Younger stars have more heavy elements because a. old stars ...

[maychende]

Younger stars have more heavy elements because
 
  a. old stars destroy heavy elements as they age.
  b. young stars burn their nuclear fuels faster.
  c. the heavy elements were made in previous generations of stars.
  d. heavy elements haven't had time to settle to the core of these younger stars.
  e. All of the other choices are correct.

Question 2

How can we find the distance to a star that is too distant to have a measurable parallax?
 
  What will be an ideal response?

[mcarey591]

Answer to Question 1

c

Answer to Question 2

Most stars are too distant to have measurable parallaxes. These distances can be estimated from the star's spectral type, luminosity class, and apparent magnitude in a process called spectroscopic parallax, which relies on the location of the star in the H-R diagram. If you record the spectrum of a star, you can determine its spectral class, and that tells you its horizontal location in the H-R diagram. You can also determine its luminosity class by looking at the widths of its spectral lines, and that allows you to estimate the star's vertical location in the diagram. Once you plot the point that represents the star in the H-R diagram, you can read off its absolute magnitude, and find the distance by comparing the star's apparent and absolute magnitudes.