Slides posted at: http://astro.cornell.edu/~pslii -> click on “astro1101” link on right hand side -> scroll down to “Week 8”
Tools of Astronomy: Terms to Know Kepler’s Laws • What does each of the laws say? Doppler shift Parallax • p = 1/d Apparent brightness Luminosity Inverse square law
Telescopes Q1 What is the purpose of adaptive optics? • To improve the angular resolution of telescopes in space • To eliminate the distorting effects of atmospheric turbulence for telescopes on the ground • To increase the collecting area of telescopes on the ground • To increase the magnification of telescopes on the ground • To allow several small telescopes to work together like a single larger telescope.
Telescopes Q2 Which of the following is not a good reason to place observatories on mountain tops? • To reduce light pollution • To reduce light distortion • To reduce light absorption • To be able to observe at infrared wavelengths • To be able to observe at radio wavelengths
Telescopes: Terms to Know CCDs • what are the advantages of CCDs over film? exposure time light collecting area angular resolution refracting vs reflecting telscopes • what is the primary focusing mechanism of each? spectroscopy Light pollution Adaptive optics • turbulence • the “seeing” • How does AO work? Interferometry • What is the advantage over single dish? What are the disadvantages?
The Sun Q1 When is/was gravitational contraction an important energy-generation mechanism for the Sun? • Only during solar minimum • Only during solar maximum • When the Sun was being formed from a collapsing cloud of gas • When the Sun transports radiation through the convective zone • Right after the Sun began fusing hydrogen in its core
The Sun Q2 What is the proton-proton chain? • The specific set of nuclear reactions through which the sun fuses hydrogen into helium • It describes the linkage between protons into long chains that occurs at high temperatures • It is an alternative method of generating energy by nuclear fusion beside fusing hydrogen into helium • It is another name for the force that holds protons together in atomic nuclei.
The Sun Q3 What are the core and surface temperatures of the Sun respectively: • 1 million and 3000 K • 10 million and 6000 K • 10 million and 10000 K • 100 million and 8000 K • 1 billion and 4000 K
The Sun: Terms to Know Gravitational equilibrium • What two forces are being balanced? • Unique property of negative heat capacity Nuclear fusion/fission • What’s the difference? • Heaviest element that can be fused? Gravitational contraction Proton-proton chain • What two elements are involved? Occurs for what masses of stars? CNO cycle • Occurs for which masses of stars?
Properties of Stars Q1 Which of the following statements about apparent and absolute magnitudes is false? • The magnitude system that we use now is based on system used by the ancient Greeks over 2000 years ago • A star with apparent magnitude of 5 is brighter than one with apparent magnitude 1 • The absolute magnitude of a star is another measure of its luminosity • A star’s absolute magnitude is the apparent magnitude it would have if it were 10 pc from Earth • All of the above are true.
Properties of Stars Q2 What can we infer, at least roughly, from a star’s luminosity class? • Its radius • Its mass • Its age in years • Its surface temperature
Properties of Stars Q3 Two stars, Tom and Jerry, have the same spectral type. Tom is luminosity class V and Jerry is luminosity class I. Which star is bigger? • Tom • Jerry Which star is more luminous? • Tom • Jerry Which star is hotter? • Tom • Jerry
Properties of stars: Terms to Know HR Diagram (pg 504) • Where are the main sequence, giants, supergiants, white dwarfs • Where are the lines of constant radius/mass • How does a star like the Sun move on the HR diagram? • What does the HR diagram of an old cluster look like? Spectral types • OBAFGKMLT – Oh be a fine girl kiss me, less talk • which are hottest/coldest. biggest/smallest, brightest/dimmest, longest/shortest living etc. Luminosity classes • I, II, III, IV, V Binary star systems • Visual, spectroscopic, eclipsing Apparent vs absolute magnitudes
Star Stuff Q1 As a solar mass protostar moves onto the main sequence, • Its surface temperature and luminosity increase • Its surface temperature increases and its luminosity decreases • Its surface temperature and luminosity decrease • Its surface temperature decreases and its luminosity increases • Its surface temperature and luminosity stay the same
Star Stuff Q2 Which of the following sequences correctly describes the stages of life for a low-mass star? • red giant, protostar, main sequence, white dwarf • white dwarf, red giant, protostar, main sequence • protostar, main sequence, white dwarf, red giant • protostar, red giant, main sequence, white dwarf • protostar, main sequence, red giant, white dwarf
Star Stuff Q3 Degeneracy pressure is the source of the pressure that stops the crush of gravity in all the following except • A brown dwarf • A white dwarf • A neutron star • A very massive main sequence star • The central core of the Sun after hydrogen fusion ceases but before helium fusion begins
Star Stuff Q4 You discover a binary system in which one member is a 15 Msun main sequence star and the other star is a 10 Msun giant. Why should you be surprised, at least at first? • It doesn’t make sense to find a giant in a binary system • The odds of ever finding two such massive stars in the same binary system are impossibly small • The two stars in a binary system should both be at the same point in stellar evolution • The two stars should be the same age, so the more massive star should have become a giant first • A star with a mass of 15 Msun is too big to be a main-sequence star
Star Stuff: Terms to Know Low vs high mass stars • How do each of these evolve? (see page 552) Protostar Protostellar disk Thermal, degeneracy and radiation pressure Red giant Shell burning Helium flash Thermal pulses White dwarf, brown dwarfs • How are they formed? • Supported by degeneracy pressure • Compositions? Planetary nebula Supernova