effect.
At 254 K the Earth would be colder than the freezing point of water. The reason the Earth isn’t this cold is because of the greenhouse HEATING effect.
At 254 K the Earth is at a comfortable temperature for life. Our simple analysis shows why life is possible on Earth. The same analysis for Venus and Mars would show why life as we know it would be unlikely there. Both Venus and Mars would be too cold. (Venus would be too cold despite being located closer to the Sun because of its high reflectivity.)
The Doppler effect for light causes:
the wavelength of a wave phenomenon to change (or shift) when its SOURCE AND RECEIVER are moving with respect to each other along the source-receiver line
the wavelength of a wave phenomenon to change (or shift) when its SOURCE (but NEVER its RECEIVER) is moving along the source-receiver line.
the wavelength of a wave phenomenon to change (or shift) when its RECEIVER (but NEVER its SOURCE) is moving along the source-receiver line.
the Sun to appear redder at sunset and sunrise than at midday.
One light source is moving directly away from you; another light source is moving exactly perpendicular to your line of sight to it for the length of time of the observation: i.e., its moving on a CIRCLE centered on you.
The first source is Doppler shifted to the RED (i.e., to longer wavelength). The second source is NOT significantly Doppler shifted unless its velocity is not small compared to the vacuum speed of light.
The first source is Doppler shifted to the BLUE (i.e., to shorter wavelength). The second source is NOT significantly Doppler shifted unless its velocity is not small compared to the vacuum speed of light.
NEITHER source is Doppler shifted. There can only be a Doppler shift if the velocity is specified in the problem
BOTH sources are Doppler shifted to the RED by about the same amounts.
The lines of atomic line spectra are not infinitely narrow in wavelength. There is a natural intrinsic width which is broadened by thermal and collisional effects. But let’s ignore those effects for this question. How would an atomic line from a rapidly rotating star appear different from the same atomic line as measured in the laboratory?
The star line would be divided into three lines: a fast line, a slow line, and an intermediate line.
The star line would NARROWER due to the Doppler effect.
The star line would be BROADER due to the Doppler effect. The part of the star moving toward the observer would broaden the line in the LONG WAVELENGTH (REDWARD) DIRECTION. The part of the star moving away from the observer would broaden the line in the SHORT WAVELENGTH (BLUEWARD) DIRECTION.
The star line would be BROADER due to the Doppler effect. The part of the star moving toward the observer would broaden the line in the SHORT WAVELENGTH (BLUEWARD) DIRECTION. The part of the star moving away from the observer would broaden the line in the LONG WAVELENGTH (REDWARD) DIRECTION.
The diameter of the Sun is about:
1 Earth diameter.
30 Earth diameters.
109 Earth diameters.
1 astronomical unit.
The solar luminosity is L⊙ is:
100 W.
3.846 × 10^−26 W.
3.846 × 10^26 W.
1.496 × 10^11 m
The temperature of the solar photosphere is about:
300 K.
600 K.
273 K.
6000 K.
“Let’s play Jeopardy! For $100, the answer is: It is the electromagnetic radiation energy per unit time per unit area from the Sun at 1 astronomical unit from the Sun.”
What is the solar (BLANK), Alex?
wind
variable
eclipse
constant
The solar constant (i.e., the electromagnetic radiation energy per unit time per unit area from the Sun at 1 astronomical unit from the Sun) is:
1367.6 W/m^2 .
1000.00 W/m^2 .
0.
−1367.6 W/m^2 .
The solar constant (i.e., the electromagnetic radiation energy per unit time per unit area from the Sun at 1 astronomical unit from the Sun) is about 1367.6 watts per square meter. If you were at 1 astronomical unit from the Sun in space and had a square kilometer of solar panels (of 100 % efficiency), how many 100 watt light bulbs could you run on solar power?
1.3676 × 10^11.
1000.
1367.6.
1.3676 × 10^7 .
“Let’s play Jeopardy! For $100, the answer is: This astrophysical body has three main interior layers: 1) a core (in which thermonuclear reactions occur) that extents out to about 25 % of the body’s radius; 2) a radiative transfer zone which extends OUT to about 71 % of the body’s radius; 3) a convective zone that extends FROM about 71 % of the body’s radius to the body’s surface.”
What is (BLANK), Alex.
the Moon
Venus
the Milky Way
the Sun
Out to about 71 % of the Sun’s radius, the dominant energy transfer mechanism is:
electron conduction.
neutrino transfer.
radiative transfer (i.e., transfer by electromagnetic radiation).
convection.
Why can’t we see deeper into the Sun than the photosphere?
Line spectra overlap too severely at deeper layers.
The question is absurd. We see right through the photosphere to the bottom of the convection layer.
