Correct answers for Exam 2, AST 2008, Fall Term, 2007-08

The questions are listed in an order different from that in your exam because question numbers differ from one exam to another.



"Thermal (i.e. temperature-based) broadening ...."   radial velocities

"Whether an astronomical object is a point ...."   depends on its distance and on the instrument used to observe it

"The difference between laboratory gases and ...."   nebulae; infrequent in the nebulae

"Any definite location (i.e. point) within an H-R ...."   a definite star luminosity, star temperature, and star size

"The diagram of Solar neighborhood stars ...."   less; more; 3

"As an idealization, an HR diagram main sequence ...."   all have the same chemical composition but a variety of masses

"If two stars have the same amount of proper motion...."   larger transverse velocity

"Main sequence stars that are unusually massive, ...."   they do not live long enough to be around after ...

"Which of the following is true of the eight known planets ...."   All have negative orbital energies

"A bright star that rotates very fast ...."   its rotation axis points toward the observer

"The famous radiation at 21 centimeters wavelength ...."   their proton's spin; electrically neutral hydrogen atoms

"A way to tell whether wiggly star motion ...."   parallactic motions of all stars have the same period while binary motions do not

"A hydrogen atom's main energy levels ...."   integer (whole number) levels, with the numbers going arbitrarily high

"Which characteristic of a star spectral line ...."   strength

"To understand why normal stars have dark line spectra ...."   most of a star is opaque, its outermost layers are transparent, and temperature increases inward

"High luminosity is a very important ...."   otherwise very distant standard candles would not provide enough light ....

"The energy of a photon associated with a spectral line ...."   energy difference

"A star of magnitude 5.0 is ____ times ...."   a million

"Because of the way that scattering of starlight by interstellar dust ...."   redder; bluer

"Comparing surface temperature and mass, ...."   mass; often line wavelengths of only one of the stars ....

"How do Doppler shifts in star spectra depend on ...."   The shifts do not depend on that motion

"Imagine a white dwarf star of 5,000 kilometers ...."   between 100 and 1,000

"A figure on the exam illustrates proper motions ...."   the two end stars (at the left end of the handle and a bowl star ...

"A 'standard candle' star whose absolute magnitude ...."   1000 parsecs