- The Milky Way was once thought to be “murky” or “milky” but is now considered to be made up of point sources. Explain.
- A star is in equilibrium when it radiates at its surface all the energy generated at its core. What happens when it begins to generate more energy
- Describe a red giant star. List some of its properties?
- Select a point on the H-R diagram. Mark several directions away from this point. Now describe the changes that would take place in a star moving in
- Does the H-R diagram reveal anything about the core of a star?
- Why do some stars end up as white dwarfs, and others as neutron stars or black holes?
- Can we tell, by looking at the population on the H-R diagram, that hotter main-sequence stars have shorter lives? Explain.
- If you were measuring star parallaxes from the Moon instead of Earth, what corrections would you have to make? What changes would occur if you were
- Cepheid variable stars change in luminosity with a typical period of several days. The period has been found to have a definite relationship with the
- What is a geodesic? What is its role in General Relativity?
- If it were discovered that the red shift of spectral lines of galaxies was due to something other than expansion, how might our view of the universe
- All galaxies appear to be moving away from us. Are we therefore at the center of the universe? Explain.
- If you were located in a galaxy near the boundary of our observable universe, would galaxies in the direction of the Milky Way appear to be
- Compare an explosion on Earth to the Big Bang. Consider such questions as: Would the debris spread at a higher speed for more distant particles, as
- If nothing, not even light, escapes from a black hole, then how can we tell if one is there?
- What mass will give a Schwarzschild radius equal to that of the hydrogen atom in its ground state?
- The Earth’s age is often given as about 4 billion years. Find that time on Fig. 33-25. People have lived on Earth on the order of a million years.
- Explain what the 2.7-K cosmic microwave background radiation is. Where does it come from? Why is its temperature now so low?
- Why were atoms, as opposed to bare nuclei, unable to exist until hundreds of thousands of years after the Big Bang?
- Under what circumstances would the universe eventually collapse in on itself?
- Using the definitions of the parse and the light-year, show that 1 pc = 3.26ly.
- A star exhibits a parallax of 0.38 seconds of arc. How far away is it?
- The parallax angle of a star is 0.00019o. How far away is the star?
- A star is 36pc away. What is its parallax angle? State (a) In seconds of arc, and (b) In degrees.
- What is the parallax angle for a star that is 55ly away? How many parsecs is this?
- If one star is twice as far away from us as a second star, will the parallax angle of the farther star be greater or less than that of the nearer
- A star is 35pc away. How long does it take for its light to reach us?
- We saw earlier that the rate energy reaches the Earth from the Sun (the “solar constant”) is about 1.3 X 103 W/m2. What is? (a) The apparent
- What is the relative brightness of the Sun as seen from Jupiter as compared to its brightness from Earth? (Jupiter is 5.2 times farther from the Sun
- Estimate the angular width that our Galaxy would subtend if observed from the nearest galaxy to us. Compare to the angular width of the Moon from
- When our sun becomes a red giant, what will be its average density if it expands out to the orbit of Earth (1.5 X 1011m from the Sun)?
- When our sun becomes a white dwarf, it is expected to be about the size of the Moon. What angular width will it subtend from the present distance to
- Calculate the density of a white dwarf whose mass is equal to the Sun’s and whose radius is equal to the Earth’s. How many times larger than
- A neutron star whose mass is 1.5 solar masses has a radius of about 11km. Calculate its average density and compare to that for a white dwarf and
- Calculate the Q-values for the he burning reaction of Eq. 33-2. (The mass of the very unstable 8/4Be is 8.005305u.)
- Suppose two stars of the same apparent brightness are also believed to be the same size. The spectrum of one star peaks at 800nm whereas that of the
- Stars located in a certain cluster are assumed to be about the same distance from us. Two such stars have spectra that peak at λ1 = 500 nm and
- Show that the Schwarzschild radius for a star with mass equal to that (a) Of our Sun is 2.95km, and (b) Of Earth is 8.9mm.
- What is the Schwarzschild radius for a typical galaxy (like ours)?
- Describe a triangle, drawn on the surface of a sphere, for which the sum of the angles is (a) 359o, and(b) 180o.
- What are the maximum sum-of-the-angles for a triangle on a sphere?
- If a galaxy is traveling away from us at 1.0% of the speed of light, roughly how far away is it?
- The red shift of a galaxy indicates a velocity of 3500km/s. How far away is it?
- Estimate the speed of a galaxy (relative to us) that is near the observable “edge” of the universe, say 12 billion light-years away.
- Estimate the observed wavelength for the 656-nm line in the Balmer series of hydrogen in the spectrum of a galaxy whose distance from us is (a) 1.0 x
- Estimate the speed of a galaxy, and its distance from us. If the wavelength for the hydrogen line at 434nm is measured on Earth as being 610nm.
- What is the speed of a galaxy with z = 0.600?
- What would be the red shift parameter z for a galaxy traveling away from us at v = 0.50c?
- Starting from Eq. 33-3, show that the Doppler shift in wavelength is ∆Λ/Λ0 ≈ v/c (Eq. 33-5b) for v
- The critical density for closure of the universe is pc ≈ 10 –26 kg/m3 state pc in terms of the average number of nucleons per cubic meter.
- The scale of the universe (the average distance between galaxies) at any one moment is believed to have been inversely proportional to the absolute
- At approximately what time had the universe cooled below the threshold temperature for producing (a) Kaons (M ≈ 500 MeV/c2). (b) Y (M
- Suppose that three main-sequence stars could undergo the three changes represented by the three arrows, A, B, and C, in the H €“ R diagram
- Assume that the nearest stars to us have an absolute luminosity about the same as the Sun’s. Their apparent brightness, however, is about 1011
- Use conservation of angular momentum to estimate the angular velocity of a neutron star which has collapsed to a diameter of 20km, from a star whose
- By what factor does the rotational kinetic energy change when the star in Problem 36 collapses to a neutron star?
- A certain pulsar, believed to be a neutron star of mass 1.5times that of the Sun, with diameter 20km, is observed to have a rotation speed of
- The nearest large galaxy to our Galaxy is about 2 x 106 ly away. If both galaxies have a mass of 3 x 1041kg, with what gravitational force does each
- Estimate what neutrino rest mass (in eV) would provide the critical density to close the universe. Assume the neutrino density is, like photons,
- Two stars, whose spectra peak at 600nm and 400nm, respectively, both lie on the main sequence. Use Wien’s law, the Stefan-Boltzmann’s equation,
- Suppose we can measure distances with parallax at 100 parsecs. What is our minimum angular resolution (in degrees), based on this information.
- Through some coincidence, the Balmer lines from singly ionized helium in a distant star happen to overlap with the Balmer lines from hydrogen (Fig.
- What is the temperature that corresponds to 1.8-TeV collisions at the Fermilab Collider? To what era in cosmological history does this correspond?
- Astronomers have recently measured the rotation of gas around what might be a super massive black hole of about 2 billion solar masses at the center
- A galaxy is moving away from Earth. The “blue” hydrogen line at 434nm emitted from the galaxy is measured on Earth to be 650nm.(a) How fast is
- In the later stages of stellar evolution, a star (if massive enough) will begin fusing carbon nuclei to form, for example, magnesium;(a) How much
- How large would the Sun be if its density equaled the critical density of the universe, pc ≈ 10 – 26 kg/m3? Express your answer in