Radiation from deeper layers escapes too easily.
Radiation from deeper layers is absorbed before it can escape the Sun.
A granule is:
a kind of cereal.
a grain of dust.
the top of a rising current of HOT gas in the Sun. Granules are seen in the solar photosphere. They last about 10 minutes and then lose their identity with their surroundings. The risen gas COOLS and then sinks.
the top of a rising current of COLD gas in the Sun. Granules are seen in the solar photosphere. They last about 10 minutes and then lose their identity with their surroundings. The risen gas HEATS up and then sinks.
The five outermost layers of the Sun (defining layers of the Sun generously) can be labeled:
convection zone, photon, chromosome, coronation street, and solar sail.
convection zone, photosphere, chromosphere, corona, and solar sail.
convection zone, photosphere, chromosphere, corona, and solar wind.
convection zone, photon, chromosome, corona, and glabron.
Two of the five outermost layers of the Sun (defining layers of the Sun generously) are:
photosphere and chromosphere.
carnation and corona.
corona and paloma.
rio and sands.
The corona of the Sun is only visible to the naked eye:
at sunset.
when the Moon is a crescent in the western sky
during partial solar eclipses.
during total solar eclipses.
The solar corona has no sharp boundary, but it has been traced out to about 30 solar radii. The Sun’s equatorial radius is 6.96342×108 m and the astronomical unit in meters is 1.49597870700×1011 m. How far has the corona been traced out in astronomical units and does this trace of the corona reach to the orbit of Mercury which has a mean radius of 0.38709893 AU?
0.387 AU and yes.
0.14 AU and yes.
0.14 AU and no.
0.387 AU and no.
The solar wind is:
the air that blows off the northern hemisphere oceans during geomagnetic storms.
the plasma gas that cools the Sun’s photosphere.
the plasma gas that streams from the Sun out into INTERSTELLAR SPACE.
the plasma gas that streams from the Sun out into INTERGALACTIC SPACE.
The solar wind is a stream of particles that moves approximately along radial paths outward from the Sun: inward is the negative direction and positive is the outward direction. The solar wind near the Earth is typically moving at a radial velocity of about:
−200 km/s.
−200 m/s.
400 to 500 km.
400 to 500 km/s.
The Sun loses mass at a rate of about 2 × 109 kg/s. Convert this rate into solar masses per year to the same number of significant figures as given. NOTE: The mass of the Sun is M⊙ = 1.9885 × 1030 kg and the length of a year in seconds to 0.5 % accuracy is π × 107 s.
a) 2 × 10^30 kg/yr.
2 × 10^−30 M⊙/yr.
3 × 10^14 M⊙/yr.
3 × 10^−14 M⊙/yr
Stars are spheres:
of hot gas.
with a core of solid iron and a hydrogen outer layer.
with a core of liquid iron and a hydrogen outer layer.
with a core of pure helium gas and a hydrogen outer layer.
The Sun’s surface composition by mass (which approximates the average cosmic composition and is typical of non-ancient stars) is about:
71 % hydrogen, 27 % nitrogen, and 20 % everything else.
71 % carbon, 27 % nitrogen, and 2 % everything else.
71 % hydrogen, 27 % nitrogen, and 2 % everything else.
71 % hydrogen, 27 % helium, and 2 % everything else.
“Let’s play Jeopardy! For $100, the answer is: The angular motion of stars on the sky as seen against the background of more distant stars due to the Earth’s motion around the Sun.” What is (BLANK) , Alex?
the Doppler shift
planetary parallax
stellar parallax
stellar paradox
Van Maanen’s star has a stellar parallax of 0.232 arcseconds. About how far away is this star? Recall the distance formula for stellar parallax is
dparsec = 1/ θarcsecond
, where θarcsecond is the parallax angle in arcseconds and dparsec is the distance in parsecs.
0.232 pc.
1 pc.
4.3 pc.
2.32 pc.
The closest star to Earth (not counting the Sun) is (BLANK) at 1.30 pc (4.22 ly).
Barnard’s Star.
Jeffery’s Star.
Sirius A.
Proxima Centauri.
If all the stellar parallaxes (i.e., parallax angles measured during a half revolution of the Sun) were INCREASING with time, this would mean that the stars were all:
getting smaller.
moving away
getting dimmer.
moving closer.
A dim star is located at about 2 million astronomical units from Earth. Recall 1 AU = 1.496 × 10^11 m and 1 pc = 3.09 × 10^16 m. Approximately, what is the distance to the star in parsecs?
1.5 × 10^11 pc.
2 × 10^6 pc.
3 pc.
10 pc.
