95 terms

Astronomy final


Terms in this set (...)

Stellar parallax is used to determine which of the following properties of a nearby star?
its distance from the Sun
Stellar parallax exists because
Earth moves in space
The riple star system < Centauri has the largest known stellar parallax angle, namely 0.75 arcsecond. How far is this star system from the Sun in light-years?
4.33 ly
If a nearby star shows a parallax of 0.5 arcsecond, what is its distance from Earth in light-years?
6.52 ly
Suppose that, at night, the brightness of a light bulb is measured from a certain distance and then the light bulb is moved to a distance twice as far away. How bright will the light appear compared to the earlier measurement?
1/4 as bright
The luminosity of a star is a unique measure of its
total energy output
The absolute magnitude of a star is the brightness the star would appear to have if it were placed at what distance from Earth?
32.6 ly
What does apparent magnitude tell us about a star?
the brightness of a star as it appears in our sky
The spectral type of a star is most directly related to (and determines uniquely) its
surface temperature
The chemical makeup of a star's surface is usually determined by
spectroscopy of the light emitted by the star
What is "metal" to an astronomer?
Any element heavier than helium
The Hertzsprung-Russel diagram is a statistical plot of which of the following two stellar parameters
luminosity and surface temperature
The spectral class of the Sun is G2 and the star Enif is K2. From this information, we know that Enif is
cooler than the Sun
Where do we find the most massive stars on the main sequence in a Hertzsprung-Russel diagram?
upper left
Which important stellar parameter can be determined by the study of binary stars?
stellar masses
If the Sun were the same temperature but twice its present diameter, the amount of energy we would receive would
increase by a factor of four
What happens to the positrons produced by the nuclear reactions in the core of the Sun?
They collide with electrons, producing energy
Where is the Sun's energy generated?
The core
The neutrino is
A tiny particle that interacts very weakly with matter, with extremely low or zero mass and no charge
Which of the following seems to be the correct explanation for the low neutrino rates detected by Homestake experiments (1960s)?
The neutrinos oscillate and change their nature en route from the Sun to Earth
The photosphere is the level of the Sun from which most of the visible radiation we see originates. The temperature of the base of the Sun's photosphere is roughly
6000 K
The visible light coming from the solar chromosphere is dominated by light at what wavelength(s)?
the red hydrogen Balmer H(a) emission line
What is the corona on the Sun?
The Sun's outer atmosphere
The temperature of the corona of the Sun is
very hot-- about 10(6) K
What is the solar wind?
the Sun's outer atmosphere streaming out into space
In the thermonuclear process that heats the Sun, the nuclei of which chemical elements are converted to other nuclei to produce requisite energy?
hydrogen to helium
sunspots appear dark because they
are cooler than the surrounding surface
Galileo observed the phenomenon of solar rotation in the early 1600s by
watching sunspots move across the solar surface with a telescope
What is the rotation period of the Sun?
about one rotation per month
The 11-year sunspot cycle on the Sun is
an irregular, sometimes absent variation in the number of visible sunspots
The dark lines in the solar spectrum are caused by
wavelengths that have been absorbed by atoms between us and the source of light
What are the most energetic eruptive events to occur on the Sun?
coronal mass ejections
An H II region looks red, just as the metal filaments in a toaster glow red when heated. Are these colors produced in the same way?
No--the metal's red is produced by a blackbody curve. The H II region glows red because of a specific emission line in hydrogen
What radiation ionizes the hydrogen in an H II region
ultraviolet radiation from O and B stars
Protostars, when they first form from the interstellar medium, are usually
hidden from sight by dust clouds that emit infrared radiation
The source of the protostar's heat is
gravitational energy, released as the star contracts
The smallest mass that a main-sequence star can have is about 0.08 solar mass. The reason for this is that
the temperature in the core of a contracting protostar of less than 0.08 solar masses does not get high enough for nuclear reactions (Hydrogen "Burning") to start
New stars are formed
In huge, cool dust and gas clouds
A brown dwarf is
an object intermediate between a planet and a star, with not enough mass to begin nuclear reactions (Hydrogen "Burning") in its core
T-Tauri stars are at what stage of stellar evolution?
