Short Questions about Stars

  1. Sunlight is composed of a mix of colours: effectively all of the colours our eyes can appreciate. Anything that produces fairly similar amountsof all kinds of visible light appears white to our eyes.
    When sunlight bounces off a blue shirt, the shirt doesn't look white.
    What is happenning to blue light that comes from the sun and strikes the shirt?
    What happens to light of other colours?

  2. Parallax. Two people are sitting in a car driving along a road towards the sun at sunset so that the sun is level with the car in the vertical direction. Each person sitting in his or her seat is 1 metre to either side of the centre of the car and there is a traffic light 100 metres directly ahead of the centre of the car.

    a. What is the angle between the traffic light and the sun for the driver?
    You may wish to draw a diagram to help you visualize this. I will also describe the situation if asked.
    b. Will the angle between the traffic light and the sun increase or decrease as the car moves closer to the light?

  3. Parallax and proper motion are both movements of stars in the sky. Describe an experiment which will "untangle" the two effects.

  4. What can be said about a star's radial velocity if its spectrum shows no Doppler shift?

  5. Which of the following pairs of quantities can be plotted against each other to produce an H-R diagram?
    a) Temperature and Distance
    b) Temperature and Spectral Class
    c) Luminosity and Spectral Class
    d) Luminosity and Temperature
    e) Luminosity and distance
    f) distance and spectral class

  6. Why are most stars in the H-R diagram on the main sequence?

  7. How does the brightness of a giant star compare with the brightness of a main sequence star of the same spectral class?

  8. Describe what happens to a blackbody's brightness and color as the temperature increases.

  9. What evidence do we have that stars form in the "clumps" of Giant Molecular Clouds?

  10. Why is it impossible for a gas with all its atoms in the ground (lowest-energy) state to produce emission lines?

  11. The photosphere is where most of the light we see coming from the sun originates.

    Briefly describe the physical processes involved in setting a depth for the photosphere. Think in terms of a specific photon moving outward at some depth within the sun.

  12. The solar cycle lasts 22 years.

    (a) Describe the way that the sun changes as the solar cycle approaches a maximum.
    (b) Explain why there are solar maxima every 11 years.

  13. What is the principle difference between stars that determines the observed colour of the star? This difference is apparent in the photosphere of the star.

  14. A rough guide to the apparent brightness of a star is as follows:
    Brightness = constant x Area of surface x (Temperature4)
    This assumes that the star is close to a blackbody emitter of light.

  15. Stars are brighter when they are larger because there is a greater area of star emitting light.
    What other property of massive stars contributes to the greater amount of light energy being emitted by them compared to less massive stars?

  16. A Red giant star is an old star that has expanded in size. It is much brighter than the original star.
    a. If the radius of the star has increased by a factor of 1000 (engulfing the inner planets) how would you expect the brightness to change?
    b. How could you explain it if the brightness increased by a factor of 500,000 when the star became a red giant? Assume that the radius of the star was still increased by a factor of 1000. Please give a numerical estimate of the change.

  17. Stars are hot and produce light before they start to burn Hydrogen into Helium using fusion. What is the early source of energy?

  18. (a) Why is it that converting Hydrogen into Helium produces energy?
    (b) For which elements does the process of converting those elements into heavier elements using fusion not produce energy?

  19. What is the difference between an optical double and a true binary star system?

  20. What property of each individual star can we attempt to measure when the star is a member of a binary star system that we can't measure for single stars? (Hint: using Newton's Law of Gravity)

  21. Variable Stars result from an instability in the way the shells where fusion is occuring in the star burn. State a way a variable star might change periodically that results in greater and lesser amounts of light coming from the star.

  22. (a) What is required for a star to be able to burn heavier elements than Hydrogen (what condition must the star achieve in its core?)
    (b) What happens to a star when is starts to run out of the current element it is burning in its core? (hint: This will happen to the sun in 4-5 billion years when it has exhausted all the Hydrogen in its core)
    (c) What property of a star determines the heaviest element it can burn?
    For example, how can we tell if a star will eventually burn Carbon into heavier elements?

  23. Why is it that we saw neutrinos before we saw the light from Supernova 1987a?

  24. Degenerate Electron pressure holds up white dwarf stars. Explain how this makes the star stable and not prone to the dramatic expansion and collapse phases that it underwent when it was still using fusion to produce energy. (hint: consider what held the star up before)

  25. Neutron stars are the size of mountains and weigh as much as a star. Why do neutron stars spin so fast?

  26. For a very large black hole of the type thought to occupy the centres of galaxies the tides near the event horizon are too weak to harm a space traveller.
    Could you tell when you passed through the event horizon of such a black hole?

  27. Why would no pulses be observed from a rotating neutron star if its magnetic axis and spin axis were aligned?

  28. What does angular momentum have to do with the rapid rotation of neutron stars?

  29. Describe the main difference between the mass-radius relationship for main sequence stars and the mass-radius relationship for white dwarfs.