In galaxy collisions, direct star-star collisions in which star matter impacts star matter occur:
very rarely because interstellar distances are very large compared to star sizes.
with high frequency.
never.
never: such collisions are physically impossible.
Because gravity is a long-range, inverse-square-law force, significant gravitational interactions between two stars:
almost never occur.
are relatively common.
never occur.
occur only when the star matter impacts on star matter.
The total power of a star (i.e., energy output per unit time) is called:
brightness.
rightness.
lightness.
luminosity.
The brightest stars are of order (BLANK) times more luminous than the Sun and the dimmest are of order (BLANK) times the Sun’s luminosity.
10^−4 ; 10^6
1/2; 2
infinite; zero
10^6 ; 10^−4
“Let’s play Jeopardy! For $100, the answer is: This is the energy per unit time per unit area OR the energy per unit time per unit area in some wavelength band OR the energy per unit time per unit area per unit wavelength (or frequency) from some light source (e.g., a star or the Sun).”
What is (BLANK), Alex?
fugue
flow
luminosity
flux
The light from astronomical bodies is often studied by observering their light flux in BROAD wavelength bands using colored filters. (The emission is usually reported in astronomical magnitudes, but one doesn’t need to know that.) The study of emission in this way is called:
spectroscopy.
optometry.
trigonometry.
photometry.
The flux (energy per unit time per unit area perhaps in a wavelength band or per wavelength) of light from a star as a function of distance from the star in the absence of extinction by the interstellar medium obeys a/an:
inverse-cube law.
reverse-cube law.
gravity law.
inverse-square law.
“Let’s play Jeopardy! For $100, the answer is: The inverse-square law describing how the light flux from a star decreases with distance is proven from THIS general physical principle when applied to a star and its surrounding vacuum space in a steady state condition.”
What is the (BLANK), Alex?
principle of equivalence
cosmological principle
perfect cosmological principle
conservation of energy principle
If you knew the luminosity of a star, then it distance could be determined directly:
from its luminosity alone.
a measurement of its flux using the inverse-cube law.
a measurement of its flux using the inverse-square law.
a measurement of its flux using any inverse power formula.
According to one standard reference, the solar luminosity L⊙ = 3.846 × 1026 W http://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html 2013 and the solar constant (i.e., the solar flux at the mean distance of the Earth) f = 1367.6 W/m2 . Stellar luminosity L and flux f are related by the inverse-square law f = L 4πd2 , where d is the distance from the center of the star to the location where f is measured. Solve for d analytically and then find mean Earth-Sun distance.
d = p L/(4πf) and d = 1.496 × 1011 m.
d = p L/f and d = 1.496 × 1011 m
d = √ L and d = 1.496 × 102 m.
d = p L/(4πf) and d = 1.496 × 102 m.
“Let’s play Jeopardy! For $100, the answer is: This metaphorical expression is the name for the collection
of distance measurement techniques used to establish cosmic distances on all scales.”
What is the (BLANK), Alex?
Gandalf distaf
distance distaff
distance adder
distance ladder
The first rung of the distance ladder is uses the distance measurement technique of:
stellar parallax.
spectrosoopic parallax.
Cepheids.
the Tully-Fisher relation.
The surface (i.e., photosphere) temperature of an ordinary star can be determined from:
the shape of its NON-BLACKBODY spectrum (particularly the location of the peak).
an analysis of its EMISSION line spectrum.
no known means.
the shape of its approximately BLACKBODY spectrum (particularly the location of the peak) and/or an analysis of its ABSORPTION line spectrum.
The surface (i.e., photosphere) temperature of an ordinary star can be determined by:
measuring its mass.
identifying its luminosity class.
identifying its spectral type.
any means at all.
The main sequence spectral star types are:
OBIWANKEN.
OBAFGKM.
OBGKMAF.
OAGKMAO.
“Let’s play Jeopardy! For $100, the answer is: Each stellar spectral types is divided into these subtypes.”
What are (BLANK), Alex?
0 Ia, Ib, II, III, IV, V, VI, VII
Chico, Groucho, Gummo, Harpo, Karlo, Zeppo
Larry, Curly, and Moe
0, 1, 2, . . . , 9
The Sun’s spectral type is:
G2.
red giant.
A−.
Z9.
The hydrogen Balmer lines in main sequence stars:
always increase in strength with increasing temperature.
are strongest at surface temperature of order 10, 000 K.
always decrease in strength with increasing temperature.
cannot be seen at all.
The approximate colors of the hydrogen Balmer lines Hα, Hβ, Hγ, and Hδ are, respectively:
blue-green, red, violet, and blue-violet.
red, blue-green, blue-violet, and violet.
red, white, blue, and mauve.
rouge, mauve, lime, and tangerine.