early phase, just after the formation of the protostars
The Orion Nebula is a
larbge interstellar gas and dust cloud containing many young stars
Thermonuclear reactions convert hydrogen to helium in the core of a star during which phase of a star's life?
the main-sequence phase
The main factor that determines the rate at which a protostar evolves is its
initial mass, larger masses evolving faster
The effect of interstellar dust on starlight is
to dim and redden distant stars by preferentially scattering their blue light
The total lifespan of the Sun is believed to be
12 billion years
How do two unequal mass stars move around each other in a binary system?
In elliptical orbits, about a common "center of mass"
Two stars are found to have the same luminosity. However, one star has twice the surface temperature of the other. From this information, what can you determine about their radii?
The hotter star has a quarter the radius of the cooler star
Which of the following particles or types of radiation will provide the most direct information on the process of nuclear fusion that are occurring in the solar core?
Certain stages of stellar evolution, such as birth of a protostar and post-main-sequence red giant evolution, come about because of an imbalance between gravity and
Internal gas pressure
Spectroscopic parallax is the
Method of calculating the distance to a star using the spectral-luminosity class of the star, it's apparent brightness, and the inverse-square law
At what stage of its evolutionary life is the Sun?
main-sequence--middle age
The evolution of a star is controlled by its
initial mass
The main-sequence lifetime of a star with half the mass of the Sun
is longer than that of the Sun
When the Sun first becomes a red giant star its energy generation will be produced by
shell hydrogen fusion
Helium fusion begins in the core of a low-mass star after the helium flash. Where did this helium come from?
It was produced by hydrogen fusion during the main-sequence phase
Horizontal-branch stars, which have a range of temperatures with luminosities between 50 and 100 times that of the Sun, are in what stage of their lives?
core helium burning
What happens to the surface of a low-mass star after the helium core and helium shell nuclear fusion "burning" stages are completed?
It is propelled slowly away from the core to form a planetary nebula
The major source of light in the expanding shell of gas in a planetary nebula is
fluorescence of the atoms, caused by UV light from the hot central white dwarf star
In a binary system, the first star to fill its Roche lobe is usually in red giant. What can we say about the nature of the other star when this happens?
The two stars in a binary system are formed at the same time, so the other star must be a main-sequence star.
A Type Ia supernova is the
explosion of a white dwarf in a binary system after mass has been transferred onto it from its companion
Why can we not have a white dwarf of two solar masses?
A white dwarf of more than 1.4 solar masses could not be supported by electron degeneracy
An old high mass star can have a number of shells (hydrogen, helium, carbon, neon, oxygen, silicon) plus an iron core. Furion generally takes place everywhere except the
iron core
The core collapse phase at the end of the life of a massive star is triggered when
nuclear fusion has produced a significant amount of iron in its core.
What is the source of most of the heavy elements on the Earth and in ur own bodies?
explosive nucleosynthesis during supernova explosions of massive stars
What is a Cepheid variable star?
a high-mass star that pulsates regularly in brightness
What is a pulsar?
a rapidly rotating neutron star, producing beams of radio energy and in some cases, light and X rays
A neutron star will be detected from Earth as a pulsar by its regular radio pulses only if the Earth lies
almost directly in line with the magnetic axis of the neutron star at some time during the star's rotation
a nova is a sudden brightening of a star that occurs when
material from a companion is transferred onto the surface of a white dwarf in a binary system and is subsequently blasted into space by a runaway thermonuclear explosions, leaving the white dwarf intact to repeat the process
The Hertzsprung-russel diagram of a globular cluster does not contain any stars with high luminosity and high temperature on the main sequence because
these high-mass stars evolved away from the main sequence long ago
The Crab Nebula is a nearby example of what type of physical phenomenon
remnant of a supernova explosion
What is "special" about the special theory of relativity?
