Why was the Hipparcos satellite able to make more accurate parallax measurements than ground-based telescopes?
By orbiting above the Earth's atmosphere, the blurring effect of the atmosphere is avoided.
A particular star with the same spectral type as the sun (G2) has a luminosity of 50 solar luminosities. What does this tell you about the star?
It must be larger than the sun.
What does luminosity measure that is different from what absolute visual magnitude measures?
Luminosity measures the total energy per second, at visible wavelengths, that a star emits.
Examine the stars Adara, Betelgeuse, Canopus, the sun, and Sirius B on this H-R diagram. A correct listing of these five stars from largest to smallest is which of the following?
Betelgeuse, Canopus, Adara, the sun, Sirius B
How do the masses of stars along the main sequence illustrate the mass-luminosity relation?
More massive stars tend to burn hotter and brighter.
Which type of binary star is illustrated in this diagram?
Which luminosity class has stars of the lowest density, some even less dense than air at sea level?
The analysis of binary star orbits revealed individual masses of many pairs of stars and the discovery of the mass-luminosity relationship. In this H-R diagram, it is apparent that the mass of a spectral type A5 main-sequence star is approximately which of the following?
2.2 solar masses
If you look only at the brightest stars in the night sky, what type of star are you likely to be observing? Why?
Giants and supergiants tend to be the brightest stars in the sky. They are very luminous due to their large size.
Why are titanium oxide features visible in the spectra of only the coolest stars?
In higher temperature stars titanium oxide is dissociated into titanium and oxygen atoms.
Where in the sun is the law of hydrostatic equilibrium at work?
at every point inside the sun
What is a protostar's energy source?
What force causes the contraction of a cloud of interstellar matter to form a star?
Which factor resists the contraction of a cloud of interstellar matter?
thermal energy, rotation, turbulence, interstellar magnetic field
At what wavelengths can we observe the early stages of protostar formation?
What evidence do we have that the Orion region is actively forming stars?
Protostars are seen here at infrared wavelengths inside their cocoons, Some stars here are between the birth line and the main sequence, Some visible stars in the Orion region have disks, Some short-lived stars are located in this region.
Why are lower main-sequence stars more abundant than upper main-sequence stars?
More low-mass main-sequence stars are formed in molecular clouds and lower main-sequence stars have much longer lifetimes than upper main-sequence stars.
Why does a star's life expectancy depend on mass?
Mass determines the amount of fuel a star has for fusion and mass determines the rate of fuel consumption for a star.
Why are interstellar absorption lines so much thinner than stellar absorption lines?
Most interstellar gas is at a lower temperature than that of stellar atmospheres and the density of interstellar gas is less than that of stellar atmospheres.
What prevents the enormous amount of energy released from the fusion reactions at a star's core from blowing the star apart?
How much longer will the sun last?
about 5 billion years
This figure shows the post main-sequence evolution of different stars on the H-R diagram. When the sun leaves the main sequence to become a giant, what happens to its surface temperature and luminosity?
The luminosity increases and the surface temperature decreases.
Why will a helium flash never occur in some stars?
Some stars do not develop degenerate helium cores.
What is the general trend in the ages of the two types of star clusters?
Globular clusters are older than open clusters.
What event marks the end of every star's main-sequence life?
the end of hydrogen fusion in the core
What type of spectrum does the gas in a planetary nebula produce?
an emission line spectrum
What prevents gravity from shrinking a white dwarf to a smaller size?
What happens to a star when it becomes a giant if it has a close binary companion?
Matter can be transferred from the giant to the companion.
Why can't massive stars generate energy from iron fusion?
Iron fusion consumes energy.
Which type of supernova leaves NO core remnant?
supernova type Ia
How do neutron stars and white dwarfs differ?
White dwarfs are produced by the final gravitational contraction of the cores of low- to medium-mass stars. Neutron stars are produced from the collapsing core of a massive star as it undergoes a supernova explosion.
Why is there an upper limit to the mass of neutron stars?
There is a maximum mass that can be supported against gravity by the outward pressure of degenerate neutrons.
What does the short length of pulsar pulses tell you?
Pulsars must have much smaller diameters than normal stars
Why are all pulsars not located in supernova remnants?
Pulsars persist longer than supernova remnants and some pulsars given high velocities upon formation can flee the scene of destruction.
Why do the millisecond pulsars spin so fast?
Accretion of matter from a nearby binary companion spins them up.
Which of the following describes the gravitational redshift?
A reduction in the energy of photons as they move away from objects.
What is the origin of the X-ray bursters?
matter accreting around a binary system in which there is a neutron star
What may be responsible for the observed gamma-ray bursters?
neutron star merger and hypernovae
What changes would occur if the sun were replaced with a one-solar-mass black hole?
Earth's orbit would not change and the planets would disappear from view.
If the sun has a Schwarzschild radius, why isn't it a black hole?
Not all of the sun's mass is inside its Schwarzschild radius