“Let’s play Jeopardy! For $100, the answer is: It is a plot of stellar luminosity (or absolute magnitude) versus star temperature (or spectral type).”
What is a (BLANK), Alex?
butterfly diagram
Hertz-Avis (HA) diagram
mass-luminosity diagram
Hertzsprung-Russell (HR) diagram
The main sequence on a Hertzsprung-Russell (HR) diagram is a curve (actually a narrow band) of (BLANK) luminosity with increasing (BLANK).
increasing; surface temperature
decreasing; surface temperature
constant; surface temperature
increasing; hydrogen content
Main sequence stars, giants, supergiants, and white dwarfs all give rise to easily identifiable groups on a:
Hertzsprung-Russell (HR) diagram.
butterfly diagram.
Zipf plot.
HarleyDavidson (HD) diagram.
On a Hertzsprung-Russell diagram contours of constant radii run:
linearly UPWARD to the right.
horizontally across the diagram.
vertically up the diagram.
linearly DOWNWARD to the right.
Stars:
can always be resolved.
can never be resolved.
usually cannot be resolved, but with special techniques remote, small ones can be.
usually cannot be resolved, but with special techniques close, large ones can be.
The luminosity classes of stars are:
Chico, Groucho, Gummo, Harpo, Karlo, Zeppo.
bright, very bright, super-bright, unbelievable.
1, 2, 3, 4, 5, 6.
0, Ia, Ib, II, III, IV, V, VI, VII.
They are the most luminous stars (i.e., luminosities of order 106 L⊙) and put in luminosity class 0. They are called:
giants.
dwarfs.
horizontal branch stars.
hypergiants.
“Let’s play Jeopardy! For $100, the answer is: These objects appear on Hertzsprung-Russell diagrams and they are assigned a luminosity class VII.”
What are (BLANK), Alex?
hypergiants
white dwarfs
black holes
green dwarfs
“Let’s play Jeopardy! For $100, the answer is: They are the kind of stars to which the mass-luminosity relation applies.”
What are (BLANK) stars, Alex?
supergiant
red giant
red dwarf
main-sequence
On a log-log plot the mass-luminosity relation approximates a:
straight line that increases with mass.
horizontal line.
vertical line.
quadratic curve.
Two stars gravitationally bound to each other and orbiting their mutual center of mass constitute a:
binary star system.
triple star system.
single star.
galaxy
The evolution of stars in a close binary systems have additional complexity beyond single single star systems because the binary stars:
are always very massive.
are always very far apart.
can interact.
cannot interact.
“Let’s play Jeopardy! For $100, the answer is: These are loosely-bound, irregularly-shaped groups of stars consisting of order 100 to 1000 stars and having size scales of order 4 to 20 pc.”
What are (BLANK), Alex?
singles
binaries
open clusters
globular clusters
“Let’s play Jeopardy! For $100, the answer is: A physical group of stars in the constellation Taurus, sometimes called the Seven Sisters or, in Japan, Subaru, of which at least 6 stars are usually visible to the naked eye under reasonable seeing conditions.”
What are the (BLANK), Alex?
Toyotas
Wives of Chauntecleer
Brides of Dracula
Pleiades
“Let’s play Jeopardy! For $100, the answer is: These are structures of a few to a few hundred stars and span of order 10 to 100 pc. They are generally gravitationally unbound though gravitationally interacting.”
What are (BLANK), Alex?
singles
binaries
associations
globular clusters
“Let’s play Jeopardy! For $100, the answer is: These are compact, dense, spherical, gravitationallybound systems of stars. They can have from of order 20,000 to several million stars and their central concentrations have diameters of order to 5 to 25 pc.
What are (BLANK), Alex?
singles
binaries
associations
globular clusters
The ages of the stars in globular clusters put a lower limit on the age of the observable universe. The calculated ages of these stars are about:
12.5 Gyr.
12.5 million years.
100 million years.
4.6 Gyr
Although there is in fact a continuum of star age and metallicity, the distribution of core-hydrogenburning stars for convenience breaks two main groups: 1) relatively young and metal rich (metallicity of order 2–4 % by mass) and 2) relatively old and metal poor (typical metallicity of order 0.1 % by mass, but with a huge range). These two groups are called, respectively:
Population I and Population II.
Population A and Population B.
dwarfs and giants.
white dwarfs and red giants.
The life history of our own star, the Sun, is known to us by:
direct observations of all of its stages.
direct observations of most of its stages plus observations of other stars in all their stages and modeling.
direct observations of its current stage plus observations of other stars in all their stages and modeling.
modeling alone.
The interstellar medium (ISM) consists of:
planets.
molecular clouds only.
stars.
gas and dust.