It deals only with objects moving in a straight line at constant speed
In what way is the general theory of relativity more general (deals with more situations) than the special theory?
It includes accelerated motion and gravitation
Suppose you are in a rocket ship traveling toward Earth at 95% of thee speed of light. Compared to when your ship was at rest on Mars, you measure the length of your spaceship to be
the same as when it was on Mars.
Suppose you are on Earth and see a spaceship with a clock on it hurtling past you at 80% of the speed of light. As it goes by, the second hand on the ship's clock ticks off 5 seconds. How much time elapsed on your clock while this was happening?
more than 5 seconds
According to Newton's law of gravity, why does Earth orbit the Sun?
The Sun exerts a gravitational force on Earth across empty space.
According to General Relativity, why does Earth orbit the Sun?
Space around the Sun is curved and Earth follows the curved space
What is believed to be the maximum mass for a neutron star?
3 solar masses
A black hole is believed to form
at the end of the evolution of a very massive star
The diameter of the black hole candidate Cygnus X-1 has been estimated by
measuring how quickly it flickers in intensity
Black holes are so named because
no light or any other electromagnetic radiation can escape from inside them
Why is the orbit of Mercury important from the standpoint of General Relativity?
General relativity predicts the correct value for the advance of the perihelion of Mercury's orbit while Newtonian mechanics does not
Gamma-ray bursters are great distances from us, yet we receive tremendous amounts of energy from them. What accounts for this?
The energy is released along jets rather than uniformly in all directions. If Earth is in the path of one of these jets we see a gamma-ray burster
What is a barred spiral galaxy?
a galaxy with a bar through the nuclear bulge, and the spiral arms starting from the ends of the bar
What is an elliptical galaxy galaxy?
A galaxy with an elliptical outline and a smooth distribution of brightness (no spiral arms)
The method used by Hubble to determine the distance to the Andromeda Galaxy (M31), thereby establishing the concept of separate and individual galaxies throughout the universe, was the
observation of Cepheid variable stars
What is the brightest "standard candle" found so far, and therefore the one that can be seen to the greatest distance?
Type Ia supernovae
The primary evidence for the expanding universe concept is
the redshift of light from distant galaxies, which increases with distance of the galaxy from Earth
The Hubble Law, representing observations of distant galaxies in the universe, relates which two parameters?
the distance to a distant galaxy and its recession velocity
The rotation curve of a galaxy is a graph showing the galaxy's speed of rotation at different distances from the center. The observed rotation curve in the outer parts of a typical large spiral galaxy
is quite flat (roughly the same speed at all distances).
As much as 90% of the matter in the universe may be unseen "dark matter". Where is this dark matter?
It appears to be concentrated in spherical haloes around galaxies, but extending several times the radius of visible matter
What scientific method is used to observe the pulsation in size of a Cepheid variable star?
Doppler shift of absorption lines in its spectrum
How much brighter than its main-sequence luminosity will a Sun-like star become at the asymptotic giant branch (AGB) phase of its life?
10 4 times brighter
Type II supernovae show prominent lines of hydrogen in their spectra, whereas hydrogen lines are absent in spectra of Type Ia supernovae. Why is this? (Hint: Think about the type of star that gives rise to each of the two types of supernova.)
Massive stars contain large amounts of hydrogen, whereas white dwarfs are mostly carbon and oxygen
If nothing can ever leave a black hole, can the mass of a black hole ever decrease?
Yes, if particle--antiparticle pairs are created outside the event horizon and one particle enters the event horizon while the other escapes
For galaxies in the Hydra cluster, the recessional velocity is 61,000 km/sec. Assuming the non-relativistic solution, what is the shift in frequency for the Balmer Ha line, the rest wavelength of which is 656.3 nm?
133 nm