In modern astronomy, a nebula (plural nebulae) is a:
cloud of a gas in space.
large main sequence star.
small main sequence star.
bright star.
The dense, cold component of the interstellar medium from which stars are believed to form is made of:
H II (ionized hydrogen) regions.
white dwarfs.
protostars.
molecular clouds.
The composition of molecular clouds in the interstellar medium is dominated by:
carbon dioxide.
molecular oxygen only.
helium gas only.
molecular hydrogen gas and helium gas.
Molecular clouds are probably about 1 per cent dust by mass.
The dust is VERY IMPORTANT to these clouds. It is HIGHLY OPAQUE to visible and ultraviolet light, and so keeps most hard electromagnetic radiation out of the inner regions of the clouds. This prevents the destruction of molecules by hard radiation. Moreover, it is probable that many molecules form on dust grains: free atoms stick onto the grains, meet there, bond, and then escape in molecular form: i.e., the grains act as catalysts. Dust tends to promote molecule formation and molecules tend to need dust. Thus, whenever you have a lot of dust, you often have molecules and vice versa.
The dust is VERY IMPORTANT to these clouds. It is COMPLETELY TRANSPARENT to visible and ultraviolet light, and allows plenty of hard electromagnetic radiation into the inner regions of the clouds. This prevents the destruction of molecules by hard radiation. Moreover, it is probable that many molecules form on dust grains: free atoms stick onto the grains, meet there, bond, and then escape in molecular form: i.e., the grains act as catalysts. Dust tends to promote molecule formation and molecules tend to need dust. Thus, whenever you have a lot of dust, you often have molecules and vice versa.
The dust is COMPLETELY UNIMPORTANT to these clouds. True, the dust is HIGHLY OPAQUE to visible and ultraviolet light, and so keeps most hard electromagnetic radiation out of the inner regions of the clouds. This prevents the destruction of molecules by hard radiation. Moreover, it is probable that many molecules form on dust grains: free atoms stick onto the grains, meet there, bond, and then escape in molecular form: i.e., the grains act as catalysts. Nevertheless, there are plenty of molecular clouds that are COMPLETELY DUST-FREE. In such clouds, the whole process of star formation is laid bare to visible light observers.
The dust is VERY IMPORTANT to these clouds. It is HIGHLY OPAQUE to visible and ultraviolet light, and so keeps most hard electromagnetic radiation out of the inner regions of the clouds. This prevents the destruction of molecules by hard radiation. Moreover, it is probable that many molecules form on dust grains: free atoms stick onto the grains, meet there, bond, and then escape in molecular form: i.e., the grains act as catalysts. Nevertheless, there are plenty of 4 molecular clouds that are COMPLETELY DUST-FREE. In such clouds, the whole process of star formation is laid bare to visible light observers.
Interstellar dust probably varies widely in composition, size scale, and structure. But there some ideas about typical dust that are generally accepted.
Although size scale probably varies widely, a typical dust grain may be of order 1 µm = 10−6 m in size, but it won’t be perfectly spherical. There may be a core of VOLATILE material of order 0.05 µm consisting of silicates (silicon and oxygen compounds that make up most terrestrial rock), iron, or graphite. The GRAIN MANTLE may be mostly NONVOLATILE ICES: e.g., H2O (water ice), CO2 (carbon dioxide ice or dry ice), CH4, and NH3. The grain surface may have complex molecules forming tarry substances. Dust probably forms in STELLAR WINDS AND SUPERNOVA EJECTA. There relatively dense VOLATILES condense out forming the cores as the ejected gas cools. As the gas cools more, NONVOLATILES condense out on the cores.
Although size scale probably varies widely, a typical dust grain may be of order 1 µm = 10−6 m in size, but it won’t be perfectly spherical. There may be a core of NONVOLATILE material of order 0.05 µm consisting of silicates (silicon and oxygen compounds that make up most terrestrial rock), iron, or graphite. The GRAIN MANTLE may be mostly VOLATILE ICES: e.g., H2O (water ice), CO2 (carbon dioxide ice or dry ice), CH4, and NH3. The grain surface may have complex molecules forming tarry substances. Dust probably forms inside the event horizons of BLACK HOLES. There relatively dense NONVOLATILES condense out forming the cores as the infalling gas cools. As the gas cools more, VOLATILES condense out on the cores. The dust then escapes scot-free from the black hole.
Although size scale probably varies widely, a typical dust grain may be of order 1 µm = 10−6 m in size, but it won’t be perfectly spherical. There may be a core of NONVOLATILE material of order 0.05 µm consisting of silicates (silicon and oxygen compounds that make up most terrestrial rock), iron, or graphite. The GRAIN MANTLE may be mostly VOLATILE ICES: e.g., H2O (water ice), CO2 (carbon dioxide ice or dry ice), CH4, and NH3. The grain surface may have complex molecules forming tarry substances. Dust probably forms in STELLAR WINDS AND SUPERNOVA EJECTA. There relatively dense NONVOLATILES condense out forming the cores as the ejected gas cools. As the gas cools more, VOLATILES condense out on the cores.
Although size scale probably varies widely, a typical dust grain may be of order 1 µm = 10−6 m in size, but it won’t be perfectly spherical. There may be a core of VOLATILE material of order 0.05 µm consisting of silicates (silicon and oxygen compounds that make up most terrestrial rock), iron, or graphite. The GRAIN MANTLE may be mostly NONVOLATILE ICES: e.g., H2O (water ice), CO2 (carbon dioxide ice or dry ice), CH4, and NH3. The grain surface may have complex molecules forming tarry substances. Dust probably forms inside the event horizons of BLACK HOLES. There relatively dense NONVOLATILES condense out forming the cores as the infalling gas cools. As the gas cools more, VOLATILES condense out on the cores. The dust 5 then escapes scot-free from the black hole.
“Let’s play Jeopardy! For $100, the answer is: It happens whenever a star changes its luminosity and/or its surface temperature.”
What is (BLANK), Alex?
explodes
collapses
turns green
movement on the Hertzsprung-Russell (HR) diagram
Star formation in a dusty molecular cloud probably requires some triggering event to initiate the collapse to dense cores that will become stars. Two possible trigger mechanisms are:
SUPERNOVAE which compress molecular clouds and CLOUD-CLOUD COLLISIONS which also compress the colliding molecular clouds.
WHITE DWARFS which ram into and thereby compress molecular clouds and CLOUDCLOUD COLLISIONS which also compress the colliding molecular clouds.
WHITE DWARFS which ram into and thereby compress molecular clouds and PROTOSTARPROTOSTAR COLLISIONS which also compress the molecular clouds.
WHITE DWARFS which ram into and thereby compress molecular clouds and BLACK HOLE FORMATION which also compresses the molecular clouds.
In a FREE-FALL contraction of part of molecular cloud:
the part starts fall to toward a high density point because of gravitational attraction. Pressure forces slow the fall from the beginning.
the part starts fall to toward a high density point because of gravitational attraction. Pressure forces are negligible in slowing the fall because it is a free-fall contraction.
the entire molecular cloud collapses to form a black hole.
the part collapses to form a black hole.
The collapsing dense regions that develop into stars and initially have temperatures of order 10 K are called:
dense cores.
dilute cores.
main sequence stars.
white dwarfs.
A protostar is sometimes conveniently defined to be a:
star that can no longer burn hydrogen to produce heat energy.
white dwarf.
dense core of gas contracting to become a star that is hot enough to radiate in the infrared, but not yet sufficiently hot for nuclear burning.
molecular cloud that will become a star.
The contraction of a protostar is halted eventually by:
the thermal energy generated by the contraction which DECREASES the gas pressure inside the protostar.
the thermal energy generated by the contraction which INCREASES the gas pressure inside the protostar.
the action of magnetic fields.
the heat generated by the turning on of nuclear burning which INCREASES the gas pressure inside the protostar.
Star formation in giant molecular clouds often results in the formation of OB associations: collections of hot, bright OB stars that ionize the surrounding molecular cloud and evaporate dust because of their strong ultraviolet emission. The gas region ionized by an OB associations is called a/an:
H II region.
small molecular cloud.
a black hole.
a dark cloud.
“Let’s play Jeopardy! For $100, the answer is: They are relatively thin, round objects consisting of gas and/or dust and/or particles: the material goes around some large astro-body in nearly circular orbits of varying radii in the same direction.”
What are (BLANK), Alex?
CDs
planets
disks
satellites
Disk formation is:
in star formation, in the formation of accretion disks about putative black holes, and in the formation of spiral galaxies. In the case of black holes, matter is sprayed out of the black hole in random orbits and in a collisional-relaxation-dissipation process, similar to what happens in star formation, relaxes into a disk.
in star formation, in the formation of accretion disks about black holes, and in the formation of spiral galaxies. In the case of supermassive black holes at the centers of galaxies, it is thought that matter, at least originally, is somehow gravitational captured by the black hole in random orbits and in a collisional-relaxation-dissipation process, similar to what happens in star formation, relaxes into a disk. This matter gradually loses rotational energy through viscous forces in the disk and spirals into the black hole. While spiraling into the black hole the matter cools down.
in star formation, in the formation of accretion disks about black holes, and in the formation of spiral galaxies. In the case of supermassive black holes at the centers of galaxies, it is thought that matter, at least originally, is somehow gravitational captured by the black hole in random orbits and in a collisional-relaxation-dissipation process, similar to what happens in star formation, relaxes into a disk. This matter gradually loses rotational energy through viscous forces in the disk and spirals into the black hole. While spiraling into the black hole the matter heats up due to infall kinetic energy being transformed into heat. Consequently, the infalling material radiates electromagnetic radiation. The object Sgr A∗ near or at the dynamical center of the Milky Way, thought to be a black hole of mass of order 3 × 106 M⊙, is a strong radio source.
in star formation, in the formation of accretion disks about black holes, and in the formation of impact craters. In the case of supermassive black holes at the centers of galaxies, it is thought that matter, at least originally, is somehow gravitational captured by the black hole in random orbits and in a collisional-relaxation-dissipation process, similar to what happens in star formation, relaxes into a disk. This matter gradually loses rotational energy through viscous forces in the disk and spirals into the black hole. While spiraling into the black hole the matter cools down.
A star lying on the main sequence on a Hertzsprung-Russell diagram is a:
main-sequence star.
pre-main-sequence star.
post-main-sequence star.
white dwarf.
“Let’s play Jeopardy! For $100, the answer is: It is a star that as observed over relatively short times scales (e.g., all of human history) is burning hydrogen to helium in its core at a constant rate and is in hydrostatic equilibrium.”
What is a/an (BLANK), Alex?
dense core
protostar
pre-main-sequence star
main-sequence star
For a main sequence star, the energy radiated away as electromagnetic radiation is almost exactly compensated by:
gravitational energy converted to heat energy during rapid collapse.
neutrinos from space being absorbed by the star.
energy produced by nuclear burning on the surface.
energy produced by nuclear burning in the deep interior.
Atomic nuclei are made up of:
protons and neutrons.
protons and electrons.
positrons and electrons.
positrons and neutrals.
The nucleus is occupies (BLANK) of the volume of an atom and has (BLANK) of the atomic mass.
a small part; none
a small part; almost all
most; almost all
most; none
Nuclei with the same number of protons, but different number of neutrons are (BLANK) of each other.
isochrones
isobars
isotopes
isodopes
“Let’s play Jeopardy! For $100, the answer is: These isotopes of hydrogen have 1 and 2 neutrons, respectively.”
What are (BLANK), Alex?
uranium-235 (235 92 U) and uranium-238 (238 92 U)
helium-3 (3 2He) and helium-4 (4 2He)
the deuteronomy (D or 2 1H) and trident (T or 3 1H)
the deuteron (D or 2 1H) and triton (T or 3 1H)
Nuclei are bound together by:
gravity.
the strong nuclear force.
the electromagnetic force.
the centrifugal force.
Nuclear fusion is the (BLANK) bonding of nuclei to form (BLANK) nuclei.
chemical; larger
nuclear; larger
nuclear; smaller
chemical; smaller
In stellar hydrogen fusion to helium, the rest mass energy of the products is (BLANK) less than that of the reactants. The missing rest mass energy went mostly into (BLANK).
70 %; heat energy
170 %; magnetic field energy
0.7 %; heat energy
0 %; chemical binding energy
1 kg of matter is equivalent to about how much energy? Recall that the speed of light is 3.00 × 10^8 m/s.
8 × 10^16 J.
9 × 10^16 J.
9 × 10^8 J
3 × 10^8 J.
The energy emitted as electromagnetic energy from main sequence stars is supplied by the:
nuclear burning of helium to hydrogen
nuclear burning of hydrogen to helium
nuclear burning of hydrogen to carbon.
nuclear burning of helium to carbon.
Thermonuclear reactions happen only in a star’s core (which for the Sun is the region within about 0.25 solar radii of the Sun’s center) because only there is it (BLANK) enough.
cold and dilute
hot and dense
hot and dilute
bland and fragile
Why don’t thermonuclear reactions happen on the surface of main sequence stars?
Not hot and not dense enough.
Too hot and too dense.
Too green.
Too bad.
In addition to observations of a star and physics theory, in order to understand the star in detail one needs:
a few calculations on a scrap of paper.
detailed computer modeling.
experiments on Sun-size gas balls.
nothing else at all.
“Let’s play Jeopardy! For $100, the answer is: This is a set of calculated distributions of temperature, density, luminosity, and other physical quantities for a star.”
What is (BLANK), Alex?
the star mass
the star itself
a model of the star
the star luminosity
In a main sequence star (e.g., the Sun) temperature, density, and pressure:
vary strongly from center to surface (i.e., photosphere).
are constant throughout the star.
are never higher than about 6000 K, 2 × 10−7 g/cm3 , and 0.8 Earth atmospheres, respectively.
are all equal to 6000 in MKS units.
Hydrostatic equilibrium means that:
pressure and other forces in a fluid are UNBALANCED, but the fluid is exhibiting a SMOOTH FLOW (at least in the reference frame of the fluid center of mass).
pressure and other forces in a fluid are UNBALANCED and the fluid is exhibiting a TURBULENT FLOW (at least in the reference frame of the fluid center of mass).
pressure and other forces in a fluid are BALANCED and there is NO FLUID MOTION (at least in the reference frame of the fluid center of mass).
the temperature is a constant throughout a fluid.
“Let’s play Jeopardy! For $100, the answer is: It is an everyday example of hydrostatic equilibrium.”
What is (BLANK), Alex?
a boat’s wake
stirring coffee
a river
water at rest in a cup
Main sequence stars of low mass are mainly supported against collapse ( >∼ 90 % for M <∼ 8M⊙) by:
the pressure of liquid water.
the ideal gas pressure of ions and electrons.
the gravitational force.
angular momentum.
An everyday example of heat transfer by radiative transport (or radiative transfer) is
boiling water in a pan.
a spoon in boiling water growing warm.
sunlight warming.
a refrigerator cooling.
In convection between a lower hot layer and an upper cold layer (with downward being the direction of gravity):
hot blobs rise and cold blobs rise too.
hot blobs rise and cold blobs sink.
hot and cold blobs both sink.
hot and cold blobs don’t form.
A common reason why some astrophysical systems are described as poorly understood is that these systems involve three-dimensional hydrodynamic effects (e.g., convection).
Three-dimensional hydrodynamics cannot be ACCURATELY COMPUTATIONALLY TREATED at all.
Three-dimensional hydrodynamics cannot be TREATED EVEN QUALITATIVELY.
Three-dimensional hydrodynamics can OFTEN be understood qualitatively and this SOMETIMES allows us to predict three-dimensional hydrodynamical phenomena. Accurate computations of three-dimensional hydrodynamic effects are also possible in some cases.
Three-dimensional hydrodynamics can OFTEN be understood qualitatively and this SOMETIMES allows us to predict three-dimensional hydrodynamical phenomena. Accurate computations of three-dimensional hydrodynamic effects are also possible in some cases. For 8 example, when ELECTROMAGNETIC EFFECTS are present, they actually simplify threedimensional hydrodynamic effects and allow accurate computations in all cases. Maybe someday all three-dimensional hydrodynamic effects will be accurately calculable.
During a star’s MAIN SEQUENCE LIFE, the star is relatively unchanging. But, of course, it is actually changing slowly on the road to its demise. The key change is that:
carbon dioxide (CO2) is being expelled by the star’s wind.
molecular nitrogen (N2) is being expelled by the star’s wind.
hydrogen fuel is being exhausted in its core.
hydrogen fuel is being exhausted on its surface.
Most nuclear-burning stars are main sequence stars. The reason for this is that the main sequence phase of the nuclear-burning life of star of any mass is the:
shortest phase.
most popular phase.
wettest phase.
longest phase.
As a MAIN SEQUENCE STAR ages, its luminosity (i.e., total energy output):
decreases.
increases.
oscillates wildly.
becomes tangential.
At the time the Sun first became a main sequence star, its luminosity was probably than (BLANK) at present.
30 % greater
100 % greater
50 times greater
30 % lower
These main sequence stars have masses in the range 0.08–0.4 M⊙. They have the lowest temperatures and densities in their cores of all main sequence stars and subsequently burn hydrogen to helium most slowly. Convection occurs throughout these stars and eventually they will be converted entirely into helium. They will never burn any other nuclear fuel and eventually must become helium white dwarfs. Their main sequence lifetimes are predicted by models to be hundreds of billions of years. According to our current cosmological theory the age of the universe is only about 14 billion years. Thus, none of these stars has ever left the main sequence. These stars are called:
brown dwarfs.
red dwarfs.
white dwarfs.
red giants.
Red dwarf stars are convective:
in no region.
only above the photopshere.
from center to photosphere.
only in the nuclear burning core.
Because red dwarf stars are convective throughout (i.e., from center to photosphere), they will
burn helium to hydrogen only in their cores.
never burn hydrogen at all.
eventually burn almost all their hydrogen to helium.
never burn either hydrogen or helium.
An object that forms in a star formation region with less than about 0.08 M⊙, but more than about 13 Jupiter masses (according to one school of thought), and which never burns ordinary hydrogen is called a:
white dwarf.
white dwarf.
red dwarf.
red giant.
Brown dwarfs are:
not main sequence stars ever.
unarguably main sequence stars.
main sequence stars at three different times.
sometimes main sequence stars.
